R. A. Van Steenwyk & R. M. Nomoto
Department of Environmental Science
Policy and Management
University of California, Berkeley, CA 94720
Abstract
An insecticide evaluation study was conducted in a commercial 'Bartlett' pear orchard in Fairfield. Eighteen treatments were evaluated that included: a number of new IGR insecticides used alone or preceding Azinphos-M applications, a new pyrethroid (Brigade) and a commercial standard. This trial was conducted against a very high codling moth (CM) population with over 55% infested fruit at harvest in the untreated control and over 2% infested fruit in the grower standard (three applications of Azinphos-M at 3.0 lb/ac). No treatment achieved the grower acceptable level including the grower standard. However, Brigade (a new pyrethroid insecticide which is near registration), CM-002X (a new IGR) and Knack and difenolan (two IGR insecticides), which were applied once and then followed by two applications of Azinphos-M, had CM infestation levels similar to that of the grower standard treatment. It appears that only Brigade and possibly CM-002/X could be used as a direct replacement for Azinphos-M. Knack and difenolan will have to be used in a combination program with Azinphos-M.
Confirm is an insect growth regulator (IGR) which was recently registered on walnuts for CM control. Registration in pears is expected next year. Confirm is environmentally safe, selective for worm pests and has low mammalian toxicity. Three large plot studies were conducted in the Sacramento Delta. The results of these three large plot studies indicate that Confirm cannot be used in a stand alone program for CM control and that the effectiveness of Confirm will be enhanced by increased coverage through increased spray volume and/or reduced sprayer speed. The most promising use of Confirm is as a supplemental insecticide to be used in conjunction with CM pheromonal control which provides leafroller control and some additional CM control.
CM larvae that infest over-ripe pears do not complete their larval development. The pears are rotting faster than the larvae can complete their development. The application of a plant growth regulator such as ethephon shortly after harvest promotes early ripening and fruit drop. Post-harvest use of ethephon would largely eliminate the overwintering CM population without the use of insecticides or post-harvest fruit removal. Post-harvest ethephon studies were conducted in Sacramento and Fairfield. In the Sacramento study, 4 and 6 pt of Ethrel/ac were applied with the grower's air-blast speed sprayer. This study demonstrated that post-harvest ethephon will suppress overwintering CM larvae through increased fruit maturity and fruit drop. In addition, CM that infested the pears before an ethephon application were also unable to complete their larval development. In the Fairfield study, 4 and 6 pt Ethrel/100 gal were applied by hand gun immediately after harvest and twice more at weekly intervals. This study indicates that ethephon needs to be applied as soon as possible after harvest to gain the greatest benefit from its use.
Post-harvest ethephon studies that were conducted in 1995 showed that using 1, 2 and 4 pt of Ethrel per 100 gal showed no adverse effects on return bloom or fruit set in the spring of 1996. In addition, there was some indication that the post-harvest applications of ethephon caused a reduction in the number of rattail fruit the next spring.
Post-harvest CM infestation can vary tremendously between pear orchards, growing regions and years. To determine the need for post-harvest control, it is important to determine which orchards will develop CM infestation. During the past two years we have developed a mutivariate model based on accumulated pheromone trap catch to harvest, in-season insecticide use and degree days accumulation to harvest to predict post-harvest infestation. Three predictive models have been developed for Mendocino/Lake Counties, Suisun Valley and Sacramento Delta. These models have r squared values between 0.6 to 0.8 which means that they explain between 60 to 80% of the variation.
The implementation of a post-harvest CM control strategy using either a Lorsban or Penncap-M application has been well received by growers in the Sacramento Delta. Growers and PCAs have perceived a suppression of the next years overwintering CM flight. The implementation of a post-harvest CM control strategy using fruit stripping in Suisun Valley has been slow because of the perceived cost. However, if the stripped fruit can be sold for juice for a net profit to the growers, then fruit stripping should gain greater grower acceptance in the future.
Introduction
Codling moth (CM) is the key insect pest of pears, with annual control costs of approximately $150.00 per acre. Control of CM in pears has relied on repeated applications of Guthion or other insecticides. The repeated use of insecticides has resulted in the outbreak of a number of secondary pests, such as pear psylla and spider mites, which require additional insecticides for their control. Also, the repeated use of insecticides has resulted in the development of CM resistance to Guthion and cross-resistance to most alternative insecticides.
Pears are harvested early in the season (mid-July through mid-August) relative to other CM host crops, such as apples or walnuts. After commercial pear harvest, it is common to find a large number of unharvested fruit remaining on the trees. Since insecticides used for the CM control are usually terminated two or more weeks before harvest, the unharvested fruit serve as excellent sites for CM oviposition and allow for a rapid increase in the CM population. The CM which develop in these fruit after mid-August will enter the overwintering stage (diapause) and emerge as adults the following spring. A large overwintering population of CM can have a detrimental effect on the efficacy of either a pheromone- or insecticide-based control program.
Studies were conducted from 1992 to present to determine if post-harvest CM control either by fruit removal or insecticide applications could suppress the overwintering CM population. These studies have demonstrated that post-harvest control can reduce the overwintering CM female population by 70 to 80%. The suppression of the overwintering CM population will increase the efficacy of either insecticide- or pheromone-based control programs.
During the course of the post-harvest CM control studies, it was observed that CM larvae that infest ripe pears do not complete their larval development before the pears rot. The application of a plant growth regulator, such as ethephon, shortly after harvest could promote early ripening and fruit drop. If the fruit remaining in the orchards after harvest can be induced to drop or ripen rapidly, then the CM overwintering population can be largely eliminated without the use of insecticides. Plant growth regulators could substitute for post-harvest hand stripping of fruit or insecticide applications at a much reduced cost to the grower. In addition, repeated applications of post-harvest insecticides will eventually lead to CM resistance to those insecticides while no CM resistance is expected to develop with the use of plant growth regulators.
Also, during the course of our post-harvest CM control studies, it was observed that not all orchards developed a large CM infestation after harvest. In past years of study, all orchards developed some degree of infestation. However, in 1994, there was no large third CM flight after harvest. The decision to implement post-harvest control of CM by either fruit removal or insecticide application needs to be based on some objective criteria. Growers need some assurance that the cost of the post-harvest treatment will be justified by a reduction in the overwintering CM population. A model needs to be developed that will predict post-harvest infestation before this control strategy will be readily accepted by growers.
Reported here are the results of our 1996 studies which include:
Methods and Materials:
A study was conducted in a commercial 'Bartlett' pear orchard planted on a 25 ft. x 25 ft. spacing (70 tree/acre) in Fairfield, California. Eighteen treatments were replicated four times in a randomized, complete block design. Each replicate was an individual tree. Foliar sprays were applied with a handgun operating at 200 psi with a finished spray volume of 200 gal/acre (2.87 gal/tree). Applications were scheduled based on degree days (DD). DD were calculated with a biofix of 31 March for the first generation and a 17 June biofix for the second generation using a single sine horizontal cutoff model with a lower threshold of 50°F and an upper threshold of 88°F. Maximum and minimum air temperatures were obtained from the IMPACT weather station at Cordelia, CA. Flight activity of male CM was monitored with a pheromone trap placed high in the tree canopy. Target application timings were: Knack and difenolan at 100 and 500 DD from 1st biofix; CM-001 at 200 and 600 DD from 1st biofix and 200 DD from 2nd biofix; CM-002/X, Brigade and Azinphos-M (grower standard) at 250 and 650 DD from 1st biofix and 250 DD from 2nd biofix. Due to rain on 15 through 18 May and again on 21 May and high winds through 25 May, the 600 DD and 650 DD applications were postponed until 28 May (699 DD). In addition, Knack and difenolan, which were applied on 14 May, were retreated on 28 May. The treatments and application timings are found on Table 1. Control of the first CM generation was evaluated on 6 June by inspecting 50 fruit from both the bottom and top of the tree canopy per replicate for CM infestation (400 fruit per treatment). Control of the second generation was evaluated at harvest on 22 July by inspecting a maximum of 125 fruit from both the bottom and top of the tree canopy per replicate for CM infestation (1,000 fruit per treatment). Due to the low crop this year, the number of fruit inspected varied by treatment. Control of pear psylla nymphs, motile twospotted spider mites and European red mites was evaluated by sampling 10 exterior and 10 interior leaves per replicate weekly from 18 June through 16 July. Pear psylla nymphs and motile twospotted spider mites and European red mites were brushed from the sampled leaves and counted under magnification (20X).
Results and Discussion:
Flight Activity - The first or overwintering CM flight, as measured by a pheromone trap placed high in the tree canopy, indicated that flight began between 28 March and 5 April (Fig. 1). Biofix for the first generation was set on 3 March. On 31 March, maximum air temperature exceeded 70°F. A maximum air temperature of 70°F. is correlated with a sunset temperature of 62°F. which is the minimum temperature needed for CM oviposition. The biofix for the first generation was set on 31 March. The overwintering flight was not bimodal as observed in previous years. The first peak of the first flight occurred on 29 April at ca. 280 DD and the second peak of the first flight, which was very low, occurred on 28 May at ca. 700 DD. The first peak of the first CM flight usually occurs between 200 to 300 DD after biofix and the second peak of the first flight usually occurs between 650 to 750 DD after biofix. The overwintering flight was completed by 16 June at ca. 1,050 DD. The first flight is usually completed between 1,000 to 1,100 DD in pears. The second biofix was set on 17 June. The first peak of the second CM flight occurred on 1 July at ca. 280 DD.
First Generation Evaluation- There was not a great deal of difference between the percent infestation from fruit high in the tree canopy as compared to fruit from low in the tree canopy in the first generation evaluation (Table 2). The fruit high and low in the tree canopy were combined for the total infestation. All insecticide treatments had significantly lower CM infestation as compared to the untreated control. There was no significant difference in CM infestation among all insecticide treatments except that the CM-001 and Knack at 0.11 lb (AI)/ac treatments had significantly higher infestation as compared to the grower standard (Azinphos-M). There was a rate response with Brigade, CM-001 SC, CM-002/X but not CM-001 EC, and Knack. The EC formulation of CM-001 at 0.045 lb (AI)/ac had significantly fewer CM as compared to the SC formulation but there was no significant difference between the EC or SC formulations at 0.089 lb (AI)/ac.
Harvest Evaluation - The crop was very low this year and the number of fruit inspected at harvest was less than the desired 250 fruit per replicate (125 low fruit and 125 high fruit). The low crop was the result of a lack of winter chilling which caused an extended bloom period. The extended bloom period coupled with unusually frequent and heavy spring rains resulted in poor pollination and fruit set. In addition, the spring rains caused an increase in the number of fire blight infestations this year which reduced the number of fruit per tree even further. The number of fruit inspected was less than 250 fruit per replicate in all treatments except CM-002/X at 0.0089 lb (AI)/ac (Table 3). The total CM infestation in the untreated control was extremely high (56%) and was significantly higher than all other treatments (Table 4). There was no significant difference in CM infestation among the grower standard (Azinphos-M), Brigade at 0.06 and 0.1 lb (AI)/ac, Azinphos-M followed by Brigade at 0.06 lb (AI)/ac, CM-002X at 0.0178 lb (AI)/ac, Knack at 0.066 and 0.11 lb (AI)/ac followed by two applications of Azinphos-M, and difenolan at 0.1875 (AI)/ac followed by two applications of Azinphos-M. There was a rate response with Brigade, CM-001, and difenolan but not Knack and CM-002/X. There was not a great deal of difference between the EC and SC formulations of CM-001.
Secondary Pest Evaluations - The pear psylla, twospotted spider mite and European red mite populations, in general, were higher in those treatments that contained two or more Azinphos-M applications (Table 5 and Table 6). The Azinphos-M applications depleted the predatory arthropod populations (Western predatory mite, Western flower thrips, six-spotted thrips, green lacewing, big-eyed bug etc.) which may have suppressed the mite and psylla populations.
Conclusions:
This trial was conducted against a very high CM population with over 55% infested fruit at harvest in the untreated control and over 2% infested fruit in the grower standard (three applications of Azinphos-M at 1.5 lb (AI)/ac. The acceptable CM infestation level for growers is less than 0.5%. Thus no treatment approached the grower acceptable level including the grower standard. However, Brigade at 0.06 and 0.1 lb (AI)/ac applied three times, Brigade at 0.06 lb (AI)/ac applied twice with one applications of Azinphos-M, CM-002/X at 0.0178 lb (AI)/ac applied three times, difenolan at 0.1875 (AI)/ac and Knack at 0.066 (AI)/ac applied once with two applications of Azinphos-M had CM infestation levels similar to that of the grower standard treatment. It appears that only Brigade and possibly the high rate of CM-002/X could be a direct replacement for Azinphos-M. Knack and difenolan will have to be used in a combination program with Azinphos-M. However, the combination of Knack and difenolan with Azinphos-M may result in an increase in mite or psylla populations.
2. Evaluation of Confirm for CM and Leafroller Control
A. Full Season Evaluation of Confirm for CM Control
Methods and Materials:
A study was conducted in a commercial 'Bartlett' pear orchard in Hood, California. Three unreplicated treatments of approximately five acres each were applied using an air-blast speed sprayer operating at 1.75 mph and applying 100 gal of finished spray per acre. The three treatments were: Confirm 2F applied four times during the season, Confirm 2F applied five times during the season and Guthion 50WP applied three times during the season. Applications were scheduled based on DD and moth flight activity as an indicator of egg hatch. DD were calculated with a biofix of 31 March for the first generation and 11 June biofix for the second generation using a single sine horizontal cutoff model with a lower threshold of 50°F and an upper threshold of 88°F. Maximum and minimum air temperatures were obtained from the IMPACT weather station at Lodi, CA. Flight activity of male CM was monitored with a pheromone trap placed in the experimental area. Target application timings were: Confirm at 200 DD or beginning of egg hatch of the A peak of the first flight, two weeks after the first application (5 application treatment only), 700 DD or beginning of egg hatch of the B peak of the first generation, 200 DD or beginning of egg hatch of the A peak of the second generation and a final application at the "stop drop" timing. The grower standard (Guthion) target application timing was: 250 DD or egg hatch of the A peak of the first and second generations and at the "stop drop" timing. The treatments and application timings are found on Table 7. Control of the CM infestation and leafroller damage was evaluated on 11 June (end of the first CM generation) and 15 July (beginning of commercial harvest) by inspecting 250 fruit from the bottom of the tree canopy from four widely separated areas within each unreplicated treatment (a total of 1,000 fruit per treatment per evaluation).
Results and Discussion:
Flight Activity - The first or overwintering CM flight, as measured by a pheromone trap, indicated that flight began between 26 March and 3 April (Fig. 2). Biofix for the first generation was set on 3 March. On 31 March, maximum air temperature exceeded 70°F. A maximum air temperature of 70°F. is correlated with a sunset temperature of 62°F. which is the minimum temperature needed for CM oviposition. The overwintering flight was distinctly bimodal as observed in previous years. The first peak of the first flight occurred on 7 May at ca. 400 DD and the second peak of the first flight on 28 May at ca. 762 DD. The first peak of the first CM flight usually occurs between 200 to 300 DD after biofix and the second peak of the first flight usually occurs between 650 to 750 DD after biofix. The reason for the delay in the first peak of the first flight is unknown but may be due to the combination of unusual winter chilling and warm spring temperatures. The overwintering flight was completed by 10 June at ca. 1,050 DD. The first flight is usually completed between 1,000 to 1,100 DD in pears. The second biofix was set on 11 June. The first peak of the second CM flight occurred on 18 June at ca. 138 DD and the second peak of the second flight was on 16 July at 720 DD.
First Generation Evaluation - The CM infestation was significantly higher in the Confirm four application treatment than that in the Confirm five application treatment which was in turn significantly higher than the grower standard (Table 8). At the time of this evaluation, the Confirm four application treatment had only two applications (3 May and 3 June) while the Confirm five application treatment had three applications (3 May, 18 May and 3 June). The 18 May application of Confirm was responsible for the significantly lower infestation in the five Confirm application treatment. In comparison, only one application of Guthion (grower standard) on 9 May resulted in 0.1% infested fruit. No leafroller damage was observed in any of the treatments.
Harvest Evaluation - The CM infestation after the completion of all applications showed a similar pattern of infestation to the first generation evaluation. However, the CM infestation in the Confirm treatments was extremely high and required bin sorting before the fruit could be delivered to the shed. Again, no leafroller damage was observed in any of the treatments.
Conclusions:
This study was conducted against a moderate CM population. However, it appears that Confirm cannot be used in a stand alone program for CM control. The five Confirm application treatment had over 6% damage despite Confirm applications at approximately two week intervals. Confirm will have to be augmented with conventional insecticide to achieve grower acceptable infestation levels.
B. Evaluation of Spray Volume of Confirm for CM Control
Methods and Materials:
A study was conducted in a commercial 'Bartlett' pear orchard in Grand Island, California. Four unreplicated treatments of approximately five acres each were applied using an air-blast speed sprayer. The four treatments were: Confirm 2F applied at 400 gal of finished spray per acre, Confirm 2F applied at 250 gal of finished spray per acre, a grower standard applied at 250 gal of finished spray per acre and a grower standard plus pheromone disruption. Applications were scheduled based on DD and moth flight activity as an indicator of egg hatch. DD were calculated with a biofix of 22 April for the first generation and 22 June for the second generation using a single sine horizontal cutoff model with a lower threshold of 50°F and an upper threshold of 88°F. Maximum and minimum air temperatures were obtained from the IMPACT weather station at Lodi, CA. Flight activity of male CM was monitored with two pheromone traps placed in the experimental area. Target application timings were: the grower standard of Imidan at 250 DD or egg hatch of the A peak of the first flight, Guthion at two weeks after the first application of Imidan, Penncap-M at 700 DD or egg hatch of the B peak of the first generation and a final application of Guthion at the "stop drop" timing. Confirm treatments of 250 and 400 gal of finished spray per acre were targeted to proceed each of the grower standard applications by 50 to 100 DD. A fourth treatment consisted of the aforementioned grower standard treatment program combined with three applications of Checkmate CM pheromone applied on 28 March, 8 May and 22 June. The treatments and application timings are found on Table 9. Control of the CM infestation and leafroller damage was evaluated on 13 June (end of the first CM generation) and 15 July (beginning of commercial harvest) by inspecting 250 fruit from the bottom of the tree canopy from four widely separated areas within each unreplicated treatment (a total of 1,000 fruit per treatment per evaluation).
Results and Discussion:
Flight Activity - The overwintering CM flight, as measured by two pheromone traps, indicated that flight began between 18 April and 24 April (Fig. 3). The biofix for the first generation was set on 22 April since the maximum air temperature exceeded 70°F. on this date. A maximum air temperature of 70°F. is correlated with a sunset temperature of 62°F. which is the minimum temperature needed for CM oviposition. The overwintering flight was distinctly bimodal as observed in previous years. The first peak of the first flight occurred on 1 to 8 May at about 169 to 263 DD and the second peak of the first flight on 10 June at ca. 863 DD. The first peak of the first CM flight usually occurs between 200 to 300 DD after biofix and the second peak of the first flight usually occurs between 650 to 750 DD after biofix. The overwintering flight was completed by 21 June at ca. 1,050 DD. The first flight is usually completed between 1,000 to 1,100 DD in pears. The second biofix was set on 22 June. The first peak of the second CM flight was not observed but should have occurred the first week of July.
First Generation Evaluation - The CM infestation was significantly higher in the Confirm at 250 gal per acre treatment than in the Confirm at 400 gal per acre and grower standard treatments (Table 10). It is speculated that the increased spray volume caused a more thorough coverage of the fruit with Confirm. No leafroller damage was observed in any of the treatments.
Harvest Evaluation - The CM infestation showed a similar pattern to the first generation evaluation. However, the CM infestation in the Confirm treatments was high compared to the grower standard treatment, particularly in the 250 gal per acre treatment which required bin sorting before the fruit could be delivered to the shed. Even the 400 gal per acre treatment had a CM infestation level that was unacceptable to the grower. Again, no leafroller damage was observed in any of the treatments.
Conclusions:
This study was conducted against a moderate CM population. An increased spray volume caused a significant increase in CM control. Similar findings were reported by Pons and Riedl in 1995. The use of Confirm requires thorough coverage with a spray volume of approximately 400 gal per acre to be effective. However, this volume of finished spray may meet with grower resistance since typical spray volumes range between 100 to 250 gal per acre and 400 gal per acre would add additional cost to the application.
C. Evaluation of Supplemental CM and Leafroller Control with Confirm
Methods and Materials:
A study was conducted in a commercial 'Bartlett' pear orchard in Courtland, California that was under pheromonal control for CM. Three unreplicated treatments of approximately five acres each were applied using an air-blast speed sprayer operating at 1.75 mph and applying 100 gal of finished spray per acre. The three treatments were: Confirm 2F applied at the "B" peak of the 1st CM flight and at the "stop drop" timing, Penncap-M applied at the "B" peak of the 1st CM flight and Guthion 50WP applied at the "stop drop" timing. Applications were scheduled based on the expected life of the Checkmate pheromone dispensers (45-60 days) and the anticipated beginning of the B peak of the first codling moth (CM) flight. Flight activity of male CM was monitored with a pheromone trap baited with 10 mg of codlemone placed in the experimental area. Target application timings for Confirm and Penncap-M were mid-May (45 days after Checkmate pheromone dispensers were applied) and a second application of Confirm at the "stop drop" timing. The untreated control required an application of Guthion at the "stop drop" timing because of damaging levels of leafroller. The treatments and application timings are found on Table 11. Control of the CM infestation and leafroller damage was evaluated on 11 June and 15 July by inspecting 250 fruit from the bottom of the tree canopy from four widely separated areas within each unreplicated treatment (a total of 1,000 fruit per treatment per evaluation). The 11 June sample was taken at the completion of the first CM generation and the 15 July sample was taken at the beginning of commercial harvest.
Results and Discussion:
Flight Activity - Since the orchard was under pheromonal control it was not possible to monitor the seasonal CM moth flight activity accurately. A total of 7 moths for the season (19 March through 23 July) were captured in the pheromone trap. However, the highest CM catch (3 moths) occurred on 7 May. This would indicate that the 10 to 11 May applications of Confirm and Penncap-M were applied at the beginning of B peak of the first flight and/or that the Checkmate pheromone dispensers were losing their effectiveness.
First Generation Evaluation - There was no CM infestation in any of treatments and only 0.1% leafroller damage in the Guthion treatment (Table 12 and Table 13). At the time of this evaluation, the Guthion treatment could be considered an untreated control since Guthion had not been applied while Confirm and Penncap-M had been applied about one month earlier. These results would indicate that the CM pheromonal control had suppressed the CM population and that Penncap-M and Confirm were of little additional benefit in CM control.
Harvest Evaluation - There was no significant difference in CM infestation among the treatments. The lack of significant difference among the treatments was due to the very low CM infestation observed in the study. CM infestation ranged from 0.1% for Confirm and Guthion to 0.2% for Penncap-M. Again, these results would indicate that the CM pheromonal control had suppressed the CM population and that Guthion, Penncap-M and Confirm were of little additional benefit in CM control. However, Confirm and Penncap-M treatments had significantly lower leafroller damage as compared to the "stop drop" Guthion treatment. Although the Guthion treatment may have prevented much greater leafroller damage, it had a combined CM infestation and leafroller damage of 0.5% which is unacceptable to pear growers.
Conclusions:
This study was conducted against a low CM population which had been under CM pheromonal control for the past three years. It would appear that the application of Penncap-M at the B peak of the first CM flight timing or applications of Confirm at the B peak of the first CM flight and "stop drop" timings had little benefit in CM control. However, both Penncap-M and Confirm were successful in suppressing leafroller damage. In orchards where CM has been suppressed by pheromonal control and leafrollers have become a problem, Confirm, with its desirable mammalian toxicity and environmental effects, would be the material of choice.
General Conclusions of Confirm Studies: These three large plot studies indicate that Confirm cannot be used in a stand alone program for CM control and the effectiveness of Confirm will be enhanced by increased coverage through either increased spray volume or reduced sprayer speed. The most promising use of Confirm is as a supplemental insecticide to be used in conjunction with CM pheromonal control.
3. Effect of Post-harvest Ethephon on Fruit Maturity, Fruit Drop and CM Survival
Methods and Materials:
The trial was conducted in a commercial 'Bartlett' pear orchard in Courtland, California. Three treatments were replicated four times in a randomized complete block design. Each replicate was 8 trees long by 11 rows wide (0.5 ac). The trees were planted on a 11 ft. by 22 ft. square (180 trees/ac). The treatments were applied with an air-blast speed sprayer operating at 1.75 mph with a finished spray volume of 100 gal/acre. The three treatments were: ethephon at 1200 and 1800 ppm (4 and 6 pt Ethrel per 100 gal) and an untreated control. The treatments were applied on 14 August.
The effect of ethephon on fruit drop was evaluated weekly from 21 August through 2 October. On the day preceding application, 25 rattail and 25 mature green fruit were flagged per replicate (100 fruit of each type per treatment). Percent fruit drop was based on the number of flagged fruit remaining on the trees at the weekly evaluations. The effect of ethephon on fruit maturity (fruit pressure and fruit color) was evaluated weekly from 14 August though 28 August for mature green fruit and 14 August through 11 September for rattail fruit. Fruit color and pressure were determined on 10 rattail and 10 mature green fruit per replicate (40 fruit of each type per treatment). Fruit color was determined using standardized peach maturity color chips which were provided by the California Tree Fruit Agreement. The chips were modified to reflect more accurately pear maturity. We assigned color A = 1, C = 2, D = 3, H = 4, I = 5, and J = 6. Fruit pressure was determined with a penetrometer taking three readings per fruit.
The effect of ethephon on CM survival was determined by infesting 10 rattail and 10 mature green uninfested fruit per replicate (40 fruit of each type per treatment) on 14 August and 5 rattail and 5 mature green uninfested fruit per replicate (20 fruit of each type per treatment) on 21 and 28 August. Fruit was infested by placing two recently hatched CM larvae on the calyx end of each fruit. A small plastic cup was placed over the larvae and sealed to the fruit to prevent predation or larvae falling off the fruit. The fruit was removed from the trees two weeks after infestation and placed individually in a large plastic container. The plastic container had a layer of single-sided corrugated cardboard above and below the infested fruit to serve as a site for pupation or diapause. The containers were inspected weekly for six weeks to determine if a larva had infested the fruit and had successfully completed development. In addition, 25 rattail and 25 mature green naturally infested fruit per treatment were removed from the trees on 21 August and placed in the large plastic containers.
Results and Discussion:
Mean percent rattail and mature green fruit drop was accelerated with the application of ethephon as compared to the untreated control (Figure 4 and Figure 5). Two weeks after application, 67% and 75% of the mature green fruit had dropped at the 4 and 6 pt Ethrel/ac, respectively, while only 36% of the fruit had dropped in the control. Five weeks after application, 25% and 26% of the rattail fruit had dropped at the 4 and 6 pt Ethrel/ac, respectively, while only 6% of the fruit dropped in the control. The fruit drop was much greater in the ethephon treatments and untreated control than had been observed in previous years studies. The increased fruit drop was the result of the late application date (14 August) of ethephon. If we had applied ethephon in the first week of August, then we would have observed a lower percentage fruit drop particularly with rattail fruit.
In addition to fruit drop mean rattail and mature green fruit pressure was reduced with the application of ethephon as compared to the untreated control (Figure 6 and Figure 7). One week after application, mean mature green fruit pressure was 8.5 and 7.4 kg/cm2 at the 4 and 6 pt Ethrel/ac, respectively, while the mean pressure in the control was 11.8 kg/sq cm. Two weeks after application, mean rattail fruit pressure was 6.4 and 5.4 kg/cm2 at the 4 and 6 pt Ethrel/ac, respectively, while the mean pressure in the control was 14.4 kg/sq cm. A corresponding increase was also observed with fruit color (Figure 8 and Figure 9). One week after application, mean mature green fruit color was 3.0 and 3.7 at the 4 and 6 pt Ethrel/ac, respectively, while the mean color in the control was 2.6. Two weeks after application, mean rattail fruit color was 4.0 and 4.4 at the 4 and 6 pt Ethrel/ac, respectively, while the mean pressure in the control was 2.4. Past research has shown that if pears reach a fruit color of 3 (D color) or greater and fruit pressure of 10 kg/sq cm or less, then the pears cannot support the complete larval development of CM. Since mature green fruit pressure reached these perimeters by one week after application and rattail fruit reached these perimeters by two weeks after application with both 4 and 6 pt Ethrel/ac, few larvae should be able to complete their larval development within two weeks after application.
The percent mature green or rattail fruit producing a CM larva was significantly reduced on the day of application with both 4 and 6 pt Ethrel/ac (Table 14 and Table 15). On the day of application, mean percent mature green fruit producing a larvae was 2.5% and 0.0% at the 4 and 6 pt Ethrel/ac, respectively, while the mean percent in the control was 15.0%. The mean percent rattail fruit producing a larvae was 2.5% at both the 4 and 6 pt Ethrel/ac while the mean percent in the control was 35.0%. Total percent mature green fruit producing a larva was 1.3 % and 2.5% when treated with 6 and 4 pt Ethrel/ac, respectively, while 11.3% of the fruit produced a larva in the control. Total percent rattail fruit producing a larva was 3.8 % and 1.3% when treated with 6 and 4 pt Ethrel/ac, respectively, while 27.5% of the fruit produced a larva in the control. The low number of mature green fruit producing a larva in the control was the result of the late application date (14 August) of ethephon. The untreated control fruit were ripening rapidly and dropping from the trees in late August. If we had applied ethephon during the first week of August, we would have had much higher larval survival in the control. The low number of mature green fruit producing a larva at the day of application indicates that ethephon will prevent complete larval development of previously infested fruit. This was also observed when we caged naturally infested mature green fruit that had been infested two or more weeks prior to the ethephon application. Although, this effect was not observed with rattail fruit (Table 16). It appears that the rapid ripening action of the ethephon on mature fruit was effective in preventing complete larval development. However, in rattail fruit that are less mature than green fruit, the ethephon cannot act fast enough to prevent complete larval development of fruit infested before the ethephon application.
Conclusions:
This was the first study that demonstrated that Ethrel applied at 4 and 6 pt/ac with a grower's air-blast speed sprayer delivering 100 gal of finished spray per acre could significantly reduce the number of overwintering CM larvae through increased fruit drop and fruit maturity. In previous studies, we applied Ethrel with a handgun delivering 200 to 300 gal/ac to individual trees and it was uncertain whether the results from these handgun trials would be indicative of the results from a grower's air-blast speed sprayer. Also in previous studies it was not possible to infest fruit with CM larvae because of the limited sample size (individual trees). These encouraging results will lead to further investigations with emphasis on applications earlier in the season and the reach back effect of ethephon.
4. Effects of Applications Timing of Post-harvest Ethephon on Fruit Maturity, Fruit Drop
Methods and Materials:
A study was conducted in a commercial 'Bartlett' pear orchard planted on a 24 ft. x 24 ft. spacing (75 trees/acre) in Fairfield, California. Seven treatments were replicated four times in a randomized, complete block design. Each replicate was three trees. Foliar sprays were applied with a handgun operating at 300 psi with a finished spray volume of 250 gal/acre (1.3 gal/tree). The seven treatments were: ethephon at 1200 and 1800 ppm (4 and 6 pt Ethrel per 100 gal) applied immediately after harvest (5 Aug.) and at weekly intervals for two weeks (12 and 19 August).
The effect of ethephon on fruit drop was evaluated weekly from 12 August through 10 September. On the day preceding application, 25 mature green fruit were flagged per replicate (100 fruit per treatment). Percent fruit drop was based on the number of flagged fruit remaining on the trees at the weekly evaluations from 12 August through 10 September. The effect of ethephon on fruit maturity (fruit pressure and fruit color) was evaluated weekly from 5 August though 3 September for mature green fruit and 5 August through 10 September for rattail fruit. The effect of ethephon on mature green fruit maturity was terminated one week before that of rattail fruit because of excessive green fruit drop. Fruit color and pressure were determined on 10 rattail and 10 mature green fruit per replicate (40 fruit of each type per treatment). Fruit maturity was based on color using standardized peach maturity color chips which were provided by the California Tree Fruit Agreement. The chips were modified to reflect more accurately pear maturity. We assigned color A = 1, C = 2, D = 3, H = 4, I = 5, and J = 6. Fruit pressure was determined using a penetrometer taking 3 readings per fruit.
Results and Discussion:
Mature green fruit drop in the untreated control increased substantially as the season progressed (Table 17). However, one week after application both rates of ethephon caused significantly more fruit drop as compared to the untreated control except 4 pt Ethrel/100 applied on 12 August. In addition, 6 pt Ethrel/100 gal caused significantly more fruit drop then the 4 pt Ethrel/100 gal one week after application except on the last application date of 19 August. Since we flagged 100 fruit preceding each application, the effect of ethephon on drop was independent to the date of application, particularly at the 6 pt/100 gal rate. Thus an ethephon application should be made as soon as possible after harvest to gain the greatest benefit in fruit drop. We did not measure rattail fruit drop because of the low number of rattail fruit per tree.
Mean mature green fruit pressure was significantly decreased and fruit color was significantly increased within one week of application of ethephon (Table 18 and Table 19). There was not a strong rate response between 4 and 6 pt Ethrel/100 gal and the effectiveness of the ethephon increased as the season progressed due to the natural ripening of the fruit. Past research has shown that if pears reach a fruit color of 3 (D color) or greater and fruit pressure of 10 kg/sq cm or less then the pears cannot support the complete larval development of CM. These perimeters were reached two weeks after application when the application was made on 5 August, one week after application when the application was made on 12 August and less than one week when the application was made on 19 August.
Although, a similar pattern to mature green fruit was observed with rattail fruit, rattail fruit pressure was twice the pressure of mature green fruit on the same date. Mean rattail fruit pressure was significantly decreased and fruit color was significantly increased within two or three weeks after applying ethephon (Table 20 and Table 21). There was a strong rate response with 6 pt Ethrel which caused a higher degree of ripening than the 4 pt rate. Again using a maturity target of color 3 or greater and pressure of 10 kg/sq cm or less, these perimeters were reached four weeks after application when the application was made on 5 August, two weeks after application at 6 pt Ethrel/100 gal and three weeks after application at 4 pt Ethrel/100 gal when the application was made on 12 August and two weeks when the application was made on 19 August.
Conclusions:
This study shows that ethephon caused a rapid ripening and drop of mature green fruit, there was not a strong rate response with ethephon and the sooner an application can be made after harvest the greater the benefit in suppressing overwintering CM population in mature green fruit. However, in the rattail fruit which were far less mature than green fruit, ethephon was much slower in its action but had a strong rate response. This would indicate that, unlike mature green fruit, there will be less benefit in applying ethephon immediately after harvest with rattail fruit as with mature green fruit and that 6 pt Ethrel/ 100 gal is too low of rate a ethephon to be effective.
5. Effects of Ethephon on Return Bloom
Methods and Materials:
In 1995, two ethephon trials were conducted in commercial pear orchards in Fairfield and Grand Island, California. In each trial, ten treatments were replicated four times in a randomized complete block design. Each replicate was an individual tree in Fairfield and two trees in Grand Island. The treatments were applied with a handgun operating at 200 psi with a finished spray volume of 400 gal/acre. In Fairfield the ten treatments were: ethephon at 0, 300, 600 and 1200 ppm (0, 1, 2 and 4 pt Ethrel per 100 gal) with and without Silwet L-77 at 0.05% and 0.10% by volume. The treatments were applied on 27 July. In Grand Island the ten treatments were: Ethephon at 0, 300, 600 and 1200 ppm (0, 1, 2 and 4 pt Ethrel per 100 gal) with and without gibberellic acid at 25 and 50 ppm (10 and 20 oz. ProGibb 4% per 100 gal). The treatments were applied on 8 August.
In 1996, we evaluated the effects of ethephon on return bloom and fruit set by counting all floral bunches, "popcorn" buds, flower and fruit on four 1/2 meter limbs per replicate weekly from 15 March through 25 April in Fairfield and 19 March through 22 April in Grand Island. In addition, we counted all rattail flowers and fruit on four 1/2 meter limbs per replicate weekly from 22 April through 17 May in Grand Island. In addition, all rattail fruit per tree were picked and counted on 10 July in Grand Island.
Results and Discussion:
There was no significant difference in the mean number of flowers or fruit between the various treatments and untreated control for both Fairfield and Grand Island trials (Table 22, Table 23, Table 24 and Table 25) In addition, there was no significant difference in the mean number of floral bunches or "popcorn" buds the various treatments and untreated control for both the Fairfield and Grand Island trials (data not shown). The only hint of an adverse effect of ethephon was a possible delayed bloom in the Fairfield trials. However, this effect was not observed in the Grand Island trial. These results are similar to those of last year's research and are particularly encouraging in that we applied 1, 2 and 4 pt Ethrel/100 gal at a rate of 400 gal/ac which is equivalent to 4, 8 and 16 pt Ethrel/ac. However, the treatments in these trials were single tree replicates and not a great deal of confidence should be placed on the findings. Next spring we will evaluate the large air-blast speed sprayer trials which has replicate size of ca. 1/2 acre. If we again observe no adverse effect of ethephon in the large plot work, then we will be fairly confident of the safety of ethephon on return bloom and fruit set. We will continue the large plot work for a number of years to determine if ethephon has an adverse chronic effect on the trees.
In our study on return bloom and fruit set in Grand Island, we observed a large number of rattail bloom that occurred after the main bloom. This was not observed in Fairfield. Rattail bloom and fruit were significantly reduced in the 2 and 4 pt Ethrel/100 gal treatments as compared to the untreated control and there was a rate response (Table 26 and Table 27). In addition, the number of rattail fruit per tree from the 10 July sample was also significantly reduced in the 4 pt Ethrel/100 treatment as compared to the untreated control (Table 28). This was an unexpected and interesting finding since rattail bloom is associated with a increase in fire blight and rattail fruit is associated with large overwintering CM population. However, the treatments in this trial were two tree replicates and not a great deal of confidence should be placed on the findings. Next spring we will evaluate the large air-blast speed sprayer trials which has replicate size of ca. 1/2 acre. If the effects of ethephon on rattail development is again observed, hopefully a pomologist will examine this effect further.
Conclusions:
Post-harvest ethephon studies that were conducted in 1995 showed that using 1, 2 and 4 pt of Ethrel per 100 gal showed no adverse effects on return bloom or fruit set in the spring of 1996. In addition, there was some indication that the post-harvest applications of ethephon caused a reduction in the number of rattail fruit the next spring.
6. Predictive Model for Post-harvest CM Infestation
Methods and Materials:
The base data to construct a predictive post-harvest CM infestation model was developed by determining the CM infestation in 18 orchards in the Suisun Valley, 12 orchards in the Sacramento River Delta and 12 orchards in Mendocino County. In each orchard, 500 fruit were inspected for CM infestation about two to three weeks after final harvest. The fruit was collected from around a pheromone trap from which the accumulated moth captures were obtained from cooperating PCAs. A record of insecticides used during the growing season for each orchard was obtained from the cooperating growers, PCAs or the local Agricultural Commissioner's Office. Degree day accumulations from biofix to harvest were calculated for each growing district.
Results and Discussion:
Data collected during the 1995 and 1996 seasons were used to construct a multivariate regression model to predict the post-harvest CM infestation at 2 to 3 weeks after harvest. The variables used were: accumulate pheromone trap moth catch to harvest, total pounds of Guthion or Azinphos, total pints of Penncap-M, and, for the combined 1995 and 1996 model, the number of DD to harvest. Models were constructed for each growing district and all had acceptable r squared values (Table 29). A combined model for all areas for both 1995 and 1996 resulted in a unacceptable r squared value and the model was discarded. Using these models, we will verify if they can predict accurately those orchards which will develop greater than 5% post-harvest CM infestation in 1997.
Conclusions:
During the past two years we have developed a mutivariate model based on accumulated pheromone trap catch to harvest, in-season insecticide use and degree days accumulation to harvest to predict post-harvest infestation. Three predictive models have been developed for Mendocino/Lake Counties, Suisun Valley and Sacramento Delta. These models have r squared values between 0.6 to 0.8 which means that they explain between 60 to 80 % of the variation.
7. Implementation of a post-harvest control strategy for CM control
Methods and Materials:
Demonstration orchards of 15 to 25 acres in size were established in the Suisun Valley and the Sacramento Delta. In addition, companion orchards not practicing post-harvest CM control were used for comparison. The companion orchards were adjacent to the demonstration orchards, or if the demonstration orchards were large enough (i.e., >50 acres) the companion orchards were a portion of the demonstration orchards. In the Suisun Valley, three demonstration orchards were stripped of all remaining fruit immediately after harvest, while in the Sacramento Delta, five demonstration orchards were treated with Lorsban or Penncap-M immediately after harvest. Lorsban or Penncap-M was used because they show negative cross-resistance to Guthion resistant CM (Welter, unpublished data). The cost required to strip or spray the orchards was recorded.
The CM infestation was monitored weekly from August through September in insecticide-treated and companion orchards in the Sacramento Delta and the unstripped portion of the orchards in Suisun Valley by inspecting 100 fruit per orchard. CM infestation was not monitored in the stripped orchards because there were very few fruit present to inspect. The overwintering CM flight activity will be monitored weekly from mid-March through June by bait-pan traps and pheromone traps next spring.
Results and Discussion:
In the Suisun Valley, fruit removal is the most cost effective means of post-harvest CM control because of the open tree structure and low number of trees per acre (70-110 trees/ac). Fruit removal in 1995 reduced the overwintering CM flight in 1996 by over 70% in traps placed in the center of the orchards and by over 50% for all traps as compared to the companion orchards where the fruit was not removed after harvest. In 1996, a number of growers practiced post-harvest fruit removal at the same time or shortly after commercial harvest. The removed fruit were then sold as juice pears. This practice paid for the cost of fruit removal and removed about 70% of the fruit as compared to the companion orchards. The CM infestation in the unstripped companion orchards were 63%, 27% and 0.5%. Next spring, the CM overwintering flight will again be monitored with an anticipated reduction of 50 to 75% in overwintering moth flight.
In the Sacramento Delta, an insecticide application is the most cost effective means of post-harvest CM control because of the closed tree structure and high number of trees per acre (150-300 trees/ac). Insecticide application costs were about $45 per acre. In 1995, post-harvest insecticide treatments suppressed CM infestation but treatments were applied too late to eliminate infestation. Insecticide treatments were applied about one week after the beginning of egg hatch of the second peak of the second CM flight. The delay in insecticide applications was the result of the late registration of Lorsban and the late harvest completion date in relation to the CM flight. Lorsban was the insecticide of choice because Lorsban exhibits negatively correlated cross-resistance to Guthion resistant CM. Grower acceptance of the post-harvest insecticide application was tremendous with over 500 acres of pears treated with Lorsban. A large number of growers treated their entire acreage with Lorsban and it was difficult to find growers willing to leave 20 acres untreated for our comparisons. Six pear growers (those willing to leave 20 acres untreated) and all but one PCA in the Sacramento Delta directly participated in our demonstration project. In 1996, the cooperating growers and PCAs were extremely pleased by the suppression of the overwintering CM flight. However, our data did not show a significant reduction in the overwintering. This was because the six growers who were willing to leave untreated areas chose those areas with little or no CM infestation while treating areas with known CM infestation. This biased our data to be less favorable to post-harvest insecticide applications. In 1996, orchards with significant CM flight during or shortly after harvest were treated with Lorsban or Penncap-M. Penncap-M, like Lorsban, also exhibits negatively correlated cross-resistance to Guthion resistant CM. We estimate that about 1,000 acres were treated this year. The CM infestation did not develop in either the treated or untreated portions in two of the five orchards while in the three other orchards, an average of 22% of the fruit were infested in the untreated portion and only 8% of the fruit was infested when treated with Penncap-M or Lorsban. Next spring, the CM overwintering flight will again be monitored with an anticipated reduction of 50 to 75% of the overwintering moth flight.
Conclusions:
The implementation of a post-harvest CM control strategy using either a Lorsban or Penncap-M application has been well received by the growers in the Sacramento Delta. Growers and PCAs have perceived a suppression of the next year's overwintering CM flight. The implementation of a post-harvest CM control strategy using fruit stripping in Suisun Valley has been slow because of the perceived cost. However, if the stripped fruit can be sold for juice for a net profit to the growers, then fruit stripping should gain greater grower acceptance in the future.
Acknowledgments:
We gratefully acknowledge the following growers and PCAs whose assistance made the above studies possible: John Callas, Bob Castanho, Jim Dahlberg, Bob Hansen, Randy Hansen, Doug Hemly, Ted Horsky, Robert Merwin, Bill Oldham, Don Quesenberry, Miguel Rivera, Pat Weddle and Thom Wiseman.