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Dr. Harvey Reissig of Cornell University recently wrote the following comprehensive article entitled: "Using New Tools to Manage the Plum Curculio" which appeared in Scaffolds, Vol. 8, 1999:
Biology and Traditional Chemical Control Programs
The plum curculio, Conotrachelus nenuphar (Herbst) (PC), is a native pest of stone and pome fruits that has plagued orchardists since the first settlers planted fruit trees. The PC flourishes in wild, unsprayed habitats, because population levels and fruit infestation levels are not regulated effectively by natural enemies. In natural habitats, unsprayed apple and plum fruit is usually heavily damaged by this pest. Therefore, the prospects of developing an effective biological control for PC by conserving natural enemies in commercial apple orchards does not appear to be feasible.
Adult PC overwinter under ground debris, often along hedgerows or along the borders of woodlots. Although a few adult PC may overwinter in commercial orchards, the majority survive in adjacent overwintering sites. In the spring, as soon as ambient temperatures begin to reach 50 F, adult PC emerge from their overwintering quarters and begin to move into orchards. Beetles can be found in apple orchards even before apples bloom, but the adults are usually most numerous after blossoms begin to open. New adults may continue to immigrate into orchards for a 4-6-week period in early spring. Although adults are present in apple trees during Bloom, developing apple fruit is not susceptible to PC injury until after petals have dropped from the young fruitlets. After Petal Fall, beetles damage apples either by feeding (making holes in the apple with their beak-like mouthparts) or by ovipositing (cutting crescent-shaped oviposition scars in the fruit). There is only one generation of PC annually. Since there are no resident populations of PC in most commercial apple orchards in NY, it is only necessary to control overwintering adults during their oviposition cycle. Usually, feeding damage from surviving adults emerging late in the summer is not found in commercial orchards.
PC activity and oviposition are greatly affected by temperature. Adults are relatively inactive when temperatures remain below 50 F. During cool springs, adult movement and oviposition may be lengthy (4-6 weeks), but in warmer seasons, the oviposition period may be relatively short (2-3 weeks). Growers using traditional chemical control programs usually apply a protective insecticide to the whole orchard to maintain a protective residue on apple fruit and foliage during the entire PC oviposition cycle in the spring. Since insecticide residues are usually effective for 10-14 days, depending upon the amount of rainfall, traditional control programs usually require an initial spray at Petal Fall, followed by 2-3 insecticide sprays depending upon the weather and precipitation during the spring.
Control and Management Options
Compared with many other insect pests, the PC is not highly mobile and capable of dispersing uniformly throughout an entire orchard during one growing season. Damage from curculio tends to be extremely spotty, and is usually confined to the outer rows of commercial orchards. Since most PC problems result from immigration into orchard borders from outside sources, past history of damage is very useful in deciding whether or not any particular orchard or portions of an orchard are likely to be severely injured by this pest. Sprays of broad spectrum insecticides, such as organophosphates, applied to control PC will also provide control of the first generation of codling moth. Traditionally, growers in NY who treated entire orchards with organophosphate insecticide sprays for plum curculio have not had to apply special sprays against the first generation of codling moth. Growers opting to control PC with reduced insecticide schedules should also be aware that this strategy may require more consideration of management of the first generation of codling moth. In addition, growers in the Hudson Valley and Champlain Valley should also be aware that petal fall sprays of organophosphates have also usually prevented early season damage from the European sawfly.
Standard Control, Timing of Sprays Using PC Oviposition Model
Most studies in western NY have shown that applying a spray of insecticides at the Pink bud stage is no more effective in protecting apples from PC damage than starting control sprays at Petal Fall. However, some trials in the Hudson Valley have suggested that a Pink spray does help in preventing subsequent PC fruit injury in programs in which additional treatments are applied at Petal Fall. Although growers realize that initial post-bloom sprays for plum curculio control should begin at Petal Fall, they are often unsure how many additional sprays will be necessary to maintain protective chemical residues to prevent subsequent damage throughout the PC oviposition cycle, which varies according to temperatures and weather patterns after Petal Fall.
Recently, researchers at the Geneva Station have developed an oviposition model to determine when control sprays after Petal Fall are no longer necessary to protect fruit from PC damage. This model is based on the assumption that residues from control sprays after Petal Fall only need be maintained on fruit and foliage until about 40% of the oviposition cycle is complete, which is predicted by the model to occur at 340 DD (base temp 50 F) after Petal Fall. A more detailed discussion of this model and its validation can be found in the article published in the New York Fruit Quarterly Vol. 2, No 2: "Timing Insecticide Applications for Controlling Plum Curculio Using a Predictive Model". No one knows exactly why it is not necessary to apply PC control sprays after 40% of the oviposition cycle is complete. This parameter was chosen from initial experiments designed to compare the effectiveness of different schedules of control sprays after Petal Fall in protecting fruit from PC injury. Probably, this strategy works because, after 40% of PC oviposition is complete, adults usually are not moving into the orchard from outside sources, or moving around within orchards from tree to tree. Therefore, by this time, adults residing in treated trees have already been killed by insecticide residues and are unable to complete the remainder of their normal oviposition cycle.
In order to use this strategy: (1) Treat the entire orchard at Petal Fall with a broad spectrum insecticide. (2) Start calculating the accumulation of DD after Petal Fall (Base temp 50° F). (3) No additional sprays are necessary whenever the date of accumulation of 340 DD falls within 10-14 days after a previous spray.
This conventional strategy is probably only necessary for commercial apple orchards in which PC fruit damage has been observed frequently, or for orchards thought to be particularly vulnerable to infestation from codling moth or the European apple sawfly. Usually, orchards that chronically suffer fruit damage from PC are relatively small blocks located next to abandoned orchards or surrounded by woods or woodlots, which are favorable sites for overwintering of PC adults. Some larger orchards bordered by woods on one or more sides may also be at risk for chronic infestations of PC.
Petal Fall Spray, Oviposition Model Border Sprays
This program is similar to the previous program, except that after the Petal Fall spray is applied, additional sprays as determined by predictions from the oviposition model are applied only to the border rows of the orchard (outer 2-4 rows). When using this strategy, it is difficult to treat the ends of orchards in which rows are perpendicular to hedgerows or wooded areas. The only practical way to protect these edges is to drive along the edge of the end trees, with only one side of an airblast sprayer activated to attempt to blow spray back into the block to cover as many trees near the end of the row as possible. Usually, depending upon the size and spacing of trees, at least 2-4 of the end trees in each row will be adequately covered by the single-sided s sided sprayer application. Using this strategy assumes that any PC that have migrated into an orchard prior to Petal Fall will be killed by the Petal Fall spray, and any additional adults coming in after Petal Fall will be killed by border row sprays before they can damage fruit in the outer rows of treated trees or migrate into the interior of the block. This strategy will probably be effective in controlling plum curculio in typical commercial apple orchards that have had no previous history of observed fruit damage from plum curculio at harvest.
Border Sprays, Petal Fall and Oviposition Model
In this program, only the border rows and end trees within each row are treated at Petal Fall for control of the PC. Subsequent sprays are applied only to border rows and end trees according to oviposition model predictions. This strategy can be used in orchards having no previously observed history of plum curculio damage in which there is a desire to use only selective pesticides to encourage the buildup of natural enemies for biological control of mites and other foliar pests. In orchards in which this strategy is used, it may be necessary to consider applying a limited program of selective insecticides for control of the first generation of codling moth. It is also a good idea to closely examine fruit from both border rows and interior rows for damage at harvest from PC. If traces of PC damage are observed in fruit harvest evaluations, it may be necessary to apply one of the more conservative PC control programs during the subsequent growing seasons until PC damage is eliminated.
Coming Events:
Codling Moth: Calculate degree days (250-360 DD base 50F) from 1st CM moth capture in pheromone traps to time insecticide spray in blocks where CM are a problem.
Obliquebanded Leafroller (OBLR): Hang pheromone traps in orchard. Begin to accumulate DD (base 43 F) from 1st capture.
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