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Early Options for Psylla Management. April 10th, 2017

Overwintering Pear Psylla Adult on Bartlett Stem.

Recent snow in late March provided a welcome delay in bud maturity that has recently developed to ½” green as of this report. With temperatures now moving into the upper 70’s, reaching 80oF by Tuesday, the pear psylla adult will be increasingly active throughout the Hudson Valley as we move through the pre-bloom period.

As psylla egg counts build from 0.0 per bud on 3rd of April to 0.6 or 29 eggs / 50 buds as of the 10th April now at ½” green green, management to inhibit intensive egg laying should begin. Considerations for management in southern blocks and orchards along the Hudson River provide a timely window as dry weather and orchard access permits. Cooler temps and rain are expected later in the week the week when temps move back into the mid 60’s over the weekend.

In the overwintering stage, the adult lingers about the orchard and woodland edge from fall, through the winter into spring. Adults are often seen in flight during the warm hours of the day, with increasing movement of woodland adults into the orchard over the next few weeks. After mating, females begin to produce the first of three to four generations beginning with egg laying and nymph hatch from late March through June.

Strategies to manage pear psylla include prebloom applications of ovipositional deterrents, ovicides and insecticides aimed at the adult and nymph populations. Early management should begin upon the first signs of the egg. To delay the insect from laying eggs, Surround WP or oil, both acting as a barrier film, can be used. Either of these products will reduce egg laying by adult pear psylla. Delaying oviposition of the adults buys time for a greater number of over wintering psylla to enter the orchard from the hedgerows and woodland for a later adulticide application.

2016 Pear Psylla Egg Nymph Reduction Using Early Oil Applications

In 2016 we made two applications of oil at 1 and 2%, collecting egg and nymph presence over the past month. The results of the data from data collections from this trial is shown below (Graph 1.). Simply, we see a dramatic reduction in both nymphs and eggs with the use of these two applications. The use of Surround, used exclusively during the prebloom stage has provided excellent reduction of the 1st generation nymphs through reduced egg laying management with no observed clay residue on fruit at harvest.

We often think a single application of oil and a pyrethroid will ‘do the job’ during the pre-bloom period. This data suggests that the use of oil alone showed significant difference in oviposition and nymph reduction this season. Since two applications were made, using 2% over 1% appeared to also make a numeric difference in egg and nymph numbers. Now that the adults are in the orchard, it would be wise to consider the use of insecticides to control the adult population as we move toward bloom. However, pyrethroids are known to have reduced efficacy when used during warm temperatures above 70oF. We have seen pyrethroids completely fall down in psylla management over the past 5 years, likely due to the insects’ ability to detoxify this class of insecticides. Considerations for bee attractiveness for pollination by not employing pyrethroids near bloom due to bee repellency, and for general pollinator conservation, should also be a part of our strategy this season as the honeybee is not particularly fond of pears relative to other tree fruit.

The advantages of using oil to control this insect are many. Oil is still a relatively inexpensive material for which there has been no mechanism for resistance development by the insect. It provides a degree of egg laying deterrence to treated buds and wood lasting a week or two depending on rates and weathering. Higher rates would be applied at the dormant stage this week, using one spray of 3% oil, or two of 2% to green cluster. This rate will also reduce overwintering populations of San Jose scale, European red mite, pear leaf blister mite, and Comstock mealybug. If you begin at swollen bud, one spray at 2% or two at 1% up to white bud would suffice. Contact of the adult by oil droplets will cause mortality while applications over top of the egg will reduce adhesion, often causing them to dislodge from the tree. Oil applied prior to oviposition acts to delay and synchronize egg laying later into the season, producing subsequent emergence of the nymphs for a concentrated management approach using a single insecticide application. Negative observable impact of oil applications has been shown to cause enlarged lenticel on developing stems which may have impact of plant respiration.

Ovicides can also be employed to kill the eggs prior to hatch. The use of Esteem and Centaur work as insect growth regulators (IGR’s) to inhibit development of various life stages. Esteem 35WP, used prebloom to kill the egg stage of psylla and reduce the viability of eggs laid by treated adult, should be applied prior to sustained egg laying with 0.25% v/v horticultural spray oil. Esteem may be applied once at delayed dormant to “pink stage” at 5 oz/A, or two applications at delayed dormant to “petal fall” stage at 4-5 oz/A, as a tactic for both psylla reductions and as a resistance management strategy. Remember, its mode of action is as an ovicide, so it will not reduce the adult or nymph population directly, most effectively used if the material is on the wood or foliage prior to the eggs being deposited.

Using an ovipositional deterrent (oil, Surround WP) is a prerequisite to at least two follow-up strategies. One option, upon completed migration of the adults into pear orchards, the use of an adulticide is made to kill the adults, before significant eggs have been laid. Adulticides would be employed this season from mid to late April to significantly reduce the adult population. The choices for managing adult psylla include the neonicotinoids Actara 25WDG at 5.5 oz/A and Assail 30SG at 4–8 oz/A; and the pyrethroids, Ambush 25WP and Pounce 25WP at 12.8–25.6 oz/A; Asana XL 0.66EC at 7.3-12.8 fl oz/100 gal.or 9.6-19.2 fl.oz/A (from dormant to white bud stage; postbloom rates are lower); Proaxis 0.5CS at 2.6–5.1 fl oz/A; Danitol at 16-21.3 fl oz/A; or Warrior II at 1.26-2.56 fl oz/A. The older insecticide Thionex is no longer labeled. Multiple applications often need to be applied in order to achieve optimum early season control.

Seasonal Pear Psylla BIology

Cool weather provides conditions to optimize the use of pyrethroids. However, the use of these insecticides over the past 20 years has decreased pear psylla susceptibility to the pyrethroids such as Asana (esfenvalerate) and Warrior (Lambda-cyhalothrin). Their use should be limited and used only during periods of cool temperatures.

The economics in management is a driver in decision-making for pear production. Surround WP is most effective at the highest labeled rate of 50 lbs. / A (roughly $1.00 per pound) costing about $50.00 / A. Two to three applications during the pre-bloom and petal fall period have shown to be a viable approach to early psylla management. Although it does not kill the adult, it will inhibit egg laying as long as there is sufficient material on the foliage and stem to keep adults from the tree. The use of a single prebloom application at 50 lb./A Surround was comparable to a single 2% application of Damoil in reducing oviposition when applied at the same time. Yet as the season progressed, the Surround treatment performed better in reducing the nymph presence on foliage during later assessments compared to other pre-bloom choices.

The stratification or layering of the kaolin clay, the active ingredient of Surround, builds on the limbs to maintain the product on the tree. Using early season applications through to petal fall have additional benefit of controlling plum curculio along with reducing egg laying from the 1st generation of psylla adults. Surround has not been shown to be toxic to the insect and as such, is an important tool for use in resistant management strategies for this insect. The additional information on this topic review the 2012 Scaffolds article addressing early Surround WP followed by 1% oil strategy.

Ending the use of Surround WP at Petal Fall will reduce the overall cost of management using this product while reducing the potential for clay residue depositing on the fruit at harvest. However, pear will require the continued use of management of pear psylla throughout the remainder of the season. We have found the use of 1% oil at a two-week interval to provide sufficient control of the nymph population by reducing both egg laying and nymph survival. See 2015 RESULTS OF INSECTICIDE AND ACARICIDE STUDIES IN EASTERN NEW YORK; Hudson Valley Laboratory, Highland, NY pgs 25-30.