As pear IPM becomes more challenging, growers and consultants have turned to WSU for help. In 2017 WSU-TFREC Beers lab and the DuPont Extension lab teamed up with area consultants to expand our efforts toward sustainable pear IPM. Funding support is provided by the Tree Fruit Research Commission and WSDA Specialty Crop grants. Check our What’s New section frequently for the latest updates on research you can use today.
Challenges for Pear IPM
Growers and consultants tell us that pear IPM is having a tough fight. 2016 was a difficult psylla year after a challenging mite year in 2015. We are faced with the challenges of growing resistance to available products,
Insect resistance to pesticides is measured several ways. Technical resistance is measured based on the LD50 (dose at which 50% of the population is killed). This can occur when field rates are still reasonably effective but is a sign of growing break down in efficacy. Growers are often more interested in mortality when a field rate is applied.
Psylla – Based on 2016 data from Dr. Thomas Unruh at USDA Wapato, the following is a summary of mortality of a range of products: Nexter and Delegate show no evidence of resistance or tolerance. Agrimek and Admire are showing moderate efficacy but some sites show modest resistance to these two materials. Psylla at all sites show extreme resistance to Pounce and Warrior.
Mites – In 2014 and 2015 Dr. Betsy Beers, Washington State University, screened mite adulticides and ovicides for resistance. Using a resistance ratio that compares the lethal concentration for 50% of the population compared to what it would be for a susceptible population they predict a resistance ratio (RR=LC50 (R)/ LC50 (S). In general, a resistance ratio (RR) <3 = no resistance, RR 3-7 = transitional, and RR > 7 = resistant (Flexner 1988). Agri-Mek, Acramite, Onager and Zeal had resistance ratios where most populations were over 10, considered resistant. In some populations the lethal concentration was 10,000 times higher than that of the susceptible population.
High resistance ratios translates to low predicted mortality in the field. Mite populations collected from Chelan county varied from 2 to 22% mortality for Agri-Mek and 10-45% for Acramite adulticides. Ovicides were more highly variable with no mortality predicted in some populations and 100% in others for Onager and Zeal. This will put increasing pressure on the two materials Fujimite and Zeal which are working well.
Difficulty managing vegetative growth
Water sprouts provide succulent leaves for psylla in June and July. Because water sprouts provide one of the only sources of succulent leaves at this time of the year, water sprout removal technique can help reduce the psylla population (Hodkinson 2009).
Historically, growers had crews remove water sprouts in late June and early July. This technique can eliminate a large portion of the psylla population. With increasing pressure on labor it is more difficult to employ this management.
Psylla reproduction tends to be higher in high nitrogen tissue. For example, Daugherty (2007) found 60% more nymphs and eggs on high nitrogen vs low nitrogen treatments. However, nitrogen management is more difficult to predict in large trees because a significant portion is cycled in the plant tissue.
Natural Enemies in Pear Orchards
Why look to natural enemies for sustainable Pear IPM?
With evolving resistance to pear chemistries and the loss of some chemistries on the horizon there is increasing interest in how we can optimize the work natural enemies do in our orchards.
Past projects have supported beneficials and reduced pests before. For example, in the Wenatchee Valley Pear IPM project, natural enemies were far higher in the soft blocks; the principal ones found were Deraeocoris brevis, Campylomma verbasci, lacewings, earwigs and Trechnites sp. Pear psylla populations were higher in the soft blocks in the first year, but declined in subsequent years to levels similar to the conventional blocks. Fruit marking was higher in the first year in the soft blocks due to pear psylla, but damage levels were similar in later years.
Since these projects were completed in the 90s pear chemistries have changed and it is time to take another look.
Who are the Key Natural Enemies in Washington Pear Orchards?
Deraeocoris brevis piceatus is an abundant predator found in Pacific Northwest apple and pear orchards. They overwinter as adults and have multiple generations per year. Deraeocoris tends to emerge from winter quarters in March. For more information.
Anthocoris spp are particularly well adapted for feeding on pear psylla and can play a major role in the biological control of this pest. Anthocorids overwinter as adults (multiple habitats). They have multiple generations per year and tend to be active very early. They have a strong preference for psyllids. They are common outside of orchards and have a strong preference for trees and shrubs such as willow, alder, poplar, bitterbrush (Horton 2017). For more information.
Campylomma verbasci (Miridae; mullein bug) Generally thought of as a pest in apple, campylomma is an omnivore that also consumes large amounts of pests in pear orchards including aphids, psylla and other soft-bodied arthropods. It overwinters in an egg stage (i.e., in apple wood) and has multiple generations per year. It is common outside of orchards in herbaceous plants (i.e., mullein) and woody plants.
Brown lacewings (Hemerobius spp.) Brown lacewings are an important predator of aphids, psylla and mites and can become abundant where soft IPM programs are used. They overwinter in a mix of stages and have multiple generations per year. They are among the earliest of our predators. For more information.
Green lacewings (Chrysoperla carnea, Chrysopa nigricornis) Green lacewings are good predators of aphids and to some extent psyllids. They overwinter as adults. They are fairly early to emerge post-winter with larvae present from late June to early September. They are common outside of orchards on many plants both woody and herbaceous.
Earwigs Often thought of as a pest, the European earwig is an important predator in pear and apple orchards feeding on aphids, pear psylla, mites and insect eggs.
When are natural enemies in the field?
Dr. David Horton, USDA ARS has recently done extensive work tracking natural enemies in orchards. The figure below shows a summary of when adults and immatures were available in a number of orchards tracked. The result is like a relay where different natural enemies are more prevalent at different points of the season.
Pear IPM Strategies
Conserve Natural Enemy Populations in your Orchard
Consider the table below and the non-target impacts of pesticides in your pesticide decisions.
Good coverage of both sides of the tree where the volume of water is sufficient to thoroughly wet and cover the tree (110+ gal/acre) are always important for good pesticide efficacy. Surfactants help achieve better coverage. Alternate row sprays are not recommended.
Pruning to Avoid Excess Vigor
Remove 1-2 large branches per year for renewal. Pruning that is too aggressive will result in excess vigor the following year.
Remove Water Sprouts
Water sprouts are the only source of succulent leaves in June for psylla. Remove water sprouts before they develop woody attachment to limbs, normally before the end of June.
Pear trees should receive the minimum nitrogen fertility to maintain proper tree and fruit growth. Over-fertilization can extend terminal growth and delay hardening off. This provides optimal late feeding conditions for psylla.
What’s New in Pear IPM
Pear IPM Delayed Dormant Materials
By Betsy Beers and Louis Nottingham, March 23, 2017
Delayed dormant materials are about to go out for pears this season. We have been receiving questions about which materials will have the best efficacy. Here are the results from two bioassays conducted this spring. The first trial (Fig. 1) was done using a new protocol directly spraying psylla using a Potter spray tower and should be interpreted with caution. The second experiment was done by dipping psylla in materials, instead of directly spraying (Fig. 2). Please keep in mind that this efficacy could change quickly in the OPs that can gain resistance as they are used again more frequently.
By Betsy Beers and Louis Nottingham, April 10, 2017
Growers are asking about a number of new and old materials designed to repel winterform psylla adults from entering the orchard and reduce egg laying. Below are the results from the first round of assays screening 14 materials.
Individual pear trees (potted d’Anjou, two years old, bud-break stage) were sprayed with materials and placed into a large cage in the greenhouse (Figure 1). Overwintering psylla were collected from an untreated pear Orchard in Wenatchee in March of 2017, and released into the cage. After a week, adults and eggs were counted on each pear tree. Two identical experiment were conducted; each containing 3 replicates of treatments.
The results of this experiment were not astounding from a statistical standpoint; however, the general trends will help narrow down which materials are worth pursuing in future experiments and field trials. Overall, Surround appeared to be the most effective at repelling psylla, having the lowest numbers of adults (Figure 2) and eggs (Figure 3). Cedar oil, pine oil, and Microna AG also seem to be in the upper bracket of repellency. CNI paraffin oil, dormant oil and Cinnerate showed marginal levels of repellency; while the rest did not appear to have a detectable effect. Additionally, no materials resulted in visibly detectable phytotoxicity.
Surround WP appears to be the best product for repelling adult psylla, of those we tested. There is certainly potential for other products such as the Surround-like products (Microna appears especially promising based on these results) and conifer oils. Surround-type products should be of particular interest for a few reasons. Surround WP is becoming more expensive with greater use, and seasonal demand often outweighs the supply. Although, similar products were not as effective in this trial, field results may differ. Also, formulations may improve in the future to increase efficacy; remember, the formulation for Surround has changed and improved since initial release. Conifer oils (pine and cedar) are probably too expensive to justify largescale use, currently. However, these products are not manufactured for agricultural use, which could change if the using conifer oils appears to be a method worth pursuing. It is reasonable to think that an agricultural-use product could be developed for a reasonable price if the demand is present.
Table 1. Product list and reason for selection in trial
|Product||Active Ingredient – % product in solution||Expected type of Repellent and Reason for Selection|
|Summer Oil||Light Petrol oil – 4%||Tactile repellent. Commonly mixed with insecticides.|
|Dormant Oil||Light Petrol oil – 4%||Tactile repellent. Commonly mixed with insecticides.|
|CNI Paraffin Oil||Mineral oil – 1%||Tactile repellent. Commonly mixed with insecticides.|
|Rex Lime Sulfur||Calcium Polysulfide – 7%||Olfactory repellent. Strong smell of sulfur which is toxic to many arthropods.|
|Cedar Oil||Cedar essential oil – 2%||Olfactory repellent. Psylla thought to migrate away from conifers (overwintering sites) in early spring.|
|Pine Oil||Cedar essential oil – 2%||Olfactory repellent. Psylla thought to migrate away from conifers (overwintering sites) in early spring.|
|Cinnerate||Cinnamon oil – 0.2%||Olfactory or tactile. Strong smell and known toxin to mites and soft-bodies insects.|
|Ecotrol EC||Rosemary and Peppermint oils – 0.5%||Olfactory repellent. Strong smell and occasional use as insecticide|
|Raynox||carnauba wax and modified clay – 6%||Tactile repellent or visual masking. Similar to Surround. Liquid formulation of clay product.|
|PurShade||calcium carbonate – 2.5%||Tactile repellent or visual masking. Used for protection against fruit sunburn.|
|Surround WP||Kaolin Clay – 10g/100ml||Tactile repellent or visual masking. Unpleasant powdery/dry surface. Odd color prevents host detection.|
|Diamond K Gypsum||Gypsum, Calcium, Sulfur – 10g/100ml||Tactile repellent or visual masking. Similar to Surround.|
|Microna AG||Calcium Carbonate – 10g/100ml||Tactile repellent or visual masking. Similar to Surround.|
|Microthiol Disperss Wettable Sulfur||Sulfur – 6.8g/100ml||Olfactory repellent. Strong smell of sulfur which is toxic to many arthropods.|
Pear IPM Scouting
Beginning in early March 2017 the Pear IPM team has been scouting in 19 pear orchards in the Wenatchee River Valley. This information will be used to create an IPM scorecard based on pest and natural enemy numbers. Below are the first six weeks of pear psylla data. More updates will be included here over the course of the season.
Pear IPM Project
WSU Research and Extension Betsy Beers, Louis Nottingham, Tianna DuPont and Christopher Strohm in collaboration with many consultants in the area launched a renewed effort in pear IPM this spring. This project includes new research trials and extension efforts to find solutions to pear pest management challenges. Keep tuned to the news section of treefruit.wsu.edu for updates (subscribe here).
Department of Entomology
Washington State University
Tree Fruit Research & Extension Center
Wenatchee, WA 98801Phone: 509.663.8181 x234
Postdoctoral Research Associate
Washington State University
Tree Fruit Research & Extension Center
1100 N Western Ave., Wenatchee, WA 98801
WSU Tree Fruit Extension
(509) 663-8181 ext 211