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 Psylla Management using Reflective Plastic Mulch
By Betsy Beers and Louis Nottingham, June 1, 2017
In this experiment we evaluated a non-spray method for managing pear psylla: reflective plastic mulch. The reflective plastic mulch used in the experiment is a thin polyethylene film infused with aluminum manufactured by Star Metal Plating Inc; one side is reflective while the other is black (referred to as ‘metallized”). When laid on the ground with the reflective side facing up, light is reflected back up into the canopy, which may deter psylla adults from colonizing and ovipositing. Past research has demonstrated that this technique reduces densities of various insects in multiple crops, including the closely related Asian citrus psyllid. In addition to insect control, reflective ground covers can provide horticultural benefits in pears such as early fruit onset, increased flower bud formation and yield, and greater fruit production in lower portions of the canopy.
Three treatments were tested: ‘metallized’ plastic, black plastic, and bare soil. Each plot consisted of one tree with two 4 × 25 ft sheets of plastic laid on each side (Fig. 1), or no plastic for control plots. There were 6 replicates of each treatment. Adults, eggs and nymphs were counted weekly (data collection is ongoing).
Data will be collected for the remainder of the 2017 season, but initial results show clear treatment differences. Metallized mulch plots have shown significantly lower densities of adults (Fig 2), eggs (Fig 3) and nymphs (Fig 4) throughout the early season. Black plastic mulch generally had fewer psylla than bare ground, but reductions were less substantial than those from metallized plastic.
Pear Psylla Nymph Bioassay
By Betsy Beers and Louis Nottingham, June 1, 2017
A laboratory bioassay was conducted to test the toxicity of various insecticides/miticides to pear psylla nymphs (Fig. 1). Nexter (pyridaben), Vendex (fenbutanin-oxide), Nealta (cyflumetofen), FujiMite (fenpyroximate), and Bexar (tolfenpyrad), were chosen due to their similar modes of action: disrupting mitochondrial function. Bexar (tolfenpyrad) is still undergoing registration for pears. This assay is a part of a series involving Bexar which will help determine its most apt placement in future pear IPM programs, if approved. Actara (thiamethoxam) was included for comparison to a common product used in late spring and early summer.
Leaves with heavy pear psylla nymph infestations were gathered from potted plants in the greenhouse at WSU-TFREC, and sprayed in the lab with the products listed in Table 1. There were 5 replicated of each treatment. Percent mortality of 4th and 5th instars, combined, was analyzed.
Bexar was the most toxic product to pear psylla nymphs. Of the registered products, Actara 25 WG and Nexter 75 WP were the most toxic (killing ca 60% of nymphs), while FujiMite SC and Vendex 50 WP were marginally toxic (killing 25 and 10% of nymphs, respectively), and Nealta showed no toxicity (killed 0 nymphs). No phytotoxicity by any treatment was observed.
Pear Psylla Insecticide Bioassay – Egg Mortality
by Louis Nottingham
Two identical experiments were conducted in the greenhouse at WSU TFREC to test the ovicidal activity of various insecticides. The first involved nine insect growth regulator insecticides (IGRs), the second tested Bexar and Assail; both experiments included water as a control.
Experiment 1: The objective of the first experiment was to determine if and which IGRs commonly used in pears would prevent nymph development when applied to psylla eggs. Eggs were sprayed, then given time to hatch. Once sufficient numbers of honeydew producing nymphs were observed on control trees (9 days after application), all other treatments were sampled. All treatments began with similar numbers of eggs; therefor, differences in the numbers of nymphs should represent varying levels of toxicity among treatments. At nine days after treatment, no differences were observed in the numbers of nymphs that developed among treatments or the control in the first experiment.
- Key Finding: None of the IGRs tested reduced nymph development when applied to eggs.
Experiment 2: A second experiment was conducted to test the validity of this method, since no treatment effects were observed in Experiment 1. Two insecticides with recent evidence of ovicidal activity (Bexar and Assail 70WP) were tested in the same manner as Experiment 1. All treatments began with similar numbers of eggs; therefore, differences in the numbers of nymphs should represent varying levels of toxicity among treatments. At nine days after treatment, both Assail 70WP and Bexar had significantly fewer healthy nymphs than the water control.
- Key Findings: 1) The method was effective for detecting egg toxicity.
2) Assail 70WP and Bexar both inhibited the development of eggs into nymphs compared to the control.
Pear IPM Scouting
From March to September 2017, the Pear IPM team scouted 19 pear orchards on a weekly basis for pear psylla, mites, and their natural enemies. Orchards were managed conventionally, selectively, or organically, and all were located in the Wenatchee River Valley. This information will be used to create an IPM scorecard based on pest and natural enemy numbers.
Bubble Plots 1-4, In the plots below, each dot represents abundance of pests or natural enemies at one site from one date.
Plot 1 – Pest and Natural Enemy Seasonal Abundance
The size of the dot is relative to the highest catch average of the season. For example, the highest catch for Campylomma was 115 so the largest dot on the Campylomma line represents 115 and all other dots are relative to this. But for the Nigricornis lacewing the highest average was only 10 and all smaller dots are relative to this.
Plot 3 – Comparison of Scouting Methods – Seasonal Abundance
For the natural enemy categories (Campylomma, Deraeocoris, Lacewings, and Trechnites), the size of the dot is relative to the highest catch average of the season for that species using that scouting method (trap or beat tray).
Plot 2 – Natural Enemy Abundance Relative to Each Other
For the natural enemies (final 7 lines), the size of the dot is relative to the largest catch average of any species (in this case 115 Campylomma). In this graph you can compare the population from one site to another.
Plot 4 – Comparison of Scouting Methods – Relative Abundance
For the natural enemy categories (Campylomma, Deraeocoris, Lacewings, and Trechnites) the size of the dot is relative to the highest catch average of the season for any species (115 Campylomma) using that scouting method (trap or beat tray).
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 98801
Phone: 509-663-8181 x234
Louis Nottingham, PhD
Postdoctoral Research Associate
Washington State University
Tree Fruit Research & Extension Center
1100 N Western Ave.,
Wenatchee, WA 98801
WSU Tree Fruit Extension
1100 N Western Ave.,
Wenatchee, WA 98801
Phone: 509-663-8181 x211