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Pear Psylla Repellency Asssay

by Louis Nottingham and Betsy Beers, 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.

Background

Pear psylla control is becoming increasingly difficult, especially in regions of the Pacific Northwest like the Wenatchee Valley where pear orchards dominate the landscape. In high pressure locations, an important factor in pear psylla control is delaying their immigration and egg laying in the early spring. A method that is gaining popularity is early season repellency, as is seen in the increased use of the kaolin clay product Surround WP. Repelling overwintered adults during the early season delays egg laying until later in the spring, which causes psylla generations to occur in clear increments, and thus allowing for more precise insecticidal control. Additionally, trying to control overwintering adults with insecticides is often a fruitless effort (no-pun intended), because of their high mobility among orchards and uncultivated areas, as well as their increasing resistance to most insecticides. Due to the success of Surround WP as a repellent, we sought to determine if other agricultural and non-agricultural products may also act as repellents for overwintering psylla. Products were chosen based on stated interest from field advisors, growers or researchers. Table 1 has each product listed and the reason it was chosen.

Methods

Figure 1. Potted trees under experimental cage/arena in greenhouse.
Figure 1. Potted trees under experimental cage/arena in greenhouse.

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.

Results

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.

Conclusions

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.
Figure 2. Average (±SEM) psylla adults found per tree for each treatment. Bars not sharing a letter are significantly different according to a Student’s t test.
Figure 2. Average (±SEM) psylla adults found per tree for each treatment. Bars not sharing a letter are significantly different according to a Student’s t test.
Figure 3. Average (±SEM) psylla eggs found per tree for each treatment. Bars not sharing a letter are significantly different according to a Student’s t test.
Figure 3. Average (±SEM) psylla eggs found per tree for each treatment. Bars not sharing a letter are significantly different according to a Student’s t test.
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