Dispersal of Typhlodromus pyri into Apple Blocks

The predatory mite, Typhlodromus pyri, has been shown to be a very effective predator of the European red mite in apple orchards. Lorraine Los (University of Connecticut IPM Program) and Dr. Chris Maier (Connecticut Agricultural Experiment Station, New Haven, CT) have introduced this beneficial mite into Connecticut orchards. This is part of a large multi-state project coordinated by Dr. Jan Nyrop from Cornell University.

T. Pyri is slow to spread from release blocks. If T. pyri is present in your orchard, there are several ways that you can help move them to other blocks. The first method discussed in the article below (dispersal of prunings) can be done in the winter. Jan Nyrop and David Kain from Cornell University have outlined these methods in the following article, which was originally published in Scaffolds, 4/16/99.

Lorraine M. Los, Fruit Crops IPM Coordinator, University of Connecticut

Release the Hounds

The mite predator Typhlodromus pyri can give biological control of European red mite when the predator is conserved in apple orchards. Experiments have shown that, once established in an orchard, this mite can completely eliminate the need for miticides. While T. pyri is endemic throughout much of western New York, it can take as many as three years in specific orchard blocks for predator numbers to increase to the point where biological control is realized. Moving T. pyri from blocks where they are abundant to sites where more predators are desired (seeding) can speed this process.

T. pyri feeding on European red mite

T. pyri feeding on European red mite
photo: Jan Nyrop, Cornell University

Instances will occur when it is necessary to use pesticides that are toxic to T. pyri to control other orchard pests. To combat the resulting disruptions of mite biological control caused by these pesticide applications, it has been suggested that orchardists establish sites to be used as mite “nurseries.” These sites would not be treated with pesticides harmful to T. Pyri, and would be used as sources of predators that could be moved to orchards where predators are scarce. The practice of transferring them could, therefore, become an important ingredient of any integrated mite control program.

The first method of moving T. pyri from one orchard block to another is to place wood pruned from a source orchard in winter or early spring into a recipient orchard. Because T. pyri over-winter as adult females, prunings harbor predators, although numbers in each section of prunings are highly variable. We suggest placing all the prunings from one tree into another tree. It is probably not effective to simply spread the prunings beneath recipient trees. Pruned wood need not be placed in the recipient trees immediately after pruning, but should be placed there before or just when trees begin to produce green tissue the following spring.

The second method consists of transferring flower clusters from a source orchard to a recipient site. T. pyri move into flower clusters at Tight Cluster and remain there through bloom, probably to feed on apple pollen. As many as two to three predators can be found in each flower cluster and surrounding leaves. To transfer predators in this manner, at least 20 flower clusters (and associated wood and leaves) should be placed in each recipient tree. The flower clusters are easily attached with paper clips, staples or twist ties. Flower clusters may be stored for several days in a cooler before being affixed to receiver trees.

The third method of transferring T. pyri consists of collecting leaves during the summer from trees where T. pyri are abundant and placing them into recipient trees. Leaves are easily affixed to the target sites using staples. The number of leaves to use depends on the density of T. pyri in the source orchard. As a guide, at least 50 predators should be released in each target tree.

The fourth method of transferring T. pyri is perhaps the easiest and does not carry the risks of also moving unwanted pests that the three prior methods have. Artificial overwintering sites for T. pyri can be created by gluing burlap to the inside of tree wrap. These composite bands, approximately 12 to 16 inches in length, are then placed on source trees in early to mid-September by stapling them around the tree and/or large scaffold branches. In early December, these bands should be collected, tightly rolled with a rubber band used to hold them so, and placed in a sealed plastic bag with a bit (i.e. a “puff”) of wet cotton. The bag should be placed in an insulated storage container, which in turn should be placed in a cold, thoroughly protected environment that will buffer large temperature fluctuations. Ideally, temperatures should be maintained right at the freezing point. The following spring, the burlap bands should be placed around recipient trees at around the Half-Inch Green bud growth stage. While the number of predators that overwinter in bands is variable, as many as 400 predators can be transferred in each band. We suggest placing a single band on each recipient tree if the bands were collected from trees that harbored moderate to high numbers of T. pyri (one to two per leaf) the prior fall, and two bands in each tree otherwise.

While T. pyri overwinter throughout the tree, there are apparently many predators that overwinter on large branches or the trunk itself and that move into the canopy as foliage appears. Use of nurseries in which T. pyri are cultivated and transfer of branches harboring T. pyri from these nurseries to target sites should allow biological mite control to be more persistent on a farm-wide scale. The second season after seeding T. pyri and using non-disruptive pesticides in our IPM demo blocks in western New York, predator numbers were at levels of more than one/leaf by the end of August, and true biological control (that is, no oil or acaricides applications) of ERM was realized in all blocks by the third year.

Unlike petroleum oils applied early in the growing season, oils applied during the summer can have an adverse effect on phytoseiid numbers. However, this effect is apparently only significant when high volumes of oil suspension are applied. Our opinion is that oil applied using conventional airblast sprayers will have only a minimal negative effect on phytoseiid numbers. As such, summer oil applications can be recommended as a way to help manage European red mite numbers if predator numbers are insufficient for biological control.

For a more detailed discussion of the ins and outs of establishing predator mites, refer to New York IPM Pub. #215, Achieving Biological Control of European Red Mite in Northeast Apples: An Implementation Guide for Growers, by D.Breth, J. Nyrop and J. Kovach (1998), from which much of this information was adapted.

Written by: Jan Nyrop and Dave Kain, Entomology, Cornell University, Geneva, NY

Published in: Yankee Grower. 1999. Vol. 1, No. 6. November/December 1999. p.13-14.

Photo by Jan Nyrop, Cornell University

Reviewed by: Mary Concklin, UConn IPM. 2012

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