Insert for: Achieving Biological Control of European Red Mite in Northeast Apples: An Implementation Guide for Growers

Monitoring European Red Mite in Apples

Damage by European red mites (ERM) to apple leaves is best related to cumulative mite density, which is measured as mite-days. Apple trees with a normal crop load can tolerate approximately 500 mite-days before reductions in fruit yield or quality occur. Therefore, one goal of any mite monitoring program is to ensure that miticide treatments are recommended so as to prevent 500 mite-days from occurring. Another goal of a mite monitoring program is to allow biological control to take its course when mite natural enemies (phytoseiid mites) are present. So, a mite monitoring program should not recommend intervention with pesticides when treatments are not necessary. A final goal of a mite monitoring program is to indicate when the pest population should again be sampled to determine its status. If, at the time of sampling, mite densities are very low, then it is not necessary to sample the population again in a short period of time. On the other hand, if densities are currently close to but not greater than a treatment threshold, the population should be assessed again in a short period of time. The monitoring program described here meets these goals.

This monitoring procedure classifies ERM density into one of three categories:

1. greater than treatment threshold, indicating application of a miticide is necessary,

2. less than treatment threshold, but requiring assessment again in about 7 days,

3. much less than a treatment threshold and not requiring assessment again for 14 days.

ERM are small and often numerous. This makes counting these pests a tedious and often difficult task. For monitoring purposes, it is only necessary to record the number of leaves infested with 1 or more motile mites. A mathematical relationship between the proportion of infested leaves and actual density can then be used to classify mite density. Because higher mite numbers can be tolerated as the season progresses, three sampling procedures are used at different times of the growing season; one each for June, July and August with treatment threshold of 2.5, 5, and 7.5 mites per leaf , respectively.

The sampling guides are used as follows:

• Sampling trees from throughout the orchard block, collect five intermediate aged leaves from each of four trees. To make sure the leaves are of an intermediate age, pick them from the middle of the fruit cluster before July and from the middle of fruit clusters or terminals thereafter.

• Using a magnifier, examine the top and bottom surface of each leaf for motile mites (anything but eggs), and keep track of the number of leaves with mites on them.

• When all 20 leaves have been examined, compare this number with the numbers on the decision guide. If the number of leaves with mites is equal to the values on the guide, the decision is shown in the area below the value. When the counts fall into any of the shaded regions, sampling is terminated and a decision to either "Treat", "Sample in 7 days," or "Sample in 14 days" is made. If the counts fall in the region labeled "Continue sampling" collect and examine groups of 10 leaves until the counts fall into one of the shaded regions.

Relative Toxicity of pesticides¹ to the mite predator, Typhlodromus pyri.

Materials with a low toxicity can be used when needed. Pesticides with moderate toxicity should be used sparingly. Those with high toxicity must be avoided. Refer to your State Extension Pesticide Recommendations for ratings of relative efficacy and application timing for specific target pests.

¹ Check EPA and state registration status by contacting local Cooperative Extension representative. Registration status is changing annually and is not universal across all state lines. Use of product names does not imply endorsement of particular products. Read all labels for rates and timing.

For an updated version of this insert, contact Deborah I. Breth, CCE, PO Box 150, Albion, NY,14411

Authors:
Deborah I. Breth, Cornell Cooperative Extension, Lake Ontario Fruit Program
Jan Nyrop, Dept. of Entomology, NYSAES, Cornell University
Joseph Kovach, NYS IPM Program, Cornell University