European Red Mite sampling date estimates
- Background

        Estimates for key points in European red mite population cycles are based on lifecycle studies by S.E. Lienk, C.M. Watve, and R.W. Weires, New York State Agric. Exp. Sta. (NYSAES), Cornell University as reported in "Common Tree Fruit Pests" by Angus J. Howitt, Michigan State University Extension, NCR 63, October 1993.

         Optimum resample intervals are estimated as the number of days required for European red mites (ERM) to complete half of one egg-maturation-next generation eggs cycle when scouting finds the population density is below threshold.  If the ERM population density is "Far below threshold", the next sample date is estimated as the number of days required for ERM to complete a full generation cycle. 

        Dr. Jan Nyrop of Cornell University and NYSAES devised the Presence/Absence sequential sampling scheme for efficient determination of whether pest mites on apple foliage require suppression.

        The University of Maine Apple IPM Program recommends adjusting dates of the NY system for use in Maine as indicated in tables below.  The unadjusted NY dates may be more appropriate for other New England states.  Check your state guidelines.

Procedure: Start with a randomly selected tree and choose subsequent trees to get leaves from throughout the block. Collect 5 leaves per tree, with leaves from each quadrant of the canopy. Choose only middle-aged leaves from the middle of fruit clusters or shoots. Do not collect the youngest or oldest leaves as they can give a biased count. Examine the top and bottom of each leaf with a magnifying lens. Count as infested only those leaves that have one or more moving hatched European red mites or twospotted spider mites. Mite eggs do not count toward the threshold.

Interpretation: Compare the number of mite-infested leaves to the values in columns 1,2 and 3.  Sample results are interpreted as follows:

less than column 1 – If the number of infested leaves is less than or equal to the number in column 1, the sample is far below threshold and resampling can wait for 11-16 days (depending on temperatures).

between columns 1 and 2 – If the number of infested leaves is greater than column 1, but less than the value in column 2, the orchard is below threshold now but needs to be resampled in 6-10 days (depending on temperatures).

between columns 2 and 3 – If the number of infested leaves is greater than column 2 and less than column 3, more leaves must be examined to decide if the mites are above or below threshold. A decision is always reached by the time the sample size reaches 100 leaves.

equal or greater than column 3 – If the number of infested leaves is equal to or greater than the value in column 3, the sample is above threshold for this time of year and prompt treatment is recommended.

      Threshold values and timings vary between states.  The estimates of European red mite re-sampling dates reflect reproduction rates as affected by temperatures since the last sample date.  The optimum re-sample date can be used with whatever threshold values are recommended in your state on that date.

Presence/Absence Chart for Threshold of 1 mite per leaf or 30% of leaves infested
Petal fall to June 1 in NY, Petal fall to June 15 in Maine.
Collect sample leaves from middle of fruit clusters.

(Stop limits on this chart for samples of 40-80 leaves are not directly from NY recommendations but are extrapolated from charts for higher thresholds)

Presence/Absence Chart for Threshold of 2.5 mites per leaf or 59% of leaves infested
June 1-30 in NY, June 16 - July 15 in Maine.
Collect sample leaves from middle of fruit clusters or from middle of shoot terminals.

Presence/Absence Chart for Threshold of 5 mites per leaf or 77% of leaves infested
July 1-31 in NY, July 15 - August 1 in Maine.
Collect sample leaves from middle of shoot terminals.

Presence/Absence Chart for Threshold of 7.5 mites per leaf or 86% of leaves infested
August 1-15 in NY, August 1-15 in Maine