|
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). There is no "far below threshold"
value for the first sample period of Petal Fall to June 1 (or June 15).
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)
Number of
leaves examined |
column 1:
not used for early season samples |
column 2:
if number of infested leaves is < or = to value in this column, then mites are
estimated to be
BELOW threshold |
column 3:
if number of infested leaves is = or greater than value in this column, then mites are
estimated to be
ABOVE threshold |
40 |
-- |
6 |
24 |
60 |
-- |
11 |
30 |
80 |
-- |
16 |
30 |
100 |
-- |
29 |
30 |
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.
Number of
leaves examined |
column 1:
if number of infested leaves is < or = to value in this column, then mites are
estimated to be
FAR BELOW threshold |
column 2:
if number of infested leaves is < or = to value in this column, then mites are
estimated to be
BELOW threshold |
column 3:
if number of infested leaves is = or greater than value in this column, then mites are
estimated to be
ABOVE threshold |
40 |
8 |
15 |
30 |
60 |
15 |
28 |
42 |
80 |
23 |
40 |
54 |
100 |
36 |
58 |
59 |
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.
Number of
leaves examined |
column 1:
if number of infested leaves is < or = to value in this column, then mites are
estimated to be
FAR BELOW threshold |
column 2:
if number of infested leaves is < or = to value in this column, then mites are
estimated to be
BELOW threshold |
column 3:
if number of infested leaves is = or greater than value in this column, then mites are
estimated to be
ABOVE threshold |
40 |
13 |
19 |
37 |
60 |
24 |
39 |
52 |
80 |
34 |
55 |
67 |
100 |
52 |
76 |
77 |
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
Number of
leaves examined |
column 1:
if number of infested leaves is < or = to value in this column, then mites are
estimated to be
FAR BELOW threshold |
column 2:
if number of infested leaves is < or = to value in this column, then mites are
estimated to be
BELOW threshold |
column 3:
if number of infested leaves is = or greater than value in this column, then mites are
estimated to be
ABOVE threshold |
40 |
18 |
27 |
40 |
60 |
31 |
47 |
57 |
80 |
44 |
65 |
74 |
100 |
63 |
85 |
86 |
|
