Notes on Stone Fruit Insects & Mites: Mites

Identification

European red mite (ERM), two-spotted spider mite (TSSM), pear rust mite and pear leaf blister mite are potentially serious orchard pests.

Mites are small and are best counted and identified with a microscope. Nymphs have three pairs of legs while adults possess four pairs. Female ERM are bright red while males are a dull greenish-brown. Both have white spots and six to eight hairs. Two-spotted spider mites are pale green to straw coloured, with two dark spots on their backs. High populations of two-spotted spider mites produce characteristic webs on the underside of leaves.

ERM and two-spotted mites remove sap, chlorophyll and nitrogen from leaves. High populations cause a condition called "bronzing". Prolonged feeding, particularly if populations are heavy in early to mid-summer, leads to a reduction in shoot growth and fruit bud set the next year. Fruit colour, soluble solids, firmness and size can also be affected.

Period of activity

ERM overwinter as eggs on the bark of trees. Two-spotted spider mites overwinter as adults on bark, weeds and orchard debris. Development of mites is correlated to temperature. From egg to adult takes seven days at 27°C and 40 days at 13°C. There are several generations per year.

Monitoring and thresholds

Count mites through examination of field-collected leaves under a microscope or with a 16× hand lens. Include the total number of eggs, nymphs and adults in the count. Loring and Babygold are useful indicator cultivars. See Table 1. Thresholds for ERM and TSSM on Peaches.

Table 1. Thresholds for ERM and TSSM on Peaches
Stage of crop development Threshold
(in absence of predators)		 Comments
Petal fall to 21 days after calyx 5-7 active mites/leaf Foliage still young and expanding
June to mid-July 7-10 active mites/leaf Control earlier if bronzing appears in the outer leaf canopy before this threshold is reached
Early July 10-15 active mites/leaf Abide by preharvest intervals
Postharvest 50 mites/leaf  
Non-bearing 30 mites/leaf  

Management notes

Miticides can be effective against mite eggs, nymphs or both. Apply Superior Oil in early spring to control overwintering ERM eggs. See Table 2. Timing of Superior Oil for European Red Mite Control on Tender Fruit, for more information. This spray is especially important in blocks where pyrethroids are used for control of other orchard pests. Critical timing for summer miticide applications, when thresholds are reached, is in early July.

Table 2. Timing of Superior Oil for European Red Mite Control on Tender Fruit
Crop Stage of Growth
Apricot dormant
Sour cherry prebloom, as buds are breaking
Peach ½ inch green to first pink
Pear green tip
Plum green tip

* Do not use Captan, Maestro or Bravo within 14 days of an oil application or crop injury could result.

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