Notes on Apple Insects
Mites

Identification

European red mite (ERM), two-spotted spider mite and apple rust mite are all pests of Ontario apples. These mites are difficult to see with the naked eye so use a microscope or hand lens to examine leaf samples. ERM nymphs and adult females (0.4 mm) are dark orange to brown-red in colour. The ERM passes through three immature stages between egg-hatch and adulthood; these are called the larva, protonymph and deutonymph. A newly hatched larva has three pairs of legs while subsequent nymphs and adults have four pairs. Straw-coloured males (0.28 mm) are smaller than females, with a pointed abdomen and proportionately longer legs.

Two-spotted spider mites (TSSM) are also straw coloured but can be distinguished from ERM by two dark spots on their backs. When populations of TSSM are high, they create a characteristic webbing on the under surface of the leaf.

Apple rust mites occasionally cause problems. Rust mites are much smaller in size than other pest mites, are beige or tan in colour and are carrot-shaped.

All of these mites remove sap, chlorophyll and nitrogen from leaves. High populations of mites can cause "bronzing" of the leaves. Prolonged feeding by high levels of mites in early to midsummer can lead to a reduction in shoot growth and fruit bud set the subsequent year. Fruit size, colour, soluble solids and firmness can also be affected.

Period of activity

ERM overwinter as eggs in the crevices and under scales of the bark. ERM nymphs are present on leaves around tight cluster. TSSM appear later in the season, generally from mid to late summer. By August ERM have begun to lay overwintering eggs on the calyx end of apples and no longer threaten the crop. In mid to late summer TSSM adults migrate from the tree canopy to weeds on the orchard floor, where they overwinter.

Monitoring and thresholds

Collect two leaves from each of 25 trees and count mite eggs, nymphs and adults using a microscope. Note the presence of beneficial mites. In general a ratio of one Amblyseius fallacis (a predatory mite) for every 10-15 pest mites provides effective biological control.

The economic threshold for mites varies with the time of year. Early in the season, when there is little foliage on the trees, thresholds are lower. Later in the season, when there is more foliage and more leaves are available for photosynthesis, the thresholds are higher.

Table 1: Thresholds for European Red Mite and Two-spotted Spider Mite on Apples

Management notes

ITSSM is generally more difficult to manage than ERM. Use miticides at the highest labelled rate if necessary and refer to the pesticide label for details. Be aware that miticides are not effective on all mites and may target a specific life-stage of the mite. Refer to Table 2. Activity of Miticides Registered on Apple and/or Pear in Ontario, on this page.

The use of pyrethriod insecticides in orchards can cause mite outbreaks. Avoid their use whenever possible. Some research suggests that repeated applications of neonicotinoids like Assail may also increase mite populations.

Wait two weeks after spraying a miticide to determine if the product was effective, as some are slow to act.

Table 2: Activity of Miticides Registered on Apple and/or Pear in Ontario*

* Registered for use on apple or pear unless indicated otherwise. Use established thresholds to time applications. Miticides are most effective when applied alone, using recommended rates and water volumes. Apply each miticide only once per season to delay the development of resistance.

Learn more...

• Mite Pests and Their Predators
• Notes on Apple Diseases and Insects
• OMAFRA Publication 360 Apple Calendar
• OMAFRA Publication 360 Fruit Production Recommendations
• OMAFRA Apple Index page