The dry and hot weather conditions are very conducive to some insects, including mites. We are seeing higher than expected mite incidence at the West Madison Agricultural Research Station in our day-neutral strawberry plot and have heard reports in apple as well. Several species of mites can be present including two-spotted spider mites (Fig 1), European red mite (Fig 2), and apple rust mites (Fig 3).

Two-spotted spider mites (TSSM; Fig 1) overwinter in ground cover and as the ground vegetation dries, they move up into trees. The adults have two distinct spots located behind the eyes. They build webbing on the underside of leaves.

European red mites (ERM; Fig 2) overwinter as eggs in the bark around the base of buds and spurs. They hatch in spring around tight cluster. Adult females are bright red and males are dull green to yellowish brown. 

Apple rust mites (ARM; Fig 3) overwinter as adult females under the bud scales of apple trees and become active at budbreak. They are very difficult to see and examination of the leaf midrib with a hand lens is usually required. 

Management

Mites can be kept in check with biological control from naturally-occurring predatory mites. A ratio of one predatory mite to 10 pest mites or at least one predatory mite per leaf should provide adequate biological control. If you see predatory mites at these levels, treatment can be delayed by a week and mite populations reassessed to preserve predatory mites. In addition, avoid applying excessive nitrogen fertilization as it may cause TSSM population to build up. As mentioned before, dry and hot conditions are favorable to mite build up so make sure to scout for mite presence. Finally, pyrethroid insecticides are known to cause mite flare ups and early season insecticide applications can reduce natural enemy populations such as predatory mites, minute pirate bugs (Orius spp.) and lady beetles that will help control mite populations. This emphasizes the need to use action thresholds for early season pests to reduce chemical interventions early in the season that would kill biological control agents.

It is recommended to scout summer populations on 50% spur leaves and 50% shoot leaves throughout the orchard and use different thresholds depending on the time of year:

• 2-3 mites/leaf from mid-May to mid-June
• 5-7 mites/leaf from mid-June through July
• 10-15 mites/leaf in August

Many products are available to control pest mites and Michigan State University recently published an article with a table of products for you to refer to. You can also refer to the Midwest Fruit Pest Management Guide for more pesticide recommendations and, as always, read and follow the labels.

Happy growing season!

This article was posted in Apples, Insects and tagged apple rust mites, Apples, Christelle Guédot, European red mites, insects, Mites, two-spotted spider mites.