Pest description and crop damage Tiny, spider-like animals on the undersides of leaves. Mite damage in potatoes is a minute stippling of the leaves and sometimes a bronzing. Mites reproduce rapidly and can build up to unmanageable populations in just a few days under the right conditions. What causes them to explode and take down fields is uncertain, but entomologists, growers, crop advisers, and others name some contributing factors:

1. Application of nonselective pesticides, such as pyrethroids, and certain carbamates and organophosphates, which negatively impact mite predators and allow spider mites to flare.

2. Proximity to certain crops such as corn, alfalfa, and mint, which tend to harbor mites.

3. Proximity to dusty roads.

4. Hot, dry weather.

The first is the most important factor. In most cases, mite outbreaks in potatoes are an induced problem, brought on by management practices aimed at other pests.

Mite management requires early scouting. Initial mite infestations can be very spotty within fields, making it important to sample for mites in several locations in each field. Because mites reproduce better on stressed plants, it is a good idea to check areas of fields that you know tend to be stressed for some reason (e.g., dry spots, low spots, and edges). It is also wise to check the edges of fields nearest to crops likely to have many mites. Try to recognize mite populations before significant damage is noted and certainly before webbing occurs.

Management—chemical control

Miticides must be applied at low thresholds in order to achieve effective control. Once populations exceed 5 mites per leaf, control with miticides may be difficult.