Two-spotted spider mite (Tetranychus urticae)
Pest description and crop damage Spider mites (Acari, Family Tetranychidae) are tiny, spider-like animals that produce webbing and are generally found on the undersides of leaves. Mite damage in hemp 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. The cause of this population explosion is proximity to dusty roads and hot, dry weather.
Biology and life history Spider mites overwinter in leaf litter and other debris on the soil surface. Twospotted spider mite has a very wide host range and in spring colonizes many weeds, crops, and native plants. It thrives in hot weather and can build up large populations rapidly during summer.
Scouting and thresholds Mite management requires early scouting. Initial mite infestations can be 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 tend to be stressed for some reason (e.g., dry spots, low spots, and edges). There is no established treatment threshold for spider mites in hemp, but it is well-known that treatments must be applied early in the infestation process to achieve control.
Spider mites are known to be strongly affected by predatory mites. Many species of insects are also known to feed on spider mites, including predatory bugs, thrips, lacewings, and ladybird beetles.