Pest: spider mite

Common spider mite, copper fire, "Red spider" Tetranychus urticae (Koch) - English. two-spotted spider mite

Meaning:
Spider mites occur particularly strongly on light, sandy soils and in hot, dry years also on heavier soils. Substantial yield and quality losses are then possible.

Body:
The wintering of the spider mite on hops Tetranychus urticae takes place via yellow-orange, mated winter females preferably on dead leaves or side shoots. These "winter females" lay in spring glassy to slightly yellowish, about 0. 13 mm large, round eggs preferably on the underside of the leaf. Depending on weather conditions, the first six-legged larvae hatch between March and April (later larvae stages are eight-legged). A female can lay about 94, in extreme cases up to 125 eggs. In the course of the year, 6-7 generations are created.
Contrary to the term "red spider", spider mites are usually yellowish with two dark back patches.

Damage: The infestation begins at the lower leaves of the plant. The spider mite population then migrates very quickly upwards. Depending on the variety, there are more or less pronounced yellow spots on the leaves. These arise from the forming air chambers of the infected and destroyed leaf cells. With a trained eye or with a magnifying glass the spider mites and possibly their whitish summer eggs can be recognized. If a fine web can be seen on the undersides of the leaves already with the naked eye, the infestation is already very advanced. The spider mites use the spider mites primarily to increase their mobility, but also as protection against weather influences and predators (e. g. predatory mites). In addition, it creates a better microclimate for the spider mite population. In case of strong infestation by the spiders of the animals and their sucking activity the leaves and cones become copper red within a short time; hence the damage designation "copper fire" and "red spider" for the pest.

Development:
The significant influence of temperature on the development rate from the egg to the adult animal (Imago) can be seen from the following table:
Tab. : days for the development time of spider mites at 65-80% rel. LF
 

	<10°C	13°C	23°C	30°C	35°C	>40°C
Tage vom Ei bis Imago	-	36	13	7	6	-

Development cycle spider mite

Fig. 1: Annual cycle of the common spider mite (drawing: I. Hollweck)


Fig. 2: Spider mite infestation