TETRANCHUS URTICAE AND THE
GREENHOUSE STRAWBERRY PLANT
Mites belong to the Chelicerata, a branch of arthropods and the second largest group of terrestrial animals. Within the order Acari, spider mites belong to the Acariformes with fossils dating from the Lower Devonian period 410 million years ago (Edgecombe, G. D., 2010). The two-spotted spider mite, Tetranychus urticae, is a web-spinning mite. The name refers to their ability to produce silk-like webbing used to create a colonial micro-habitat, protect against predators, communicate via pheromones, and provide a vehicle for dispersal. Tetranychus urticae represents one of the most polyphagous arthropod herbivores, feeding on more than 1,100 plant species belonging to more than 140 different plant families including species known to produce toxic compounds. It is a major pest in greenhouse production and field crops, destroying annual and perennial crops such as tomatoes, peppers, cucumbers, strawberries, maize, soy, apples, grapes and citrus. This report will concentrate on the greenhouse strawberry host plant. My management program is based on a 12 foot by 18 foot greenhouse with screened vents, air conditioning, dehumidifier, and two octagonal coliseums with four tiers each holding at least 16 plants, for a minimum 128 plants total. A successful harvest should be 90-100 pints of berries per season. Strawberry cultivars vary in susceptibility to two-spotted spider mite. Short-day cultivars are generally more tolerant of mite feeding than day-neutral cultivars, particularly later in the fruit-production cycle. Vernalization directly promotes plant vigor. Supplemental cold storage can promote a plant's vernalization. This can be accomplished in the controlled environment of a greenhouse. Plants with low amounts of chilling will have low vigor and will often develop intolerable mite infestations. Starting field berries as well as greenhouse berries in the greenhouse maximizes vegetative growth and vigor. Harden off field berries before transplant outdoors. Effective control of two-spotted spider mites will depend on an accurate scouting program. Feeding by the two-spotted spider mite consists of piercing and sucking of cell content on the lower surface of leaves. Damage appears as stippling, and bronzing of the leaves and leaf veins (Crenshaw, W., 2004). A good sampling program will give the grower an excellent idea of the presence and amount of spider mites in the greenhouse. Without a good scouting program, a grower might not realize that he has an outbreak of spider mites until it is too late. The conditions outside the greenhouse need to be observed as well as inside conditions. Remember to maintain proper hygiene practices inside the greenhouse and at least 20 feet around the outside. In many cases, spider mite infestations develop from debris in the greenhouse from the previous crop season. Remove the weeds inside and out.
Two-spotted spider mite eggs are laid on the undersides of leaves and are spherical, clear, and colorless when laid but become pearly white as hatch approaches. Nymphs as well as adults are oval shaped and generally yellow or greenish in color. There are one or more dark spots on each side of their bodies, and the top of the abdomen is free of spots. Diapause is indicated by a change in color to a burnt orange, but in coastal growing areas it is rare to have much of the population undergo diapause. Mating and egg laying typically occur year round in all coastal strawberry-growing regions (Jeppson, L. R., Keifer, H. H. & Baker, E. W., 1978). Their rapid developmental rate (approximately one to three weeks) and high reproductive capability (about 50-100 eggs per female) allows them to reach damaging levels very rapidly under good environmental conditions. Make predatory mite releases early in the season before spider mite populations begin to build or following winter spider mite...
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