|University of Kentucky Entomology|
FLOAT PLANT PESTS
By Lee Townsend, Extension Entomologist
University of Kentucky College of Agriculture
FUNGUS GNATS, SHORE FLIES, AND BLOODWORMS
Bloodworms are common in stagnant water-- animal watering troughs and other accumulations of standing water. These insects are close relatives of the mosquito but the adults do not have sucking mouthparts and are not blood feeders. The larvae have chewing mouthparts and generally feed on algae or other organic matter in the water. They may be found in plant roots that grow through the bottoms of float trays but apparently do not cause significant injury. While fungus gnats and shore flies live in "very wet" situations, bloodworms generally live entirely in water. Elimination of standing puddles around the area and having a minimum amount of exposed water surface in the float bed will reduce the presence of these insects.
Because of their high moisture requirement, avoiding excessive watering to reduce moisture in growing media will help regulate these pests. Highly organic soils and potting mixtures containing peat are attractive to egg laying fungus gnats.
Thrips are slender, tiny insects about 1/25" long and range in color from light brown to black. They have 4 long, fringed wings that are held flat over the back. Thrips feed by rasping the plant surface and sucking up the exuding sap. Heavily infested leaves have a mottled or silvery appearance. Female thrips insert eggs into slits in the leaf. Eggs hatch in 2 to 7 days. Nymphs feed similar to adults and molt 4 times during development. They are inactive during the last nymphal stage prior to becoming an adult.
Winged adults are carried into the greenhouse on contaminated plant material or fly in during the summer and continue to breed throughout the winter. Prevention of infestations through the use of screens on ventilators, inspection of new material entering the greenhouse, and weed control in the greenhouse will help to manage thrips.
Several species occur in greenhouses. Thrips attack a wide range of plants in the greenhouse, highly susceptible hosts include azalea, calla lily, croton, cyclamen, cucumber, fuchsia, ivy, and rose. Various thrips species also transmit plant diseases. The most serious are the western flower thrips and onion thrips, which are vectors of tomato spotted wilt virus or impatiens necrotic spot virus. This virus attacks a wide variety of plants.
CUTWORMSAll caterpillars are the immature stages of moths. They chew on leaves, stems, and fruits of many kinds of plants. Infestations may begin from moths entering through ventilators or by bringing infested plants into the greenhouse.
Sanitation is important for slug control. Keep the greenhouse free of plant debris (leaves, pulled weeds, etc.), old boards, bricks, or stones that provide cool moist hiding places for slugs. Metaldehyde bait pellets can be distributed beneath the benches in greenhouses for slug and snail control on ornamentals. Do not allow pellets to come in contact with plants.
Cultural Controls are Essential
Cultural controls are the primary defense against insect infestations. Good practices include:
Orthene 75S is labeled for use in greenhouses and tobacco float systems for control of several insect pests. The product, applied to the foliage, should kill these flies. Impact on the larval stages will be minimal. Therefore, cultural controls are needed in advance to minimize the potential for infestation.
CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.
Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!
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