Flower thrips, Frankliniella tritici
Onion thrips, Thrips tabaci
Tobacco thrips, Frankliniella fucas
Western flower thrips, Frankliniella occidentalis
Description. The most common species of plant feeding thrips encountered in Texas cotton include western flower thrips, flower thrips and onion thrips. The predominate species in High Plains, Rolling Plains and Trans Pecos areas is the western flower thrips, while the flower thrips tends to dominate in the remainder of the state except in the Lower Rio Grande Valley where onion thrips often is the predominate species in cotton near onion fields.
Thrips are slender, cigar shaped, straw colored insects about 1/15 inch long, with piercing and sucking mouthparts. Adults are winged and capable of drifting long distances in the wind. Thrips have cone-shaped mouthparts, and their wings are narrow and fringed with hairs.
Thrips appear on growing plants throughout the year in most areas. Eggs, inserted into the plant tissue by the female’s sharp egg-laying tube (ovipositor), hatch in about 6 days. There are two larval stages that require about 6 days for completion. The prepupal and pupal stages require an additional 4 days. Egg to adult development requires about 16 days. The average life span of a mated female is about 35 days. Fifty or more eggs may be produced per female. Thrips can reproduce without mating. Mated females produce both males and females
Thrips appear on growing plants throughout the year in most areas. Eggs, inserted into the plant tissue by the female’s sharp egg-laying tube (ovipositor), hatch in about 6 days. There are two larval stages that require about 6 days for completion. The prepupal and pupal stages require an additional 4 days. Egg to adult development requires about 16 days. The average life span of a mated female is about 35 days. Fifty or more eggs may be produced per female. Thrips can reproduce without mating. Mated females produce both males and females while unmated females produce only males.
Thrips are early-season pests of seedling cotton. In much of the state, thrips are a minor pest, but in areas prone to cool, wet conditions when plant growth is slowed, they are often a severe pest. Thrips are especially numerous in cotton grown near maturing small grains, near onion fields or seedling corn.
Damage. Thrips attack leaves, leaf buds and very small squares and may cause a silvering of the lower leaf surface, deformed or blackened leaves, terminal loss and square loss. Feeding most often occurs in the new terminal growth and on the underside of the leaves. Their feeding ruptures cells which cause stunted plants and crinkled leaves that curl upward. During severe infestations terminal buds may be destroyed, causing excessive branching of the plants and delaying plant growth.
Although thrips are primarily thought of as a pest of cotton, the larvae of the western flower thrips is an important predator of mite eggs.
Thrips damage is most evident during cool, wet periods when small cotton is growing slowly and damage often is further compounded by plant damage resulting from rain, wind, blowing sand, nematodes and diseases. Under some conditions, heavy infestations may reduce stands, stunt plants, and delay fruiting and maturity.
Management and decision making.
Cultural management. Avoiding early planting during cool conditions can often effectively avoid the period when plants are most susceptible to thrips damage. Additionally, avoiding planting cotton near small grains and onions may help alleviate thrips immigration into the field. Varietal selection may also help alleviate the risk of thrips damage. Research has demonstrated that cotton varieties with hairy leaves are less injured by thrips than smooth-leaf varieties.
Biological control. Although thrips are fed on by a large number of small predators such as predaceous thrips, minute pirate bugs and spiders, since the thrips enter the field during and soon after plant emergence, these predators are usually not present in high enough number to manage an infestation. However, these control agent are often very important in reducing thrips numbers at the infestation source such as small grains and weeds.
Scouting. Inspections should begin once cotton has reached approximately 50 percent stand emergence. Thrips should be scouted for at least on a weekly basis until the cotton has 5 to 7 leaves or is initiating squaring. Where postemergence sprays are to be used, fields should be scouted as often as twice a week as cotton emerges. Thrips can migrate in heavy numbers from adjacent weeds or crops, especially small grains, and cause significant damage within a few days and prior to the appearance of true leaves.
Randomly select 25 plants from 4 regions of the field and closely go through the plants looking for adult and immature thrips. Look carefully through the terminal growth, picking it apart with a pencil lead or other pointed object, uncurling all of the leaves. Thrips are often found hiding in very tight locations. This is especially true during rainy, windy conditions. Look at the tops and underside of each leaf paying particular attention between the leaf veins where they intersect the petiole.
Chemical control and Action threshold. In areas with a history of frequent, heavy thrips infestations, the use of in-furrow systemic insecticides or seed treatments should be seriously considered. Where in-furrow or seed treatments have been used, base subsequent applications of foliar insecticides on the action threshold and the occurrence of thrips larvae. The appearance of larvae will indicate that the preventive insecticide is no longer preventing thrips colonization. Research has shown that the application of foliar sprays after significant thrips damage has occurred generally does not result in increased yields. The decision to apply insecticide should be based on the number of thrips present and the stage of plant development.
|Suggested Insecticides and Rates for Managing Thrips in Cotton
ingredient per acre
|Acres treated per gal or lb of
|Mode of Action Group (IRAC)|
|Imidacloprid (Velum Total/ Admire Pro)||0.237-0.305/ 0.266-0.331||14-18 fl oz/ 7.4-9.2 fl oz||9.14-7.11/ 17.30-13.91||1A|
(Orthene 97/ Acephate 90, 1generics)
2.5-3 oz/ 2.5-3.3 oz
(Bidrin 8EC )
|0.1-0.2||1.6-3.2 fl oz||80-40||1B|
(Dimethoate 4, generics)
|0.125-0.25||4-8 fl oz||32-16||1B|
(Gaucho 600, generics)
|—||0.375 mg AI/seed||—||4A|
(Cruiser 5, Avicta Complete)
|—||0.34 mg AI/seed||—||4A|
0.375 mg AI/seed
|1rates vary depending on formulation.|