Thrips Damage Symptoms and Control Methods Explained in Detail
Thrips adults and nymphs rasp and suck the sap of young, tender plant tissues (shoot tips, leaves, flowers, fruits, etc.). The damaged young leaves and shoot tips become hard, curled and withered, plant growth slows, and internodes shorten. Young fruits (such as eggplant, cucumber, watermelon, etc.) become hardened after damage, and in severe cases fruit drop occurs, seriously affecting yield and quality. Let's take a look at the control methods for thrips pests below!
Damage Characteristics of Thrips
1. Leaf damage: After young leaves are damaged, the leaves become thinner, grayish-white or grayish-brown streaks appear on both sides of the midrib, the epidermis turns grayish-brown, deformation and curling occur, and growth vigor is weak. It is easily confused with damage caused by the broad mite (Polyphagotarsonemus latus).
2. Young fruit damage: The oil cells in the epidermis rupture, gradually losing water and shrinking. The scars expand as the fruit enlarges, showing suberized silvery-white or grayish-white spots of various shapes, though a small number also occur on areas such as the fruit's waist.
Agricultural Control of Thrips
1. In early spring, clear weeds and dead branches and fallen leaves from the field, burn them in a centralized manner or bury them deeply, to eliminate overwintering adults and nymphs.
2. Strengthen fertilizer and water management to promote robust plant growth and reduce damage.
3. Taking advantage of the thrips' tendency to be attracted to blue, set up blue sticky boards in the field to trap and kill adults. The height of the sticky boards should be level with the crops.
Chemical Control of Thrips
1. Rice: For rice thrips, thiamethoxam-type products are recommended, including the imported variety Ruìshèng 30% thiamethoxam suspension seed coating agent, and the domestic trial variety Bǎiruì 35% thiamethoxam suspension seed coating agent.
2. Vegetables: For thrips on solanaceous fruits, cucurbits, legumes, etc., use 25% thiamethoxam water-dispersible granules at 3000-5000 times dilution for root drenching, to reduce the occurrence of viral diseases and at the same time reduce damage from soil-dwelling pests. Imported variety Ākètài, well-known domestic variety Dàgōngniú.
3. Fruit trees: For crops heavily damaged by thrips such as mango, 25% thiamethoxam Dàgōngniú can be used as a spray, but the application rate should be increased, such as an 800-times spray, and it can also be tank-mixed with microemulsion-type abamectin.
4. Tobacco: For tobacco, root drenching before transplanting or root spraying at planting can use imidacloprid, thiamethoxam, clothianidin: 25% imidacloprid at 1000 times, 25% thiamethoxam Dàgōngniú at 3000-5000 times.
Key Points for Thrips Control
1. Based on the thrips' habit of hiding by day and coming out at night, it is recommended to apply the pesticide in the afternoon.
2. Thrips have strong concealment, so the pesticide should be systemic or have an organosilicon adjuvant added, and products with a long residual effect should be chosen as much as possible.
3. If conditions permit, it is recommended to combine pesticide fumigation of the greenhouse with foliar spraying.
4. Thrips should be prevented in advance; do not wait until they have proliferated before applying pesticide. When growing vegetables during high-temperature periods, if plastic film mulching is not used, the pesticide should ideally be sprayed simultaneously on the middle and lower parts of the plants and the ground, because these places are the habitat of thrips nymphs.
Symptoms and Control Methods of the Yellow-breasted Flower Thrips
[Damage] Tuberose, gladiolus, orchid, chrysanthemum, rose and other flowers. Nymphs and adults congregate on the flower parts of the plant, rasping and sucking sap. After the flowers are damaged, grayish-white feeding marks and egg-laying marks appear. In severe cases, the petals curl and cannot open properly.
[Morphological characteristics] Adult: The female is brown, with an orange-yellow thorax, body length 1.2-1.4 mm; the third antennal segment is yellow and the remaining segments brown; two pairs of wings, narrow and long like rods, with fringing hairs along the margins, forewings gray with a lighter base. Eggs are pale yellow, kidney-shaped. Nymphs are smaller than adults, lighter in color; wingless; with fewer antennal segments.
[Occurrence pattern] More than 10 generations occur per year. It can occur year-round in greenhouses. The female inserts her ovipositor into the epidermis of petals or stamens, laying eggs beneath the epidermis or partially exposed. Nymphs and adults hide in the flowers and cause damage. This insect has diverse feeding habits and can often transfer between different plants. High temperature and drought favor outbreaks of the yellow-breasted flower thrips.
[Control methods] A. Clear weeds around the flower nursery to reduce habitats and breeding sites for thrips.
B. When damage is found during the growing season, spray 2.5% deltamethrin emulsifiable concentrate at 4000 times dilution or 50% malathion emulsifiable concentrate at 4000 times dilution for control. When spraying, care should be taken to spray the places where thrips hide within the flowers.
Control of Thrips Pests and Diseases in Mango Cultivation
Classification: Thysanoptera, Thripidae.
I. Tea yellow thrips Scirtothrips dorsalis Hood
1. Damage
Adults and nymphs damage mango leaves, which appear scalded by hot water and finally wilt; they damage fruit, causing the surface to show brown rough spots. This insect also damages tea, banana and other crops.
2. Morphological characteristics
Adult body length about 1.0┨, yellow; wings narrow, long, gray and transparent, with many fine hairs along the wing margins; head width about 1.8 times its length; compound eyes grayish-black, slightly protruding; 3 bright red ocelli; antennae 8-segmented, about 3 times the head length; pronotum width 1.5 times its length, with a pair of thick short spines at the posterior marginal angles.
Eggs pale yellow, kidney-shaped.
Nymphs are milky white when newly hatched, later turning pale yellow, similar in form to adults.
3. Life habits
The number of generations per year is unknown. At high temperatures, one generation can be completed in just over 10 days. Both adults and nymphs can damage leaves and fruit; damaged leaves become lighter in color, appearing scalded by hot water, with a maximum of 19 insects on a single leaf; damaged fruit surfaces show brown linear markings or streaks, making the fruit surface rough and thus reducing commercial value. This insect damages mango fruit when the fruit is the size of a soybean; normally the insect hides beneath the sepals. In severe cases of damage, small fruits can dry up, and the surface of damaged small fruits shows brown lines (spots); as the small fruits grow, these lines (spots) also grow and thicken, and by the time the fruit ripens, the fruit surface becomes rough.
4. Control methods
When damage by this insect is found, spray 80% dichlorvos or 40% dimethoate at 2000 times dilution, or 20% fenvalerate or 2.5% deltamethrin at 4000 times dilution. In severe cases, spray once every 7 days, for 3 consecutive sprays.
II. Red-banded thrips Selenothrips rubrocinctus (Giard)
1. Damage
Adults and nymphs damage the leaves of mango seedlings, causing numerous dirty black spots, blackened leaf tips, and curled leaf margins, and finally all leaves drop off and the entire plant dies; this insect also excretes a red liquid on the leaves, which after drying appears as rust-brown or shiny black spots, affecting photosynthesis. This insect also damages rubber, coffee, cashew, lychee, longan, citrus and other crops.
2. Morphological characteristics
Adult elongated, dark brown, body length 1.0-1.5┨, wing margins with dense grayish-black fringing hairs.
Eggs kidney-shaped, yellowish-white, about 0.25┨ long.
Nymph elongated, yellow, with a band of bright red at the base of the abdomen; when fully grown, body length about 1.0┨.
Pupa elongated, body length about 1.0┨, similar in form to the nymph but with fully developed wing pads.
3. Life habits
About 10 generations occur per year. Females reproduce by parthenogenesis, laying eggs individually on the lower leaf surface, each accompanied by a drop of feces-like substance; the egg stage lasts 1-3 days and the pupal stage 6 days. Adults and nymphs mostly live in depressions near the main veins or in small grooves, often raising the tip of the abdomen, which bears a spherical liquid droplet at the end.
4. Control methods
When infestation occurs, spray 40% dimethoate or 50% fenitrothion or 80% dichlorvos at 1500 times dilution for control.