Control Methods for Cotton Thrips When Growing Cotton

Cotton thrips, also known as tobacco thrips or onion thrips, damages not only cotton but also tobacco, onion, garlic, cucurbits, potato, tomato, Chinese cabbage and many other crops. 

Damage symptoms: adults and nymphs mostly gather on the tender tips and undersides of cotton leaves to suck sap. After cotton seedlings are damaged, the cotyledons become thick and fleshy, with small yellow-green or silvery-white spots appearing on the underside; the growing point withers and no new branches can grow out. Cotton farmers call this “male cotton” or “headless cotton”. In some cases, although new branches can grow, the growing point splits into several forks, which cotton farmers call “multi-headed cotton” or “scattered-head cotton”. The former causes missing plants, while the latter delays the cotton growth period and reduces boll set, lowering yield.  

Occurrence pattern: adults or nymphs overwinter on green manure, rapeseed, and crops such as onion and garlic. After the weather warms in spring, they first reproduce on host crops, then migrate to cotton seedlings to cause damage. Cotton seedlings near overwintering hosts or with many nearby weeds suffer more severe cotton thrips infestation. Generally, loose soil favors their occurrence, while heavy clay soil does not. Early-sown single-cropping cotton fields suffer more damage than wheat-intercropped cotton. Cotton thrips tends to occur in relatively dry years. Especially when the temperature in May-June is below 25°C and the relative humidity is around 70%, the damage is often severe; when the temperature exceeds 25%, there is more rain and humidity is high, conditions become unfavorable for thrips occurrence. Therefore, in general years, after mid-to-late June, cotton thrips damage drops significantly.  

Control measures: 1. In areas where cotton and vegetables are mixed-planted, control of onion and garlic vegetables should be strengthened to reduce the base population. Spray with 40% dimethoate emulsifiable concentrate diluted 2000-2500 times. 2. Combined with thinning and final thinning of seedlings, pull out ‘male cotton’; after final thinning, if “multi-headed cotton” is found, remove the green tender thick tiller branches, leaving the thinner brownish branches, so that the final boll number is close to that of normal cotton plants. 3. The period of cotton thrips occurrence and damage is generally earlier than that of cotton aphid. After cotton seedlings emerge, investigation should be strengthened and control carried out early. Use 50 ml of 3% acetamiprid per mu, or 40% dimethoate emulsifiable concentrate diluted 2500 times, or 50 ml of 5% phosphamidon emulsifiable concentrate. Spray 60 kg of spray liquid per mu. 4. Control with homemade botanical pesticides. Tobacco-lime water. Materials: tobacco leaves, quicklime, water. Preparation method: first use a small amount of hot water to slake 1 kg of quicklime, pour it into 40 kg of clean water, and filter out the residue. Then tear 1 kg of tobacco leaves into pieces, soak them in 10 kg of boiling water with a lid, and when the hot water is no longer too hot to touch, rub the soaked tobacco leaves by hand, constantly changing the water, until no more tobacco leaf juice flows out (1 kg of tobacco leaves can yield 30-40 kg of tobacco leaf water). Pour the tobacco leaf water into the lime water and it is ready. Then spray with the tobacco-lime water.