Watch out for and control cotton boll rot in hot and humid weather

Currently cotton is at the flowering and boll stage and will soon enter the boll-opening stage. This is the vigorous period of cotton reproductive growth, the critical period for the growth of midsummer bolls and yield formation, and also the critical period for controlling boll rot. This year, rainfall from late July to early August was abnormally higher than usual, making boll rot more likely to occur.

Diseased bolls are black and water-soaked, with sparse white upright mycelium growing on them; they do not split open and become hard, dried bolls. Because the lower bolls on the cotton plant receive weak light, have poor ventilation and high humidity, and are exposed to rain soaking or insect bites, they are very easily infected by pathogens and develop boll rot. This year the main factor causing boll rot is excessive rain. According to field surveys, boll rot was found on August 5, 3 to 5 days earlier than in previous years, with a diseased plant rate of 5 to 15%.

Control methods:

First, improve ventilation and light penetration. Prune branches and remove axillary buds in time, remove the group tips, and push the plants apart and merge the ridges. In the early stage of boll disease occurrence, remove old leaves in time, pick off empty fruiting branches and leaf branches, pull out empty plants, improve ventilation and light conditions between cotton plants, reduce field humidity, and lessen the occurrence of boll disease.

Second, drain water and reduce humidity. On the basis of leveling the land, removing weeds, and having complete drainage and irrigation facilities, open ditches and earth up in time, which helps quickly discharge accumulated water, reduce field water content, and loosen the soil in time to dissipate moisture.

Third, reduce sources of inoculum. Remove rotten bolls in time and take them out of the field.

Fourth, control insects in time. Control the third and fourth generations of cotton bollworm to prevent insect bites and wounds and reduce opportunities for infection.

Fifth, chemical control. In the early stage of boll disease occurrence, use 50% thiophanate-methyl 1000-fold solution, or 75% chlorothalonil wettable powder 600-fold solution, or 50% carbendazim wettable powder 500-fold solution per mu, and spray it directly on the middle and lower cotton bolls.