How to prevent and control cotton seedling diseases? Detailed spring prevention and control methods

In recent years, due to low temperatures in spring, seedling diseases in direct-seeded cotton fields have occurred severely, causing large numbers of dead seedlings in cotton fields. In order to improve the economic benefits of cotton farmers and reduce the losses caused by diseases, the symptoms and prevention and control methods of several cotton seedling diseases are introduced as follows:

1. Symptoms of damaged cotton seedlings

1. Anthracnose: Both leaves and stems can be affected. After the seedlings are damaged, reddish-brown spindle-shaped streaks appear at the base of the stem, with longitudinal cracking. In severe cases, the lesions expand, turn brown, blacken, and rot, leading to seedling death. When the weather is humid, the lesions produce orange-red sticky substances. When leaves are affected, semicircular brown lesions appear on the leaf edges. When the weather is dry, the lesion edges are dark red. In severe cases, the leaves wither and fall off.

2. Damping-off: It is most prone to occur about half a month after cotton seedlings emerge. The affected part is the stem base near the ground of the cotton seedling. The lesions change from yellowish-brown to dark brown and gradually sink downward and rot. Because the affected part of the stem shrinks, the cotton seedling lodges and dies.

3. Brown spot: The affected leaves first show purple-red spots the size of needle tips. Later, the lesions expand and become yellowish-brown with purple-red edges, slightly raised, with small black dots scattered underneath. The diseased tissue easily falls off, forming a perforated appearance. Severe damage can cause premature leaf drop.

4. Ring spot: It mainly damages leaves, and sometimes damages stems, petioles, and cotton bolls. When leaves are affected, small red or light brown round spots initially appear and gradually expand into nearly circular brown lesions with concentric rings on the surface. When the weather is humid, black mold layers grow on the lesions. In severe cases, the leaves can wither and fall off, and even the whole plant can die.

2. Prevention and control of seedling diseases

The pathogens of various seedling diseases mainly overwinter on cotton seeds, in soil, and on diseased plant residues. From cotton sowing to the appearance of true leaves the following year, the pathogens infect the seedlings. To ensure full stands and strong seedlings, the main measures are:

1. Agricultural control:

(1) Carefully select seeds. On the basis of removing inferior seeds such as tender seeds, diseased seeds, insect-damaged seeds, and bald seeds, select plump seeds, then sun-dry the seeds for 3-5 days. This can significantly increase the emergence rate and enhance the disease resistance of cotton seedlings.

(2) Carefully prepare the land. Level the land in advance, generally plowing deeply 25-30 cm, and apply sufficient organic fertilizer and base fertilizer (diammonium phosphate 15 kg, potassium sulfate 15 kg), and sow later at the appropriate time (stable ground temperature at 5 cm above 10°C). Prevent sowing too early, because low ground temperature induces seed rot and diseased seedlings.

(3) Strengthen field management. After cotton seedlings emerge, loosen the soil in time to increase ground temperature, reduce soil moisture, and reduce opportunities for pathogen infection. Thin and set seedlings early to cultivate strong seedlings.

(4) In plots where damping-off and brown spot occur severely, reasonable rotation should be carried out with @#@245@#@, corn, and so on.

2. Chemical control: At sowing time, 25% carbendazim can be used, with 1 kg of pesticide per 50 kg of cottonseed, evenly mixed with the seeds 5-7 days before sowing. During the seedling stage, in affected plots, spray with 70% thiophanate-methyl 800-1000 times liquid or 50% carbendazim wettable powder 500-800 times liquid, spraying once every 5-7 days, for 3 consecutive sprays, with remarkable results.