How to prevent and control cotton seedling-stage diseases? Detailed prevention and control measures for Binzhou City

There are many types of cotton seedling-stage diseases, and the most serious ones at the cotton seedling stage in our city are damping-off, anthracnose and red rot. In recent years, the first two diseases in particular have been more severe than in previous years. Doing a good job in preventing and controlling cotton seedling-stage diseases is the key to whether our city's cotton can increase both yield and income. At present, the key to preventing and controlling cotton seedling-stage diseases is to implement the plant protection policy of "prevention first, integrated control."

1 Symptoms of cotton seedling-stage diseases

1.1 Damping-off The obvious symptom of field infection is the appearance of elongated yellow-brown spots on the roots of cotton seedlings and the base of the stem near the ground. In severe cases, the entire spot expands into a dark brown band encircling the whole root-stem, causing ring-shaped constriction, which leads to the death of the whole plant, and the roots of dead plants rot. When cotyledons are affected, irregular yellow-brown spots mostly form on the damaged leaves, and after the diseased parts dry up and fall off, holes are formed.

1.2 Anthracnose Field infection mainly shows as brown streaks on the root-stem and stem base of seedlings; in severe cases there is longitudinal splitting and sunken areas, which prevent the vascular bundles from absorbing water normally and cause the seedlings to die. When cotyledons are affected, semicircular or nearly semicircular brown spots mostly form on the leaf margins, and when field air humidity is high they can spread to the entire cotyledon. When the stem is affected, the disease mostly starts at the leaf scar, forming black round or elongated sunken spots.

1.3 Red rot Field infection mainly occurs at the root-stem area. Affected stems appear swollen, then become dark brown and dry-rotted, which is what people call "big-foot seedlings." When cotyledons are affected, string-like round or irregular brown spots mostly form on the leaf margins. When field humidity is high, red enzyme-like matter can be seen on the affected parts.

2 Prevention and control measures

2.1 Agricultural prevention and control measures

2.1.1 Cultivation management ① Promptly remove diseased plant residues from the field. Before sowing, remove the diseased residues from last year's field to prevent pathogens lurking on the residues from invading again. ② Choose a good sowing time for cotton. Because soil temperature that is too low delays seedling emergence and reduces disease resistance. In addition, sowing too late should also be avoided, so as not to affect the cotton yield to be obtained. The sowing depth in the field is about 4-5 cm, with plastic film mulching on top. Adjust flexibly according to the weather and soil moisture: on windless days with sufficient moisture it can be shallower, otherwise it should be deeper. In arid areas prone to wind, when covering soil after sowing, build small ridges along the cotton rows, which helps preserve moisture, prevent soil crusting after rain, and help seedlings emerge. ③ Field management. After emergence, cultivate and loosen the soil in time, and pay attention to intertillage after rain to prevent soil crusting, while also indirectly raising the soil temperature and the disease resistance of the plants. ④ Carry out reasonable crop rotation. As far as possible, practice crop rotation and alternation with other crops for more than 3 years.

2.1.2 Seed treatment ① Select varieties with plump seeds, a high germination rate and strong germination vigor. Remove rotten seeds, insect-damaged seeds, shriveled seeds, mixed seeds, etc. ② Treat seeds with chemicals before sowing. First wet the seeds, take them out and air-dry until the fuzz turns white, then dress the seeds in the ratio of seeds : plant ash : carbendazim = 100 : 10 : 0.5. The method is to mix the chemical and ash thoroughly, then mix them into the cotton seeds and rub and mix fully so that the chemical-ash mixture evenly adheres to the seed surface; you can also dress seeds with 75% quintozene at 0.5% of the seed amount; you can also choose 0.3% tolclofos-methyl, 2.5% Raxil suspension seed coating agent, etc. for seed dressing. ③ Hot-water seed soaking. Pour the seeds into warm water at 70°C and stir up and down, keep the water temperature at 55-60°C and soak the seeds for 30 minutes, then take them out and air-dry until the fuzz turns white before sowing.

2.2 Chemical prevention and control measures For seedling-stage infection, you can choose 50% thiram or 70% mancozeb. After emergence, spray with 1:1:200 Bordeaux mixture or 50% Tuzet 800-1000 times liquid; generally spray 2-4 times at the seedling stage, with an interval of 7 days; or in the early stage of infection spray with 50% carbendazim or 70% thiophanate 1000 times liquid.