How to prevent and control damping-off disease? These control methods are worth mastering
Damping-off disease is caused by infection with Rhizoctonia solani, a fungus of the Deuteromycotina subdivision. It has a wide host range: besides solanaceous and cucurbit vegetables, some leguminous and cruciferous vegetables can also be affected. It mainly damages the base of the stem or the underground roots of seedlings, does not produce cottony white mold, does not cause lodging, and progresses slowly, which distinguishes it from Pythium damping-off. Let us take a look at the control methods for damping-off disease below!
Symptoms of damping-off disease
Damping-off disease mostly occurs in the middle and late stages of seedling raising, mainly damaging the stem base or underground roots of seedlings. It begins as elliptical or irregular dark brown lesions. In the early stage, affected seedlings wilt during the day and recover at night. The diseased area gradually sinks and constricts, and some gradually turn dark brown. When the lesion expands to encircle the stem, the plant finally dries up and dies, but does not lodge. Mildly affected plants show only brown sunken lesions without dying. When the seedbed humidity is high, an indistinct light brown spiderweb-like mold can be seen on the diseased area.
Occurrence pattern of damping-off disease
The pathogen overwinters in the soil or on diseased plant tissue as mycelium and sclerotia. It has strong saprophytic ability and generally can survive in the soil for 2 to 3 years. It spreads through rainwater, running water, contaminated compost and farm tools. The optimum temperature for pathogen development is 20 to 24°C. Newly emerged seedlings and large seedlings can both be affected, and it generally occurs in the middle and late stages of seedling raising. It mostly occurs when the seedbed temperature is relatively high during the seedling stage or in the late stage of seedling raising, with cloudy and rainy humid conditions, overly clayey soil, and continuous cropping causing severe incidence. Sowing too densely, failure to thin seedlings in time, and excessively high temperatures easily induce this disease.
Agricultural control of damping-off disease
1. Agricultural control: Strictly select sterile new soil to mix nutrient soil for seedling raising. For seedbed soil treatment, 40% chloronitrobenzene and 41% pyrimethanil can be mixed at a ratio of 1:1, or 38% oxadixyl-propamocarb-kresoxim-methyl can be used at 25 to 50 milliliters per mu, evenly sprayed on the seedbed. Practice crop rotation; rotating with gramineous crops can reduce incidence. In melon fields, deep plow 25 to 30 cm in autumn to turn surface soil pathogens and diseased residues into the deep soil layer for decomposition. Level the land and sow at the appropriate time; generally it is best to begin sowing when the 5 cm soil temperature stabilizes at 12 to 15°C. After emergence, promptly remove diseased seedlings. After rain, cultivate to break up soil crusting, so as to raise soil temperature, make the soil loose and aerated, and enhance the disease resistance of melon seedlings.
2. Biological control: During seedling raising, use a root-type product at 2 to 4 grams per square meter and spray it on the seedbed. Before and after transplanting, it can be diluted 1500 to 3000 times, with 200 milliliters poured around the roots of each plant, used once every 3 months.
3. Seed treatment: The dosage for chemical seed dressing is 0.2 to 0.3% of the weight of dry seeds. Commonly used pesticides include seed-dressing agents such as dressingshuang, dichlone, miaobingjing, and likejun. When treating with seed coating agent, the ratio of seed coating agent to melon seeds is 1:25, or use according to the instructions.
4. Chemical control: In the early stage of disease, spray 38% oxadixyl-propamocarb-kresoxim-methyl 800 times, or 41% pyrimethanil 600 times, or 20% tolclofos-methyl emulsifiable concentrate 1200 times, or 72.2% propamocarb aqueous solution 800 times, once every 7 to 10 days. Alternatively, dilute Dajiangjun + Menmen 600 times and drench the seedbed at 3 liters per square meter before or after sowing and before transplanting. At transplanting, after transplanting, or before the expected period of frequent disease occurrence, dilute this product 600 times and drench the roots, applying once every 7 days, with the number of applications depending on the condition of the disease.