What are the control methods for the black cutworm?
The black cutworm, also known as the soil silkworm, root-cutting worm, etc., has a number of generations per year that varies with the climate of each region; the farther south, the more generations per year. It occurs rather seriously in the middle and lower reaches of the Yangtze River and the southeast coastal areas, where rainfall is abundant and the climate is humid, as well as in low-lying waterlogged areas in the north. It causes great harm to the seedlings of crops, forests and trees, causing missing seedlings and broken rows in mild cases, and in severe cases forcing the destruction of the seed and replanting. Let's take a look at the control methods for the black cutworm below!
Damage characteristics
The black cutworm is an underground pest that causes great harm to the seedlings of crops, forests and trees. It can harm more than a hundred species of plants. In the northeast it mainly harms seedlings such as larch, Korean pine, Manchurian ash and Manchurian walnut; in the south it harms seedlings such as masson pine, Chinese fir, mulberry and tea; and in the northwest it harms seedlings such as Chinese pine, Russian olive and fruit trees. The 1st to 2nd instar larvae can gather day and night at the tender leaves of the seedling growing point, feeding day and night; at this time their food intake is very small and the damage is not very noticeable. After the 3rd instar they disperse, hiding during the day between the dry and wet layers of the surface soil, and at night emerging from the soil to bite through the seedling plants at ground level and drag them into soil burrows, or to bite and eat seeds that have not yet emerged. After the main stem of the seedling hardens, they switch to feeding on tender leaves, leaf blades and growing points. The 5th and 6th instar larvae greatly increase their food intake; each larva can bite through 4 to 5 vegetable seedlings in one night, and as many as more than 10.
Occurrence pattern
The black cutworm is seen to occur and cause damage from October to April of the following year. In the northwest region there are two to three generations, north of the Great Wall generally two to three generations per year, south of the Great Wall and north of the Yellow River three generations per year, south of the Yellow River to the banks of the Yangtze River four generations per year, south of the Yangtze River four to five generations per year, and in the southern subtropical region six to seven generations per year. Regardless of how many generations occur per year, it is always the first-generation larvae that cause serious damage in production. Overwintering-generation adults appear in February in the south, and the peak emergence period in most parts of the country is from late March to early and mid-April, while in Ningxia and Inner Mongolia it is late April. The number of eggs laid by adults and the egg stage differ in each region; the main reason the egg stage varies with distribution region and generation is the difference in temperature.
Agricultural control
1. Strengthen management: extensive management and overgrown weeds are the best hosts for attracting cutworms to lay eggs and feed early; the more weeds, the higher the larval survival rate and the more severe the damage.
2. Use natural enemies: such as insectivorous birds, crows and sparrows, toads, weasels, ground beetles, parasitic flies, parasitic wasps, as well as bacteria, fungi, etc. In Hangzhou, the parasitism rate of parasitic wasps and small braconid wasps reaches 10%.
3. Adult trapping and killing: in combination with armyworm control, use a bait liquid of sugar, vinegar and wine, or fermented liquids such as sweet potato and carrot, to trap and kill adults.
4. Larval trapping: use paulownia leaves or lettuce leaves to trap larvae, and collect them in the field every morning. For older larvae, you can also check the field in the early morning; if broken seedlings are found, push aside the nearby clods of soil and kill them.
Chemical control
Different application methods should be used for black cutworm larvae of different instars. Before the 3rd instar, use spraying, dusting or poisonous soil to control them; after the 3rd instar, when broken seedlings appear in the field, use poisonous bait or poisonous grass to trap and kill them.
1. Spray control: per hectare, choose 750 milliliters of 50% phoxim emulsifiable concentrate, or 300 to 450 milliliters of 2.5% deltamethrin emulsifiable concentrate or 40% cypermethrin emulsifiable concentrate, or 750 g of 90% trichlorfon crystals, and spray with 750 L of water. The suitable spraying time should be before the peak occurrence of the 3rd instar larvae.
2. Poisonous soil control: choose 90 to 100 milliliters of 2.5% deltamethrin emulsifiable concentrate, or 500 milliliters of 50% phoxim emulsifiable concentrate or 40% isofenphos-methyl emulsifiable concentrate, add an appropriate amount of water, spray and mix with 50 kilograms of fine soil to make poisonous soil, and apply 300 to 375 kilograms per hectare along the rows near the seedling roots.
3. Poisonous bait control: generally, when the larvae are older, poisonous bait can be used for trapping and killing. Choose 0.5 kilograms of 90% trichlorfon crystals or 500 milliliters of 50% phoxim emulsifiable concentrate, add 2.5 to 5 liters of water, spray onto 50 kilograms of crushed and stir-fried cottonseed cake, soybean cake or wheat bran, and in the evening scatter small piles at fixed intervals in the fields of the affected crops, or apply around the crop root zone, using 75 kilograms per hectare.
4. Poisonous grass control: use 0.5 kilograms of 90% trichlorfon crystals, mix with 75 to 100 kilograms of crushed fresh grass, using 225 to 300 kilograms per hectare.