How to Control Fall Armyworm in Corn? These Methods Are Very Practical

The fall armyworm (Mythimna separata) is a major pest in corn production, causing considerable damage to corn. When outbreaks are severe, it often devours corn seedlings overnight, causing missing plants and broken rows, and even forcing farmers to plow up and replant. At present, it has begun to occur in some corn and millet fields in Changzhi County, and farmers should go into the fields in time to control it.

I. Occurrence, Damage Habits and Patterns

Adults hide by day and come out at night, mostly laying eggs on the withered yellow leaf tips in the middle and lower parts of wheat plants and inside leaf sheaths, with a single female laying 1000—2000 eggs. Adults have a strong tendency toward sugar-vinegar solution and black light traps; adults are very strong fliers and have the characteristic of long-distance migratory damage. Larvae are mostly active in the morning and evening, that is, from sunrise to before 10 o'clock and around dusk. The fall armyworm is a mesothermic, moisture-loving insect, with an optimum temperature of 19-23°C and an optimum relative humidity of 50-80%. It prefers to feed on gramineous crops and weeds, and its food intake increases with each instar; the fifth and sixth instars are the binge-feeding stage. It has the characteristics of clustered damage, binge feeding, and omnivorous feeding, and the larvae often migrate in clusters to cause damage, hence it is also called the “armyworm”. First and second instar larvae only gnaw the leaf mesophyll into transparent windows; after the third instar they feed along the leaf margins, making notches; when damage is severe, they eat up most of the leaf blade, leaving only a very short midrib. Larval body color changes with instar, density, and food. Young larvae feeding on tender leaves have a green to grayish-green body color; when population density is high, larvae of the fourth instar and above are black or grayish-black. Mature larvae are 38 mm long, with a yellowish-brown head and a vertical “eight”-shaped marking. The back of the body has 5 longitudinal stripes. When disturbed, larvae have the habit of feigning death and burrowing into the soil. Generally, irrigated fields, fields with a previous wheat crop that was heavily fertilized and densely planted, and intercropped fields, as well as fields where wheat and corn coexist for a long period, have sufficient food sources and suitable temperature and humidity, which favor adult egg-laying and larval growth and development, so the field population density is greater and the damage is relatively more severe.

II. Control Techniques

1. Agricultural control: After corn emerges, carry out shallow tillage in time to destroy stubble and break the habitat environment of the fall armyworm, reducing the pest source.

2. Manual capture and killing: After corn emerges, manually crush and kill the larvae in the morning and evening when they feed.

3. Chemical control:

(1) Poison bait trapping and killing: Use 100 g of 90% trichlorfon per mu, mix with an appropriate amount of water, and blend it into 1.5 kg of roasted fragrant bran to make a poison bait. Scatter it along the corn rows in the evening to trap and kill the pest.

(2) Foliar spraying: Mix 50 mL of 4.5% beta-cypermethrin or 50 mL of 40% omethoate plus 25 mL of 77% dichlorvos with 30 kg of water and spray evenly on the leaves; mix 50 mL of 4.5% beta-cypermethrin plus 50 mL of chlorbenzuron with 30 kg of water for foliar spraying.

(3) Broadcasting poisoned soil: Use 75-100 g of 40% phoxim emulsifiable concentrate per mu, add an appropriate amount of water, mix with 40-50 kg of sandy soil, and broadcast it into the corn whorl. This can both protect natural enemies and also provide incidental control of the Asian corn borer. In the process of controlling the fall armyworm, try to control it before the third instar. The control time is generally chosen during the morning and evening peak feeding periods of the larvae. As much as possible, apply the pesticide to the corn whorl, pay attention to personal protection, and strictly prevent poisoning accidents.