[Smart Farmers] Omnivorous "Big Eater" - Beet Armyworm

In recent years, as people's demand for the quality and safety of vegetable products increases, the prevention and control of vegetable pests has received great attention.

In addition to traditional projects such as the National Science and Technology Support Program, the "863" Program, the "973" Program, and the National Natural Science Foundation's key and general projects, in the past few years, the Ministry of Agriculture has successively launched a number of industry scientific research projects targeting major vegetable pests, vegetable pest resistance, chemical control of vegetable pests, and biological control of vegetable pests.

As an agricultural pest that has become increasingly harmful in recent years, the beet armyworm has caused serious losses to agricultural production. People are paying more and more attention to its understanding and related prevention and control research.

What is the beet armyworm?

Beet armyworm (Spodoptera exigua Hübner), commonly known as the cabbage brown armyworm, belongs to the order Lepidoptera and the family Noctuidae. It is a omnivorous pest that mainly harms vegetables and has a worldwide distribution and intermittent occurrence. It has caused serious damage in North China, the Yangtze River Basin, South China, and Taiwan.

There are 171 known host species of Spodoptera exigua. The body color of its larvae varies greatly, including green, dark green, yellow-brown, black-brown, etc. The lower line of the spiracles on the abdominal side is a distinct yellow-white longitudinal band, sometimes pink.

The adult body is 10-14 mm long, with a wingspan of 25-33 mm. The body is gray-brown, with a few being dark gray-brown. The inner horizontal line and the sub-outer edge line of the forewing are both gray-white, with the sub-outer edge line being thinner, and the outer edge having a row of black triangular spots. There is a kidney-shaped pattern on the outer side of the central front edge of the forewing, and a ring-shaped pattern on the inner side. The kidney-shaped pattern is about 1.5-2 times the size of the ring-shaped pattern, and is earthy red. The hind wings are gray-white with a slight pink tint, and the wing margins are gray-brown. They are oval, steamed bun-shaped, white, and have radial ridges on the surface.

The pupa is about 10 mm long and yellowish brown. The adult is hidden during the day and comes out at night. It has strong phototropism and weak chemotaxis. The older larvae have a state of suspended animation. The mature larvae burrow into the soil to spin silk and pupate.

(Pictures from the Internet)

What harm does beet armyworm cause?

The main damage caused by beet armyworm is the larvae.

There are five larvae in total, and the older larvae are 24 to 28 mm long. Newly hatched larvae gather on the back of leaves, spin silk to make webs, feed on the leaf flesh, and leave the epidermis with transparent small holes. After the third instar, they scatter and cause damage, eating the leaves into holes or notches. In severe cases, all the leaves are eaten up, leaving only the veins and petioles, causing the death of the seedlings.

After the third instar, they enter a period of gluttony, their drug resistance increases, the larvae have a tendency to feign death, and when the insect population density is too high, they will kill each other. During the day, they often lurk in soil cracks, on the soil surface, at the base of plants, and in the heart leaves.

In addition, larvae above the third instar can bore into sweet pepper and tomato fruits, burrow into onion tubes, corn female ears, etc. and excrete large amounts of feces, contaminating fruits and ears, causing fruit falling and rot.

Symptoms of beet armyworm damage (picture from the Internet)

How to prevent and control beet armyworm?

1. Forecast

Use sex attractants of beet armyworm to monitor the occurrence dynamics of adult insects in the field, select representative vegetable fields to conduct systematic field surveys of eggs and larvae, predict the occurrence period and amount of beet armyworm, and determine the appropriate period for prevention and control.

2. Agricultural prevention and control

Rationally arrange the layout of crops and vegetables, and implement intercropping or crop rotation patterns.

Remove the dead branches, fallen leaves and weeds from the vegetable fields in time, bury them deeply or compost them. Water them at the right time to increase the humidity in the field, which is conducive to the parasitism of pathogenic microorganisms on pests.

During the peak period of egg-laying to the early stage of hatching, especially when the first generation of larvae appear more uniformly after vegetable transplanting, egg masses and leaves with more young larvae are manually removed.

3. Physical prevention

Black light lamps can be placed in the fields to use the habits of adult beet armyworms for trapping.

4. Biological control

Use natural enemies for prevention and control. The main natural enemies of beet armyworm are lacewings, spiders, ground beetles, etc.

Chemical control of the larval stage of beet armyworm, especially the peak egg hatching period or the newly hatched larvae period, is the critical period for control.

It is best to apply the pesticide in the evening or early morning. The spray should be even and thorough so that the plants are fully covered with the pesticide, and the application amount and safety interval should be strictly controlled.

Use the medicine when the eggs in the field hatch to the peak period of 1st and 2nd instar. Use 15-20 ml of 24% methoxyfenozide suspension and mix it with 45-60 kg of water per mu, and spray evenly. Or use 50 ml of 10% tetrachlorantraniliprole suspension and mix it with 40 kg of water. Four days after using the medicine, the control effect on beet armyworm is still above 90%. Spraying is generally done in the evening. Spray the liquid evenly and spray both sides of the leaves.

In serious cases, spray with 20% suspension 1000-2500 times liquid, or 3% emamectin benzoate suspension 2000 times liquid + 20% tebufenozide 1500 times liquid, or 20% chlorantraniliprole suspension 2000 times liquid, or 30% cypermethrin suspension 1000 times liquid + 3.2% emamectin benzoate. Chlorpyrifos emulsifiable concentrate 2000 times liquid, etc., or 3% emamectin benzoate suspension + 15% indoxacarb suspension 1000 times liquid.

my country has more than 100 million farmers directly engaged in vegetable production, and the vegetable planting area and output rank first in the world. The vegetable industry plays a very important role in increasing farmers' income, increasing agricultural efficiency and rural development. Vegetable pests are the main factor leading to the decline in vegetable yield and quality. Therefore, the prevention and control of vegetable pests is related to the national economy and people's livelihood, social stability and people's health.

Author: Tang Zhenzhen (graduate student at the School of Life Sciences, Hubei University)

Scientific review: Xu Letian (Associate Professor and Doctoral Supervisor at Hubei University)