A Detailed Explanation of the Harm Caused by the Cabbage Worm and Its Control Methods
The cabbage worm is a small insect about five centimeters long, dark green all over, plump and chubby, with two red antennae on its head. It is the larva of the wild silkworm (also known as the "cabbage caterpillar"), belonging to the most common order in the class Insecta. Most of them live on fresh tender green vegetable leaves and gnaw on the leaves, causing a certain degree of harm to crops. Let us take a look together below at the harm and control of the cabbage worm!
The Agricultural Harm of the Cabbage Worm
The cabbage worm damages the leaf mesophyll of crops. Before the 2nd instar it can only gnaw the leaf mesophyll, leaving a layer of transparent epidermis; after the 3rd instar it can consume the entire leaf. In mild cases the leaf is riddled with feeding holes, and in severe cases only the leaf veins remain, affecting plant growth and development and head formation, resulting in reduced yield. In addition, the insect feces contaminate the cauliflower curd, lowering its commercial value. On Chinese cabbage, the feeding holes can also lead to soft rot.
The Occurrence Pattern of the Cabbage Worm
The number of generations of the cabbage worm per year varies by region. In Heilongjiang it occurs 3 to 4 generations per year, and in Hebei 4 to 5 generations. It overwinters as a pupa on fences, windbreaks, tree trunks near the host plants in autumn, and among weeds or fallen twigs and leaves. The adults are active during the day, with the greatest activity around midday, and eggs are mostly laid singly on the upper surface of leaves. The turn of spring and summer and autumn are the main occurrence periods of the larvae. If control is not timely, the leaves of the entire field are often eaten bare, leaving only the midrib and petiole.
Control Methods for the Cabbage Worm
1. Interplant cruciferous plants such as cabbage or cauliflower in the Isatis indigotica field to attract adults to lay eggs, then concentrate on killing the larvae, and plow the field in time after the autumn harvest.
2. In the early stage of young larvae, spray Bacillus thuringiensis at 800 to 1000 times dilution, or use Pieris rapae granulosis virus at 20 larval units per mu, which has a good control effect on the cabbage worm. The best time to spray is in the evening.
3. Pay attention to the natural control role of natural enemies, and protect natural enemies such as Trichogramma dendrolimi, Apanteles rubecula, and Ooencyrtus papilionis.
4. During the peak period of Apanteles, spray with Bacillus thuringiensis preparation containing more than 10 billion viable spores per gram, or Bt wettable powder at 800 times dilution. The use of chemical pesticides is prohibited.
5. During the peak period of larvae, you may choose 20% Tianda diflubenzuron suspension at 800 times dilution, 10% high-efficiency permethrin EC at 1500 times dilution, 50% phoxim EC at 1000 times dilution, 20% fenvalerate at 2000 to 3000 times dilution, 21% synergistic fenvalerate-malathion EC at 4000 times dilution, or 90% trichlorfon crystal at 1000 times dilution, and spray 2 to 3 times.