American bollworm in zucchini: symptoms, causes, control

American bollworm - the world of plants

The American bollworm causes severe damage to zucchini crops by feeding on the fruits and leaves. In this article on your site, World of Plants, we will review how to deal with it effectively.

Symptoms of American bollworm in zucchini

  • Scientific name : Helicoverpa armigera
  • the family : lepidoptera
  • In the first stages, the larva attacks the leaves and licks the skin, then feeds on the entire leaf blade.
  • It attacks the buds and young fruits and observes the black insect remains.
دودة اللوز الأمريكية في الكوسا - عالم النباتات
An image showing the symptoms of American bollworm infection in zucchini

Description of the insect

The distance between the tips of the wings is 3.5-4 cm. The color of the male is greenish-gray, while the female is yellowish-brown. The front wings have decorations, and along the outer edge there is a line consisting of 7-8 black dots, and near the terminal third of the wings there is a wide, transverse brown stripe, distinguished by the presence of clear spots with a black center. At the base of the hind wings there is a dark area, and the rest of the wings are light in color.

Caterpillar: When fully developed, it reaches a length of 3-3.5 cm and is yellow or greenish in color. It is equipped with three pairs of thoracic legs and five pairs of false abdominal legs... The head of the caterpillar is yellow-brown in color, and there is a double longitudinal line on the surface of the caterpillar’s ​​body.

The pupa: Its color is brown and its length ranges between 1.5-1.7 cm. It is contained in a cocoon.

دودة اللوز الأمريكية في الكوسا - عالم النباتات
A picture showing you what the caterpillar looks like
دودة اللوز الأمريكية في الكوسا - عالم النباتات
A picture showing you what the eggs look like
دودة اللوز الأمريكية في الكوسا - عالم النباتات
A picture showing you what an adult insect looks like

Causes of American bollworm in zucchini

  • Not taking care of planting at appropriate distances, and planting it at a very high density, which exhausts the plant and deprives it of water, food and air.
  • Climatic conditions (high temperature and humidity help the spread of the pest).
  • Failure to establish an appropriate irrigation program, and relying on random irrigation.
  • The presence of harmful weeds in the field.
  • The presence of plant waste in the field and not removing it.
  • Failure to treat the soil before planting (plowing, hoeing, leveling).
  • The presence of infected neighboring crops.

Suitable conditions for the spread of the American bollworm in zucchini

Growth is faster at high temperatures, reaching 38 degrees Celsius, and larval activity and feeding stop when temperatures drop below 12 degrees Celsius.

Development cycle of the American bollworm in zucchini

  • First instar larvae feed on soft leaves, creating small holes. When it reaches the second instar, it can penetrate the fruit through a small hole, often filled near the stem.
  • About 4-6 weeks to develop from egg to adult in summer, and 8-12 weeks in spring or fall.
  • The fertilized eggs hatch within about three days during warm weather (average 25°C) and 6-10 days in cooler conditions, and change from white
  • From brown to black head stage.
  • Eggs are laid individually on young shoots near buds, flowers, fruits or on leaves.
  • They usually go through six larval instars, although in certain circumstances five or seven instars may occur.
  • Fully-grown larvae crawl to the base of the plant, tunnel up to 10 cm into the soil and form a chamber in which they pupate.
  • Overwintering pupae take much longer to emerge.
  • Adult individuals appear when the soil temperature at a depth of 10 cm rises more than 10 m. This usually occurs in the first or second decade of May. The butterfly is active at night and lives between 3 and 28 days.
دودة اللوز الأمريكية في الكوسا - عالم النباتات
An image showing you laying eggs on paper

Losses of the spread of the American bollworm in zucchini

  • The fruits stop growing, ripen quickly and fall.
  • Huge economic losses, about 90%.
  • Injury to nearby crops.

Control strategy

Preventive measures to prevent the occurrence of American bollworm in zucchini

  • Good agricultural operations, including cultivation, weed removal, and soil leveling.
  • Physical factors can greatly influence egg survival and larval development. Heavy rain and wind can blow the eggs away from the leaves. High temperatures can dry out and kill eggs and very young larvae.
  • Follow the appropriate agricultural cycle that ensures that insect hosts are not provided in one area and in a sequential growth manner.
  • Early agriculture.
  • Early harvest of the crop.
  • Cultivation of resistant varieties

Organic control against American bollworm in zucchini

  • The use of some parasites for larvae, such as Bracon brevicornis, and among the egg parasites are species of Trichoderma sp.
  • Use plant traps
  • Using light traps with double waves to monitor and control the insect

Chemical control against the American bollworm in zucchini

  • The adult insect fights at the beginning of the season after it emerges from the hibernation, and the spraying is repeated after a week using infectious contact pesticides.
  • Use soil insecticides to control larvae.

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References

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