What is the danger of bollworm on corn: we detect the enemy, then quickly and effectively fight it
Corn is an important grain and feed crop. Protecting the crop from pests is one of the main tasks of a farmer. The main enemies of corn include the cotton bollworm. Infection of crops by these insects leads to a loss of yield of up to 20%.
Photos and descriptions of bollworms at all stages of development, as well as information on how to deal with insect infestations are in our article.
What is bollworm
The cotton bollworm (lat. Helicoverpa armigera) is a butterfly of the moth family.
The emergence of overwintered adults begins at +18… +20 ºС. The summer periods of butterflies of subsequent generations overlap, so that the cotton bollworm can be found until October-November.
Active at dusk and at night, feeding on nectar.
The damage is caused by caterpillars of winged insects that eat crops. Cotton, corn, tomatoes, soybeans, peas and others are under attack. In the southern regions of Russia, the cotton bollworm has become the second most important pest of corn.
The distribution area includes southern Europe, the Caucasus, Central Asia, tropical and subtropical regions of the world.
How it looks and develops
The size of adult sexually mature individuals (imago) ranges from 10 to 20 mm. Wingspan 30-40 mm. The forewings are grayish-yellow with shades of red, pink, greenish, with two fuzzy dark gray spots. The hind wings are paler, with a brown stripe along the outer edge and a curved spot in the middle.Females have darker wing color than males.
The adult moth lives 20-40 days. During this time, females manage to lay from 500 to 1000 eggs.
The eggs, reaching a diameter of 0.5-0.6 mm, have a characteristic rounded ribbed shape. The color changes from white to green as it develops. They are deposited one at a time, less often 2-3 on leaves, drooping parts of the stem, threads of cobs, panicles.
The duration of embryo growth is from two to four days in summer, spring and autumn - up to 12 days.
The larvae (caterpillars) are colored light green, yellow or red-brown and covered with small spines. There are three wide dark lines along the body. There is a yellow stripe on the side under the spiracle.
The larvae develop in 13-22 days and go through 6 growth stages. On the last of them, the caterpillars reach a length of 35-40 mm.
Larvae pupate in the soil at a depth of 4-10 cm or on the cob of corn. The pupa is red-brown in color, 15-22 mm long, with two parallel processes located at the narrowed end. Develops within 10-15 days.
Interesting fact. Adults emerge from the pupae and the cycle repeats. In the climatic conditions of the Krasnodar Territory, the insect develops in three generations, in the Stavropol region - in two.
Symptoms of the lesion
Plants on which the cotton bollworm has settled are clearly visible against the background of healthy ones:
- round holes are noticeable on the upper leaves, as the caterpillars feed on soft greens before the panicles appear;
- pistil filaments are eaten away or completely destroyed;
- the larvae penetrate the cobs and gnaw the grains;
- Insect excrement is visible in the cobs.
Damage caused
Direct harm is caused by the larvae (caterpillars) of the cotton bollworm, eating the filling corn grains.
The destruction of pistillate filaments leads to incomplete pollination and the formation of weakly grained ears.
Contamination of the cobs with insect waste products and damage to plant tissues contribute to the infection of corn with fungal infections: fusarium and smut.
Infection of crops with cotton bollworm reduces the quantity and quality of production. In case of mass spread of the pest, plant death is possible.
Fighting methods
The decision on the need for treatment is made based on the economic threshold of harmfulness (ELT) of the parasite. To establish it, pheromone traps are used. On fields up to 5 hectares, 3 traps are set, over 10 hectares, an additional one for every 5 hectares.
Catching 20 butterflies over three days indicates a population density within the EPV-5 larvae per 100 plants. Catching more than 25 individuals signals that the permissible level has been exceeded and the need to combat the pest.
Reference. The economic threshold of harmfulness is the minimum number of pests at which the costs of control will be recouped by the income from the saved harvest.
To combat the cotton bollworm on corn, chemical agents, biological methods, folk recipes and agrotechnical techniques are used.
Chemicals
It is recommended to apply insecticides during the period of panicle ejection.
During the phase of mass flight of butterflies, fields are treated with chitin synthesis inhibitors - drugs based on lufenuron. Pesticides of this class include the drug “Match”.
To combat caterpillars, enteric-contact drugs are used. Such means include:
- «Fascord"-α-cypermethrin emulsion concentrate. A 0.05% working solution is prepared from the concentrate. Working fluid consumption is 200-400 l/ha.During the growing season, no more than two treatments are carried out. The waiting period before harvesting is at least 28 days.
- "Decis Profi""-water-dispersible granules based on deltamethrin. Spraying is carried out during the growing season with a working fluid flow rate of 200-400 l/ha (0.05-0.07 kg of dry matter). The death of pests occurs within an hour after treatment. The drug is used 49 days before harvesting the fruits and no more than twice per season.
- "Karate Zeon"-a drug based on λ-cyhalothrin, available in the form of a microencapsulated suspension. The consumption of the drug is 0.2-0.3 l/ha. The consumption of the working solution is 200-400 l/ha for ground spraying, 25-30 l/ha for aviation.
- «Arrivo"-emulsion containing cypermethrin as an active ingredient. Working fluid consumption is 200-400 l/ha or 0.32 l/ha of concentrate. Treatment is carried out no later than 20 days before harvest.
Insecticide treatments are most effective in the early stages of caterpillar development, before they reach a length of 1.5 cm. At this age, the pests are still unstable to the effects of poisons and have not had time to penetrate inside the cobs.
In the summer, generations of the cotton bollworm overlap each other, so that the pest can be found in the population at all stages of development. Fortunately, most drugs have a broad spectrum of action and are effective against insects in all life cycles, from larvae to adults.
Important! When spraying with insecticides, the edges of crops are covered by 20-30 m.
Biological
Biological means of control are based on the targeted colonization of fields with natural enemies of the cotton bollworm and pathogens of the pest.
Trichogramma
The appearance of the first butterflies in traps indicates the beginning of egg laying, which lasts up to 22 days within one generation. During this period, Trichogramma (an insect from the genus moth) begins to settle on corn plants. Trichogramma larvae parasitize bollworm eggs.
Trichogramma in the adult insect phase is released for crops three times: at the beginning of egg laying by the cutworm, then after 5-6 days. Each time, 60-80 thousand insects per hectare are populated. Trichogramma is released in the morning or evening at no less than 50 points per hectare for uniform distribution. At the same time, the edges of the fields are also saturated.
The use of Trichogramma on corn crops reduces crop losses from pests by 20%.
Gabrobracon
Gabrobracon is effective against caterpillars. Entomophagous females lay up to 50 of their eggs in the body of the cutworm larva. Both openly living caterpillars and those that have penetrated the cobs are exposed to infection. The victim remains alive, but loses mobility and the ability to feed.
The release rate is 600-2000 individuals per hectare twice a summer.
Reference. The greatest effect is achieved by complementary releases of trichogramma (against eggs) and habrobracon (against caterpillars).
"Bitoxibacillin"
"Bitokisibacillin" contains the bacteria Baccilius thuringiensis, as well as their metabolites: beta-exotoxin and delta-endotoxin. After treatment, the drug with the leaves will enter the intestines of pests. The caterpillar loses the ability to feed and dies within 3-5 days. Spraying is carried out against each generation of cotton bollworm with an interval of 7-8 days.
The consumption rate is 2-4 kg per hectare, the consumption of working fluid is 200-400 l/ha. The solution is prepared in such a quantity that it can be used within three hours.Treatments must be carried out at a temperature not lower than +8 ºС in dry, windless weather.
You can purchase entomophages and bioinsecticides at the branches of the laboratories of the Russian Agricultural Center.
Folk recipes
Traditional methods are used on private farms. Such products are effective for minor pest infestations.
The most popular recipes are:
- Wormwood decoction. Pour 1 kg of grass with three liters of water and boil for 15 minutes. Spray the plants twice with an interval of 7 days.
- Tomato decoction. 3-4 kg of tomato tops are poured into 10 liters of water and boiled for 30 minutes, then filtered. To prepare the working fluid, take one part of the broth to 3 parts of water. Plants are sprayed at a rate of 5 liters per 10 m2.
- Hot pepper decoction. Take 0.5 kg of dry or 1 kg of fresh red hot pepper, add 10 liters of water, boil for an hour, leave for a day. For spraying, the broth is diluted with water in a ratio of 1:8.
- Garlic infusion. Grind 2 cloves and leave in 1 liter of water for 3-4 days. To process corn, the infusion is diluted with water 1:5.
- Kerosene-soap mixture. 400 g of grated laundry soap are crushed and dissolved in 1 liter of boiling water. 9 liters of water and 800 ml of kerosene are added to the solution. The resulting composition is used immediately.
Agrotechnical techniques
The set of agrotechnical measures to combat the cotton bollworm includes:
- Reduction of pest breeding areas. Since the butterfly is able to reproduce and feed on weeds (quinoa, ropeweed, ragweed) in the autumn, enlargement of field maps, plowing and development of adjacent empty lands is important.
- Destruction of wintering pests - removal of undergrowth, destruction of plant residues, digging up the edges of fields, deep plowing with a rotation of the layer to a depth of 30 cm, and in fields heavily clogged with perennials - to 35 cm.
- Cultivation of row spacing, which is especially important during the period of pest pupation.
- Destruction of weeds.
Preventive measures
To preserve the harvest, hybrids are planted and varieties, less susceptible to pest attacks.
It is worth paying attention to:
- simple hybrid Yarovets 243 MV (silage direction);
- three-line hybrid Yubileiny 390 MV (grain direction);
- grain hybrid Ladozhsky 250 MV.
Sowing at the optimal time will allow you to avoid large losses of grain corn. The plants will have time to gain strength and bloom before the mass summer and reproduction of the cotton bollworm.
Advice from experienced farmers and gardeners
A few recommendations from experienced vegetable growers:
- Place small plastic jars on the site as bait traps. Fill them with fermenting liquids (kvass, compote, molasses). Periodically clean insect traps and change bait.
- Plant fragrant herbs around the rows of corn that repel insects: basil, cilantro, marigolds.
- To attract birds that eat pests, hang feeders around the area.
Reviews
Many farmers and gardeners want to stop treating crops with chemicals, but they doubt the effectiveness of biological agents. A couple of reviews about biological products will help you make a decision.
Peter, Rostov-on-Don: “I plant corn every year. This year, on the advice of neighbors, I tried to treat the cutworm plantings with Bioxibacillin. I diluted one teaspoon of the product into half a bucket of water. It took 2 liters of solution per hundred square meters.It had no effect on the butterflies, but the caterpillars disappeared after three days. The disadvantage is a very unpleasant smell.”
Vyacheslav, Krasnodar region: “Trichogramma basically copes with the armyworm, but one release is not enough. Then we repeat the event.”
Read also:
How to get rid of cutworms on tomatoes once and for all?
Conclusion
Cotton bollworm larvae feed on plant tissue and cause serious damage to corn crops. Damaged ears and stems are often affected by fusarium and other fungal infections. All this leads to partial or complete loss of yield.
To combat the pest, insecticides, biological products, and proper agricultural technology are used. Traditional recipes are applicable only in personal gardens because of their labor intensity and low efficiency. Preventive measures include planting hybrids that are resistant to attack by insect pests.
Monitoring the population size will help to timely monitor the excess of the harmfulness threshold and take effective measures to destroy the pest.