What pesticides should be used to control cotton bollworm on corn, tomatoes, and cotton?
Corn, tomatoes, and cotton are all common crops, and they are also prone to diseases during their growth, which can lead to reduced yields or even death of the crops. So if cotton bollworm appears, what pesticide should be sprayed? How should it be treated?
What is cotton bollworm? How do you identify it?
1. Cotton bollworm belongs to Lepidoptera, Noctuidae. It damages many crops. In addition to cotton, it also damages corn, tomato, flax, sunflower, pea, pepper, and other crops as well as many kinds of weeds. Cotton bollworm has many aliases; when it damages corn, it is called the corn earworm. In recent years, in some areas with changed cultivation systems and expanded multiple-cropping area, damage by cotton bollworm to corn has shown an increasing trend, especially in southern Liaoning, the Yangtze River basin, and parts of Xinjiang.
2. Adult: a grayish-brown medium-sized moth, body length 15-20mm, wingspan 31-40mm, compound eyes spherical, green (the compound eyes of the closely related tobacco budworm are black). Female moths are reddish brown to grayish brown, male moths are bluish gray. The forewings and hindwings of the cotton bollworm can serve as the model for adult noctuids. Its forewings have a dark gray broad band outside the outer transverse line, with 7 small white dots on the band, and the kidney-shaped mark and ring-shaped mark are dark brown. The hindwings are grayish white, with a dark brown broad band along the outer margin, and 2 connected white spots in the center of the broad band. There is 1 crescent-shaped brown spot on the anterior margin of the hindwing.
Egg: hemispherical, height 0.52mm, 0.46mm, slightly raised at the top; the surface is covered with longitudinal and transverse lines. From the top, there are 12 longitudinal lines, and between the 2 middle longitudinal lines there are 1-2 short lines, mostly with 2-3 branches, so from the middle there are 26-29 longitudinal lines.
Larva: has 6 instars in total, sometimes 5 instars (those feeding on pea seedlings and sunflower heads). A mature 6th-instar larva is about 40-50mm long, with a yellowish-brown head bearing indistinct markings. The larval body color is variable and divided into 4 types: 1) body color light red, dorsal line and subdorsal line brown, spiracular line white, hair tubercles black. 2) body color yellow-white, dorsal line and subdorsal line light green, spiracular line white, hair tubercles same as body color. 3) body color light green, dorsal line and subdorsal line indistinct, spiracular line white, hair tubercles same as body color. 4) body color dark green, dorsal line and subdorsal line not very distinct, spiracles light yellow. Above the spiracles there is a brown longitudinal band formed by rows of sharp minute spines (the minute spines of the tobacco budworm are blunt and rounded, not arranged in a line). On abdominal segments 1, 2, and 5, each larva has 2 especially obvious hair tubercles.
Pupa: 17-20mm long, spindle-shaped, reddish brown to dark brown, with a pair of anal spines at the end of the abdomen, the bases of the spines separated. The spiracles are relatively large, and the peritreme is tubular and protrudes relatively high. The punctures on abdominal segments 5-7 are semicircular, relatively coarse and sparse (the spiracles of the tobacco budworm are small, the bases of the spines are joined, the peritreme is not high, and the punctures on segments 5-7 are fine and dense, with both semicircular and circular forms). It enters the soil 5-15cm to pupate, covered externally by an earthen cocoon.
When cotton bollworm appears on corn, tomatoes, and cotton, what pesticide should be sprayed? How should it be treated?
Corn:
1. Physical control
Poplar branch bundles to attract moths: during the adult moth flight period, this should be carried out over a large area, especially in cotton fields, and can eliminate a large number of adults, playing a relatively large role in reducing local insect sources.
High-pressure mercury lamps and frequency-vibration insect-killing lamps to attract moths have the characteristics of trapping and killing large numbers of cotton bollworm while causing little harm to natural enemies, and are suitable for use in areas with severe cotton bollworm outbreaks and during the peak emergence period.
2. Biological control
Releasing Trichogramma: during the peak egg-laying period of cotton bollworm, release wasps 2 times, 300,000 per hectare, with 60 release points (release 20,000 per mu, 4 release points), placing Trichogramma cards that will hatch the next day into open paper bags and hanging them on the middle and lower parts of the plants.
3. Chemical control
Before the third instar, spray the leaf surface with 2.5% cyhalothrin emulsifiable concentrate at 2000 times dilution, 5% beta-cypermethrin emulsifiable concentrate at 1500 times dilution, and other chemical pesticides. In late June, scatter insecticidal granules into the corn whorl; the pesticide and method of use are the same as for the Asian corn borer.
4. Agricultural control
Autumn plowing and winter irrigation reduce the overwintering insect population base. Optimize crop layout to avoid migration and reproduction of cotton bollworm from adjacent crops. At the edges of cotton fields and on canal banks, plant corn trap strips, select early-maturing corn varieties, about 2200 plants per 667 square meters. Taking advantage of the habit of adult cotton bollworm preferring to rest and lay eggs in the corn whorl, have a dedicated person beat the whorl leaves every early morning to eliminate adults and reduce insect sources.
Tomatoes:
Plow the land before winter and irrigate to flood the field to reduce overwintering insect sources. According to insect monitoring and forecasting, during the peak egg-laying period of cotton bollworm, combine with pruning and remove eggs to burn them.
When the number of eggs per 100 plants reaches 20—30, pesticide application should begin. If larvae per 100 plants exceed 5, application should continue. Generally, application begins when the fruit starts to expand.
Cotton:
1. Bifenthrin emulsifiable concentrate 3000-5000 times;
2. Emamectin benzoate microemulsion 7500-15000 times;
3. 52.25% cypermethrin·chlorpyrifos emulsifiable concentrate 1500-2000 times;
4. 28% fenpropathrin·phoxim emulsifiable concentrate 1000-1500 times;
5. 48% chlorpyrifos emulsifiable concentrate 500-800 times;
6. 2.5% beta-cyhalothrin emulsifiable concentrate 1500-2000 times;
7. 40% trichlorfon·chlorpyrifos emulsifiable concentrate 1000-1200 times.
Where to spray pesticide when cotton bollworm appears
When cotton bollworm lays eggs, it generally lays them on the top of the cotton plant, on the tender leaves at the tips of fruiting branches, and on the bud stalks and bracts. When spraying, the focus should be on the top of the cotton plant and the tender tips of fruiting branches, bud stalks, and bracts.
Time to spray pesticide:
The hatching pattern of cotton bollworm is that the egg is white on the first day, yellow on the second day, black on the third day, and hatches on the fourth day. After hatching, it damages the growing point on the second day, and migrates to damage young buds on the fourth day. Cotton bollworm is mostly active and feeding from 8-11 a.m. and after 4 p.m., and is rarely active during the high-temperature period at noon. The suitable control period should be after the egg-laying peak until most eggs turn black or before hatching and migration; application from 8-11 a.m. and after 4 p.m. is best. Avoid applying pesticide during high temperatures, because application at high temperatures tends to volatilize and decompose, not only making operators prone to poisoning but also giving poor efficacy.
Alternate pesticides:
Do not continuously use one pesticide, in order to prevent cotton bollworm from developing resistance to the pesticide.
Pesticide concentration:
Prepare the pesticide concentration according to the instructions; it must not be arbitrarily increased or decreased. Increasing the concentration easily causes pesticide damage to cotton plants, while decreasing the concentration reduces efficacy.
Amount of pesticide solution used:
If the amount of pesticide solution used is small, the spray on cotton plants will not be uniform and the insect control effect will be poor. When controlling the second generation of cotton bollworm, the amount of pesticide solution used per mu must not be less than 40 kg; when controlling the third and fourth generations of cotton bollworm, the amount of pesticide solution used per mu is 80-100 kg. Only when all parts of the cotton plant are evenly covered with pesticide will the effect be good.