Corn is a common field food crop in our daily lives and is planted over an extremely wide range of areas. In the corn planting process, the appearance of corn borers seriously affects the normal growth of corn.
This article will introduce the hazard characteristics and control methods of corn borer for your reference.
First, the law of occurrence
Corn borer occurs over generations and varies with latitude. Northeast and northwest regions of l to 2 generations a year, Huanghuai and North China Plain 2 to 4 generations, Jianghan Plain 4 to 5 generations, Guangdong, Guangxi and Taiwan 5 to 7 generations, southwest China 2 to 4 generations.
Corn borers overwinter as old mature larvae in the host infested areas and root stubble. The emergence of overwintering adult insects in various places is from april to early May in Guangxi, from mid-may to late June in Hunan, from may to mid-June in Shandong, from may to mid-June in Beijing, from mid-June to mid-July in Liaoning, and from mid-june to mid-July in Heilongjiang and Jilin. In the north, the overwintering larvae enter the pupal peak in mid-to-late May, and the overwintering adults bloom from late May to early June, laying eggs on spring maize or sorghum.
A generation of larvae blooms in mid-to-late June, when spring maize is in the heart leaf stage, which is very harmful. In the cotton and corn mixed areas, if the area of spring corn is small, the cotton damage will be more severe, resulting in severed heads and inverted leaves.
The second generation of larvae is harmful to summer maize in mid-to-late July. (heart leaf stage) and spring maize (panicle stage).
Three generations of larvae enter full bloom in mid-to-late August, harming the ears and stems of summer maize. In spring corn planting areas, after the corn harvest,
The second-generation adults are transferred to the cotton fields to lay eggs, which are harmful to the cotton green bells. The larvae mature and enter the overwinter in mid-to-late September. Adults are diurnal and nocturnal and phototropic.
Adults lay eggs near the midrib of the dorsal back of maize, with more than 20 to 60 eggs per egg, 400-500 eggs per female, an egg period of 3-5 days, and 5 young larvae, with an calendar period of 17 to 24 days.
The hatching larvae have a drooping habit and spread with the wind or crawl, burrowing into the heart leaf to nibble on the leaf flesh, leaving only the epidermis. After 3 years of age, moths are infested, and male ears, female ears, leaf sheaths, and leaf tongues can be affected. Mature larvae, generally pupate at the site of the victim, pupal period of 6 to 10 days.
In the years when the overwintering base of maize borer is large, the density of first-generation eggs and larvae in the field is high, and the general occurrence of damage is serious. The temperature is 25~ 260 °C, the relative humidity is about 90%, which is extremely beneficial to egg laying, hatching and larval survival, and heavy rain can increase the mortality rate of hatching larvae.
It is serious in the mixed maize area in spring and summer. The area of summer corn is large, and the area of spring corn is small, which will be aggravated by concentrated spawning. On the contrary, the large area of summer crops will also spread and occur, so as to reduce the harm.
Corn borers also have a large number of natural enemies, and the egg parasitism rate of red-eyed wasps can reach more than 80% under suitable conditions. The growth, leaf color and growth period of maize cultivars were different, and the number of maize borers showed obvious differences.
Second, the characteristics of harm
1. Corn heart leaf stage
Maize borer hatching larvae feed on young leaves in the heart leaf. When the damaged leaf is unfolded, an irregular translucent film-like row of holes is formed on the leaf. The severely damaged leaves are fragmented and cannot be unfolded, and the male spikes cannot be pumped out normally.
2. Corn gestational panicle stage
The heart-leaved corn borer larvae are concentrated in the upper part to harm the unabated male ears of corn in the buds of the young ears. After the male ear of maize is withdrawn, most of the larvae begin to inject into the male ear stalk and the stem above the male ear, causing the male panicle and the upper stem to break.
3. Corn silk filling period
The larvae of the corn borer are mainly concentrated in the filaments, and some of the older insects are injected into the female panicle axis and the female ear and its nearby stem nodes, which harm the corn grains, make them break and mold; damage the stem tissue, affect nutrient transportation, seriously affect the development of female ears and grain filling, which is also the most serious period of maize yield.
1. Agricultural control
Such as the treatment of overwintering hosts, lower the base of insect sources, according to local conditions, tillage reform, fertilizer application, etc.
2. Biological control
(1) The release of red-eyed bees in the field can control corn borer. The most suitable species of parasitic corn borer is the pine caterpillar red-eyed wasp.
At the beginning of spawning, the adult corn borer can artificially release the red-eyed bee into the field, and the red-eyed bee will lay eggs in the corn borer eggs, so that the corn borer eggs cannot hatch into larvae, so as to better control the corn borer. After 10-12 days of release into the field, the offspring of the wasps will continue to parasitize new corn borer eggs after development, maturity and feathering, and in general, the offspring of the red-eyed bees can continue to achieve control over the corn borer in the field until September.
The release of red-eyed bees to control corn borers has high technical requirements, and it is necessary to strictly grasp the time and quantity of bee release, and the humidity of the beekeeping period directly affects the amount of bee feathering. Therefore, it is affected to some extent by the climatic factors of the year.
Specific release time: when the pupal pupae rate of wintering corn borer reaches 20%, the first bee release is carried out after 10 days.
Release method: The time of bee release should be selected in the morning, and 1 corn plant should be selected at the bee point, take 1 middle leaf and tear 1/2 from the middle, roll into a cylinder, and then use straw or toothpick to snap in the cylinder.
The egg parasitism rate of red-eyed wasps in the field exceeded 70%, the prevention effect exceeded 65%, the yield increase exceeded 450kg/hm2, the control cost was about 22.5 yuan/hm2, and the input-output ratio exceeded 1:20.
(2) White zombie bacteria are sealed
Early spring sealing stacks control overwintering larvae. Before the annual overwintering larvae pupate, generally from mid-April to early May, spray 100g/m3 of white zombie spore powder on the burned host crop straw and root stubble, and spray 1 point on the stack surface of 1m2 until "white smoke" is visible on the stack.
The insecticidal effect after general stacking is more than 80%, the feathering of adult insects is significantly reduced, and the use of white zombies in the same area for continuous years has a cumulative synergistic effect.
(3) Spray Bacillus thuringiensis
It is also possible to spray the emulsion solution of Bacillus thuringiensis before the end of the corn heart leaf, but it must be sprayed comprehensively, so that the amount of the liquid medicine is in full contact with the heart leaf and the bracts of the flared mouth, in order to ensure the effect of killing borers. In addition, the centripetal leaves can be sprinkled with granules prepared with Bacillus thuringiensis, mixed with Bt emulsion 2.25L/hm2, Gaza 45-75kg/hm2, and the effect is more than 80%.
It is not advisable to apply the drug when the sun is too strong at noon, because Bt is a biopesticide, and its active ingredient is a bacillus, which will reduce the efficacy if it is irradiated by ultraviolet rays. Use with caution in sericulture areas and do not come into contact with silkworm bodies to avoid poisoning and causing a large number of deaths.
3. Pharmaceutical prevention and control
(1) Use DuPont Audeteng high-efficiency imported insecticides, use 4-5 grams per acre, mixed with water 15-20 (30-40) kg spray. The spraying time is best around July 10th, and it is carried out in the morning and afternoon when the weather is not hot, and in order to improve the efficacy, foliar fertilizer and auxiliaries can be added at the same time for spraying.
(2) Or spray with Forwitt (10g + 15g) / barrel or dart (10g + 20g) / barrel / ground work 60 ml / mu / blue ocean 40 ml / mu, corn borer can be used to prevent and control 3000-5000 times when the corn borer occurs severely.