Common Cotton Pests and Diseases and Their Control Techniques

Cotton is one of the world's most important crops. Its high yield and low production cost make cotton products relatively inexpensive, and the fiber can be made into fabrics of many specifications, from light and transparent voile to thick canvas and thick velveteen, suitable for making all kinds of clothing, furnishing fabrics and industrial fabrics. The countries with the highest yields are China, the United States and India. Now let us take a look at cotton pest and disease control techniques!

Cotton aphid

[Damage characteristics] Seedling aphids occur from emergence until after squaring. Control should begin when the rate of curled leaves reaches more than 30%. Mid-June to late July is the peak period of cotton aphid damage.

[Control methods] You can choose 10% imidacloprid wettable powder + Xin Gao Zhi Mo 800-fold solution, or 15% Jin Hao Nian emulsifiable concentrate + Xin Gao Zhi Mo 800-fold solution, and spray evenly on stems and leaves. When summer aphids occur during the bud and boll stage, because of the high temperature, you can choose 3% acetamiprid emulsifiable concentrate 2000-fold solution plus 40% chlorpyrifos 1200-fold solution + Xin Gao Zhi Mo 800-fold solution to control aphids and other pests at the same time. After the cotton plants close their rows, you can also use 80% dichlorvos emulsifiable concentrate + Xin Gao Zhi Mo 800-fold solution and spray it between the cotton ridges on a clear, windless evening. This has a good effect on summer aphids and can also control cotton red spider mites.

Cotton leaf mite

[Damage characteristics] It begins to appear in patches in cotton fields in early May. At this time the temperature is relatively low, reproduction is slow, the number of mites per leaf is small, and cotton seedlings suffer relatively little damage. From early June to late July, the temperature rises quickly, cotton leaf mites begin to reproduce in large numbers and cause concentrated damage, and in dry years the damage is rampant.

[Control methods] You can choose 15% Sao Chong Man Jing emulsifiable concentrate + Xin Gao Zhi Mo 800-fold solution, or 1.8% abamectin + Xin Gao Zhi Mo 800-fold solution for spray control.

Cotton mirid bug

[Damage characteristics] Damage to cotton by the cotton mirid bug is increasing year by year. The chemical control period is mid-to-late June. During this period the cotton plants are relatively tender. If there is a lot of rain and the relative humidity in the cotton field is high, this favors damage by the cotton mirid bug. This period is the key period for control.

[Control methods] At the cotton bud stage and boll stage, you can choose 5% acetamiprid emulsifiable concentrate + Xin Gao Zhi Mo 800-fold solution, or 4.5% beta-cypermethrin emulsifiable concentrate + Xin Gao Zhi Mo 800-fold solution for spray control. The effect is good, and it also controls cotton bollworm at the same time.

Cotton bollworm

[Damage characteristics] The cotton bollworm is the main pest during the cotton bud and boll stage, generally producing 4 generations a year. It mainly damages cotton in the second and third generations, with larvae boring into and feeding on buds, flowers and bolls. Bored bolls are prone to rot and drop off or become stiff locks.

[Control methods] 1. Physical control: Install Jiaduo frequency-vibration insect-killing lamps in concentrated cotton planting areas, one set per 60 mu; using them continuously over a large area gives a better effect. 2. Chemical control: You can choose 90% methomyl wettable powder + Xin Gao Zhi Mo 800-fold solution, 4.5% beta-cypermethrin emulsifiable concentrate + Xin Gao Zhi Mo 800-fold solution, or 1.8% abamectin + Xin Gao Zhi Mo 800-fold solution for stem and leaf spraying, once every 7 days, spraying 2 to 3 times in succession. For later cleanup of remaining pests, you can use 20% Xin Mie emulsifiable concentrate + Xin Gao Zhi Mo 800-fold solution or 20% cyanophos-malathion emulsifiable concentrate 1500-fold solution for even spraying.

Fusarium wilt

[Damage characteristics] Fusarium wilt is a disease that damages the vascular bundle tissue of cotton, causing symptoms such as leaf discoloration, drying, shedding and wilting. In severe cases, plants die in patches, affecting yield.

[Control methods] At the cotton bud stage, you can use Ku Huang Wei Ling at 40 grams per mu diluted with water for spraying (preferably spraying combined with irrigation) 3 to 4 times.

Verticillium wilt

[Damage characteristics] Symptoms generally begin to appear at the 3-to-5 true leaf stage. In the middle and late growth stages, after cotton squaring, the disease breaks out extensively in the field, and can easily cause the entire plant to die or wilt.

[Control methods] Common agents include carbendazim, thiophanate-methyl, Ke Huang Ku, Ku Huang Ji Yin Su, cotton San Qing and others, plus nutritional regulators such as monopotassium phosphate, boron fertilizer, boron plus selenium, zinc fertilizer, zinc plus selenium, Tian Feng Su, fish protein and others. The interval between sprays is 5 to 7 days, spraying 2 to 3 times in succession.

Beet armyworm

[Damage characteristics] The beet armyworm is an omnivorous pest, producing 4 to 5 generations a year, with severe overlapping of generations and uneven larval instars. High-temperature and drought climate factors and cultivation conditions with multiple crops mixed together favor the occurrence of beet armyworm. Generally, cotton fields with rough management and many weeds suffer heavier occurrence.

[Control methods] You can choose 0.2% emamectin benzoate + Xin Gao Zhi Mo 800-fold solution, or 25% diflubenzuron suspension concentrate + Xin Gao Zhi Mo 800-fold solution, and spray evenly on cotton plants and field weeds, spraying 2 to 3 times in succession. The effect is good.

Cotton Pest and Disease Control Techniques

Common Corn Pest and Disease Control Techniques

Corn is often harmed by various pests and diseases during production, causing severe yield reductions. For example, in epidemic years of northern corn leaf blight, yield can be reduced by 15—30% due to the disease, and severely affected fields can lose more than 50%; damage by the Asian corn borer usually reduces corn yield by about 10%, and in severe years by about 30%. There are many types of pests and diseases harming corn. The main diseases include northern corn leaf blight, southern corn leaf blight, head smut, stalk rot, ear and kernel rot and viral diseases, while those causing severe damage in local areas include banded leaf and sheath blight, brown spot, rust, round spot and gray leaf spot; the main pests include the Asian corn borer, cutworm, armyworm and red spider mite.

Northern and Southern Corn Leaf Blight

[Symptom identification] The typical symptom of northern corn leaf blight is that small lesions rapidly expand into long fusiform large lesions, with severe ones reaching more than 10—30 cm in length. Sometimes several lesions join together to form irregular large lesions. The lesions are initially water-soaked, quickly become bluish-gray, and finally become black moldy material, namely the pathogen's conidiophores and conidia.

[Symptom characteristics] The symptom characteristic of southern corn leaf blight is that the lesions are small, generally no more than 1 cm long and limited in width between two leaf veins, nearly elliptical, with relatively dark reddish-brown edges. In addition, the number of lesions is generally relatively large.

[Disease factors] The germination and invasion of pathogen spores and the formation and spread of spores all require certain climatic conditions, among which temperature and humidity are the main ones. The optimum temperature for the formation, germination and invasion of northern corn leaf blight pathogen spores is 20—25°C, while that for southern corn leaf blight is slightly higher, at 20—32°C. Therefore, southern corn leaf blight is more severe in summer corn planting areas, while northern corn leaf blight is more severe in spring corn areas. High rainfall and high humidity easily cause disease epidemics.

[Control methods] The epidemic of a disease is determined by three factors: first, large-scale planting of susceptible varieties; second, the presence of large amounts of pathogens; third, the presence of environmental conditions suitable for disease development. Therefore, disease control should start from these three aspects.

1. Select disease-resistant varieties: This is the fundamental way to control northern and southern corn leaf blight. Different varieties have obvious differences in disease resistance. At present, commonly used disease-resistant varieties in production include Baoyu No. 7, Tunyu No. 7, Yunrui No. 7, Haihe No. 14, Qing San, Huidan No. 4, Xinghuangdan 892, Denghai No. 3, Dianfeng No. 4, Yunrui No. 1, Yunrui No. 2, Yunrui No. 8, Ludan No. 10, Quchen No. 3, Haihe No. 2 and others.

2. Crop rotation, stubble turning and deep plowing can reduce the amount of inoculum. After corn harvest, thoroughly remove diseased residues from the field to reduce the primary infection source. In the early stage of disease, removing the lower diseased leaves before the bottom 4 leaves are affected can reduce the severity of the disease. Sowing early at the appropriate time has a disease-avoiding effect. Strengthening fertilizer and water management can improve disease resistance. Poor plant growth makes plants susceptible to infection; even resistant varieties cannot show their disease-resistant potential when water is lacking.

3. Chemical control: You can use 40% Kitazin emulsifiable concentrate 500—1000-fold solution, 50% Tuzet wettable powder 800-fold solution, 50% IBP 1000-fold solution, or 50% thiophanate-methyl 500—800-fold solution. If necessary, spray again after about 7 days.

Corn Head Smut

It mainly harms the corn ear and tassel, and once the disease occurs, the whole plant usually produces no grain at all. Therefore, the incidence rate of this disease equals the loss rate, and the damage is quite serious. It is commonly called “wumi” or “huibao”.

[Symptom identification] It is a systemic disease that invades from the corn coleoptile at the seedling stage, with symptoms mainly appearing after tasseling. Diseased ears look shorter than normal ears, with a large base and pointed tip, and no silks emerge from the top. Sometimes the husk on one side splits open, exposing black powder. The diseased ear completely becomes a blackish-brown spore mass, and the spores do not scatter easily; remnants of corn vascular bundles are mixed in. Plants with diseased tassels generally have no tassel branches; the tip of the newly emerged tassel axis becomes a small pile of black spores, and sometimes after the tassel emerges, the florets are deformed into leaf-like structures.

[Disease factors] The pathogen's chlamydospores fall into the soil, mix into manure, or are carried by seeds to overwinter. The next year, under suitable conditions, the chlamydospores germinate and invade host seedlings through the coleoptile. After invasion, the hyphae enter the plant growing point and, as the plant grows, spread to the ear and tassel, forming spore masses. After maturity, spores are released again, completing its once-a-year infection cycle, with no secondary infection. When soil temperature is relatively low and the soil is relatively dry, corn emergence is delayed, increasing the chance of pathogen infection, the incidence rate is high, and this favors the epidemic of head smut. Therefore, in cool regions, head smut occurs more severely. This pathogen can survive in the soil for about 3 years, and a 3-year rotation can effectively control the disease.

[Control methods]

1. Select disease-resistant varieties: At present, commonly used disease-resistant varieties in production include Dianfeng No. 4, Ludan No. 10, Quchen No. 3, Baoyu No. 7, Haihe No. 14, Yunrui No. 1, Yunrui No. 2, Yunrui No. 7, Yunrui No. 8 and others.

2. Practice crop rotation and deep plowing: Continuous cropping for many years easily increases the amount of pathogens in the soil and leads to severe disease. Practicing crop rotation for more than 3 years can basically eliminate the harm of pathogens in the soil. Deep plowing of the soil presses pathogen spores below the sowing layer, which can reduce the source of inoculum and lessen the disease.

3. Pull out diseased plants early: Pull out diseased plants before the white membrane of the diseased ear ruptures, and take the diseased plants outside the field to bury deeply or burn, so as to prevent the pathogen from falling into the soil.

4. Chemical control: This disease is a one-time infection disease at the seedling stage. Using chemicals at the seedling stage to prevent pathogen invasion will effectively control the occurrence of this disease. First, use 25% triadimefon or hydroxy triadimefon at a seed dressing dose of 0.3%; the control effect can reach about 90%. Corn paste can also be used as an adhesive to increase efficacy. Second, use seed coating agents to prevent disease. At present, there are many coating agents in production that can effectively control pests and diseases.

Corn Ear and Kernel Rot

Corn ear and kernel rot is divided into many types because of the different pathogens harming corn, mainly Fusarium rot, Aspergillus ear rot, Penicillium ear rot and dry rot caused by Diplodia species, among others.

[Symptom identification] The ear begins to develop the disease from the tip or base, with large areas or the entire ear rotting. Diseased kernels are shrunken, lusterless and not plump, and sometimes pink or grayish-white mycelium is produced between kernels. Some symptoms appear only on individual or localized kernels, on which dense red powdery material grows, and diseased kernels break easily. Some pathogens (such as Aspergillus flavus and Fusarium) produce toxins during growth. Kernels with ear and kernel rot caused by these pathogens can cause dizziness, nausea and vomiting when made into products or eaten directly by people. When diseased kernels are used as feed, they often cause vomiting in pigs, and in severe cases can cause the death of livestock and poultry.

[Disease factors] Infected seeds, diseased residues and the diseased residues of other crops can all cause field disease, and in years with heavy rain in the later period, they easily cause disease epidemics.

[Control methods]

First, select disease-resistant varieties. At present, relatively disease-resistant varieties include Baoyu No. 7, Tunyu No. 7, Yunrui No. 7, Haihe No. 14, Qing San, Huidan No. 4, Dianfeng No. 4, Yunrui No. 1, Yunrui No. 2, Yunrui No. 8, Ludan No. 10, Quchen No. 3, Haihe No. 2 and others.

Second, collect diseased residues, burn or bury them deeply, and practice 2—3-year crop rotation.

Third, use coated seed.

Fourth, strengthen field management so that plants grow robustly and disease resistance is improved. Timely control the Asian corn borer, because the Asian corn borer is a vector for infection by ear and kernel rot pathogens.

Fifth, during storage, keep ventilation, dryness and low temperature.

Corn Stalk Rot

Corn stalk rot mainly occurs at the late grain-filling stage. It is an explosive, destructive disease that easily causes severe yield losses.

[Symptom identification] At the late grain-filling stage of corn, it often appears as sudden green wilt, with the whole plant's leaves drying and fading as if scalded by water; the ear droops and the husk dies; the stem base is initially water-soaked, then gradually becomes light brown, feels hollow when squeezed by hand, and often causes lodging.

[Disease factors] First, caused by Fusarium; second, caused by Pythium; third, caused by combined infection by Pythium and Fusarium. Heavy rain from the grain-filling to milk-ripe stage has an important influence on the occurrence of the disease, and high water content in the soil is an important condition for the occurrence of stalk rot.

[Control methods] Select disease-resistant varieties Tunyu No. 7, Ludan No. 10, Yunrui No. 1, Yunrui No. 2, Baoyu No. 7, Yunrui No. 7, Haihe No. 14, Qing San, Huidan No. 4, Dianfeng No. 4, Yunrui No. 8, Quchen No. 3, Haihe No. 2. In cultivation measures, attention should be paid to drainage.

Corn Viral Diseases

Corn viral diseases mainly include corn dwarf mosaic virus disease and corn rough dwarf disease.

[Symptom identification] Corn dwarf mosaic virus disease, also called mosaic stripe disease, can infect corn throughout the entire growth period. At the seedling stage, chlorotic dotted mosaic first appears from the base of the heart leaf and gradually spreads to the whole leaf. The veins remain green while the mesophyll tissue loses green and turns yellow, forming obvious symptoms of alternating yellow and green stripes. Severely diseased plants cannot tassel or set ears, or die prematurely.

The typical symptom of corn rough dwarf disease is plant dwarfing. Infected corn appears dark green, with thick, stiff mesophyll, and sometimes the heart leaf curls together and bends in an arch shape because the base continues to grow. Short raised stripes appear on the veins of the leaf underside, leaf sheath and husk, initially grayish-green and later grayish-brown. Diseased plants are often less than half the height of healthy plants and cannot tassel or set ears.

[Disease factors] Corn dwarf mosaic virus disease can be inoculated by sap rubbing. It is mainly transmitted by aphids, but aphid transmission of the virus is non-persistent. In addition to harming corn, the virus of this disease can also infect sorghum, foxtail millet and various gramineous weeds. In the south, the virus can overwinter with multiple crop and weed hosts.

In addition to transmitting viruses, aphids themselves also cause very serious harm to corn. Aphids often gather on the tassels and the backs of leaves of corn, sucking sap from corn tissues with piercing-sucking mouthparts. At the same time they secrete a saliva that inhibits corn growth, affects corn flowering and pollination, and causes empty ears and bare tips.

Corn rough dwarf virus is mainly transmitted by the small brown planthopper and is persistent in transmission. The virus can overwinter in the nymphs of the small brown planthopper, and can also overwinter in wheat seedlings infected before winter.

[Control methods]

First, select resistant and tolerant varieties.

Second, control insects with chemicals early, eliminating aphids and small brown planthoppers before they migrate to corn fields. Spray with 40% omethoate 3000-fold solution; or use 50% pirimicarb wettable powder 15—20 grams diluted with 50—75 kg of water for spraying. To control insects in corn fields, you can use 40% dimethoate emulsifiable concentrate stock solution 1 kg, add 5—6 kg of water, and on the stem base of damaged corn, use a brush or cotton ball dipped in the solution to smear it, coating all around half of the stem section; this can also kill insects through systemic action.

Third, strengthen cultivation management to improve plant disease resistance.

Corn Gray Leaf Spot

[Symptom identification] It mainly harms corn leaves, and also infects leaf sheaths and husks. In the early stage of disease, circular, oval reddish-brown rectangular streaks form between leaf veins. Lesions are mostly limited between leaf veins and parallel to the veins. When mature, the center of the lesion is gray and the edges are brown, with a size of (4—20) mm × (2—5) mm. When humidity is high, gray moldy material grows on the underside of the lesions.

[Disease factors] This disease is caused by fungi. The pathogen mainly overwinters with corn diseased residues, and under suitable conditions produces conidia. Conidia spread with airflow and splashing raindrops. After corn becomes diseased, conidiophores and conidia are produced again on the lesions, causing multiple secondary infections in one growing season.

The disease mostly begins on lower leaves at the tasseling stage. Low temperature (20°C—25°C), abundant rain and relative humidity in the atmosphere as high as above 90% cause severe occurrence of gray leaf spot, easily leading to an epidemic; while high temperature and drought inhibit the disease epidemic.

[Control methods]

1. Select resistant (tolerant) varieties: Haihe No. 1, Haihe No. 2, Yunrui No. 1, Beiyu No. 2, Yunyou 196, Changcheng 799, Baoyu No. 12, Yuyu 22, Nongda 108 and other varieties are relatively disease-resistant, with Haihe No. 1 and Beiyu No. 2 performing particularly well.

2. After corn harvest, promptly remove diseased plant residues, burn them in a centralized way or bury them deeply, and carry out large-area crop rotation.

3. Chemical control: Spray in time for prevention at the early stage of disease. Select 70% thiophanate-methyl wettable powder 500-fold solution, 10% difenoconazole water-dispersible granules 50 grams, 70% chlorothalonil wettable powder 500-fold solution, 68.7% Yin Zhuo Li suspension concentrate 100 ml per mu, or 50% carbendazim wettable powder 500-fold solution for spraying. Spray once every 7—10 days, continuously 2—3 times. Alternating several agents gives a better effect.

Corn Rust

At the early stage of disease, you can use 25% triadimefon wettable powder 1500—2000-fold solution or 50% sulfur suspension concentrate 300-fold for control.

Cutworm

Cutworm is also called soil silkworm, earth silkworm or root-cutting worm. There are many species of cutworm, and the commonly occurring and damaging ones are the black cutworm and the yellow cutworm.

[Life habits] Cutworms generally cause severe damage with the first-generation larvae, and the life and damage habits of larvae differ by instar. First- and second-instar larvae are active day and night, nibbling harvested leaves or tender leaves; after the third instar they hide in the soil during the day and come out at night to damage plants, biting off the tender stems at the base of seedlings and causing missing plants; after the fourth instar, larval resistance to pesticides is greatly enhanced, so chemical control should eliminate larvae before the third instar.

[Occurrence factors] Abundant rain in autumn is a precursor to major outbreaks of both cutworm species. In early spring, if there is abundant rain in February—March and little rain in April, when larvae have just hatched or are in the first and second instars, this favors cutworm occurrence, and first-generation larvae may cause severe damage. Conversely, from mid-April to early May, if there are many rainy days with moderate rain or above and large rainfall amounts, causing massive death of first- and second-instar larvae, the possibility of severe damage by first-generation larvae is lower.

[Control methods] For cutworm control, measures combining moth trapping, weed removal, chemicals and manual control must be adopted.

1. Trap and kill adults: Trapping and killing adults is the best strategy for cutworm control and can greatly reduce the number of first-generation larvae. The method is to use black light lamps and sugar-vinegar liquid for trapping and killing.

2. Remove weeds: Weeds are the main place where adults lay eggs and also an important route for larvae to move onto corn seedlings. Thoroughly remove weeds before corn emergence, and promptly move them outside the field for feed or composting; do not discard them randomly. Removing weeds will effectively reduce the insect population base.

3. Chemical control: After emergence, based on fixed-point surveys, when there is an average of 0.5 insect per square meter, it is the appropriate time to apply pesticide.

4. Use coated seed or dress seed with chemicals: You can use carbofuran seed coating agent for seed dressing at 1% of corn seed weight. You can also use 50% phoxim emulsifiable concentrate 0.5 kg, add 30—50 kg of water, and dress 350—500 kg of seeds.

5. Apply poisoned soil: Use 3% carbofuran granules at 1.5 kg per unit, or 50% methamidophos emulsifiable concentrate 0.5 kg per mu, add 40 kg of fine soil, mix evenly and broadcast.

6. Poison bait trapping: Poison bait trapping is more effective for larvae above the fourth instar. Dissolve 0.5 kg of 90% trichlorfon in hot water, add about 5 kg of clean water, spray it on roasted oil residue (cottonseed hulls can also be used as a substitute), and stir evenly. Use 4—5 kg of poison bait per mu and scatter it in the evening.

Asian Corn Borer

The Asian corn borer, also called the corn heartworm, is a major worldwide corn pest. The Asian corn borer is a polyphagous pest with many host plants, and the main crops it harms are corn, sorghum and millet.

[Symptom identification] Asian corn borer larvae are boring pests. The typical symptom they cause is that after the heart leaf is bored through, the unfolded corn leaves show neat rows of small holes. After the tassel emerges, the larvae bore into the tassel to damage it, often causing the tassel base to break. After the ear appears, the larvae move to the ear to feed on silks and tender husk leaves, bore into the cob, or feed on tender kernels. Some larvae bore into the stem from between the stalk and leaf sheath, feeding on the pith, making the stalk easy to break in strong wind. Affected plants have unplump kernels, premature green wilt and early decline, and some ears even have no kernels, causing severe yield reduction.

[Life habits] Depending on climatic conditions in different places, the Asian corn borer can produce 1—6 generations a year. It overwinters as larvae in corn stalks and corn cobs, with some larvae overwintering in weed stems. The occurrence period is extremely uneven, and generation overlap occurs.

[Occurrence factors]

1. Insect population base: A large insect population base, under suitable environmental conditions, often causes severe damage.

2. Temperature and humidity: The Asian corn borer is suited to growth and development under high temperature and high humidity. The optimum temperature for the growth and development of each life stage is 16—30°C, with relative humidity above 60%. The Asian corn borer mainly occurs from June—September.

3. Corn varieties: Different corn varieties differ greatly in damage. There is a borer-resistant substance called DIMBOA in corn tissue. When adults lay eggs on corn varieties with high DIMBOA content, the mortality of hatched larvae is very high. The tissue morphology of some corn varieties can avoid adult egg-laying and reduce borer damage; for example, if the hairs on the leaf surface and stalk are long and dense, borer damage is very light.

4. Natural enemies: There are many kinds of natural enemies of the Asian corn borer, and the one with a relatively large suppressive effect on it is Trichogramma.

[Control methods]

1. Overwintering period control: The vast majority of Asian corn borer larvae overwinter in corn stalks and ear cobs, and pupate in them the following spring. Before the end of April, corn stalks and ear cobs should be burned as fuel or crushed for feed, and overwintering hosts such as cocklebur weeds should be removed, which can reduce the overwintering insect population base.

2. Heart leaf stage control: Control should be carried out when the rate of bored leaves in the late heart leaf stage reaches 10%, or at the silking stage of summer and autumn corn when the ear infestation rate reaches 5%. Control methods can include granules and liquid pouring. Use 3% phoxim granules or 3% carbofuran granules at 2 kg per mu mixed with 5 times fine sand to make poisoned sand, and sprinkle it into the corn heart leaf. For the liquid pouring method, you can use 80% dichlorvos emulsifiable concentrate diluted to 2500—3000-fold solution, pouring 10—15 ml per corn plant. The control effect can reach more than 85%, and it also has a concurrent control effect on corn thrips.

3. Ear stage control: Use 50% dichlorvos emulsifiable concentrate 0.5 kg, add 500—600 liters of water, open a small hole at the top of the ear husk, and inject a small amount of the solution. Generally, 1 kg of solution can be injected into 360 ears.

4. Biological control: Trichogramma plays a very significant role in eliminating the Asian corn borer and has a low cost. Release Trichogramma at the beginning, peak and end of Asian corn borer egg-laying, releasing 10,000—30,000 per mu, with 2—4 release points. Roll up the egg cards with corn leaves, and the height of the egg cards should preferably be 1 meter above the ground. In addition, use microbial pesticides such as Bacillus thuringiensis for corn borer, 7216, and Beauveria bassiana. There are two application methods: one is to pour into the heart leaf, using 1 kg of bacterial powder containing more than 10 billion spores per gram, add 1000—2000 kg of water, and pour into the heart leaf. The other method is to prepare bacterial soil or granules. Bacterial soil is generally made with 1 kg of Bacillus thuringiensis for corn borer plus 100—300 kg of fine soil or stove ash. Granules are generally prepared at about 20 times (1 kg of Beauveria bassiana powder mixed with 20 kg of cinder granules), applying about 2 grams per plant.

5. Select insect-resistant varieties.

Armyworm

Armyworm is an explosive, destructive pest. It is commonly called cotton worm, armyworm, army cutworm, night thief or leaf-cutting worm.

[Symptom identification] Armyworm larvae feed exposed on the plant surface. First- and second-instar larvae mostly hide in the crop heart leaf or leaf sheath and feed day and night, but their feeding amount is very small; they nibble the mesophyll and leave the epidermis, causing semi-transparent small streaks. Fifth- and sixth-instar larvae are in the ravenous feeding stage, eating leaves and nibbling the ear cob.

[Life habits] Armyworm has no diapause phenomenon and can reproduce continuously under suitable conditions. It likes to lay eggs on the tips of withered seedling leaves and has migratory characteristics. Larvae have a death-feigning habit, and their resistance to pesticides increases with larval instar. Armyworm has strict requirements for temperature and humidity. The optimum temperature for adult egg-laying is 15—30°C. Above 30°C or below 15°C, adult egg-laying decreases or eggs cannot be laid. If migratory armyworm moths encounter wind and rain and are forced to land, then local armyworm damage is severe. However, natural enemies also greatly inhibit the occurrence of armyworm. The main natural enemies of armyworm include parasitic flies, parasitic wasps, nematodes, ants, ground beetles, red spider mites, flower spiders and some fungi.

[Control methods] Armyworm control should combine moth trapping, egg collection and larval killing. Three key links should be grasped: eliminating adults before egg-laying, collecting eggs before hatching, and chemically killing larvae before the third instar.

1. Trap and kill adults (moths): Use millet straw bundles and sugar-vinegar liquid for trapping and killing. Sugar-vinegar liquid ratio: 3 parts sugar, 1 part liquor, 4 parts vinegar, 2 parts water; mix evenly. Trap and kill at night.

2. Trap and collect eggs: Utilize the egg-laying habits of adults to eliminate egg masses before hatching. From the beginning of egg-laying to after the peak period, place small millet straw bundles in the field and sprinkle sugar-vinegar-liquor liquid on the millet straw bundles to attract moths to lay eggs; the effect is very good. Promptly pick egg masses and eliminate them.

3. Chemical control: In corn fields, when there are 20—30 insects per 100 plants at the seedling stage, or 50—100 insects per 100 plants in the middle and late growth stages, chemical control should be applied. You can use 2.5% trichlorfon powder, spraying 2—2.5 kg per mu, or about 2 kg of 2.5% trichlorfon powder mixed with 10—15 kg of fine soil and broadcast along the rows after mixing evenly to control older larvae; or spray 90% trichlorfon 1000—2000-fold solution, 50% parathion 1605, or 80% dichlorvos 2000—3000-fold solution; the effects are all very good; you can also use 2.5% deltamethrin emulsifiable concentrate or 20% fenvalerate emulsifiable concentrate 1500—2000-fold solution for control.

Red Spider Mite

The corn red spider mite belongs to the mite group and is also called fire dragon, fire spider or red sand, among other names.

[Symptom identification] Spider mites generally begin to damage corn after tasseling; in years when they occur early, they begin damaging corn at the 6-leaf stage. Spider mites pierce and suck nutrients from the leaf tissue of the crop, causing the damaged leaves to show dense, tiny yellowish-white spots, which then gradually lose chlorophyll and turn yellow, and finally dry up and die. The damaged corn kernels are shrunken and thin, causing yield reduction.

[Life habits] Adult corn spider mites overwinter in soil cracks in the root zone. After temperatures rise in early spring, the spider mites emerge from the soil, gather on some weeds to feed and reproduce, and after spring corn emerges, they move to nearby corn seedlings through wind, crawling, and other means to cause damage. Spider mites cause damage in the field in patchy spots; spreading from the source area to the entire corn field takes a relatively long time. Their numbers decline after heavy rain, while in dry conditions with little rain, their numbers increase.

[Control methods]

① Eliminate overwintering adults: irrigation in early spring and after autumn can eliminate large numbers of overwintering spider mites.

② Chemical control: use a mixture of 40% dimethoate emulsifiable concentrate and 20% dicofol (1:1) at 1000—1500 times dilution; the effect is very good.

③ Use natural enemies: the natural enemies of corn spider mites include Stethorus punctillum, predatory thrips that feed on mites, and green lacewings.

Aphids

The reproduction of aphids differs from that of general pests, having the characteristic of alternating parthenogenesis and sexual reproduction, so their life history is relatively complex, and several generations often occur “under the same roof”; more than 20 generations can occur in 1 year. The insect density is very high, the damage period is long, and the losses caused to corn are also relatively serious.

[Control methods]

① Chemical control: spray with 40% omethoate at 3000 times dilution; or use 50% pirimicarb wettable powder 15—20 grams mixed with water 50—75 kg for spraying. To kill insects in corn fields, use 40% dimethoate emulsifiable concentrate stock solution 1 kg, add water 5—6 kg, and at the base of the stem of the damaged corn, use a brush or cotton ball dipped in the solution to apply it, coating all around half a node of the stem, so that it can kill insects through systemic action.

② Use natural enemies: the main natural enemy of corn aphids is the aphidid wasp.