What are the control measures for the Athetis lepigone pest in summer corn?
How to control the Athetis lepigone pest in summer corn? Athetis lepigone is a newly emerging pest in the main summer corn producing areas of China in recent years. Once it breaks out, it is extremely harmful to summer corn yields. How to control the Athetis lepigone pest when it occurs in summer corn? What are the control measures?
I. Identification of main morphological features
1. Adult
The adult body length is 10-12 mm; wingspan is about 20 mm; the forewings are grayish brown to dark brown, and the main identifying feature is a very obvious small black dot in the middle and at the end of the median cell, hence the name Athetis lepigone; around the small black dot at the end are scattered white scales, and the outer margin of the forewing has a row of small black dots; the hindwings are white with a slight brown tinge, and the terminal area is dark brown; it is phototactic and hides by day and comes out at night, generally hiding under wheat straw during the day; flight height is about 1 m, and each flight distance is 3-5 m.
2. Larva
The larval head is yellowish brown; the 1st to 3rd instars are 2-10 mm long and yellowish brown; before the 2nd instar the prolegs are not fully developed and cannot walk; by the 3rd instar the first and second pairs of prolegs have developed and can walk normally; the 4th to 6th instars are 10-25 mm long and grayish brown; after the 5th instar, on both sides of the parietal region of the head there is a dark brown inverted “”-shaped marking; each abdominal segment has a “V”-shaped marking; it has a death-feigning habit, curling into a “C” shape when startled.
3. Egg
The egg is steamed-bun shaped with longitudinal ridges; freshly laid eggs are yellow-green and gradually become earth yellow; diameter is less than 1 mm; laid on the moist soil surface under wheat straw and in the soil.
4. Pupa
After the mature larva enters the soil, it makes a silken earthen cocoon, surrounds itself with it, forms a covering, and then pupates inside the covering. The pupa is 10 mm long; at the early pupal stage it is light yellowish brown and gradually becomes brown.
II. Causes of Athetis lepigone outbreaks
Both adults and larvae of Athetis lepigone like concealed, humid environments. The larvae mainly damage corn seedlings at the base of corn seedlings covered with wheat straw or within the 2-5 cm deep surface soil layer. There are two types of damage: one is boring into the stem base of corn seedlings to feed, forming round or oval holes; when the boring is deeper, they enter the stem core, cut off the growing point, continue feeding upward, the heart leaves lose water and wilt, forming dead-heart seedlings, and then the whole plant gradually dies, causing missing plants and broken rows;
the other is that as the corn seedlings grow, the epidermis at the stem base ages, and larval damage shifts to the young corn root system, biting off part of the main roots and secondary roots and other roots, so corn plants lodge in the wind, and severely affected ones die. In areas damaged by this pest, generally 3-5 larvae are found per corn seedling, sometimes as few as 1-2, and sometimes more than 20. The larvae have the habit of transferring between plants; generally after each larva kills a corn seedling, it can continue to transfer and damage 5-8 plants in succession.
In 2005, Athetis lepigone first appeared in Hebei, and it has now spread throughout the entire Huang-Huai-Hai Plain. In many areas it has gone from absent to present and from few to many, with damage levels going from light to heavy and from heavy to outbreak. The reasons include the following aspects:
1. Sufficient food: The peak occurrence period of Athetis lepigone larvae coincides highly with the corn seedling stage. Summer corn is generally sown in early to mid-June, emerges in mid to late June, and the seedling stage is from mid-June to early July. The corn seedling stage is also the peak damage period of Athetis lepigone larvae, and the two coincide highly. The young roots and stems of summer corn provide a sufficient food source for its occurrence and development.
2. Good environment: Athetis lepigone lays many eggs and has strong reproductive capacity. The peak occurrence period of Athetis lepigone adults basically coincides with the wheat harvest period, providing good environmental conditions for adult egg laying. One female can lay hundreds of eggs, thereby hatching large numbers of larvae and causing serious damage to summer corn growth.
3. Wheat straw cover: Wheat straw cover provides a suitable living environment for Athetis lepigone. In recent years, with the improvement of agricultural production conditions, mechanized wheat harvesting has basically become widespread in plain areas, and consequently large amounts of straw are left in the fields. This provides favorable conditions for the survival of Athetis lepigone and has become the best environment for adults to hide, rest and lay eggs and for larvae to move and damage crops. According to surveys, the field damage of Athetis lepigone larvae mostly occurs in multiple spots, mainly closely related to the amount of wheat straw. Fields and areas with a large amount and thick cover of wheat straw and wheat chaff have heavier pest occurrence. Generally, high-yield wheat fields have more wheat straw and wheat chaff and a larger field coverage area, and Athetis lepigone occurrence is relatively heavier; low-yield wheat fields have less wheat straw and wheat chaff, and Athetis lepigone occurrence is relatively lighter; places without wheat straw and wheat chaff cover are basically not damaged by this pest.
Therefore, the large amount of straw left in the field after mechanized wheat harvest creates a very important living environment for pest occurrence and is the key factor causing Athetis lepigone outbreaks.
4. Sufficient moisture: Rainfall and watering provide favorable conditions for Athetis lepigone occurrence. The summer corn seedling stage coincides with the rainy season, with much rainfall and high field humidity, providing a favorable living environment for Athetis lepigone egg laying, hatching and larval growth; even without rainfall, the vast majority of fields are irrigated to ensure summer corn growth during the seedling stage.
In dry years, although soil moisture increases after watering, the water dissipates relatively quickly, and the favorable effect on Athetis lepigone occurrence is smaller than that of rainfall. Long rainfall duration and many rainy days, especially continuous overcast and rainy weather, are very favorable to pest occurrence. When air humidity rises, adult lifespan lengthens and egg production also increases, while egg hatching time shortens and hatching rate rises. After rain, soil moisture increases, larval survival rate increases greatly, and damage severity worsens, but heavy rain and rainstorms reduce adult lifespan and egg hatching rate, and waterlogging in the field inhibits larval occurrence and development.
Therefore, frequent rainy weather and high soil and air humidity are the most important climatic factors leading to Athetis lepigone outbreaks.
5. Strong concealment and great difficulty of control.
Athetis lepigone larvae hide in wheat straw or in the soil layer to move and damage crops, and are not easy for people to find, so the suitable control period is often missed; spraying chemicals or spreading poisoned soil can hardly pass through the wheat straw layer to contact the pests; older larvae have thicker body walls, and the pesticide liquid that contacts them does not easily penetrate into their bodies, increasing the difficulty of control.
III. Integrated control measures
Plots where Athetis lepigone damage has occurred in previous years and adjacent plots should be taken as key control areas, with early observation, timely discovery and timely integrated control measures.
1. Ecological control
For plots with slight Athetis lepigone occurrence, after summer corn sowing, clear all wheat straw, wheat chaff and weeds covering the corn rows into the wide corn inter-row spaces far from the plants.
For plots with relatively heavy Athetis lepigone occurrence, after wheat harvest and before summer corn emergence, promptly remove coverings such as wheat straw, wheat chaff and weeds covering the corn rows out of the field for composting organic fertilizer or use as industrial raw material, so that the soil in the corn sowing rows is exposed, destroying the environmental conditions favorable to pest occurrence and protecting corn seedlings from damage; even if pest occurrence happens, the difficulty of control can be greatly reduced; mechanical stubble cleaning can also be carried out first, followed by sowing.
2. Killing adults
Athetis lepigone adults mainly rest and lay eggs under wheat straw, wheat chaff and other firewood and grass. After corn sowing and before emergence, use tools such as an iron fork or wooden stick to stir the field coverings such as wheat straw. If Athetis lepigone adults are seen flying out, immediately spray pesticide to kill them at their resting places before egg laying, such as with 2.5% lambda-cyhalothrin emulsifiable concentrate, or 4.5% beta-cypermethrin emulsifiable concentrate, or 30% acephate emulsifiable concentrate, or 48% chlorpyrifos emulsifiable concentrate and other contact pesticides. The prepared concentration can generally be controlled at 1000-1500 times dilution, and where wheat straw and wheat chaff are thick, increase the amount of pesticide liquid; it can also be combined with pre-emergence chemical weed control in corn fields for whole-field spraying.
3. Controlling larvae
Athetis lepigone larvae are relatively sensitive to pesticides before the 3rd instar, and control becomes more difficult after the 3rd instar. Control should adopt the principle of “early and small&rdquo. One larval instar of Athetis lepigone generally lasts only 3-4 days, so preparations should be made in advance and control carried out early, and before control the wheat straw and wheat chaff in the plot should be promptly cleaned up. The earlier the control, the less labor used and the better the effect.
(1) Control of 1st to 3rd instar larvae
The 1st to 2nd instar larvae are generally under the coverings between corn rows, with no larvae surrounding the corn seedlings, and the damage symptoms are not obvious; the 3rd instar larvae have already gathered around the corn seedling roots and begun biting roots and boring holes, and individual corn plants in the field show wilting heart leaves. Control methods: poisoned bait or poisoned soil can be spread for control. Spreading poisoned bait: use 500 g of 90% crystalline trichlorfon per mu, or 500 mL of 48% chlorpyrifos emulsifiable concentrate, mix with 3-3.5 kg water and spray-mix with 4-5 kg of roasted wheat bran or crushed and roasted cottonseed cake, plus chopped green vegetable leaves or green grass to make poisoned bait, and scatter it along the rows at the base of corn seedlings in the evening; where wheat straw cover is thicker, appropriately increase the amount of poisoned bait. Spreading poisoned soil: use 300-500 mL of 80% dichlorvos emulsifiable concentrate per mu, or 500 mL of 48% chlorpyrifos emulsifiable concentrate, mix with 25 kg fine dry soil, and scatter it along the rows at the base of corn seedlings in the morning.
(2) Control of larvae after the 3rd instar
After the 3rd instar, larval damage gradually worsens, corn seedling damage symptoms are obvious, larvae will transfer between plants to damage, and they also gnaw corn seedlings during the day. Corn plants in the field show wilting heart leaves or leaning in all directions, and severely damaged plots show dead seedlings. Control methods: for older larvae in the heavy-feeding stage, spraying or irrigating the seedling roots or applying pesticide to the whole field can be used for control.
Spray-irrigating seedling roots: use 48% chlorpyrifos emulsifiable concentrate at 1500 times dilution, or 30% acephate emulsifiable concentrate at 1000 times dilution, or 4.5% beta-cyfluthrin emulsifiable concentrate at 2500 times dilution, or 1% emamectin benzoate emulsifiable concentrate at 5000 times dilution, or 20% chlorantraniliprole suspension concentrate at 4000-5000 times dilution, and use a straight spray nozzle aimed at the root-stem part for spraying. The pesticide liquid volume should be large, ensuring that about 10 cm around the corn rhizosphere, where pests hide, can all receive the pesticide. Whole-field pesticide irrigation: use 1 kg of 48% chlorpyrifos emulsifiable concentrate per mu, and pour it into the field with water during irrigation.
(3) Precautions
For plots where nicosulfuron herbicide is used, avoid using organophosphorus pesticides such as chlorpyrifos, acephate, dichlorvos and trichlorfon in the 7 days before and 7 days after application, and instead use pyrethroid pesticides, so as to avoid pesticide damage to corn seedlings.
IV. Remedial measures
For corn seedlings that have lodged after some roots were bitten off by Athetis lepigone larvae, generally do not blindly destroy and replant. While actively controlling the pests, promptly straighten and earth up the plants, and timely topdress and water to promote root development and recovery.