How to control the insect pest of Spodoptera litura in summer corn? (with prevention and control measures included)

How to control the insect pest of Noctuidae in summer corn? Spodoptera litura is a new pest in the main producing areas of summer corn in China in recent years. once it breaks out, it does great harm to the yield of summer corn. How to control the insect pest of Spodoptera litura in summer corn? What are the prevention and control measures?

I. Identification of main morphological features

1. Adult worm

The adult body is 10 to 12 mm long, the wingspan is about 20 mm, and the forewings are grayish brown to dark brown. The main feature of the recognition is that there is a very obvious small black spot in the middle and end of the middle chamber, so it is called Spodoptera litura. The outer edge of the front wing has a row of small black spots; the hind wing is white and brownish, the end area is dark brown; it has phototaxis and diurnal habits, and it is generally hidden under the wheat straw during the day. The flying height is about 1 meter, with a distance of 3 to 5 meters each time.

two。 Larva

The head of the larva is yellowish brown; the body length of the 1st instar is 2 mm 10 mm, yellowish brown; the abdominal foot of the 2nd instar is not fully developed and does not have the function of walking; the first pair and the second pair of ventral feet of the 3rd instar have grown up and can walk normally; the length of the 4th instar is 10 mm 25 mm, grayish brown; after the 5th instar, there are dark brown inverted "eight" lines on both sides of the parietal cranial region; and there are V "shaped stripes in each segment of the ventral back. There is false death, frightened and curled up into a "C" shape.

3. Egg

The eggs are steamed bread-shaped with longitudinal ridges; the first birth is yellowish green and gradually becomes yellowish yellow; less than 1 mm in diameter; laid on the surface and soil under wet wheat straw.

4. Pupa

After burying into the soil, the mature larvae make a silk soil cocoon, surround themselves, form a coating, and then pupate in the coating. The pupa is 10 mm long, yellowish brown at the initial stage of pupation, and gradually becomes brown.

2. Reasons for the outbreak of Spodoptera litura

The adults and larvae of Spodoptera litura prefer a hidden and moist environment. The larvae mainly harm the corn seedlings in the base of the corn seedlings covered with wheat straw or in the topsoil layer 2 cm deep. There are two ways of damage: one is to drill to the base of the stem of the corn seedlings to feed, forming round or oval holes, and when the holes are deeper, they enter the stem center, cut off the growth point, continue to feed upward, lose water and wilt the heart leaves, form withered seedlings, and then gradually die, resulting in missing seedlings and broken ridges.

The other is that with the growth of maize seedlings, the epidermis at the base of the stem is aged, and the damage of the larvae is transferred to the young maize roots, biting off part of the main roots and secondary roots, the maize plants lodge in the wind, and the serious ones die. In the areas affected by the insect, there are generally 3-5 larvae per plant of corn, less than 1-2 larvae and more than 20 larvae. The larvae have the habit of transforming plants to do harm. Generally, after each larva bites the corn seedlings to death, it can be continuously transferred to damage 5 to 8 plants.

Spodoptera litura first appeared in Hebei Province in 2005, and has so far spread to the entire Huang-Huai-Hai Plain. Many areas have grown from scratch, from few to many, and from mild to serious, and from severe to outbreaks, for the following reasons:

1. Adequate food: the peak occurrence period of Spodoptera litura larvae is highly consistent with the maize seedling stage. Summer corn is generally sown in the first and middle of June, emerges in the middle and late June, and the seedling stage is from mid-June to early July. The seedling stage of corn is also the peak of damage to Spodoptera litura larvae, which is highly consistent with each other. The young rhizome of summer corn provides a sufficient food source for its occurrence and development.

two。 The environment is good: the number of eggs laid by Spodoptera litura is large, and the reproductive ability is strong. The peak period of adult occurrence is basically consistent with the wheat harvest period, which provides good environmental conditions for adults to lay eggs. A female can lay hundreds of eggs and then hatch a large number of larvae, which causes serious damage to the growth of summer corn.

3. Wheat straw mulching: wheat straw mulching provides a suitable living environment for Spodoptera litura. In recent years, with the improvement of agricultural production conditions, mechanized harvesting of wheat in the plain area is basically popular, followed by a large amount of straw left in the field. This provides favorable conditions for the survival of Spodoptera litura, and has become the best environment for adults to conceal and lay eggs and larvae. According to the investigation, the occurrence of multi-spot damage caused by Spodoptera litura larvae in the field is closely related to the quantity of wheat straw, and the occurrence of insect pests is more serious in the plots and regions covered with wheat straw and wheat bran. In general, in high-yield wheat fields, the number of wheat straw and wheat bran is large, the field coverage area is large, the occurrence of Spodoptera litura is relatively serious; in low-yield wheat fields, the number of wheat straw and wheat bran is less, and the occurrence of Spodoptera litura is relatively light; where there is no wheat straw and wheat bran cover, basically not affected by the insect.

Therefore, a large amount of straw left in the field after mechanized wheat harvest creates a very important living environment for the occurrence of pests and is the key factor for the outbreak of Spodoptera litura.

4. Sufficient water: rainfall and watering provide favorable conditions for the occurrence of Spodoptera litura in the rainy season, with more rainfall and high humidity in the field, which provides a favorable living environment for the spawning, hatching and larval growth of Spodoptera litura. Even if there is no rainfall, most fields will use irrigation to ensure the growth of summer corn at seedling stage.

Although the soil moisture increased after watering in the dry year, the water dissipation was faster, and the favorable degree to the occurrence of Spodoptera litura was less than that of rainfall. Long time and many days of rain, especially the continuous rainy weather, are very beneficial to the occurrence of insect pests. With the increase of air humidity, the life span of adults was prolonged, the number of eggs laid was also increased, and the hatching time was shortened and the hatching rate was increased. With the increase of soil moisture after rain, the survival rate of larvae will be greatly increased and the damage degree will be aggravated, but heavy rain and rainstorm will reduce the life span of adults and egg hatching rate, and stagnant water in the field will inhibit the occurrence and development of larvae.

Therefore, heavy rainfall and high soil and air humidity are the most important climatic factors leading to the outbreak of Spodoptera litura.

5. The concealment is strong, and the prevention and treatment is difficult.

Spodoptera litura larvae hide in wheat straw or soil layer, which is not easy to be found, and often miss the appropriate period of control; spraying or spreading poisoned soil is very difficult to get in touch with pests through the wheat straw layer; the skin of the older larvae is thicker, and the contact solution is not easy to penetrate into their bodies, so the control is more difficult.

III. Comprehensive prevention and control measures

The plots and adjacent plots where the pests of Spodoptera litura occurred in previous years should be taken as the focus of control, early observation, timely detection and timely comprehensive control measures should be taken.

1. Ecological prevention and control

For the slight plot of Spodoptera litura, after the summer corn was sown, all the wheat straw, wheat bran and weeds covered in the corn row were cleared into the corn row far away from the plant.

For the plots with heavy occurrence of Spodoptera litura, the mulch such as wheat straw, wheat bran and weeds covered in the corn row should be removed out of the field in time from wheat harvest to the emergence of summer corn, which can be used for retting to produce organic fertilizer or as industrial raw materials. the soil in the corn sowing line is exposed, the environmental conditions conducive to the occurrence of insect pests are destroyed, and the corn seedlings are protected from harm, and even if insect pests occur, the difficulty of prevention and control can be greatly reduced. You can also implement mechanical stubble first, and then sow seeds.

two。 Kill adults

The adults of Spodoptera litura mainly lay eggs under firewood and grass such as wheat straw and wheat bran. After sowing corn and before emergence, iron forks or wooden sticks are used to stir up mulch such as wheat straw in the field. If the adult flies out, the habitat should be sprayed immediately before spawning, such as 2.5% cyhalothrin EC, 4.5% cypermethrin EC, or 30% acephate EC. Or 48% chlorpyrifos EC and other contact pesticides, the preparation concentration can generally be controlled in 1000-1500 times liquid, wheat straw wheat bran thick place to increase the amount of medicine. It can also be combined with pre-seedling chemical weeding in corn field to carry out whole-field spraying control.

3. Control of larvae

The larvae of Spodoptera litura were sensitive to pesticides before the 3rd instar, and the control became more difficult after the 3rd instar, so the principle of "treating early and treating small" should be adopted. The first instar of Spodoptera litura larvae is generally only 3-4 days, so it is necessary to prepare in advance, control as early as possible, and clean up the wheat straw and wheat bran in the plot in time before control, the earlier the control, the less labor, and the better the effect.

The main results are as follows: (1) Control of 1st and 3rd instar larvae.

The 2nd instar larvae are generally under the mulch between the corn ridges, and there are no larvae around the maize seedlings, and the damage symptoms are not obvious; the 3rd instar larvae have concentrated around the roots of maize seedlings and began to bite roots and drill holes, and wilting symptoms appear in the heart leaves of individual corn plants in the field. Prevention and control methods: the method of spreading poison bait or poisonous soil can be adopted for prevention and control. Poison bait: with 500 grams of 90% crystal trichlorfon or 48% chlorpyrifos EC, spray 4 kilograms of fried wheat bran or crushed cottonseed cake to 3: 3.5 kilograms of water, plus chopped green vegetable leaves or grass mixed into poison bait, sprinkle it on the roots of corn seedlings in the evening, and appropriately increase the number of baits in areas covered with thick wheat straw. Spread poisonous soil: use 80% dichlorvos EC 300 ml 500 ml, or 48% chlorpyrifos EC 500 ml, mix 25 kg of fine dry soil, sprinkle on the base of corn seedlings along the ridge in the morning.

(2) Control of larvae after the third instar.

The damage of the larvae after the 3rd instar was gradually aggravated, the symptoms of maize seedlings were obvious, and the larvae would turn to damage, and they would also eat corn seedlings in the daytime, the corn plants in the field showed the symptoms of heart leaf wilting or stagnation, and the serious damaged plots appeared dead seedlings. Control methods: for the older larvae in the overeating period, sprinkler irrigation can be used to control the roots of seedlings or the whole field.

Spray irrigation seedling root: use 48% chlorpyrifos EC 1500 times, or 30% acephate EC 1000 times, or 4.5% cyhalothrin EC 2500 times, or 1% methamidyl salt EC 5000 times, or 20% chlorobenzamide suspension 4000 times 5000 times, spray at the rhizome with a large amount of medicine to ensure that the drug can be found in the hiding place of about 10 cm around the corn rhizosphere. Whole field irrigation: 48% chlorpyrifos EC 1 kg per mu, poured into the field with water when irrigating the field.

(3) points for attention

For the plots where nicosulfuron herbicide is used, the organophosphorus pesticides such as chlorpyrifos, acephate, dichlorvos and trichlorfon should be avoided in the first 7 days and 7 days after use, and pyrethroids should be used to avoid drug damage to corn seedlings.

IV. Remedial measures

Corn seedlings with lodging in part of their roots bitten off by Spodoptera litura larvae should not be destroyed blindly, but should be strengthened while actively removing insects, fertilizing and watering in time, so as to promote root development and rejuvenation.