A Detailed Guide to the Harm Caused by Armyworms and Their Control Methods
According to the National Agricultural Technology Center's Plant Disease and Pest Forecasting Division, the number of first-generation armyworm adults has surged recently in the Jianghuai, Huanghuai, and North China regions. In Jiangyan, Jiangsu, and Changdao, Shandong, high-altitude monitoring lamps captured over ten thousand moths per lamp per day; in Northeast China, the number of trapped moths was significantly higher than last year. So, what are the harmful effects of armyworms? And how should they be controlled? Let's take a closer look below.
Armyworms cause these kinds of damage!
The armyworm belongs to the order Lepidoptera, family Noctuidae, and is also known as the twig-cutting worm, five-colored worm, marching worm, and night thief worm. It is an important migratory pest on corn and other crops in China, characterized by gregarious behavior, voracious feeding, and migratory damage, and in previous years it caused severe damage to autumn crops in different regions.
In severe cases, it often eats all the corn seedlings overnight, causing gaps in the stand and broken rows, and even forcing farmers to plow and replant.
This year's first-generation adults are characterized by an early peak period, a wide occurrence area, and high local pest numbers, and the second-generation armyworm's damage period coincides with small corn plants that have weak resistance. Especially for northern spring corn, once it is fed upon, there is a risk of destroying the crop, delaying farming operations, and affecting the safety of autumn crop production.
The habits and patterns of armyworms
Larvae are mostly active in the morning and evening, that is, from after sunrise to before 10 a.m. and around dusk. They often migrate in groups to cause damage, hence the name “marching worm&rdquo.
The body color of the larvae changes with instar, density, and food. Young larvae feed on tender leaves and their body color is green to grayish green; second-instar larvae only gnaw the leaf mesophyll; after the third instar they feed along the leaf edges, and when the damage is severe they eat most of the leaf blade, leaving only a very short midrib; larvae of the fourth instar and above are black or grayish black. Mature larvae are 38 mm long, with a yellowish-brown head bearing a “”-shaped vertical mark, and five longitudinal stripes on the back.
The armyworm is an insect that prefers moderate temperatures and moisture, with an optimum temperature of 19-23°C and an optimum relative humidity of 50-80%. It prefers to feed on gramineous crops and weeds, and its food intake increases with each instar, with the fifth and sixth instars being the voracious feeding stage.
Generally, irrigated fields, fields with a previous wheat crop that was heavily fertilized and densely planted, relay-cropped fields, and fields with a long wheat-corn coexistence period have sufficient food sources and suitable temperature and humidity, which favor adult egg-laying and larval growth. The pest hides by day and comes out at night, mostly laying eggs in the lower-middle part of wheat on withered yellow leaf tips and inside leaf sheaths, with a single female laying 1000-2000 eggs.
Adults have strong flying ability and the characteristic of long-distance migratory damage.
Technical control measures for armyworms
1. Adult trapping and killing techniques:
(1) Sex pheromone lures. Use dry moth traps equipped with armyworm sex pheromone lures, with one stake-mounted trap per mu hung in the field.
(2) Insect-killing lamps. During the adult occurrence period, set up insect-killing lamps in the field with a spacing of 100 m, turning the lamps on from 8 p.m. to 5 a.m. Concentrated and contiguous use gives significant control effects.
2. Larval control techniques:
(1) Biological pesticides:
Spray Bacillus thuringiensis (BT) preparations in the early stage of armyworm egg hatching. Note that fields near mulberry orchards must not use it. For young larvae, diflubenzuron can be used.
(2) Chemical pesticides:
When armyworm larvae are found, it is best to choose fast-acting insecticides for spraying, such as beta-cypermethrin + emamectin benzoate, hexaflumuron + beta-cypermethrin, etc. These agents mainly work through contact killing and stomach poisoning, and spraying should reach the places where armyworms rest and are active. Slow-acting insecticides such as chlorantraniliprole, diflubenzuron, and tebufenozide had best not be used alone.
In the process of controlling corn armyworms, try to control them before the third instar. The control time is generally chosen during the morning and evening peak feeding periods of the larvae, and the spraying site should preferably be the corn whorl. Pay attention to personal protection when spraying to strictly prevent poisoning accidents.
In addition, armyworms have the habit of dropping to the ground when startled. When spraying, be sure to spray the ground surface to eliminate the “escapees” that fall to the ground. At the same time, also spray the weeds along field edges and roadsides, striving to eliminate the “outlaw” pests resting there.