Beet Armyworm Control: Identification, Damage, Prevention & Organic Treatment Methods

Beet Armyworm (Spodoptera exigua) is a medium size caterpillar insect pest that is highly adapted to a wide range of vegetable, field and ornamental host plants. Beet armyworm larvae​ feed on leaves and tender plant tissues and in high numbers can defoliate rapidly. Infestations can increase rapidly on the conditions of favorable weather and crop conditions, given the ability of the adults to lay large numbers of eggs and multiple generations can occur in a growing season. For beet armyworm identification, then, is the first step to being able to successfully beet armyworm control, especially before it becomes the larger, more damaging caterpillar.

Its distribution extends to much of the agriculture areas and may infest vegetables, leafy green crops, peppers, tomatoes, beans, onions and any other cultivated plants. Unlike some insects which are only partial hosts, beet armyworm is able to move between available hosts, or weeds. The knowledge of the range of its hosts is especially significant as an infestation can start outside of the main crop and then work its way into productive areas of the field.

What are the signs of beet armyworm eggs and caterpillars?

It is important to have both eggs and larvae present in the plant in order to assess and make an early diagnosis of beet armyworm. The female moths typically lay masses of eggs on foliage, sometimes covered with scales or hairs from their body. These egg masses can signal early in the season that larvae are about to be an issue in the crop.

Once the beet armyworm caterpillar hatches from the egg, it will go through a series of larval stages before it emerges as an adult. Young larvae are comparatively small and they will feed in the protected sites of plants and on the underside of leaves. They develop into a habitable nest with frequent irregular feeding holes or window-like damage and then can cause considerable defoliation as they increase in size. Body color can vary widely as a child matures and/or in different settings, and should not be used for beet armyworm identification. It is important for farmers to determine the larva markings, feeding habits, where the larva is feeding and the kind of feeding it is causing on the plant.

Beet armyworm egg appearance is valuable to monitoring as it can be found early in the development and can inform the grower what action may be necessary to control the damage and thus give them time to plan for intervention. While it is possible to determine if young leaves and leaf injury are present, the development of leaf populations can also be observed by examining the plant terminals, sheltered foliage or young growth regularly.

What kinds of beet armyworm damage cause the crops?

Severity of beet armyworm attack is related to larval density, the stage of the crop and extended period of undetection. Young larvae will skeletonize or scrape leaves, and older larvae will eat larger parts of the leaves. When infestation is heavy leaves may be ragged or may have big holes or large amounts of tissue missing.

Beet armyworm caterpillars may cause significant damage if they are present in high numbers and the caterpillar is a large size. The plant cannot photosynthesize and grow properly if there is a leaf rollup. Young plants may be sensitive and lose up to 50 percent of their cover in the vicinity of normal vegetation without a significant reduction in reservoir life; normally flowering and fruiting may also be affected by substantial leaf severance.

Other issues are that damage to the feed may be non-uniform over a field. Feeding injury may be apparent in the healthy looking plants in one area while in another area close to them, the feeding injury is quite severe. The scouting done in the field is crucial and not visual assessment of a few plants. Prevention can be achieved by early detection which can stop any localised population problem from becoming a larger crop management issue.

The beet armyworm has four life stages, and it is essential to manage it at the right time

The knowledge of the beet armyworm life cycle assists in determining when actions for management will be more effective. Adult moths lay eggs on host plants and the cycle starts again. Eggs develop into larvae which go through several stages of development before becoming pupae. Eventually the adults emerge from the pupae and start a new generation.

The damaging stage is the beet armyworm caterpillar which is actively feeding on plant tissues. But, not all the larval stages are the same and are equally sensitive to biological treatments. Young larvae feed on less plant material and can be most effectively controlled with some biological control methods and are generally easier to control.

Therefore, the decision to start armyworm treatment should not wait until there are large caterpillars in the field and significant amounts of defoliation are evident. Scouting to detect beet armyworm eggs and very young larvae can be used to take advantage of that time. Beet armyworm control, therefore, can be achieved at the proper time to reduce damage and to promote sustainable IPM.

How can the farmer help control and prevent beet armyworm infestation in the field in a natural manner?

How to treat armyworms? The important beet armyworm control measure is to scout regularly, not until armyworms are visible being defoliated. Leaves, growing points and protected sections of the plants should be checked for eggs, young larvae and new feeding injuries by the farmers. Keeping an eye on weeds around crop fields is important, since they can serve as alternative hosts that enable weeds to persist between crops.

Some potential breeding and feeding sites can be minimized by field management with sanitation and weed beet armyworm organic control. Assessments and monitoring of crops should be done along with control of beneficial insects such as predators and parasitoids which are naturally present and control armyworm eggs & larvae. It is important to avoid uncalled for broad-spectrum insecticide applications to help maintain these natural enemies.

Growers need to evaluate the crop, stage, population and pest management solutions before applying any armyworm treatment. Registered, well-used conventional insecticides may be used, as can biological control and cultural measures as needed, in an integrated approach. Where multiple treatments that are compatible can be used, changing treatments to other similar treatments to effectively control the organism but avoid selection pressures for resistance.
For armyworms, a more successful or practical treatment program is one that is based on pest development, not necessarily a calendar or schedule. 

Treating armyworms with Bacillus thuringiensis

Some strains of Bt act only when insect larvae eat target plants that have been coated with bti.A few strains of Bt that kill susceptible caterpillars through the digestive tract after consuming treated plants. This disruption of feeding and gut function may prevent affected larvae from feeding and killing them.

Bt is especially pertinent when young armyworm caterpillars are actively feeding on treated foliage. However good spray coverage and correct timing are important as the bacterial insecticidal proteins must be eaten by the larva. Applications should be targeted to the foliage areas where young larvae are feeding in accordance with the product label and local regulations.

A biological approach, based on Bacillus thuringiensis, is available and is included in an integrated approach for caterpillar management with BT Thuricide. Farmers should not consider it a product for their own use, but rather as a component of an integrated management that may include scouting, sanitation, weed management, and beneficial organism conservation. This will help to manage the beet armyworm, while minimizing reliance on successive general purpose chemical sprays.

Please note that larva size and population density are also key factors in deciding whether or not to treat armyworms. Biological armyworm treatment are most effective when used in a programme that kills those larvae that are susceptible in an early stage when populations have not become unaffordable.

Does Bacillus amyloliquefaciens aid in beet armyworm control?

In recent years, beneficial bacteria of the genus Ben. are showing great interest in sustainable agriculture due to their plants and microorganism-related effect with contribution in biological-based crop management systems. Bacillus amyloliquefaciens is one such beneficial bacterium that has been studied for plant health and applications of plant-based microorganism competition and biological crop protection.

However it is necessary to differentiate the role of various biologic factors. The insecticidal proteins produced using Bt are of particular interest as they are ingested by susceptible caterpillar pests. Note - Bacillus amyloliquefaciens biocontrol for armyworm treatment should be viewed not as a magic bullet for Bt for beet armyworm, but as a biological approach to crop and plant-health management.

Depending on the particular biology involved, different microbial technologists may play a complementary role for growers putting together a complete beet armyworm management program. An integrated insect management strategy could include specific insect management to overall crop health and helping to establish beneficial biological relationships. Proper use of any of the products should be based on the registered target, the label directions and recommended use.

What should farmers do to develop a long-term beet armyworm management program?

How to treat armyworms? The first step to success with a long-term program is the identification of the beet armyworm in addition to frequent field scouting. Insects should be scouted prior to widespread infestation for beet armyworm eggs and to check for young larvae and fine feeding damage. A knowledge of the development of the pest enables better timing of the interventions and avoids only responding to defoliation once it is quite considerable.

Crop sanitation, proper weed control, frequent scouting and the preservation of enemies of the beet armyworm, as well as the proper timing of biological controls, can be used together in a single control strategy. Bacillus thuringiensis germainiae products are especially effective if there are susceptible early life stages (insects actively feeding).

The goal of armyworm treatment should be to contain them to not cause economic loss, not to "kill every other insect. Farmers should assess the efficacy of treatments based on ongoing monitoring and modify treatments based on the crop and the insect pressure.

However, once you know what the armyworms are, you also need to understand the different biological products, their mode of action and that they target different pests. Other microbial inputs can be components of integrated biological crop management but Bt is a direct target of caterpillars vulnerable to the toxin. Thus, bacillus amyloliquefaciens biocontrol for beet armyworm pesticide of caterpillars with appropriate products and practices and Bacillus amyloliquefaciens as part of an integrated sustainable agriculture strategy are viable alternatives.

In conclusion, good beet armyworm control depends on the prevention of beet armyworm damage and early detection coupled with timely intervention. A combination of biological products and good farming practices provides a better way to control this adaptable pest, but also adds to long-term crop productivity.

Reference: 

• Buntin, G. David, et al. "Plant-incorporated Bacillus thuringiensis resistance for control of fall armyworm and corn earworm (Lepidoptera: Noctuidae) in corn." Journal of Economic Entomology 97.5 (2004): 1603-1611.
• Fontana Capalbo, Deise Maria, et al. "Solid-state fermentation of Bacillus thuringiensis tolworthi to control fall armyworm in maize." Electronic journal of Biotechnology 4.2 (2001): 9-10.