Cutworms on Tomato Plants: Identification, Damage, and Effective Control Methods

Although tomato is the world's most widely grown vegetable crop, it is susceptible to early growth stage insect pests. Of these, the cutworms are the most damaging since they feed on plants at the soil surface and often kill healthy vigorous plants in a night. In order to manage pests effectively, the pest must be identified, the biology understood and sustainable pest tomato cutworm control​ measures will need to be applied without compromising crop productivity or the environment.

What are those cutworms on tomato plants?

Cutworms also attack tomato plants, as larvae of numerous species of night-feeding moths, primarily Noctuidae. These are agricultural pests, as they bore in the top layer of soil or the top of young stems, leading them to fall down, and leave behind broken shoots. Some fields of tomatoes might require growers to step out of them in only a few nights and whole fields to be eliminated if the pest is problematic.

The typical symptom of damage to tomatoes by cutworms is clean vertical cuts in the stem at the ground level with some species chewing off leaves, roots or immature fruit. Cutworms are nocturnal and active at night and damage often is not noticed until large numbers of cutworms have nipped off the plants. Early detection and timely response are essential in minimizing the losses on investments and in sum ensuring the establishment of healthy crops.

Cutworm: Identifying the Pest

It is important to correctly identify the cutworm species and properly locate the crop to properly utilize management tools for successful control. The black cutworm (Agrotis ipsilon), variegated cutworm (Peridroma saucia) and granulate cutworm (Feltia subterranea) are several species that attack tomatoes. There are some variations in species for appearance, but feeding habits and life cycles are similar.

Agrotis ipslon is the most frequently reported scientifically tomato cutworm used in commercial tomato production (s.s.). 

Larvae pests cause more damage to trees than do adult moths. Patterned forewings, gray or brown in color, lay their eggs on crop residues and in low vegetation. Seedling scouting is very beneficial especially in the first few weeks after transplanting since disease can be more easily detected by targeting it early in the growing season, which facilitates early tomato cutworm control​ efforts and reduces the amount of damage to the crop.

Understanding the Cutworm Life Cycle

Eggs hatch within several days to provide very small larvae which start feeding. Caterpillars feed on young tomato plants during successive larval stages, hiding under contrasting crop residues or under soil clods during the day and venturing out at night. Food consumption becomes so high as the larvae grow that later-instar larvae cause the highest damage.

When mature, larvae pupate and emerge as adult moths which can repeat the process. The cutworm scientific name and a knowledge of the cutworm life cycle, producing several generations per year in warm climates, enables the grower to plan for monitoring, cultural management and biological control well in advance of damaging cutworm populations. Discuss the effects of cutworms on tomato plants, natural control of tomato cutworms, and biological control (Metarhizium anisopliae and Novobac Met Zone) (Part 2).

The different ways cutworms attack tomato plants

Cutworms are most destructive when early crops of tomatoes are being grown, because of their feeding habits. Easily injured by a single feeding, tender young seedlings are extremely susceptible. Healthy seedlings are cut by cutworms at the soil surface or just below it, causing the stems to suddenly stand up straight and fall.Cutting healthy seedlings at the soil surface or just below it results in plants standing upright and falling, the most easily noticed symptom of attack. The caterpillars do most of their feeding at night so they may be found in the morning without any pest being seen.

Extensive stand losses of tomato can be caused by cutworms, especially if the infestations are heavy. TPGs may have to replant affected stands, adding to production costs. Leaves, petioles, roots and sometimes developing fruit upon or close to the soil are also eaten by older larvae. Fungi and bacteria cause secondary infections of plants, and further reduce plant vigour and yield potential where plants have been damaged.

Much crop loss often occurs just after transplanting when seedlings aren't well established with strong rooting systems. Field scouting is encouraged during the evening or early morning hours and a careful examination of the soil near injured plants to determine the presence of cutworms before they become abundant.

How to control cutworms on tomatoes?

It is important to implement environmentally friendly pest management along with proper cultural methods and frequent monitoring to control tomato cutworm. In modern integrated pest management (IPM) programs, chemical insecticides are not the only tool used to control pests, instead using various other tools to decrease the pest population while maintaining beneficial organisms which naturally keep the insect population under control.

Preventing weeds and crop residues from growing should be the first step for growers trying to control cutworms on tomato plants since these are excellent egg laying grounds for adult moths. Good field clean-up techniques, shallow planting before transplanting and clearing volunteer plants minimize initial pest levels. Larvae that tend to bite down on stems when seedlings are most susceptible also may be prevented by protecting collars around young plants.

It is also critical to monitor regularly. Field inspections between evening/early morning time will help the grower to find larvae before widespread damage. Good soil practices and promotes beneficial insects, ground beetles and birds will help continuously suppress cutworm populations.

The sustainable practices help to decrease the need for reapplying chemicals and enhance the crop's overall resilience. However, when pest problem is high biological control options can be part of integrated management programmes offering more effective and environmentally friendly control.

Presenting why biological control of cutworms is gaining ascendancy.Discussing the reasons for preferring biological control over cutworms.

Biological control of cutworms has been promoted by many growers under an IPM program, due to the growing issue of pesticide resistance, environment safety and pesticide residues. Biological methods involve using naturally occurring microorganisms to control pests and may offer long-term control with little effect to non-target insects or ecosystems.

Despite intensive research, Metarhizium anisopliae is arguably one of the best-studied biological control agents, being naturally present in the soil infesting a variety of insect pests including cutworms. Metarhizium anisopliae enters insects by direct contact; a distinguishing feature from traditional, chemically formulated insecticides which have a singular mode of action. The spores attach to the insect cuticle, germinate and bore through the cuticle and give rise to masses of spores inside the insect which ultimately kill it.

As a biological infection process, it provides an excellent alternative to a multitude of existing insecticide cutworm programs while minimizing development of cutworm resistance to the product. Studies have shown that under ecological conditions, applying Metarhizium anisopliae could markedly decrease cut worm populations and hence be useful in sustainable tomato production systems.

Biological controls also fit into integration of other cultural and mechanical controls, empowering growers to contribute their more productive management methods while maintaining environmental sustainability.

Novobac Met Zone helps maximize yield and reduce losses in cutworm populations while enjoying the protection of sustainable agricultural practices

Novobac is a biotechnology firm focused on novel Cropland Solutions and technologies based on biology and microorganisms that foster sustainable agriculture. Also, as part of its biological insect management solutions is Met Zone, a granular formulation of the beneficial entomopathogenic fungus Metarhizium anisopliae.

Met Zone is intended for biological control of cutworms, and will provide a beneficial fungal population in the root zone, which is where cutworm larvae spend a large portion of their life cycle. The fungal spores make contact with their susceptible larvae after the application to the soil, where they begin the natural process of suppressing pest levels with a minimum of interference by the organism of other beneficial organisms.

Met Zone can be integrated into a comprehensive tomato cutworm control strategy to provide long-term control that is more sustainable, including crop rotation and sanitation, field monitoring, and other integrated pest management (IPM) practices. Canada, the United States, Mexico, Europe, India and other agricultural areas have seen an increasing use of biological agent containing products based on Metarhizium anisopliae in cutworm management programs to reduce reliance on chemicals while still getting a good yield of control.

Long-Term Prevention using Integrated Management Strategy (IMS)

An integrated approach that involves one or more of the following methods helps to manage pests to levels that are below economically threshold: cultivation practices (prevention), monitoring, biological control product, targeted intervention.

The first step in things is preparing the field. A few weeks before transplanting weeds should be removed and these will reduce the number of available egg laying areas for adult moths. Where possible crop residues from previous years and crop residues should be removed or included, for protection of larvae. Crop rotation with non-host crops can also help delay or check the build-up of the number of overwintering cutworms, and may be effective.

Healthy soil is significant for not only sustainable pest management, but also for other purposes. Healthy soils are teeming with beneficial bacteria, fungi, invertebrates and other organisms that form natural biological systems that help to tomato cutworm control​ insect pests and promote healthy plant growth. Good drainage, with balanced soil fertility and copped irrigation will help the roots to grow stronger and faster providing better response of tomato plants on small soil feeding attacks.

A helpful management tool is the routine scouting. It is important that growers examine fields for pests regularly in the first 4 to 6 weeks after transplanting especially after warm weather when larvae may be active. An inspection of damaged seedlings and a careful, but gentle, digging around the base of affected plants, may sometimes reveal caterpillars before splits take place when populations are not widespread. Early detection means early intervention and can help minimise the financial consequences/losses.

If the level of pest pressure is above a threshold when biologically-tolerated, then an integrated approach involves the use of a biological insecticide along with other IPM methods and yields long-term suppression that is more reliable than repeat applications of conventional cutworm control insecticide products. Biological solutions decrease the forces driving resistance in beneficial insects like predatory beetles, lacewings, spiders and parasitic wasps, which help to control pests naturally.

When planning management programs, environmental conditions should also be taken into account. Irrigating too much right after transplanted vegetation, poor plant spacing which can result in poor airflow, and mishandling adjacent vegetation can create less favorable habitats for cutworms and other soil-inhabiting pests.

Conclusion

The first step in preventing tomato loss to cutworm is to understand its biology and to be aware of the early signs of cutworm attack. Despite the efforts of various researchers to develop control strategies, cutworms attack seedlings early in the season, when tomato plants are most susceptible to injury, and continue to cause severe losses on tomato plants. Knowing the cutworm life cycle and precise cutworm identification of the cutworm and early recognition of cutworm damage on tomatoes allow growers to take actions before substantial damages are done by this predator.

Current cotyledon insecticidal control strategy relies more on integrated management methods, where repeated spraying with chemical insecticide is not a priority anymore. Field sanitation, crop rotation, weed control, and regular scouting are cultural practices that serve as a basis for sustainable pest control. Biological control of cutworms with a proper system in combination with chemical control may provide more uniform coverage with lower environmental impact and lack of detrimental impacts to beneficial species.

Metarhizium anisopliae-based biological products like Novobac Met Zone can enhance IPM programs. These methods are natural and nonharmful solutions that work on soil dwelling grubs and help growers lower their need for conventional pesticides while fostering sustainable agriculture.

A comprehensive program that integrates good cultural practices, established monitoring, promotes healthy soils, and includes judicious biological control methods is one of the most successful and environmentally responsible methods to long-term suppression of cutworms as tomato production continues to evolve. Supporting prevention methods not only safeguards current yields but also helps in the development of healthier production systems that will be able to accomplish future agriculture challenges.

Reference: 

• Ibrahim, H. "Virulence of entomopathogenic nematodes and fungi and their interaction in biological control of black cutworm, Agrotis ipsilon Hufnagel (Lepidoptera: Noctuidae)." Int. J. Entomol. Res 4.6 (2019): 45-50.
• Ahmad, Imtiaz, Maria del Mar Jimenez-Gasco, and Mary E. Barbercheck. "Water stress and black cutworm feeding modulate plant response in maize colonized by Metarhizium robertsii." Pathogens 13.7 (2024): 544.