Fall armyworm is an occasional field crop pest that can damage a wide range of plants. It is a tropical species that migrates north from the southern United States in the summer. Fall armyworms are voracious feeders and can quickly defoliate crops.
The adult fall armyworm is a moth that does not feed. Moths lay eggs that hatch into caterpillars, which are the crop-damaging stage. The caterpillars go through several stages of development before pupating in the soil.
Fall armyworm management relies heavily on scouting to detect the caterpillars while they are still relatively small. Early-instar caterpillars are easy to miss because they are small and eat relatively little. As the caterpillars age, they grow quickly and eat progressively more. By the time they reach the final instar, they are up to 1 ½ inches long, eat a huge amount, and damage crops very quickly.
Chemical control should take place when caterpillars are ¾ inch long or smaller (the first three instars). Freezing temperatures will quickly kill fall armyworms. If frost is expected soon, control may not be needed.
Understanding Fall Armyworm's Lifecycle and Behavior
The adult fall armyworm, a moth that refrains from feeding, lays eggs that later develop into caterpillars, the stage responsible for crop damage. These caterpillars undergo multiple development stages before entering the pupation phase within the soil.
Effective Management Strategies:
- Scouting and Early Intervention: The key to successful fall armyworm management lies in early detection. Young caterpillars, referred to as early-instar caterpillars, can be elusive due to their size and limited consumption. As these caterpillars mature, their appetite grows significantly, resulting in rapid crop damage. Timely scouting is essential to identify the pests while they are still small and manageable.
- Chemical Control: Applying insecticides when caterpillars are small (¾ inch or smaller) is effective. However, larger caterpillars tend to be less susceptible to chemicals. Chemical treatment should commence during the first three instars, which is when caterpillars are around ¾ inch long. Moreover, freezing temperatures rapidly eliminate fall armyworms, so control might not be necessary if frost is imminent.
- Scouting and Threshold Guidelines: Monitoring for fall armyworms involves using pheromone traps, which provide insights into pest presence. While such monitoring aids in awareness, it's imperative to supplement it with scouting. Generally, taking management action is recommended if three or more caterpillars are observed per square foot of the crop.
- Sampling Techniques: In lower vegetation areas like forage, soybean, and cover crops, sampling methods such as sweep nets or beat sheets prove effective. A sweep net is used in a 180-degree arc motion, capturing caterpillars within the net for examination. A beat sheet, a sturdy fabric mounted on a frame, is placed under vegetation, and shaking the plants onto the fabric reveals the pests.
- Treatment Recommendations: For fields with caterpillars measuring less than ¾ inch, Southern states advise mixing chemicals with dual modes of action. This combination includes a pyrethroid for swift knockdown and a product with prolonged residual effects, such as chlorantraniliprole, diflubenzuron, or methoxyfenozide. These chemicals cater to small caterpillars and are effective even after rainfall.
- Natural Enemies: Beneficial organisms like parasitoids, ground beetles, soldier bugs, birds, rodents, and fungal and viral diseases play a role in curbing fall armyworm populations. However, they may not always suffice during periods of intense adult colonization, leading to outbreaks.
In the ever-evolving battle against fall armyworm infestations, proactive monitoring, early detection, and targeted interventions are crucial components of successful management strategies.
Photo Credit: manitoba-agriculture
Categories: Ohio, Crops