Corn earworm feeding on foliage (A; Photo by J. Villegas) and pod damage (B; Photo by Scott Stewart, University of Tennessee).
Recently, there have been increased reports of corn earworms infesting soybean fields across the state. Corn earworm (aka bollworm or soybean podworm) can cause occasional but severe damage to soybean. The primary damage caused by corn earworm occurs during the larval stages when the insect feeds on the soybean flowers and pods. This feeding activity leads to direct yield losses as pods abort, or the larvae consume or injure developing seeds. The most severe damage typically occurs in the latter reproductive stages of soybean growth. Typical symptoms of corn earworm damage to soybean include flower feeding injury, entry holes in the pods, seed consumption, and the presence of frass (insect excrement) near the feeding sites. Severely damaged pods may also become susceptible to secondary infections by fungi and bacteria, further compromising seed quality.
Monitoring corn earworm infestations is crucial for timely and targeted intervention. Corn earworm moths are particularly attracted to soybeans during the R1-R5 growth stages, as adults prefer to lay their eggs on flowering soybeans. As soybean fields mature, they become less desirable for corn earworm colonization. Producers are advised to begin sampling for corn earworm larvae at the initiation of flowering (R1), with particular attention to later-maturing soybean fields. Scouting efforts should be intensified when large numbers of moths are visually observed during sampling or when the number of moths captured using pheromone traps has increased. Sampling for larvae using sweep nets is recommended, with 25 sweeps per location at four or more different locations within the field. Larger fields should have a higher number of sampling sites, especially those fields exceeding 50 acres. Additionally, it is essential to document the presence of other pests, such as fall armyworm, which may contribute to pod feeding or leaf-feeding caterpillars such as soybean looper, green cloverworm, or velvetbean caterpillar.
Determining the appropriate treatment for corn earworm infestations depends on the growth stage of soybean plants. Treatment is most effective during the flowering and early-pod development periods (R2-R5). However, treatment is generally not recommended prior to flowering. The suggested treatment threshold in Louisiana, based on sweep net sampling, is 38 worms per 100 sweeps (9-10 worms per 25 sweeps). Before any treatments are applied to the field, consider the crop value and the cost of insecticide application.
|Insecticide Active Ingredient and Trade Name||Amount formulation per acre||Amount active ingredient per acre|
|1.2 – 2.5 oz.||0.047 – 0.098|
|5.6 – 9.6 oz.||premix|
|1.7 – 2.2 oz.||0.038-.049|
Asana XL (0.66)
Warrior II (2.08)
Mustang Maxx (0.8)
Baythroid XL (1)
*** NPV (Heligen) is specifically effective against corn earworms. It is recommended to apply the virus when the larvae are small. It is important not to apply the virus if the majority of the larvae are already large or if the infestation levels exceed the treatment threshold.
Dr. James Villegas
Assistant Professor - Extension and Research
Field Crops Entomology
Email: firstname.lastname@example.org | Mobile: 225-266-3805