Southern Indiana and Kentucky
Corn earworms (CEW) are an unwelcome pest in corn fields. Their feeding can damage kernels, reduce overall grain quality, and can, but not always, lead to the development of ear molds. Ear molds are more closely tied to the ear mold resistance of each corn product. Corn products that are highly susceptible to ear molds are likely to develop more ear mold when conditions are favorable regardless of any CEW feeding. Corn products with more ear mold resistance have a lower potential for ear mold development when the worms are present.
What do farmers need to know about CEW?
- They don’t overwinter in most areas of the Corn Belt as they cannot survive if the temperature dips below 30° F.1
- Adult moths migrate from the southern states by wind and lay eggs on green silks.
- Late-planted or replanted corn is often more susceptible because migrating moths are attracted to the green silks.
- Adult female moths can lay between 200 to 500 eggs over the course of their three-to-four-week life cycle — that is a lot of eggs!
- The larvae are cannibalistic; therefore, one CEW larva per ear is usually found.
- Unlike some ear-feeding pests, CEW larvae only feed within the safe confines of the ear. Insecticide applications to kill larvae are largely ineffective because they are protected by the husk.
- When timing is right, the larva leaves the ear and moves to the soil to pupate (Figure 1).
- Feeding is generally localized on the ear tip. This feeding often damages the protective husk, which can allow moisture to be in contact with the ear. Water around the ear along with favorable environmental conditions could potentially cause ear rot and mold development (Figures 2 and 3).
What are our best CEW management strategies?
- Plant early. Late-planted corn acts like a trap crop and attracts moths to your field!
- Plant a corn product, such as Trecepta® Technology, which contains Vip3Aa20 protein and is effective against CEW.
- Control of larvae with insecticides is ineffective because of the husk coverage.2
While scouting for CEW, it is also a good time to scout for ear rots and ear molds. This can help to prioritize fields for harvest to help preserve yield.
It is important to appropriately identify the ear mold in the field. Some ear rots and molds produce mycotoxins, which can limit end use or the ability to safely feed grain to livestock.3 Examples include Gibberella ear rot (vomitoxin) (Figure 4) and Aspergillus ear rot (aflatoxin) (Figure 5).
- Prioritize harvest. When ear molds are found, it is best to prioritize harvest to avoid continued infection and disease spread in the field.
- Drying. Once in the bin, it is best to get grain moisture content between 13% and 14% to prevent disease growth in storage. Should bin temperatures fall below 32° F, disease growth ceases.
- Prioritize crop rotation in infected fields as many ear molds can overwinter in fields and cause infection the subsequent year.
- Corn product selection. Select corn products with characteristics that reduce the opportunity for the development of ear mold.
1Cook, K.A. and Weinzierl, R. Corn earworm. Insect Fact Sheet. University of Illinois Integrated Pest Management (IPM). University of Illinois. https://ipm.illinois.edu/.
2Tilmon, K., Paul, P., and Michel, A. 2019. Corn earworm in field corn; watch for molds. C.O.R.N. Newsletter. 2019-27. Agronomic Crops Network. The Ohio State University. https://agcrops.osu.edu/.
3Murillo-Williams, A., Collins, A., and Esker, P.D. 2018. Corn ear rots and mycotoxins. PennState Extension. The Pennsylvania State University. https://extension.psu.edu/
Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.
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