Late-Season Scouting to Plan for Harvest and Next Season

• Late season corn scouting can help prepare for harvest and plan for next season.
• Scouting can help pinpoint any issues that occurred during the growing season and identify management strategies to minimize the issues going forward.

Stalk and Ear Issues

Insects

Depending on geography, there are a handful of caterpillars that can be found attacking the ear or stalk during late season scouting. The European corn borer (Figure 1a) and the southwestern corn borer (Figure 1b) can be found feeding within the ear shank, stalk, or ear and occasionally on kernels.^1,2 The western bean cutworm (Figure 1c), corn earworm (Figure 1d), and fall armyworm (Figure 1e) are found almost exclusively feeding on the ear.

The usual feeding location of the corn earworm is at the ear tip, and occasionally larvae can be found at the ear butt. The corn earworm color can be extremely varied ranging from green to almost black. The larvae are cannibalistic, so usually no more than one is found per ear. The diagnostic character for this species is the tan colored head.

The western bean cutworm is often found feeding at tip as well, but the larvae bore into the ear at any location along the ear. There can be multiple larvae on each ear. The diagnostic character for this species is the two black to dark brown bars behind the head.

The fall armyworm also bores into the husk at any location along the ear but feeds along the side of the ear consuming the kernels. The diagnostic character for this species is the inverted white Y between the eyes with a black or dark brown head capsule.¹

Figure 1. (a) European corn borer, (b) southwestern corn borer, (c) western bean cutworm (Images (a), (b), and (c) courtesy of Frank Peairs, Colorado State University, Bugwood.org), (d) corn earworm (Image courtesy of R.L. Croissant, Bugwood.org), (e) fall armyworm (Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org).

Figure 2. (a) Anthracnose stalk rot and (b) Gibberella stalk rot.

Figure 3. (a) Aspergillus ear rot, (b) Diplodia ear rot, (c) Gibberella ear rot.

Malformed Ears

Occasionally, while scouting corn late in the season, unusual shaped or malformed ears may be found. Environmental, insect, and chemical stress during the vegetative and early reproductive stages of corn (V5 to R3) can cause abnormal or malformed ears. Distinctly different symptoms develop depending on the timing, type, and severity of the stress. Pesticide applications can be a source of stress on corn if the application occurs outside of product label conditions or other stresses increase corn susceptibility.

For additional information on malformed ears, please visit Abnormal Corn Ear Development.

Weeds

Late-season scouting is an excellent way to assess the weed management plan. It can help verify weed escapes, new weed species, and distribution of weeds within the field. With this knowledge the weed management plan for the following cropping season can be adjusted to respond to the weed situation.⁴

• Identifying weed species and the extent and distribution of weed infestations in a field can help with herbicide selection and application timing to keep tough-to-control weeds in check next season.
• Weeds with late season germination and survival and/or prolific seed production, may require multiple herbicide sites of action and sequential applications.
• Weeds present at harvest may indicate that a postemergence (POST) herbicide application that includes a residual may need to be part of the weed management plan.
• The POST herbicide program may need a different mix of herbicide sites of action to cope with the weed spectrum.
• A pre-emergence (PRE) herbicide program alone may not provide the diversity and longevity of herbicide action necessary to manage the weed situation without a sequential POST application.

Nutrients

The most common nutrient deficiencies observed late season are nitrogen and potassium. Both nutrients are mobile in the plant and are translocated to newer growth. Nitrogen deficiency symptoms appear on leaves as a V-shaped yellowing, starting at the tip and progressing down the midrib toward the leaf base (Figure 4). When deficient, nitrogen can be translocated from the stalk to the developing kernels which weakens the stalks and predisposes the stalks to infection by stalk rot pathogens. Potassium deficient plants exhibit a yellowing and necrosis along the margins of the leaf on older leaves but may not exhibit symptoms on newer growth (Figure 5). Potassium deficient plants are also predisposed to lodging as potassium plays a role in maintaining stalk integrity.⁶

Figure 4. Nitrogen deficiency in corn. Photo is provided courtesy of the International Plant Nutrition Institute (IPNI) and its IPNI Crop Nutrient Deficiency Image Collection, C.Witt, J.M. Pasuquin.

Figure 5. Potassium deficiency in corn.