June 1, 2022
After the corn crop is planted, scouting begins. No matter the weather or planting conditions, scouting is necessary for early detection of pests, diseases, and weed infestations. Handy tools for scouting include a tape measure, garden trowel for digging, and paper or plastic bags for samples. The wearing of protective gloves should be considered.
First, consider taking a stand count. Table 1 provides the row length to measure, based on row spacing, that represents 1/1000 of an acre. Count the number of healthy plants within the row and multiply by 1,000 to determine the estimated plants per acre. It is best practice to take stand counts in multiple areas in the field to better understand stand establishment. If populations are less than expected or many gaps are noted, dig up seeds to investigate. Digging up seedlings is a great opportunity to evaluate planting depth.
Table 1. Row length to measure crop population
| Row Spacing (inches) | Row Length to Count (feet and inches) |
|---|---|
| 15 | 34' 10" |
| 20 | 26' 2" |
| 30 | 17' 5" |
Pests are a constant threat throughout the season. Black cutworm larvae pose a risk to seedlings in May and June. Larger larvae are capable of severe damage as they cut seedlings close to the soil line. When scouting, look for leaf feeding, wilting, and dead plants (Figure 1). Other early season pests to scout for include slugs and white grubs. Slugs feed during the night, leaving behind ragged leaves and a trail of slime. Grubs feed on roots, and mesocotyls, so check for wilted and dead plants (Figure 2). Getting out and scouting early in the season for these pests is key to effective management.
Figure 1. Black cutworm and feeding damage.
Figure 2. White grubs.
Early season diseases can cause issues. Common early diseases include Fusarium (Figure 3), Pythium (Figure 4), and Rhizoctonia (Figure 5). Pythium and Fusarium favor cool damp environments. Rhizoctonia favors warmer, damp conditions. The symptomology for these diseases, which can be similar, include slow emergence, stunted growth, and damping off after emergence. Rhizoctonia typically has a red-brown lesion near the soil line. If interested in determining the causal pathogen, consider sending a sample to a plant diagnostic lab.
A few items to keep on hand for plant collection include plastic or paper bags, a marker for labeling, and a cooler. Keeping the sample as cool as possible helps maintain viable tissue for verification. Shipping the samples on the day of collection is a good practice.
Figure 3. Fusarium infected corn root.
Figure 4. Darkening of mesocotyl caused by Pythium. Picture courtesy of and used with the permission of Don White, University of Illinois.
Figure 5. Rhizoctonia seedling blight resulting from inoculation with Rhizoctonia solani AG-4 HG-II. Picture courtesy of and used with the permission of Srikanth Kodati, University of Nebraska.
Sources:
Anderson, M., Vittetoe, R., Hinz-Rieck, A., Licht, M. Stand assessments-corn. Integrated Crop Management. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/encyclopedia/stand-assessments-corn.
Root rots of corn. 2022. Crop Protection Network. https://cropprotectionnetwork.org/encyclopedia/root-rots-of-corn.
Gerber C.K. 2022 Corn & soybean field guide. Purdue Extension. Purdue University.
Websites verified 4/26/22
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