Looking for Your Last Five Bushels of Corn?

Late-season scouting, starting about one month before crop maturity, can reveal many stressors that were present during the corn growing season. Our annual Crop Conditions Tour reveals significant variability in corn fields around Pennsylvania and considerable differences in the number of harvestable ears counted per 1,000^th of an acre. Lack of ear set can be caused by numerous stressors, most of which occur early in the growing season.

Losses from Abiotic Factors

Abiotic factors are crop stressors that are not caused by living organisms. Abiotic factors that decrease yield often include operator mistakes, chemical injury, and drought or heat stress. When scouting fields, consider the differences in your planting, target, and actual populations.

Planter-Related Issues

Planting-related stand losses are best determined in the first 1-3 weeks following planting. Be objective and critical with your scouting! Consider every component related to seed metering and placement. Are fingers, brushes, or seed disks considerably worn and affecting seed singulation? Are no-till coulters, seed openers, or gauge wheels considerably worn and affecting furrow shape and seed placement? Is every row unit placing seed at a uniform depth? Are closing wheels properly adjusted to correctly cover and firm the furrow? Are you planting too wet in no-till situations? Are you using the correct seed size for your planter? Review the operator's manual for your planter to check tolerances on common wear items. More than 1-2 skips or doubles per 1,000^th of an acre is a reason to inspect your planter.

Chemical-Related Injury

Chemical injury to corn seedlings can occur from starter fertilizers. Fertilizer injury from improper rates or placement can kill young seedlings, creating gaps in the stand that are difficult to judge at harvest – it's simply too late in the season to determine why that seedling died. If in-furrow or 2x2 starter fertilizer is applied at planting, ensure correct rates are used, and fertilizer coulters are correctly placed away from the row. No more than 10 pounds of actual nitrogen plus potassium should be applied in-furrow, or 70 pounds of nitrogen plus potassium applied 2x2 at planting.

Other Issues

Poor soil fertility can significantly contribute to slow emergence and seedling fatality, especially in colder soils with limited root activity. Strive to sample fields every 3 years and take action to correct pH and nutrient deficiencies when soil tests recommend so. In cases where early planting must occur to cover all your acres promptly, consider practices you can use to encourage early-season vigor. Are you adjusting row cleaners to clear residue from the row adequately? Have you selected hybrids with "excellent" ratings for early-season vigor? Can your seed dealer provide a cold-germination test for your chosen hybrids? Review Starter Fertilizer to see if your crop would benefit from using starter fertilizer at planting. Strive to place seed in optimal conditions at planting or plan to employ practices proven to help seedlings overcome early-season stressors.

Losses from Biotic Factors

Biotic factors for yield loss include crop stressors created by living organisms. Biotic factors include early-season pest damage, diseases, weed competition, or wildlife damage. Most biotic stressors that reduce harvestable ears per acre occur before tasseling, but in some cases (note, wildlife), ears may be damaged or removed in the late reproductive stages.

Early-Season Stand Loss: Slugs & Insect Pests

Slugs

Slugs are a sporadic and sometimes serious early-season pest of row crops in Pennsylvania. Because tillage disrupts their life cycle, slugs can be particularly challenging in no-till fields. Slugs feed on seedlings and young plants early in the season. High populations of slugs can reduce stand establishment and, in severe cases, may require replanting of crop fields.

There is no easy solution to control slugs; their populations are largely driven by cool temperatures and the amount of rain that fields receive. We recommend scouting for slugs by using refuge traps that should be checked in the morning. A slug bait is justified if you are averaging 1–2 slugs per trap and there is severe slug-feeding damage or dying seedlings. Slug baits are the most economical rescue treatment in portions of fields experiencing severe slug infestations. There are additional tips that can help reduce slug damage:

• Plant crops at the appropriate soil temperature to allow faster germination and seedling growth. Smaller seedlings with slow growth are more vulnerable to slug-feeding damage.
• Ensure good furrow closure at planting. If the furrow isn't closed well, it can create a "slug highway," allowing slugs to feed on seeds and seedlings easily.
• Scout to determine if insecticides, including insecticidal seed treatments, are necessary for your fields. Insecticides can kill predatory insects that can help with slug control. Following integrated pest management methods and only using insecticides if necessary will give ground beetles and other predatory insects a better chance to help control slugs and other invertebrate pests.
• Have some slug bait on hand for rescue treatments and apply it if you are reaching thresholds (1–2 slugs per trap and there is severe slug feeding damage or dying seedlings).

Black Cutworm

Black cutworm is a sporadic caterpillar pest of corn. Moths migrate from the southern states in spring, and females lay eggs on grasses, weeds, and debris before planting crops. Black cutworm caterpillars hatch from eggs and exhibit two types of feeding patterns. Young caterpillars feed through rolled leaves, causing lines of holes in the unfurled leaves. By contrast, older caterpillars feed entirely through stems of corn plants (growth stage V1 through V5), cutting them off at the soil surface. When soil moisture is adequate, larvae hide in the soil during the day and move to the soil surface at night, where they cut plants. One larva can cut off an average of five corn plants during its development. If soil conditions are dry, larvae will mostly stay below ground and cut stems below the soil surface, causing plants to wilt and die. Losses can be quite variable but are often confined to portions of a field, which reflects where female moths laid their eggs.

For fields that are infested year after year, removal of cool-season weeds along field edges can starve young caterpillars. Planting corn following pasture, alfalfa, or red clover can increase the risk of black cutworm damage. Only two Bt traits (the Cry1F protein, known as the Herculex 1 trait, and the Vip3a protein, known as Viptera) provide some control of black cutworms. Seed-applied insecticides provide little control, with at least one research study showing that seed-applied insecticides only provided 30% control. Because of the sporadic nature of black cutworms, timely scouting and the use of a rescue treatment are the most economical options. Widely accepted thresholds are 2, 3, 5, and 7 cut plants per 100 for seedling, V2, V3, and V4 stage plants, respectively. Using bucket traps to capture moth flights in the spring and calculating growing degree days can aid scouting efforts by predicting when cutting damage will begin.

Other minor insect pests

Seedcorn maggot and wireworm are minor early-season pests of corn in Pennsylvania. Because there are no rescue treatments, farms with a history of seedcorn maggot or wireworm issues should look to preventative and cultural control methods.

Harvest Losses

Harvest losses are another area where yield loss can add up quickly. Consider harvest loss from shatter at the header and threshing/cleaning losses towards your overall harvest losses. Ear drop and shatter losses can rise significantly as stalk diseases increase, soil fertility levels decrease, and as harvest timing moves further into the winter. Synchronize ground speed to header speed to reduce ear drop when shanks are weak, and maintain header height just below the ear to reduce the chance of ears bouncing out onto the ground.

Harvest losses can be calculated by counting the number of kernels in a 10-square-foot area. An easy measuring tool is a 30-inch by 48-inch wire frame that you can carry in the combine as you harvest. Check for losses periodically as you switch between fields, hybrids, and farms. Remember that every 20 kernels in a 10-square-foot area equals 1 bushel of yield loss.

An extensive review of measuring harvest losses can be found in the University of Nebraska's How to Estimate Harvest Losses in Soybean and Corn Fields.

Impact on Yield

Stand losses are much more important in corn than in soybeans, as soybeans can branch significantly to compensate for gaps in the stand. In corn, we consider the four components of yield that make up the yield component method to estimate yields. Using this, we can compare the outcome of missing one or more harvestable ears per 1/1,000^th of an acre.

Impact on Profitability

The chart above highlights the difference in net return per acre as harvestable ears per acre increase. Yes, there are increases in incidental costs (like trucking and storage) as yield increases, but most other production costs remain the same. You might find that investing in planter parts looks expensive upfront, but if you could realize a profit increase of $18-25 per acre, how would that stack up over all your corn acres?

What Can You Do?

At this point in the year, nothing can be done to change the outcome of your corn crop. However, scouting fields, taking some yield estimates, and keeping good records can help you learn what might have happened earlier in the year. To track emergence and growth for next year's crop, measure 1/1000^th of an acre shortly after planting. Visit the site daily, marking plants as they emerge with posts or flags that correspond to the day of emergence. Then, revisit that site weekly throughout the growing season. How long did that site take to emerge? How uniform was the emergence? How much population loss did you have between planting and emergence? Did you have stand loss from cold soils, cutworm damage, slug feeding, or poor planter performance?

We encourage growers to scout fields actively during the growing season: How many harvestable ears can you find? What is the size of the ear? How does this compare to your target? Try to determine the causes of stand loss and yield loss, as well as the management actions that can be taken to correct them in the future. In some cases, yield loss can be (incredibly) frustrating, yet provide good learning opportunities.