Corn Combat Starts Now

Give corn yields your best shot by knocking out early-season insects and diseases.

By Laura Barrera | Photos By Darren Goebel

Illustration: Robert Brinkerhoff

From the moment corn is planted, the goal is to have every seed germinate and emerge as rapidly and uniformly as possible. Many growers strive for that perfect “picket-fence” stand. 

“Corn yield is all about leading the race right from the beginning,” says University of Illinois agronomist Fred Below. “Getting the crop up, off and going—it doesn’t guarantee yield, but it certainly helps set the potential.” 

Unfortunately, early-season insect pests that bore into seed and feed on roots, and fungal diseases that rot the seed, roots or mesocotyl, can throw a wrench in this plan, cutting into yield and profits no matter how perfectly the corn is planted. If stand loss is severe enough, growers may need to replant, says DuPont Pioneer field agronomist Brian Bush.

No rescue treatments exist to help seedlings once they are under attack. But the good news is that corn growers can take proactive steps—such as scouting, hybrid selection, seed treatments and in-furrow treatments—to protect their stand, maximize yield and optimize their return on investment in the crop. 

Prime Pest Conditions

Seedcorn maggot emerging after destroying a seed corn kernel in an eastern Indiana field that had been fertilized heavily with manure.

While several factors influence the risk of early-season corn threats, the biggest one may be cool, wet soil conditions. The No. 1 fungal pest Bush sees in his region of Columbus, Indiana, and the Eastern Corn Belt is Pythium, which flourishes in these conditions and can cause both pre- and post-emergence damping-off in corn.  

Other conditions can magnify the effect of wet, cold ground on disease pressure. Tight clay soils are at a higher risk for disease because they drain poorly, Bush says. No-till fields or those in a continuous corn rotation may have heavy residue that prevents soils from drying out and warming up. Manure fertilizer also can contribute to seedling diseases and increase early-season insect pressure.

When it comes to early-season insects like white grubs and seedcorn maggots, Bush says they also tend to be more of a problem when the plant is not actively growing quickly, as often happens in a cool, wet spring. He adds that white grub is the No. 1 concern for growers with fields coming out of sod or that have been in a heavy grass cover for multiple years. He says he’d be more concerned about seedcorn maggot in fields with a history of manure applications.

Cutworms and armyworms also can be problems in fields that had cover crops or heavy weed populations, as these pests fly in from the south and are looking for lush, green fields to lay their eggs, Bush says. Then, when corn emerges, the larvae will feed on the plants. Wireworms are another early-season corn pest, but Bush says the prevalence of these is more influenced by field history than specific conditions. 

Scout, And Be Patient With Planting

Corn seedling clipped off by a black cutworm.

A grower’s first line of defense against these pests is knowing which ones lurk in his or her corn fields. Bush recommends scouting all different topographies in the field for stand loss or uneven emergence, preferably before the V4 growth stage each season, as that’s when the plant transitions from the seedling root system to the nodal roots.

If growers discover early-season pests, there are several preventive measures they can take to keep them from recurring. The first is planting when conditions are ideal. “The critical soil temperature for seedling issues that show up in corn is 50 degrees,” Bush says. “But more important than that is probably the next seven- to 10-day forecast. I would rather a farmer go out with cooler-than-ideal soil temperatures if the 10-day forecast is a warming and drying trend.”

Reduce Residue Risks

Growers also need to ensure their residue management is effective, because if residue gets in the seed trench, it will soak up moisture the seed needs and possibly delay emergence, says Jason Webster, Precision Planting® lead commercial agronomist and manager of the Precision Technology Institute (PTI). And as Below says, anything that slows the rate of emergence will give insects and disease a greater chance to cause damage.

Several corn seedlings felled by seedling blight that rotted the plants at the soil line.

Research conducted by PTI confirms the negative impacts of residue in the furrow, Webster says. He says he found that for every 1% reduction in clean furrow, corn ear potential dropped 1%, resulting in a 2.5-bushel-per-acre yield loss. 

Burying residue through tillage can help, Bush says. If residue is a problem in conventional tillage systems, Webster says growers may have sized it too small for row cleaners to move it. Bush also recommends doing primary tillage in the fall instead of spring, as this gives the residue more time to degrade in hopes of reducing disease inoculum. 

For no-tillers struggling with furrow residue, Webster says they may be planting too close to old cornstalks or need to make their row cleaners more aggressive. He adds that producers should ensure that stalk material is spread out evenly from the back of the combine during harvest.

Provide Extra Protection

Even if best practices are followed, corn may need extra protection from early-season pests and disease. Bush says that different hybrids have different tolerances toward seedling diseases, and farmers should consult their seed dealer to determine the best option for their fields. When it comes to insect pests, Below says that current seed traits only offer protection for later-season insects, like corn rootworm or corn borer.

Regardless of the traits used, growers will likely need a seed treatment and possibly in-furrow products for further protection. These products should be considered every season, Below says, because once a problem is detected, it is too late to correct. “Seed treatments protect the seed, whereas an in-furrow [treatment] protects the seedling, so it extends the period of protection,” he adds.

Travis Burnett, Beck’s Hybrids Practical Farm Research (PFR) agronomist, adds that one challenge with seed treatments is there’s a limited amount that can be applied to the seed. “When you get in those years where you have heavy rainfall and cool, wet conditions, that’s where we see the benefit of adding an additional insecticide and/or fungicide in-furrow, to get through that period of saturated soil conditions,” he explains.

Consider In-Furrow Treatments

Beck’s has tested several in-furrow crop-protection products at their PFR corn research sites across the Midwest. As of 2018, they have classified five as “PFR Proven” on the basis of providing yield gains and averaging a positive return on investment for at least three years: Headline® fungicide, Xanthion® fungicide, Capture® LFR insecticide, Ethos® XB insecticide/fungicide and Capture® LFR + VGR® Soil Amendment (Capture VGR).

It’s important to note that in order to use these in-furrow products, the planter must be outfitted for the application. Growers using Keeton® Seed Firmers or similar application systems can combine their starter fertilizer with an in-furrow product, as long as the insecticide or fungicide is compatible with the fertilizer. 

In years when young corn is graced with warm temperatures and aerobic soil conditions, it can outgrow insect and disease pressure, as happened in 2018 with in-furrow trials at PFR’s Kentucky, Iowa and Ohio sites, Burnett says. However, based on 3-year results from the multi-location study, Ethos XB provided an average $9.35-per-acre return on investment, with Serenade ASO following at $6.05 and Capture VGR at $2.61. He says this data suggests that a fungicide/insecticide product can alleviate some of the stresses and potentially provide some lucrative returns when used regularly.

Bush agrees that there are many farmers who may decide to use in-furrow products every season, even if the benefit varies year to year. “They may find it only pays off one year out of three, but in that one year they may make up enough yield benefit to pay for those years where they don’t see a benefit,” he says.

By taking these extra measures to protect corn seedlings and determine which solutions will be the most beneficial for their farms, growers can help their corn crop win the pest battle early. The prize will be strong stands with optimum yield and profit potential