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Scout Your Fields to Catch Potential Problems in Corn, Soybeans

Scout Your Fields to Catch Potential Problems in Corn, Soybeans
Early monitoring of fields for diseases and insects helps you protect young plants and potential yield.

Early-season scouting for disease and pest pressures is a key step to protecting plants for optimum yields. "It's important to pay attention to what's going on with corn and soybean plants as a stand establishes," says Paula Davis, manager for insect and disease traits at Pioneer Hi-Bred in Johnston, Iowa. "During the early part of the growing season, you should scan the field and look for stress issues in corn and soybeans. If the season turns cool or wet, some diseases and insects could become problematic."

Watch crops carefully for signs of insect pressures

Davis suggests growers monitor crops closely, then follow a management plan to resolve challenges. In corn, pests such as armyworms, black cutworms, white grubs and wireworms can surface during the early growth stages. Look for early signs of bean leaf beetle in soybeans. Pioneer has several products that offer protection against these challenges. 

One corn insect to watch for this season is the black cutworm. The pest leaves small shot holes in corn leaves. When black cutworms are about ½-inch long, they can cut the plant. Stand loss or irregular stands may result. "We've seen data showing significant flights of black cutworms in Missouri," she says. "The first captures took place in mid-March, showing it may be a threat this year to some regions."

The Herculex insect protection line of technologies protects growers against black cutworms and other corn pests.

Weather plays important role in determining insect pressure

Davis says weather plays a critical role in which pests surface. Conditions favoring good corn germination allow plants to tolerate more pressure. She says flea beetles may pose a lower risk this year due to the cold winter and growers using seed treatments. Wireworms and grubs like cool, wet environments. 

"If temperatures turn cool after planting, it could delay corn emergence, and wireworms could feed on the seeds in wet and cold conditions," Davis says. Researchers are seeing an expansion of some grub species such as Japanese beetle. They are common in Illinois and the eastern Corn Belt but even range into some areas of Iowa and into Nebraska. 

"While corn can withstand some damage from grubs, they can be fairly harmful," Davis says. "They're not just a seedling pest. We've seen silk clipping in corn, and adult beetles can defoliate soybeans." Corn seed treatments such as Cruiser Extreme 250 and Poncho 1250 protect against white grubs and other secondary soil insects.

Soybean fields need to be watched for other early pests, too

"Bean leaf beetle may be a pest to watch this season," Davis says, "especially for the earliest planted fields in the area. The first generation gravitates toward those fields. Although cold winter temperatures lower the risk of bean leaf beetle, heavy snows offered some protection and may increase survival rates. 

"Survival of bean leaf beetle could be greater than forecasted," Davis says. "The pest could pose a more significant challenge in warmer climates such as the extreme southern parts of Indiana and Illinois."

Seed treatments may reduce insect pressure in early season, but insecticide seed treatment is less effective on later generations of insects. The Pioneer Premium Seed Treatment offering includes Gaucho insecticide, and Trilex and Allegiance fungicides. The insecticide component may help prevent damage from early pests, such as bean leaf beetles.

Keep an eye on fields for signs of disease pressures, too

Scott Heuchelin, another Pioneer research scientist who specializes in field pathology and diseases, says scouting includes taking note of uneven corn and soybean emergence.

"Seed rots and damping-off may result from a variety of pathogens," Heuchelin says. "Seed rots occur when bacterial or fungal pathogens attack the seed before it can fully germinate. This is most common in saturated soils where the seed has been subjected to low oxygen conditions." Damping-off occurs when the seedling succumbs to a disease during emergence. Damping-off is caused primarily by the fungal pathogens Fusarium, Pythium and Rhizoctonia. These pathogens are present in most fields and can strike when conditions are right. 

He adds, "These conditions often are linked to cool, wet soils, but Rhizoctonia and Fusarium can attack seedlings that are stressed by dry, warm soil conditions. Though Pythium typically is seen with cool, saturated soils, there are Pythium species that thrive in sandy, well-drained soils and warm temperatures."

Does it pay to use a fungicide seed treatment?

"Fungicide seed treatments are a way to protect the seedling for the first few weeks until the plant is established," he says. "But fungicides aren't foolproof. Various pathogens still can cause problems in suboptimal field conditions."
A fungicidal seed treatment's effectiveness can diminish from prolonged saturation or dilution as water perks through the soil. "It's important to minimize stress and promote plant health with good soil fertility and seedbed conditions," he says. "Stress makes plants more vulnerable, so they succumb to pathogens more readily."

Corn growers likely will see less pathogen pressure from the V4 stage to R1. Foliar, stalk and ear diseases become most visible later during the reproductive growth stages of corn, Heuchelin says.

Soybean growers need to scout for damping-off and root rot on young bean seedlings this coming week and next week.  "Cool and wet conditions favor the growth of Pythium, Rhizoctonia and Fusarium," says Jean Liu, a Pioneer research scientist in soybean pathology. "So you should avoid excess irrigation during the first 10 days after planting and don't hope for too much rain." 

What are soybean symptoms of damping-off, root rot, etc?

If infection occurs after germination, soybean seedlings may fail to emerge and have a short, discolored root, says Liu. If infection occurs after emergence, seedlings collapse and have a rotten appearance. In fields with compacted soil and a history of damping-off and other seed- and soil-borne diseases, such as sudden death syndrome, the use of ridge tillage can improve soil drainage and hence seedling health, Liu says. 

"Soybean growers should not overreact if they see disease infection," Liu says. "In most U.S. locations, plants may grow out of the problem when the weather warms up." Stress from residual herbicides also can affect emergence and stand establishment negatively. Growers should work with an agronomist and know their rotation patterns to avoid such issues, says Davis.

The key is to monitor both corn and soybean fields early and often. Davis encourages growers to dig up samples when scouting. "The biggest thing to avoid is planting fields then not looking at them until it's time for a herbicide application," she says. "Don't forget about early-planted fields, even walking leisurely through a field can be worthwhile."
Growers with questions about stand emergence or insect pressures or replant decisions should contact their seed sales representative or a local ISU Extension agronomist.

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