Wet, cool wet weather playing havoc with crops

  • Published: Friday, May 8, 2020

COLUMBIA, Mo. – Some Missouri corn producers are seeing damage from cold, wet soil conditions and hail.

Corn growers participating in the University of Missouri Extension Plant Sciences weekly online town hall meeting on May 8 reported seeing seedling leaves of corn twist and unfurl underground.

Wet soil and cool conditions can cause this abnormal growth, says MU Extension agronomist Bill Wiebold. Environmental conditions associated with underground leafing can cause plants to turn yellow and die.

One or more combinations of the following can cause this:

  • Soil crusting after a hard rain.
  • Cold soil conditions.
  • Planter operations that lead to sidewall compaction or excessive down pressure from press wheels.
  • Improperly closed furrows.
  • Damage from herbicides such as those with cell growth inhibitors.

Producers also are assessing hail damage throughout the state, says MU Extension specialist Greg Luce. Hailstorms on May 3 and May 4 affected a good portion of southern Missouri.

Luce says growers should be patient and allow three to five days or more to assess damage and allow time for regrowth to begin.

It is important to know the corn’s growth stage when assessing hail damage. Plants in V6 stage or earlier can tolerate very high leaf loss without yield penalty. Occasionally, however, with intense hail, severely damaged and twisted corn plants may not regain growth.

To check for signs of live tissue, cut a corn stem down the center. A healthy, growing plant will have white or yellow tissue. Examine the plants for regrowth and check for reduced stands to consider replant options. Small soybean plants are much more vulnerable to stand loss from hail.

Luce adds that it is also important to contact your crop insurance agent when hail injury occurs.

Luce recommends the MU Extension guide “Corn and Soybean Replant Decisions” (extension2.missouri.edu/g4091) by Wiebold and MU Extension economist Ray Massey. The guide tells how to count and calculate stands, replant costs and yield potentials. It also offers worksheets to help growers.

In other weather-related crop news, emerging soybean plants are at risk of herbicide damage due to heavy rainfall, says Kevin Bradley, MU Extension weed scientist.

Damage occurs when there is a short time between herbicide application and planting. The specific herbicide ingredient will determine the likelihood of injury. Herbicides that contain flumioxazin (Valor) and sulfentrazone (Authority) can often cause soybean injury under prolonged periods of cool, wet soil.

When hypocotyl and cotyledon emergence coincides with heavy rainfall, “emerging plants can take a bath in the herbicide” that remains in the soil solution, says Bradley. Cool conditions slow the normal processes of herbicide metabolism in the plant.

Current weather also creates a higher risk of Fusarium head blight (FHB) or head scab in wheat, says MU Extension plant pathologist Kaitlyn Bissonnette. Fusarium affects yields and quality.

Wheat is most at risk to Fusarium infection during flowering. Susceptible varieties are most at risk during spells of warm, humid weather. Symptoms can take up to three weeks to appear. See the article “Fusarium head blight” (extension2.missouri.edu/news/fusarium-head-blight-4542) by MU Extension field agronomist Andy Luke.

Bissonnette recommends Penn State University’s Fusarium risk tool at www.wheatscab.psu.edu. The risk map gives a detailed FHS risk assessment for each state and county. She also recommends www.cropprotectionnetwork.org for more crop protection resources and articles.

If at-risk conditions exist, consider applying a triazole or SDHI fungicide, Bissonnette says. Avoid fungicides in the strobilurin class, as they have the chance to increase mycotoxins in the grain.

Bean leaf beetles also are emerging in soybean, says MU Extension entomologist Kevin Rice. Scout fields as soon as seedlings emerge.

Identify them by a black diamond behind the head. Adults feed on leaves and pods and chew oval holes in soybean leaves throughout the growing season. There is higher damage during dry, cold springs.

There are lower thresholds than other defoliating beetles, says Rice. In the seedling stage, only five or more bean leaf beetles or one destroyed plant per foot of a row meet threshold. See the MU Extension guide “Soybean Pest Management: Bean Leaf Beetle” at extension2.missouri.edu/g7150 for more information.

MU Extension offers online town hall meetings led by agronomy, livestock and horticulture specialists. For more information, visit ipm.missouri.edu/TownHalls.

Writer: Linda Geist

Media Contact

William Wiebold
573-882-0621

Gregory Luce
573-473-7079

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