Corn, beans and the pests that came to the party

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The planting season may be wrapping up, but the crop protection season has just begun. And there are a myriad of legged and rooted pests that will be doing their job to reduce your yield for the year. Scout your fields, report to your consultants what you have found, and take action to protect your revenue from the new crop of corn and soybeans.

• Corn rootworm began hatching the first week of May, which Purdue entomologist Larry Bledsoe says is the earliest hatch in the past 35 years. Illinois entomologist Mike Gray says that is significant for this year, “Unlike in previous years, corn rootworm larvae this spring will be feeding on small-rooted corn plants in drier soil conditions. I anticipate good larval establishment this season, and where densities are high, significant pressure will be exerted on the root systems of corn plants throughout May and into mid-June. With a larval hatch some 3 to 4 weeks early, anticipate the early arrival of adults, possibly by mid-June.”

• Bean leaf beetles are crawling toward your soybeans. Because of the mild winter, more of the adults have survived and are awaiting newly emerging soybeans. That implies there will be more second generation beetles, both of which will carry a viral disease that reduces the value of soybeans by discoloration. Iowa State University entomologist Erin Hodgson says the number of beetles might be reduced by the high adoption rate of insecticidal seed treatments.

• Soybean aphid researchers have long said predator insects such as ladybugs may be a better control method for aphids than insecticides. Michigan State University researchers are now recommending creating communal habitats for ladybugs and other insect predators around fields so they will be ready to pounce if the aphids arrive. They have said such a habitat within 1.5 miles is important, and have suggested that neighbors cooperate on a jointly-owned predator habitat.

• Corn seedling diseases are being reported heaviest in corn planted April 23-27, prior to a cold, wet spell. Iowa State University plant pathologists report pythium fungi are to blame for destruction of some seedlings that did not have good root growth prior to the deterioration of the mesocotyl that helped get moisture to the young seedling. Ohio State University researchers report that some seed treatments have worked to prevent problems, but not on all species of the fungus.

• Are you rotating corn herbicides?  Avoid crop injury with the careful application of post-emergent herbicides, says Purdue weed specialist Travis Legleiter. Avoid application of a contact herbicide prior to rain to prevent it washing into the whorl. Avoid the use of growth regulators after several nights of temperatures of 45º or cooler. When tank-mixing, follow the most restrictive label to determine the right crop growth stage restriction.

• Do your corn seedlings show potential herbicide injury? Illinois weed specialist Aaron Hager says there is an increasing number of such reports, but says there may be several reasons:

  1. Corn hybrids can vary in their sensitivity to certain herbicides although labeled for corn.  ALS-inhibiting products are prone to injuring corn, along with other post-emergent ones.
  2. High air temperatures and relative humidity can favor rapid absorption of foliar-applied herbicides; and environmental stresses can interrupt herbicide metabolization by the corn.
  3. Rates of herbicide absorption by the corn plant can be increased with spray additives, but those additives should carry labels that indicate potential problems.
  4. Contaminated spray tanks, containing residues from prior applications such as soybean herbicides from the prior year, can be the cause of herbicide injury to corn.
  5. Herbicide persistence in the soil, carried over from the prior cropping season, is another source of injury. Those are blamed on insufficient chemical and microbial degradation.
  6. A high soil pH will tend to slow the degradation of certain chemicals by the process known as hydrolysis. Triazines and sulfonylurea herbicides are particularly susceptible.
  7. Soil moisture is often the most critical factor in carryover, since many herbicides are degraded by microbial action and such action can be limited in soils lacking moisture.
  8. With the dry soils of the late 2011 growing season, some herbicides did not fully degrade and the early planting of 2012 may have hurt seedlings before the rotational interval expired.

Numerous insects have the potential to reduce yields this year, and fields throughout the Cornbelt need to be scouted for problems. Although weed issues can be yield-reducers also, there are many problems that might crop up as you prepare to battle weeds. Among those are herbicide injuries, and many farmers are finding that corn plant symptoms are reminiscent of herbicide injury. But it may be in the way that the herbicide was applied and when it was applied.

Source: FarmGate blog

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