Spring Struggles Put Fields at Higher Risk of Pollination Problems

When silks are growing well, corn can tolerate a moderate population of silk-clipping insects. But if silks are growing poorly and pollen viability is short, even a small number is a threat. ( Darrell Smith )

Have you been keeping good scouting notes this season? Hopefully so, because you can use that information to help prioritize today’s scouting to know where you might have problem areas during pollination.

"Early on, look for clues about how the crop is going to pollinate within individual fields," says Farm Journal Field Agronomist Ken Ferrie. "If you have growth and development problems in certain areas, map them as zones to scout later, during pollination. For example, in cold, wet seasons, plants in low-lying areas might emerge slowly and fall behind the plants in other parts of the field," he explains. 

Any areas that have fallen behind or been spot-replanted will need to be scouted longer than the rest of the field.

“Areas in the field with uneven growth are at high-risk for pollination problems,” Ferrie says. “When you find varying plant sizes that don’t break down into identifiable maturity zones, you need to scout almost every day of the pollination to make sure that all the plants get pollinated.”

Risks to watch

If you have uneven fields, it gives silk-cutting insects a buffet from which to feed longer. Look for adult corn rootworm beetles, Japanese beetles and aphids that can hurt pollination success.

Each of these pollination-hurting insects use pheromones to signal to others in their species when there’s a good spot to feed, Ferrie says. This means when one of these pests finds your field, or spots in your field that are still pollinating, they’ll call their friends and have a party.

“Pollination is affected when silks are clipped within one inch of the ear,” says Troy Deutmeyer, Pioneer agronomist in Iowa. If drought or extremely hot conditions hit at pollination, silks are under pressure already and likely to grow slower, so silk clipping could be even more detrimental.

When it comes to insecticide treatment, check for thresholds before pulling the trigger. Purdue Extension experts recommend placing at least six traps in each field and leave them for a week to count insects captured. It’s best to start trapping earlier in the season, but it could be beneficial for establishing population estimates now.

Here are common thresholds for silk clippers, according to Purdue Extension:

  • Corn rootworm: if silks are ½” or smaller before 50% of pollination is completed and beetles are present.
  • Aphids: pre-tassel, if plants are under stress and aphids are consistently found on the emerging tassel. Post-tassel if 50% of the tassels are covered with aphids.
  • Japanese beetle: look for silks at or smaller than ½” with less than 50% of pollination done and beetles actively feeding.

Pollination is critical because each pollination ‘miss’ is a lost kernel—and it can add up quickly. Get out into fields and pay special attention to fields with uneven emergence or spots with replant, as those areas will be especially vulnerable.

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