Corn requires half-inch long fresh silks at the tips of ears in order to pollinate. When pests clip silks shorter than that, pollination won’t happen.
“When pollen drops, you need the silks to receive it,” says Ken Ferrie, Farm Journal Field Agronomist and owner of Crop-Tech Consulting, Heyworth, Ill. “Ideally, ears will pollinate from their butt to tip in three to five days,” he adds.
Pollination can fail or be uneven across the field for a number of reasons, the most common being the result of pest feeding.
“Under good growing conditions, when silks grow 1" to 1½" per day, corn can tolerate a moderate level of silk-clipping insects,” Ferrie says. “But under stressful conditions, when silks are not growing well and pollen viability is short, even a small number of silk clippers is a problem.”
Adult corn rootworm beetles (both western and northern), Japanese beetles and this season the red-headed flea beetle (photo by North Carolina State University Extension) are interfering with tasseling and pollen drop.
Japanese beetles are pheromone feeders. That means when they find a corn plant they like, they give off a chemical that draws more insects to the feeding site.
In uneven corn crops, Ferrie says the pollination window is often extended from three to five days in a field to seven days or more. The longer pollination periods encourage insect populations to continue building and feeding.
Do the ear shake test to evaluate pollination success. Carefully cut the husk of an ear while leaving the silks intact. Then, shake the ear. Any silks that pollinated in the past 24 to 48 hours will fall off. If all or nearly all the silks fall, then the ear is pollinated. (Pollination photos are by R. L. Nielsen, Purdue University Extension corn specialist.)
Check 10 ears to 15 ears in the field to get a sense of how far along pollination is throughout the field.
Ferrie says he expects to see a lot of pollination in late-April and May corn to occur this week. If the silks don’t fall off most of the ears you check this week, then continue to watch for silk clippers and be prepared to spray if pest populations are building.
In soybeans, Ferrie says to be on the outlook for white mold problems.
Caused by the fungus Sclerotinia sclerotiorum, white mold is often recognized by fluffy, white growth on soybean stems. Initial symptoms generally develop from R3 to R6 as gray to white lesions at the nodes, according to The Crop Protection
Network, a multi-state and international partnership of university and provincial Extension specialists, and public and privateprofessionals Lesions rapidly progress above and below the nodes, sometimes girdling the stem.
For more information on agronomic issues underway this week, listen to Ferrie’s Boots In The Field podcast below.
