Garden Help Desk: Successful pollination is key to corn production

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High temperatures and insect damage to the silks are common causes of poor ear fill in sweet corn.

Courtesy Meredith Seaver

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Even poorly filled corn ears can still be delicious. Just add butter and salt!

Courtesy Meredith Seaver

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Stress from high temperatures, overwatering, underwatering or poor plant nutrition can cause newly fertilized or young corn kernels to stop growing and abort.

Courtesy Meredith Seaver

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High temperatures at critical stages of sweet corn development can affect the quality of the finished corn.

Courtesy Meredith Seaver

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High temperatures and insect damage to the silks are common causes of poor ear fill in sweet corn.

Even poorly filled corn ears can still be delicious. Just add butter and salt!

Stress from high temperatures, overwatering, underwatering or poor plant nutrition can cause newly fertilized or young corn kernels to stop growing and abort.

High temperatures at critical stages of sweet corn development can affect the quality of the finished corn.

I have a corn problem I hope the extension office can help me with. I grow corn every year and have always had great success. I plant four rows in an area about 50’x20′. The corn seed is sh2 variety. Last year, the ears were not fully developed. I thought it could have been grasshoppers eating the silk but I haven’t had an insect problem this year. But again, the ears are growing to a proper length but the kernels are not developing. I water every other day and put down nitrogen every week.

There are a few common reasons why corn ears may fail to fill completely and most relate to successful pollination.

The spacing of your rows and the density of the planting can affect pollination. Corn isn’t pollinated by insects. Instead, pollen falls from the tassels onto the silks or is carried on light breezes to reach the silks and pollinate each kernel. If corn plants are in widely spaced rows, it reduces the chances that each silk will be pollinated.

Uneven planting depths can also reduce good pollination because germination may not be uniform. Not all the corn plants will mature at the same time, so tasseling and silk emergence won’t be even either.

Insect damage to the silks can also interfere with pollination. Earworms are a common pest. They and their feeding on the silks will prevent successful pollination.

Poor ear fill can also be caused by high temperatures. High temperatures can cause damage to silk or pollen and prevent good pollination. Corn pollen can be damaged or killed by high temperatures. Silks can dry prematurely when temperatures are high and humidity is low.

Silk emergence and pollen shed are normally synchronized, but high temperatures can interfere with this, causing silks to emerge or pollen to shed too early or too late for the silks and pollen to meet.

Poor soil preparation and low soil fertility during the growing season can also affect pollination. If important nutrients like nitrogen are low, it can affect the timing between silk emergence and pollen shed, reducing successful pollination. Excess nitrogen can play a role in poor pollination and ear fill, too.

Poor pollination isn’t the only reason you may find ears with poor fill. Stress from high temperatures or improper watering (over or under watering) can cause developing kernels to abort even if they were successfully pollinated, leaving unfilled spaces on the ear.

So, what can you do to have a better sweet corn harvest next year?

First, have a soil test done to identify any issues that need to be corrected.
Do as much soil prep this fall as possible so you can plant easily in the spring as soon as conditions are right. Your fall prep should include problems mentioned in your soil test.
In general, sh2 (super sweet) varieties are more susceptible to heat damage than other varieties, but there are some sh2 varieties that tolerate the heat better than others. Look for varieties that are described as more heat tolerant.
Plant your corn at the right depth and spacing to maximize uniform germination and pollination. Plant at least three rows of corn with seeds spaced about 7 to 9 inches apart and space the rows within 2 to 2.5 feet of each other. Block planting with 15-inch by 15-inch spacing can also work well for good pollination.
Water deeply but not too frequently. Corn doesn’t tolerate wet soils, so daily watering isn’t helpful. On the other hand, drought stress can contribute to poor ear fill. Water deeply so that moisture has reached about 6 inches down into the soil when checked an hour or two after watering. Check soil moisture every day or two and water deeply again once the upper 1 to 2 inches of soil feels dry.
Maintain soil fertility after planting with side-dressed nitrogen applications when the corn is knee high and again when you first see tassels or silks. Don’t overapply or apply frequently because excess nitrogen can reduce the quality and yield in your garden.
Scout frequently for pest problems to catch them before they’re difficult to manage. Plan to protect emerging corn silks with regular sprays of Bt (or apply mineral oil) to prevent silk damage.

There isn’t much you can do about the weather. We’ll either have some extreme heat next summer or we won’t, but there are still things we can do to give our gardens the best chance of success.