June 24, 2013
Great progress has been made over the past couple of weeks not only for planting in Iowa but also development of insect pests and accumulation of heat units. "A colleague stated yesterday that the corn has now mostly made it through the ugly duckling stage, and I largely agree," says Mark Licht, an Iowa State University Extension field agronomist in central Iowa. "However, the 2013 corn crop is one that in general does not look as good as anyone would like."
YELLOW LEAVES: Bright yellow leaves waving in the breeze are fairly common in years where corn has been growing in cool weather and then the heat comes rapidly. If you have corn that's still "wrapped up" or "buggy whipped"—keep in mind that most of the leaves should unfurl within a few days. For more information about this condition check the ISU Extension corn website.
Licht adds, "Much of the 'ugly duckling' corn is a result of multiple things that have occurred as a result of the type of growing season we've had so far." Cool, wet soils don't promote rapid root growth. Excess rainfall pushes nitrogen deeper into the soil. The reliance on seedling roots switches to nodal roots between the 3rd and 6th leaf stage of the corn plant.
Those three things mean the corn hasn't been taking up nitrogen, sulfur or potassium very well--causing yellowish appearing corn, says Licht. "As warm weather continues, the roots will get more oxygen, and the roots will reach the nutrients in the soil as the roots go into a rapid growth phase. The unevenness of the corn stands we are now seeing in fields is simply based on which plants got to the nutrients first."
The fast growth phase Iowa's corn crop is now experiencing is causing what are commonly called "rapid growth symptoms"
Corn in many fields is now in the rapid growth phase—and that is causing some rapid growth syndrome symptoms (buggy whipping or twisted whorls) to show up in fields or areas of fields. As the new leaf comes out of a tight whorl, it produces a yellow leaf or even a white appearance briefly--due to lack of light reaching the chlorophyll. "Best case scenario for solving all of this is for the corn plants to receive more warm weather and a gentle breeze," says Licht.~~~PAGE_BREAK_HERE~~~
* What causes yellow flash? Fast-growing corn in the last week or so has resulted in "buggy-whipped" or the post buggy whipped "yellow flash" plants in some fields in other areas of the state too.
Clarke McGrath, an ISU Extension field agronomist at Harlan in western Iowa and author of the Corn-Soybean Insight column each month in Wallaces Farmer magazine, points out that these symptoms are sometimes blamed on herbicides—but herbicides usually aren't what is causing this condition.
"While some herbicides can cause the yellow flash, most of what I've seen in fields and what I have received as photos from dealers and growers are the bright yellow leaves waving above the canopy after the winds have helped the leaves unwrap," says McGrath. "Corn that's growing in 'good ground' and is around V5 to V8 growth stage seems to be the most common places where this yellow flash is showing up. The yellow upper corn leaves are sun-starved so they haven't started photosynthesizing full speed yet--since they were covered up earlier in the whorl by the more mature leaves. Corn usually grows out of this yellow leaf condition in a few days with no long-term impact."
The symptoms are common in years when corn is growing in cool conditions
These symptoms are fairly common in years where corn has been growing in cool conditions and then the heat comes rapidly. For more information, you can check the ISU Extension corn website.~~~PAGE_BREAK_HERE~~~
For farmers whose corn is still "wrapped up" or "buggy whipped"--most of the leaves should unfurl within a few days. "I saw a lot of this early in the week last week, and the winds this past Friday and Saturday had unfurled most of the fields locally here in western Iowa," says McGrath. "The storms on Monday June 24--if they don't do anything more damaging--should help alleviate the issue of yellow leaves as a result of the blowing around of the leaves by the wind."
Other crop pests and conditions to scout for at this time of the growing season
* Corn rootworm larvae hatching. Yes, it's time to think about corn rootworm larvae hatching. Enough growing degree days have been accumulated, says Licht. You should scout fields that have higher risk potential for root damage as well as fields that have protection provided by either the rootworm-traited seed corn, or an in-furrow insecticide application.
* Soybean aphids in Iowa. Soybean aphids have been found already this summer in Iowa. "But there is no need to be spraying an insecticide with post emerge herbicides in the next couple of weeks," says Licht, "especially if an insecticide seed treatment was applied. The insecticide seed treatment will likely provide protection against soybean aphids for up to 45 days after planting. Note it may not last that long in all cases."
It is best to scout soybean fields for soybean aphids before deciding to make an insecticide application, he adds. Generally, scouting should begin in central Iowa around mid-to-late July.
* Japanese beetles are emerging. With warm temperatures, enough heat units have been accumulated for the emergence of Japanese beetles. Scout soybean fields along residential areas and grassy areas to determine if control measures should be taken.
* Risk of Sudden Death Syndrome in 2013. The wet weather during planting of soybeans this spring means there is once again the potential for Sudden Death Syndrome or SDS infection to occur. SDS is a fungal pathogen that infects the root causing root rot during wet conditions at planting and early growth, notes Licht. The foliar symptoms found in late July or in August are from a toxin that the fungal infection produces. These foliar symptoms tend to be worse when the growing season is wetter than normal.
About the Author(s)
You May Also Like
Current Conditions for
Enter a zip code to see the weather conditions for a different location.