The week of April 21 to 28 was great for corn planting in central Iowa until Friday evening rolled around. Then central Iowa got between 0.5 and 2 inches of rainfall. That rain likely resulted in tile lines running in a some fields and levels in rivers rising a little. "For the most part in central Iowa available soil moisture is near 100%," says Mark Licht, Iowa State University Extension field agronomist.
"I know some farmers have wrapped up corn planting, many are well into it and some were just started as the rain began Friday April 27," he says. "Very few soybeans have been planted to date in central Iowa. I expect corn acres to quickly reach 100% planted and planted soybean acres to increase rapidly as planting conditions improve." Licht offers the following observations and information.
In the weeks to come there are some things to consider
1) Be patient to get the planters rolling again. Mudding in the corn and soybean crop can be more devastating than waiting a day or two more.
2) Keep an eye on corn yet to emerge. Any corn that has set in the soil from the early April planting should be evaluated for stand counts. To this point, corn already planted has not had ideal soil temperatures for germination and emergence. Be aware that germination and emergence in cool, wet conditions increases the risk of seedling diseases.
3) Keep an eye on corn from pre-emergence through fifth leaf for potential cutting from black cutworm larvae. Cutting dates are nearing.
Army Cutworm Moths: Most of those fuzzy brown moths that have been flying around Iowa the past couple weeks are Army Cutworm moths, says Licht. Some may be Black Cutworm moths as well (more on those below). Erin Hodgson, ISU Extension entomologist, notes that these army cutworm moths are from eggs laid last fall. They are completing development this spring with the adults migrating west to complete another generation. She said the larvae prefer grasses and are 'grazers' not 'clippers'.
Likelihood is that most Iowa corn is not going to be damaged by Army Cutworm moths or larvae since very little has emerged. Even emerged corn should be fine unless a 'severe infestation occurred'. To read more on Army Cutworm moths go to; Management of Army Cutworm Moths and Pale Western Cutworm.
Scout for Black Cutworm Cutting Corn: Black cutworm moth flights have been reaching Iowa this year and a black cutworm scouting advisory has been released at; Black Cutworm Scouting Advisory. For central Iowa that scouting advisory is for two scouting dates of May 10 and May 18. Corn should be scouted until it has reached the fifth leaf stage when it is safe from cutting.
Black cutworm thresholds are 2 to 3% wilted or cut plants when larvae are less than ¾ -inch long. When larvae are greater than ¾ -inch long the threshold increases to 5% cut plants.
Corn Emergence Delays: Last week farmers were asking if they should plant prior to a cool rain. "The rule of thumb I keep hearing is to not plant 24 hours before a cold rain," says Licht. "There is a lot of merit to this rule of thumb, but it is not justified in all cases. Planting before a cold rain would mean that soil temperatures would likely drop some. This would be more of a concern if air temperatures were predicted to stay cool."
Here's some of the reasoning behind it, explains Licht. Corn takes between 90 and 120 growing degree days from planting to emergence assuming adequate soil moisture. Other things such as planting depth and residue cover can change this slightly. Therefore, it is probably more of an issue of the 5- to 10-day forecast following a cold rain than the cold rain itself.
None-the-less, corn that has been in the ground for 90-120 growing degree units may need to be checked for viability, he says. "My personal rule of thumb is to check corn that has not emerged within 10 days of planting. Corn planting before April 15 should be emerging as growing degree units have exceeded 120 growing degree units."
Check current soil temperatures at; 4-Inch Soil Temperature Maps (currently in low 50s).
Check site-specific accumulated growing degree units at; Iowa Environmental Mesonet Accumulated Data Traces.