Corn planting in Iowa was pretty much wrapping up this week—as of May 18. It's been a different spring this year for corn planting than we've had probably since 2007 and maybe 2008. The crop is strung out all the way from mid-March to mid-May in terms of when planting took place.
"In 2010 and 2011 we were able to get the corn planted within 10 days to 2 weeks, and at the most three weeks for the state as a whole," recalls Roger Elmore, Iowa State University Extension corn agronomist. "In 2012, we've really spread the planting season over a lot longer period. Some farmers began planting corn in mid-March in Iowa this spring. And some are still planting now, in the middle of May. So we've got really a two-month window when corn planting has taken place in Iowa this spring."
The positive thing about having planting so strung out like it is this year, is that if you have a hail event occur, or a drought period hit the corn at silking time, or a horrific wind event in July that blows down the corn, the good thing is that not all of the corn will be at that same stage of growth at that moment.
Be careful applying post herbicides; watch corn growth stage differences
However, on the other side of the coin, when you are out in the field scouting now and looking at making a postemergence herbicide application for corn, you've got to recognize you could have up to a 3 leaf to 4 leaf growth stage difference in the corn plants—between one field and another one right next to it.
"That makes a huge difference in the way the herbicide affects the plants," says Elmore. "You want to avoid corn injury from the chemical application. So be very aware of the differences in growth stage when you are out there in the field looking at your corn stands and deciding when to spray. Check the stages of corn growth in your fields before you apply the herbicide and be sure to read the herbicide label and follow the directions very closely for application recommendations."
Currently, a lot of corn in Iowa is emerging from the ground, and corn in other fields has been up and growing for several weeks now. It is time for farmers to do some inspection of their corn stands, says Elmore. What should farmers be looking for as they evaluate corn stands at this point in time?
What to look for now in fields as you scout and evaluate corn stands
"This spring has indeed been different from last year," notes Jim Fawcett, Iowa State University Extension field agronomist in east-central and southeast Iowa. "Last year Iowa had most of its corn planted in a week or so and it all came up at about the same time and it came up fairly uniformly. This spring the corn planting progress has been more strung out over a fairly long period of time and we are seeing more problems with non-uniform emergence of corn plants."
There have been some issues with corn that was planted especially around April 25 to the 27 or so. It went through kind of a cold spell. "We had an usually warm March in Iowa and it's been warmer than normal in early April, too. Then we actually had several days in late April when soil temperatures dipped back below 50 degrees at the 4-inch depth. When that happens you can sometimes get emergence issues," he notes.
Corn seedlings in such a situation with cold soils take up cold water into the plant, and that can cause problems with seedling emergence. There was also some crusting and heavy rains this spring. Now there are some disease issues showing up, too. "Now is certainly a time when you need to be out there in your fields, checking to make sure you've got a decent stand of corn," says Fawcett.
Check your stands now to see if you might need to replant some corn
Make some stand counts. There has been a little replanting of corn done in the state this spring. But every spring there is usually some replanting of disappointing corn stands. "In general the stand reduction hasn't been that great this year. I don't think we have major problems out there in terms of need to replant stands," says Fawcett. "But it's better to get out there now and checking your stands, and finding out now if you have a stand problem rather than waiting until late May or early June to check stands and find a problem. At least if you find that you have a poor stand now, it's early enough that you still have time to replant corn and get decent yields.
"We're at a point here in mid-May where you might be getting a 5% to 10% yield reduction by replanting now compared to what you would get if you had replanted May 1," he says. "Normally, your corn stand has to be reduced down to fewer than 20,000 plants per acre before it is going to pay to replant. If you have a lot of big areas where there is nothing in the field, or where you've lost all or most all of the plants, then you'll want to consider replanting those areas. Most of the corn stands this spring that I've seen which have had some stand reduction, have been in the 25,000 to 30,000 plants per acre range. I'd certainly be keeping those stands. I wouldn't replant them."
What's going on with cutworm on corn? What about those weedy fields?
"I'm still seeing an occasional problem with cutworm on corn in some fields, but it's not widespread," says Fawcett. "However, there are some sporadic problems with cutworm showing up so this insect threat is something to be watching for in your fields."
What about weeds? Some farmers are reporting a lot of grass problems in cornfields. The weeds have really gotten big in a number of cornfields this spring and some of those fields haven't been sprayed with a postemergence herbicide yet. "Weeds are going to be more of an issue this year just because of that early warm weather we had," says Fawcett. "The weeds started growing early and really took off."