The middle part of August is now here and time seems to be flying by. We have to keep asking where all of the normal heat units are at and when will they get delivered. The last tally I heard was that central Iowa is now 350 to 400 heat units behind normal. So while many of acres of Iowa crops have high yield potential, heat is needed in the next thirty days for that potential to be realized.
If one is very observant and looks at nature’s signs you can see that there are trees that are beginning to show a lighter tint of yellow and certain trees are beginning to drop leaves. My treks last week took me in the area bordered by I-90 south to I-80 and from Sioux City east to Peoria. I might as well have stayed up all week checking field after field for leaf disease and insects. Farmers that had not sprayed yet and were thinking they might need to were getting nervous and wanted an outside opinion about their fields and infestations. On top of that I had the chance to visit with a few people who obtained outside observations about the state of the crops in the Midwest and the rest of the world and were doubting official reports about the size of those crops. China has their drought problems, India has the same, and the 54 degree summer temps in Russia has their crops at risk. The acreage reports still don’t make complete sense and will have a huge bearing on final bushels and carry outs. Will those carry outs actually materialize with just disappear into thin air?
Storm losses and weather risks
A few weeks ago most agronomists and farmers look at their crops and realized that their yield potential might be as high as it had ever been. However the old tale about counting the chickens before they hatched was true and they realized that between Aug. 1 and Oct. 1 they had to have the right combination of heat and moisture and avoid extreme heat, hail, and 80plus mph winds. As of two weeks ago and now again this weekend farmers in Northeast and now West Central through Central Iowa the last two items have taken a toll on a significant number of acres and growers. We drove through the storms near Manchester and Decorah on that Friday and through the Jewell area on Sunday afternoon where much of the corn was mowed off by large hail and the bean plants were reduced to sticks. Or there are acres that have been flattened. Such storm losses are never democratic, fair, or completely understandable, thus those growers are now left to deal with the hail adjusters or their revenue insurance administrators to decide what the outcome will be. Six weeks ago the issue would have been to replant of not. Now for the cattlemen in the northeast the issue will be how to get the feed their animals will need over the coming season.
Diseases and Crop Appearance
When you drive down the taller roads where you can look down on the corn crops you start to see a color change in about half of the corn crops in central and eastern Iowa. It was first widely noticeable and immediately I called a local aerial applicator to quiz him about what he could see from the air. He said that the greenness of the corn crop had changed over the past week. Thus we now we have to look at certain plant signs to figure out what has happened. A few crops people have seen the same thing and are coming to a few conclusions. Second year corn where the N was not separated from the residue seems to be one big category of yellowed corn. Another is where 28 or 32 percent was applied rather than 82 percent. The extremely wet May and June must not have been conducive to keeping the NO3-N where it was needed. But beyond those causes there seems to be other factors that are putting the corn in a situation where the top leaves are yellowing weeks ahead of schedule. We know that leaf diseases have been infesting the corn plants for about a month now and such leaf loss and reduction in sugar production is cumulative.
Another plant characteristic of check is the health of the crown area of the root. Dig a root and split the crown down the middle with a sharp knife. If the browning has moved several nodes up into the stalk the early stages of stalk rot are appearing. The only remedy is to try to preserve as much of the leaf tissue as possible so sugar producing is maximized.
Over the past two weeks I have mentioned the high levels of leaf infestation present in many corn fields. In the past week it has gotten very easy to find stalk anthracnose present on the lower one to three nodes. In fact several of us got to examine a few fields where the anthracnose had invaded the cortex of the stalk clear up to the ear already. Our conclusion was that corn reels could be a necessary piece of machinery for farmers in areas of the state this fall.
In soybeans the heavy dews was favorable for more Septoria, Downey Mildew, Frogeye Spot, and Cercospora to continue infestation new leaves. Now that the rows are closed the plants have even more hours where the leaves are carrying a moisture film. Now is the time to recognize those diseases and try to keep the plants healthy.
The main insect to still keep scouting is the soybean aphid. The population increase has not followed the normal trendline, which is to reach high levels in late July or the first week in August. There are still fields where the number of insects on the newer leaves is still less than 20 per plant. However more fields have reached threshhold or are in the 150plus range. One change in their current activity is that they are moving and surviving on the larger and older leaves as the plants move into the mid and late R5 development stage. At that stage stored carbohydrates and oils stored in vacuoles are released into the cells to facilitate grain fill. That improves the diet on the older leaves, thus the insects survive there and have to be included in any counting inspection.
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