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August is here — time to watch the calender and clock

By Staff | Aug 6, 2009

August is here and from now on every crop producer north of Highway 30 in Iowa will be watching the calendar and clock. Though we hate sweating through hot summer days we know we need the heat to get the crops mature in much of the northern half of Iowa as well as other areas in the Midwest. By now the meteorological facts have been released confirming that we just went through the coolest July in Iowa since the 1890s and in places 1870. A return to warmer temps will help the corn crop make up for lost time, but it is starting to look like the yield potential that was lost on soybeans is simply gone and the chance for recovery is slim to none. The good news is that the chance for major hurricanes that tear up the Gulf Coast states and disrupt oil and shipping operations has also been reduced due to the lowered ocean temperatures.

Most County Fairs have been held and they had a good run. Who would have ever thought that we would be attending them wearing coats to stay warm? But we are a hardy bunch and a little inclimate weather didn’t keep anyone home. So the many 4-H participants who raised cattle, hogs, sheep, veggies or other projects got to show off the end product of all their work. Let’s congratulate them for their efforts.

The big race at Newton took place again this past week. A few weeks ago they had a race calling attention to the ethanol business and it attracted a big crowd. It brought attention to the grass-root efforts of the many corn and cattle producers who built the ethanol business from scratch relying on sweat, business plans, and pulling together to help their own futures. Saturday’s event had a national forum and group of drivers. We went to the race and it was the first time I had seen a Nascar event. The cars went almost as fast as those idling down the Autobahn in Germany. One thing they need to improve on is their mufflers. I am used to 12 gauges going off while hunting or skeet shooting. But this noise was absolutely head pounding and we left before the end, and that was with a good set of ear plugs in place.

Field Happenings and Corn Leaf Diseases

After the past two weeks there are many growers and agronomists who are now seeing corn diseases and soybean aphids in their dreams. Both are now here and many farmers are either trying to determine if they need to take action soon or are assembling all the facts to make up their minds about their own fields.

First a few stories about corn diseases, which are now very common. Most years in Iowa we worry and have to scout for four main diseases. Those are anthracnose, grey leaf spot, northern corn leaf blight and eyespot. Typically eyespot is something that corn growers in Wisconsin and the extreme northeast part of Iowa have to deal with, as it proliferates in wet and cool weather. Thus it is generally not a problem in most of the state and genetic firms that are developing germplasm and hybrids for Iowa, Illinois, and eastern Nebraska don’t get the opportunity to screen for tolerance to it. Thus it has blindsided many seed companies and farmers this year. As the weather has turned drier and warmer the appearance of new lesions should slow or stop. But the ramification of having four to nine leaves of each corn plant covered by yellowed spots on 10, 25, or 60 percent of their leaf area could be huge. The tissue now occupied by a yellow spot will not form photosynthates and contribute to grain fill. That will hurt corn yields. Typically the leaves at or above the ear contribute 70 percent of the ear fill. If 20 percent of the tissue is yellowed, ear fill as well as stalk and root health will be affected by 25 percent of 70 percent, or a total of 17 percent loss. 17 percent of 200 Bu/A is 35 Bu/A. That isn’t a perfect way to figure potential loss but might be as good as any.

In both 2007 and 2008, a high percentage of the corn crop died due to a combination of fusarium and anthracnose. Those two diseases are back already and are still going to be attacking the leaves and stalks. Thus plants in a field already moderately or heavily infected by eyespot don’t have much extra leaf tissue they can lose before the plants are affected in terms of yield and plant health. Typically to see the small lesions of those two diseases one needs to scout using a 20 to 30X lens. After seeing good results from spraying near brown silk the last season I am more aggressive in calling in the sprayers.

In the past few years we have likely seen plant protection firms error by trying to entice every grower to spray every acre. Instead the proper tactic would have been to educate them more about how to gauge which variety (s) and field (s) was going to be most at risk from disease attack. Most growers could have then focused on perhaps the third of their acres most likely to benefit from treatment.

I was in southwest Iowa late last week and it was interesting to see corn plants that looked almost like Christmas trees where the top third held lots of eyespot, the middle third was heavy with anthracnose, and the bottom leaves contained lots of GLS. Plants like that need help.

Things that several agronomists are tracking are tissue analyses of heavily diseased fields and the number of traits the affected varieties possessed. The tests are indicating that the NPK as well as the MN, S, Cu, Zn, and other nutrient levels are generally extremely low. Might compaction, poor root development, or poor soil tests be to blame? In cool years it is common for the amount of moisture evaporating from the leaves to be reduced. With less nutrient loaded water moving into the roots and evaporating out of the leaves, few nutrients are pulled into the plants.

I was visiting with a very sound plant researcher who works with non-rowcrop plants. Part of the conversation covered the field days where we discussed companies that are inserting two or more events into the plants. He asked what the energy draw was on the plant to operate the protein manufacturing process involved with some of those traits. I mentioned that going clear back to Peter Carlson and his first efforts with Incide Bt I had never seen any concrete, documented studies to answer such a question. After seeing more instances of the stalk phase of anthracnose in corn plants weeks before the traditional Sept. 1 date such questioning might be valid. Can an analogy be to think of it as horsepower requirements to run each of the vital plant processes? The first priority after pollination would be to keep the plant alive, then to fill the ear, then to maintain the disease fighting systems. Is there a limit to how many systems a plant can run, especially in a year with a minimal amount of heat? That might be a good question for plant physiologists. I checked the Taiz and Zeiger “Plant Physiology” advanced textbook in the section on photosynthate allocation and sink partitioning. The authors mentioned the synchronization of sugar sinks but didn’t get into any trait discussion.

Soybean Notes

Until now the news of the last weeks has been aphids or the lack of any big infestation. They did what insects typically do, which is they never read the book and end up often doing just what we don’t expect them to do. The aphid population that is here is quite spotty, but in most of western Iowa neighborhoods there are fields that have reached threshold. One can go from field to field and find infestations from 1 to 5 per plant and in the next field are hot spots of well over 250 per plant. That creates a dilemma if you are already making a trip through the field to spray a fungicide. Do you spray to perform two tasks at once while you can still use your ground sprayer at the risk of waiting a week and having to hire a plane to spray? In those instances it is nice to be able to apply the Safe Strike and maintain the beneficial populations.

Bean leaf beetles, grape colaspis and grasshoppers are populating fields now and need to be monitored. The BLB can be significant due to their vectoring PMV.

On an ominous note most plants seem to be carrying 13 to 15 podded nodes instead of the typical 16 to 20. Those operators who used aggressive management techniques and foliar fed are counting up to 18 with four to six side branches. How many are present on your bean plants?

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