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Crop watch
August 12, 2019

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This growing season has been one of extreme paradoxes. Three months ago we were all hoping and praying that the rain would quit falling. Now as August has arrived and the crucial grain filling period is here, many of the growers in Iowa and surrounding states are hoping and praying that the rains arrive to meet the needs of the crops, which depending on the area, soil type, and the planting conditions, range from no problem to being at an extreme need for a healthy drink.

The question of how the crops tolerate the extremes of heat during pollination and how to quantify any yield loss were raised. Now the topic of how much moisture stress is being placed on the corn and beans in each respective area and how might the results show up in the grain tanks this fall.

Seeing the crop up close a week ago in the northern and northwestern part of the state, then seeing how the crops looked in southern Iowa and northern Missouri gave me the chance to see the progress, or lack of in them. In the north the June planted corn varies from very good, though a month or so behind. A number of fields look like once they got saturated the operators had no chance of getting through the field again with a ground rig to apply additional fertilizer or any other remediative trip. They the psychology must have changed to 'let's not spend any more money. It's a lost cause.'

Corn maturity

The $64,000 question on growers' minds is "What are the chances of an early or even normal frost?"

Each climatologist gives a different answer. A few have mentioned analog years, or years that resemble a past growing season that fits into the 18.7 year cycle. By some of their analyses the year 1974 keeps coming up. That was the year that when I was headed down to start the new Iowa State school year, lots of the fields on the way down from northern Iowa looked a lot like they had been frosted. That ended up being the case.

When comparing the development stage of corn planted in previous years to the 2019 crop, planted on the same date, has been running 10 to 12 days behind. The heat that was needed to catch up in vegetative growth arrived but the plants were slow to respond. In the best scenario we would have a warm August and a warm, sunny September with sufficient rain. The reports I just received from our Argentine guests who just drove in from having visited Purdue Univ. related that the corn in Indiana is showing signs of drought. Those symptoms continued though into eastern Iowa right at the time where the kernels can be aborted due to the plants inability to form enough sugar to fill them.

Too often the commodity agents and reporters like to focus on the pollination period being critical to the success or failure of the crop to meet expectations. Over the years I have seen a lot more kernels and yield loss from stress conditions in the blister through early milk stage. Tip back and unfilled 2 to 3 inches at the end of the ear are the bad signs we look for. So even if 80 percent of the planted acres actually exist and have a chance of making maturity before frost or freezing weather, the corn still needs to run the August gauntlet of high temps and dry conditions. This is when the corn growers who spent a fortune on irrigation systems begin to get a return on their investment.

I have mentioned in past columns the effect of the Mainstay Si or calcium silicate application to corn plants. The leaves get thicker, with a deeper layer of cells containing the chloroplasts that catch the energy contained in sunlight. This enhanced energy capture helps the plants form more sugars, which then act as antifreeze in the leaves and stalks to protect the plants from being damaged or killed by subfreezing temperatures. In the testing that was done at Arise Research the sugar level rose dramatically within 46 hours of application.

Corn diseases

There is no average field when discussing the disease situation in the state. In western Iowa the dry weather of the last few weeks has not been conducive to leaf diseases. Thus the pressure from NCLB and Grey Leaf Spot has been minimal, especially where the micronutrient levels on the tissue tests are high and the disease tolerance levels are high. Now in eastern Iowa where the nutrient levels are deficient and the genetic tolerance levels are low, the fields where I was rating plots last week had near 100 percent incidence levels for common rust, early GLS, and anthracnose. If heavy dews are common due to higher humidity levels the severity levels will increase if the genetic tolerance levels are low.

Thus the decisions as to whether or not to apply a fungicide depends on what the nutritional status of the plants are and the genetic tolerance of susceptibility as in which ones have a B37 vs a B14 background. The environmental factors to consider are the moisture levels as from rain or humidity, temperatures that favor or hinder each disease and source of inoculum as in rust must blow in from a southern or southwestern source. The last factor is where the causal bacteria or fungi exist or introduced from, and to what degree it becomes aggressive. Once you understand the biology of each pathogen you can better extrapolate all of those variables operating in your field and on your crop in an expert manner and draw up your own plan to manage diseases.

We are seeing constantly the problems resulting from using a single mode of action herbicide, as resistant weeds always become a problem. With many pathogens having new generations every ten or so days, the selection pressure for resistant strains of each major pathogen is high. Mixing families and altering products can help to stall resistant strains from forming.

The soybeans

In the past two weeks I have been in more fields less than knee high than over knee high. The podded node counts tend to be in the 10 to 14 range, which is short when compared to the 17 to 19 range typically needed to product yields above 65 Bu/A. In just the past week the terminal cluster of flowers and pods have been formed. Thus you can now ascertain the total pod count of each plant, knowing the plant will not be forming any new pods or branches.

Thus when I was standing in a late planted fields of 15 inch rows that held 9 nodes on plants a six inches shy of being knee high the yield prospects are not very high.

Soybean insects

Thus far the aphid populations remain low. The numbers in central Minnesota are increasing and poised to migrate into Iowa soon. Visit your local airport where the incoming small aircraft pilots can inform you if and when they begin to develop green, sticky wings as they impact the aircraft.

The Japanese beetles continue to feed on the silks and leaves of corn and leaves of the soybean plants. If they remain persistent and eat 30 percent of the tissue it may be time to pull the trigger, especially if other insects are eating their share of leaf tissue.

On soybeans the Painted Lady Caterpillar could be forming a third generation of the thistle caterpillars. Be alert to them and the percentage of leaf tissue eaten.

Bob Streit is an independent crop consultant and columnist for Farm News. He can be reached at (515) 709-0143 or www.CentralIowaAg.com.

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