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CROP WATCH

By Staff | Aug 4, 2011

It’s August and this is the month when the needed rains either arrive to fill out all of the corn kernels or soybeans, or they leave us dry with our hopes and dreams dashed.

Last year, crops were likely the most input-expensive crop most farmers have ever raised. This upcoming harvest will likely be for the most valuable crop ever, both for its monetary value and for the reason that many of the countries’ harvests have been slim.

The old market place is beginning to put the many clues together, looking at the long string of 95 daily highs along with the record stretch of 75-degree-plus or warmer daily lows.

Then using their best plant physiology knowledge and past seasonal performance, surmised that trend line yields are not going to happen in too many areas.

Many growers across the Midwest who have been walking their fields have been seeing the same thing. None of them are selling their crop because they think a record crop is going to push the prices down.

Statewide rainfall

The next two weeks are going to be very important across much of the western Corn Belt. Until now the corn and bean crops have held on quite well in spite of the extreme heat, but now symptoms are beginning to appear that indicate yield loss may be occurring in both crops. While the corn’s maximum evapotransporation of .25 to .30 inches per day period has passed, daily usage is still close to .25 inch.

So depending on how deep the roots are and the moisture holding capacity of the soils, the crops in an increasing number of fields are going to begin showing increasing problems with aborted kernels or shed pods.

Such moisture depletion is gradual and could be measured using potentiometers. Plants can thrive at soil moistures above 50 percent. They become increasingly stressed between 50 and 20 percent of soil capacity, and then die at soil moistures under 20 percent.

One big effect of dry soils is that there is a reduced moisture flow into the roots and up the plant. This means that fewer nutrients will be taken into the plant and made available for plant processes. Look for these different signs to begin appearing.

Pollination

I have written in the past few weeks that over the years we had actually seen very few actual pollination problems. Well, in recent days I have been getting into more corn fields where there were scattered and erratic kernels pollination as well as many trip kernels that seem to have not received their pollen grain.

It is possible to find up to 60 bubble kernels on each ear. These were written about and described by Emerson Nafzinger from the University of Illinois as kernels that were beginning to fill, then had their nutrient supply pulled away, so turned into a shell filled only with a watery fluid. They shrink away before harvest.

It is becoming clear that many ears are going to be shortened by 1 inch to 2.5 inches by tip abortion. The depth of kernel fill is also being hit hard by lack of moisture and the extreme daytime and nighttime heat.

I was in fields yesterday and did not have a caliper with me to measure that depth on ears on plants affected by Goss’ wilt.

I found that three quarters stacked on each other equaled the kernel depth. That is a large reduction versus what is normal. Some of those ears are beginning to show the first denting.

Plant diseases

Growers and scouts who have been walking fields have been finding treatable levels of several diseases in both corn and beans.

Due to the high value of the grain this year making a fungicide application to protect those crops was an easier decision than in 2010.

In the previous few seasons, it made sense to try to protect the 10 to as much as 25 to 50 bushels that could be gained, but now that Goss’ is present, we actually have to realize that saving the entire field is what is at risk.

People that are now taking low-level flights across farm country or operating high-clearance sprayers are relating that the corn crop has changed colors in many areas.

Don’t be afraid to call a local pilot about taking you on such a flight to evaluate the crops in your neighborhood or a larger area.

The normal diseases of gray leaf spot, northern corn leaf blight, rust and eyespot are present. The new normal of Goss’ is also here and looks like it will be for the near future.

There was a corn disease found in north central Iowa last week that may be a new one for Iowa. We are waiting for the official lab results to get back to us.

We think it is fungal in nature and is dependent on high temperatures and humidity.

I was visiting with a very good plant pathologist about the state of this crop and when he expected the now abnormal “new norm” corn and bean decline to appear.

He said what is bound to happen to the corn is that the multiple stresses of heat and lack of moisture will begin to merge with nutrient deficient plants that have a shallow root system growing in soils where the fusarium levels are quite high.

The perceptive crop advisors and famers have been noticing the past 10 days and are expecting the worst fields and some of the most disease-susceptible hybrids to go into a quick decline.

The presence of SDS in many of those fields establishes that fusarium levels are high, and there are many mycotoxins formed by those fungal strains.

Thus grain quality from a toxicological standpoint needs to be examined before it moves into the food supply.

Expect more airplanes to be flying the next few weeks as combination fungicide mixes are applied.

Remember that now is when bred in resistance and nutritional status go far in boosting the plants’ ability to mount a natural defense against invading pathogens.

Recognizing this is why many presenters at winter meetings were preaching about the value of balanced fertility programs where the value and role of micronutrients were stressed.

Maintaining plant health through the development of healthy soils rather than using rescue chemistry is what more people have to evaluate and strive for.

Because Goss’ is a bacterial issue the rule is that fungicides do no good in treating it. The No. 1 rule is still to choose resistant varieties.

Procidic is an EPA-labeled bactericide and is being used currently. In most cases losing a crop is not an option if we intend to produce the grain supply we need.

Soybeans

The issues in soybeans that are beginning to appear are the appearance of spider mites and the first signs of SDS. Both can be found if you examine plants where conditions are conducive to them or the inoculum was present.

Septoria is the fungal disease that thrives in the humid lower plant canopy causing yellow leaves and leaf drop.

Aphid number are building north of U.S. Highway 20 and are now either building toward or reaching treatment threshold.

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

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