Renewable Farming

Consultant Bob Streit: What to watch for when scouting your fields in August

August is here and it is another pivotal month. Most of the grain fill for our #1 and #2 grain crops happens in this month. Timely rains, near full sunshine, warm days with cool nights and not too hot are what we are requesting for optimum yields and good standability.

If it were a horse race we would now be at 5/8ths mark. Anyone who counts a bumper crop as already being in the bin shows how little they know about raising crops or livestock. We can hope for the best but always be willing to accept the worst. So far in central Iowa we received rain on two weekends since May ended and not much else. The showers have been consistently routing across the southern third and northern third of the state, but not in the middle section. Small rains may arrive but we will need them going into what is predicted to be a series of 90 degree days.

Some of the best things about summer would have to be fresh sweet corn and icy cold watermelons. They are both in season now. Look for the eastern Nebraska raised melons raised and labeled by Greg Heldt from Yutan as they are superior in taste and texture.

  

Cropping Items: Everything looks good from the road, right. So things are perfect inside the fields… not so fast. Going by each field at 60 mph creates complacency and ignores how sections of the growing season have gone. Some of the field events that occurred in April and May could still catch up to us and our yields.

Poor stands and their effect don’t disappear just because the plants grew tall and made the problem invisible to someone at ground level. Strong winds that blew the corn down in major areas had an effect on the ability of the plants to fill the each to their maximum. The same winds also caused significant green snap in fields. Since some of the snappage was above the ear site we were hoping they would pollinate and reach full size. It has become apparent that ear size on snapped plants was reduced by 70 – 100%.

People and so-called experts have to remember that plants can be like people in that they have good memories and early events can have consequences. Remember the high temps in June when the plants rolled dramatically. Such stress can alter plant chemistry and they can respond in a very defensive way. We just don’t recognize what the responses are immediately

The biggest negative, which has just become visible, is that average ear size is smaller than normal in many fields. Planting date, hybrid maturity, available fertility, possible soil compaction and dry soils all seem to be factors that affected this. The largest and maybe the most influential could be the high number of days that have been cloudy and devoid of direct sunlight for much of the day.

Dry soils also limit the availability of nutrient uptake by the roots. Smaller means more ears falling into the 16 X 32 – 36 count than the hoped for 18 X 38 – 42. In addition there could be additional tip kernels aborting yet to go. This effect is being seen across a major portion of the Cornbelt as those factors were in play over a wide area.  

One oddity appearing in cornfields this year are plants growing a second ear as well as a so called mitten ear, where a small third ear emerges from the husk cover of the main ear. In certain fields, 50% of the plants are showing this tendency. One colleague with plant breeding experience is speculating that corn breeders have returned to inserting the so called ‘fasciation gene’. There could be some successful second ears forming, though a portion of the second ears are turning brown and slimy as bacteria invade these potential kernels sites.       

The term ‘greensnap’ refers to a short burst of wind in the two weeks before tasseling, causing the top half of the corn plants to snap off. As little as a half minute of wind can be enough to cause problems. We saw that in a few years of the mid 80s in western and northwest Iowa and thru Nebraska. A number of people tried to dissect the problem and identify the parameters and characteristics of plant vulnerability.

Having a plant full of moisture during the two weeks prior to tasselling increases susceptibility. Also at play was the level of silica in the cells. Do certain pesticides wipe out species of microbes that best make silica available? Making decisions over greensnap weakness is difficult because strong stalked varieties can be the most susceptible: Rigid stalks can be prone to snapping.

In the bad cases there were hybrids and field conditions where 90% or more of the plants were snapped and did not produce any ears. We are seeing this year that some plants snapped above the ear site but no ear formed.

 A number of things are happening in the soybean fields. The first is that the first signs of SDS began appearing last week. They first show up on plants pushing out their last set of trifoliate leaves. Concurrent with the appearance of scorched leaves is the presence of the blue snot showing up on the roots where solid nodules existed before. Thus far the nodules have softened but the blue stuff is not visible.

The SDS incidence rate could be increasing in the infected fields but may not be visible for a week or two. Quantifying its coverage and full effects will be easier after seeing what percent of each field had the right soil and weather conditions responsible for the Fusarium vulgiforma infection. Early planting seems to be the overriding factor so far. Doing everything else right, including the best seed treatment, but planting early, as around April 25, seemed to have increased susceptibility.

In heavily infected fields the long term solution appears to be adding a commercial seed treatment or in-furrow application of a Pseudomonas (P fl.) at planting time. Scientists have now identified four metabolites of P fl. bacteria that kill the causal fungus.

The soybean aphid populations continue to increase slowly but not explode. Stay vigilant, as the beans become the best host as the plants move into the R4 growth stage. It’s nice and proper to adhere to IPM principals and not apply an insecticide until the Treatment Thresholds (TT) are reached. However, the prospects of having to pay for an aerial application a week after making a ground trip causes many growers to act proactively.      

Another insect that we ignore now — but may not in the future — are the white flies present at high numbers. In South America, researchers have documented that different viral diseases are spread by the small flies. They employ more virologists, thus are ahead of us in their pathology diagnoses.

The rains of two weeks ago seems to have stopped the increase in spider mites in soybeans. The fungus that normally kills the small spiders dies out in hot and dry conditions. Also present in many fields are thrips, also known to vector diseases and mottle soybean leaves. They are small cigar shaped insects that scurry around on the lower leaf surfaces.

 Foreboding Thoughts

Soon the many waterhemp escapes will be poking above the soybean canopies. This will be after multiple products and applications were used to control them. Each year we and nature are helping select the plants most tolerant of whatever products or methods being used to control them. Because pigweed plants cross pollinate, the 2017 offspring of the two more resistant 2016 parents will be tougher yet than this year’s survivors. The use of rye or barley cover crops together with a two or three way mix or residual pre-emerge products are performing well. Cultivations is not always possible on erosion prone soils.

By crop consultant  Bob Streit, Boone, IA     August 1, 2016       515-709-0143

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