The month of August is slightly more than half over. With it is the realization that the growing season is nearly completed, but in many cases the grain deposition part of the final yield still has to occur, so conditions still have to remain favorable for things to end up on a positive note.
Adequate rainfall, decent temperatures, lots of sun and lower humidities to squelch the leaf diseases that have become so common in a high percentage of the fields will affect the final yield tallies. By now most of the applications that could influence the yields have been applied. In most cases only airplanes or taller high clearance sprayers could make it through the corn fields during the last month.
It has been interesting to see that there are again advertisements and for-sale ads in local and regional media publication for bean bars, weed wipers, banders, and other later season applicators. Growers regrettably are reverting to the older tools to manage weeds as Nature and the value of a diverse gene pool continue to display the ability to mutate around single tactic control strategies.
Last week was a bad time for commodity prices. What sparked the reports of much better fill conditions? I had the chance to see the Illinois crop last week and it was anything but record setting. Much of the corn was only fence post high with many drowned out spots and much delayed maturity. Then to add insult, conditions have turned much drier, to the point that the high spots were being lost to lack of moisture. Those problems come on top of the monsoon conditions from Texas and Oklahoma up thru the eastern Cornbelt including KS, NE, MO, Ill, IN, OH and PA. They are not curable, no matter how August weather turned out.
The grain fill is continuing with late milk and dough stages becoming common in most areas. In a few fields and with certain hybrids, the dent stage has been reached for several weeks. Such early denting is typically thought of as a negative, as fill time can be reduced.
The leaf diseases have gotten worse in many fields, but not as bad as they could have been, with weather having been warmer and drier from mid-July to Mid August in many locations. Wet leaves along with lots of inoculums is a perfect situation when a high percentage of the plants seem to be so susceptible to both older and newer diseases.
Three prerequisites to disease problems in fields: a suitable environment, disease inoculums present and a susceptible host. Other than managing profile moisture via field tile, a non-irrigated grower can’t do too much about rainfall. The inoculums level is influenced partially by the amount of residue, but some residue is good in that it can reduce erosion.
So that leaves only the category about creating a much more resistant host plant that is able to ward off the disease because it is energetically and nutritionally strong.
By now most corn growers have read that a new stalk disease called Physoderma stalk rot was rediscovered a few years ago after it had basically not seen for quite a few decades. Those published pictures sure look a lot like the symptoms we have been noticing in the fields since about 2009 and can be found in high percentage of the Midwest corn fields.
When I first got a copy of the report, I talked to few close acquaintances and their responses were varying, such as “they had not heard much of that disease since the late 60s and early 70s in their role in plant disease govt. studies” or ‘Seed companies must have gone back to some very old and very susceptible germplasm sources if it is a problem again.”
So assume there is a story behind the story when you see it in your fields. Current wisdom is that controlling it via chemicals is next to impossible since the infection occurs very early and becomes internal until the root begins to rot later in the season. The spores produced are very numerous and remain viable for 8+ years.
Right now there are two products that have done a good job of keeping plants healthy and productive under this disease pressure. I hope to place 40 acres of the advanced version of one of these to measure the yield response. I need a few growers with Millers or Walkers that offer sufficient clearance. Are there any takers on this offer? Six years of good results among growers say that successful treatment is possible.
Otherwise, the NCLB and GLS have gotten much worse in many fields and the effects are being seen as tip back in Illinois fields, ranging from 2” to 5”. When the leaf tissue has been lost the plant has lost the capacity to meet starch demand. In future years the obvious and most sustainable solution is to address the nutritional deficits existing in the plants early so they maintain more disease resistance. Spraying late can have a beneficial effect, but it would be money not wisely spent when compared to having any labeled products applied in the blister stage or before the lesions become numerous on the plants.
Given the fact that there are so many leaf diseases causing problems in Midwest corn fields, more people need to recognize the problem does not stem from the presence of some new fungal or bacterial inoculums, but from an overall decline in health of the plants.
It will require a systems approach to understand the problem and develop a more holistic approach to overcome these diseases. In time each of the fungicide families can and will fall victim to resistance occurring due to repeated exposure. Early and mid-season tissue and sap testing are a good method of detecting plant vulnerability.
Now is good time to wander thru early field and see how the pod counts and seed fill is progressing. In most fields the closing of the rows increased humidity levels and produced more hours of leaf wetness. Septoria and Downey mildew love those conditions and they did appear in a high percentage of the fields.
SDS has also become problematic in scattered southern Iowa and Northern MO fields. The strategies of applying micronutrients in the early V stages or seed treating with the ILeVO product seemed to have helped eliminate the problem.
SDS is a sign of a serious Fusarium root infection. That fungus attacks and causes problems a wide range of crops, thus maintaining a crop rotation does not help as much as we would like. Many of the infected fields did show the slight color change in June that is an early indicator of the roots having become infected.
At this point the plants will have to form and fill more pods to compensate for the lower podded node counts. Extra branching and added seed size can help. Keeping more leaf tissue green and photosynthesizing as well as making sure the nutrients are available either thru soil or applied foliar nutrition is the best tactic to maximize seed fill.
What is August if we did not have aphids? Actually this insect is a lot spottier than in previous years. Remember that they love nitrate nitrogen and simple sugars and are attracted to fields high in those two elements. Three weeks ago most of the aphids were being found on the upper set of developing trifoliates. Once the plants develop into the R4 growth stage the plants’ physiology changes and all of the leaves become much richer in nutrition and serve as a suitable food source for the little sap consumers.
Dow AgroScience released a new product this season that serves to control aphids but is much safer to beneficial insects. It needs to be applied earlier and before the numbers increase dramatically. Keep an eye on the Transform WG product as it would be a preferred product to use. It should reduce the potential need to respray. Fewer people, even operators, like the smell of the OPs and the nasty features they possess.
For specific information, call Bob Streit, Boone, Iowa 50036 (515) 432-0907