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By Staff | Aug 28, 2009

There is now less than one week left in the month of August and we are left wondering, “where has our summer has gone?”

In 2008 most Iowa farmers scraped by a very scary cropping situation by receiving an extra two weeks of growing season and an ideal, warm and sunny month of September. Will that scenario repeat itself or reverse itself to give us a mid-September frost to average out the two years? There will be a large number of very nervous growers and grain buyers in a few weeks who will be paying close attention to nationwide weather predictions and reports.

It is too bad that the most expensive crop most farmers have ever planted may not get to produce to its potential. Too much disease pressure has been a problem in both corn and soybeans since July when eyespot was first found in corn weeks before normal.

That corn disease has been followed by four other major diseases in fields that were either planted to susceptible varieties, had too much residue, or lay with the wrong topography.

Corn leaf diseases

There are years where growers just think crop scouts or retailers have been crying ‘wolf’ about certain disease or insect infestations. This year all the hoopla about leaf diseases in corn appears to be real in much of southeast Iowa.

The wet spring and early summer conditions have been followed by a wet late summer while much of the western half of the state has dried out. Thus the major leaf pathogens have reached extremely heavy levels in many cornfields and can be expected to have a major effect on yield and standability.

It is possible to walk into a field and find that half of the productive green tissue on the leaves has been melted into a mass of diseased tissue that has turned brown and crispy. Wet conditions will get most of the blame, but also having to share the blame will be the planting of some very susceptible genetic families that were not chosen for their disease resistance.

Magnifying that was the huge amount of inoculants present in last year’s undecomposed residue.

If you were to travel east on I-80 towards Iowa City and Davenport the yellowed or browned fields outnumber the green ones. The use of fungicides helped to keep the diseases at bay, though a better solution needs to be developed long-term to solve the problem.

As we saw last fall when high winds on Oct. 26 blew many corn stalks over such problems can have a huge effect on yield and harvestability of the crop. The problems are not as bad as you move west in the state, yet there have been quite a few fields that were sprayed with airplanes or ground rigs in July and August to keep the disease from becoming severe.

Soybean diseases

By now most growers who will be spraying their beans for diseases have done so with most making that application about three weeks ago. Where products were applied the septoria, cercospora and downey mildew were controlled. The one disease that seems to be resurrecting itself is the mildew.

One can see the cottony threads on the undersides of the leaves again. Like other diseases it acts by metabolizing sugars that are necessary for seed fill.

A pair of diseases that are now gaining attention within the grain trade and among farmers east of Iowa Highway 14 are sudden death, or fusarium solani, and white mold, or sclerotinia sclerotium.

Because much of that portion of the state has stayed very wet since spring the infections took place very early and are now producing the later stages of infection and killing the plants. In the past both pathogens have proven capable of causing complete yield loss, with the percent loss determined by the percent of grain fill period that was lost.

In many of the fields the plants went from dark green on Monday to yellowing by Friday with dead spots by Sunday. Some fields will be seriously affected. Causes of SDS are typically saturated soils in June and deep compaction that limits water drainage. The disease infects in June and shortly after the last leaves are extended the leaf-scorching toxin is translocated to the leaves.

If one is looking towards the treatment for SDS it sounds like a biological inoculant that proven successful in treating the pathogen in previous years can be applied to the seed and should be available next season. That would be done after the deep compaction layers have been broken. Foliar MN and CU have also been shown to help the plants.

Bean insects

Lately it has been interesting to see an aerial show involving the big type of dragon flies where they make their swooping passes over the top of heavily infested soybean fields. They must be catching winged aphids as they take to the air. Based on surveys it looks like the aphid numbers are still rising in about 25 percent of the acres, mostly in southeast Iowa where crop maturity is late.

They are holding steady on about 50 percent of the acres, and falling in the final 25 percent. They should be ready to leave when the two local triggers of daylight hours Aug. 7 and nighttime temp of 45 degrees are reached.

In the four bouts where we have fought them they disappeared in chronological order Aug 15, Aug 22, Aug 24 and Oct 12. Thus we can only speculate on when they will grow the generation that forms wings, leave the bean fields, and fly to the treed areas to form the generation that will lay the eggs that will then over winter.

In my scouting I have pulled the trigger with growers on three more fields this week as the numbers climbed above 250 per plant and there were still pods needing to fill.

Crop tours

The Pro Farmer Crop Tour was run last week utilizing an eastern and western route through most of the major grain corn and soybean producing states last week. The scouts who come from a wide variety of professions, though definitely not trained plant pathologists, had to jump out of their vehicles every 15 to 20 miles and walk into fields to make ear-and-kernel or plant-and-plant counts to gauge what the yield prospects were for the respective crops.

The Spencer meeting was interesting to attend. By then they had only the Thursday inspections to make before forming their Midwest wide crop size estimate. What their summary pointed out was that the crop size looked bigger in the southern part of the western corn belt and on time, while the crops in the northern part was two to three weeks behind normal and was not guaranteed to reach maturity before frost.

Their findings and summary in Austin told of the eastern cornbelt acres being much behind normal and highly dependent on a late frost as well. Pod counts were well behind normal out east.

Kernel counts were high yet as many of them had not advanced past the early milk stage, thus the normal tip kernel abortion had not yet taken place.

This is also time to continue getting harvest equipment and grain storage facilities ready.

A few of you may head to Decatur to the Farm Progress Show. Enjoy it all and be safe.

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