No. 8 Article 3/May 16, 2008

Wet and Waiting: Notes on Crop Planting and Emergence

While Illinois farmers made unexpectedly good progress in going from 28% of the corn crop planted on May 4 to 60% planted on May 11, there is considerable concern that the crop was planted under less-than-ideal conditions in many fields and about the slow emergence we are seeing. Only 12% of the crop, or a fifth of planted acreage, had emerged by May 11. That is mostly because more than half of the planted crop was planted during the week before May 11. But the wet, cool conditions that have developed or persisted over parts of Illinois during the past few days also are cause for concern about how well the planted crop will emerge.

Corn usually emerges once 110 to 115 growing degree days (GDD) have accumulated after planting. The April 8 and April 23 plantings that we made in the planting date study here at Urbana emerged in about that range, though there were stragglers from the first planting, due mostly to physical barriers (clods) that made it necessary for seedlings to grow longer before they reached the surface or to wait until the soil crust was softened by more rain. The second planting emerged much more uniformly. Fields in the Champaign area that were planted the last week of April have also emerged in the 10 to 12 days that it took for adequate GDDs to accumulate.

We can't make soils warm up more quickly, but we can use the GDD guideline to tell us when corn should be emerging, and perhaps to take action to help it emerge if that's not happening. So far in May, GDD accumulations have been running somewhat behind normal. Data from the Midwest Climate Information Center indicate that from April 25 to May 14, only 95, 125, and 160 GDD have accumulated in northern, central, and southern Illinois, respectively. From May 1, these totals are about 20 GDD less than this in the northern half of the state and about 40 GDD less in the southern half. So corn planted on May 1 in northern and central Illinois would not be expected to have emerged by now, though it should have sprouted and, in central Illinois, have the coleoptile tip moving close to the soil surface. Days with highs in the 60s, when GDD accumulations are in the low single digits, do not help speed up the emergence process much.

Much of the planted corn I saw on a trip to southern Illinois on May 13 was in very wet field conditions, having received up to 5 inches of rain since it was planted. Many soils in southern Illinois tend to stay wet on the surface due to lack of structure and poor internal drainage, and in such fields the seed is sitting in saturated soil. The main problem with saturated soils is lack of oxygen, which seeds need to germinate. The cool temperatures that persist might help the seed survive longer under the limited oxygen conditions in saturated soils. First, lower temperatures mean lower levels of physiological activity on seeds, and so lower requirements for oxygen. Secondly, cool water holds more dissolved oxygen than warm water, so seeds will survive longer and may even start to germinate while soils stay cool. But some diseases of seeds and seedlings are also more active in cool, wet soil, and so the race is on about whether these plants will emerge. Corn planted on May 1 in southern Illinois should have almost enough GDD to be emerging by now. If seeds planted then have not produced a root or shoot yet, there is a good chance they are dead. In any case, be ready to replant some fields or parts of fields if they have stayed very wet since planting.

Soybean. Soybean planting progress remains slow, with only 7% of the Illinois crop planted by May 11 and very slow progress since then. There are similar, but even greater, concerns about getting a stand from planted soybean seeds as I described for corn. Soybean seed needs more oxygen, disease pressure is often worse, and the emergence process is more difficult. So we expect even greater problems with soybean emergence than with corn emergence under cool, wet soil conditions. We hope that soils will warm as they dry, so that by the time we can plant the rest of the soybean crop the conditions for emergence will be much better than they are today.

Wheat. The wheat crop in south-central and southwestern Illinois appears to be in relatively good condition, although the cool and cloudy weather has kept it from developing the dark green canopy color we would like to see. The crop is also late in heading, with only 17% headed by May 11, compared to 67% headed by this date averaged over the past five years. Tiller numbers appear to be reasonably good in most fields, meaning that head numbers should be average to above-average. There are few leaf diseases in most fields, though I did see some fields in Randolph County that were badly infected with barley yellow dwarf virus. The infestation was more uniform than we normally see with fall infection, which often occurs in circular patches as a result of aphids spreading the disease from where it started in the field. In this case, it's likely that infection took place in the fall, since conditions then were much better than they have been in the spring for spread of aphids. I am guessing that the symptoms are so uniform and severe due to very large numbers of infected aphids that moved into the fields last fall. Fields where a seed-applied insecticide had been used showed considerably less BYDV.

Another problem with wheat is occurring where the crop is standing in water, in some cases for the second or third time. Compared to dry springs such as we had in 2007, the root system in this year's wheat crop has likely been compromised to some extent by the fact that soils have not dried out much. Roots proliferate poorly in soils that stay wet, and it's possible that some of the N applied in these fields has moved to below the zone of active roots. Nitrogen spread patterns are easy to see in many fields, not because application uniformity was unusually poor but because the crop has not had much chance to explore the soil and to take up the N that is there. The pale color of the crop in many fields is related to this, but also to the fact that there has been less sunlight on these fields than we would like. One benefit of dry weather is that it is accompanied by high sunlight. With a large amount of growing and grain filling to do over the next month to six weeks, the wheat crop will benefit greatly from a return to sunnier days.--Emerson Nafziger

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