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Erratic Weather and Early Season Cereal Crop Development

May 15, 2003

Joel K. Ransom, NDSU Extension Agronomist for Cereal Crops

As a newcomer to North Dakota, I have been surprised by the wild swings in our spring weather this year. After talking with a few "old timers" and reviewing climatic data for the past 30 years, I now appreciate the fact that we are currently enjoying a "typical" (variable and unpredictable) North Dakota spring. The first few weeks of spring represent only a fraction of the total growing season, but the weather during the first few weeks after planting can have a dramatic effect on the overall productivity of a crop. Although there is little one can do to change the weather, there are a few management practices that can be employed to reduce the detrimental effects of adverse weather and exploit the "opportunities" of good weather. During the last month, temperatures have varied from above average in April to below average in May. April was unusually dry, and May has been wet. In the last week there have been reports of water logging, hail damage and freezing temperatures.

The warm and dry weather of April enabled many farmers to plant their small grains early. These early planted crops have now emerged and after the recent moisture and cool days, are beginning to develop nicely. One farmer that called me earlier this month said that his crop of wheat was the best he had had for years. Planting early generally favors the development of high yield potential in small grains as it enables the seedling to be exposed to cooler temperatures, which promotes the development of more uniform and larger spikes and a larger leaf area to support the filling of these larger spikes. Planting early is a management practice that can consistently enhance productivity in small grains.

Many farmers were able to plant some or all of their corn before the heavy and widespread rains that begin on May 3^rd put the breaks on planting. May 1^st is considered the optimum date for planting corn in all parts of the state. Corn germination, emergence and early growth requires warmer temperatures than small grains, but high yield potential in corn is also favored by moderately cool temperatures during the early growth and development of the corn plant. I have heard reports that corn is starting to emerge, but the corn I planted the last week in April in Fargo has not yet seen the light of day.

Plant growth and development is closely related to the accumulation of growing degree days (also referred to as heat units and growing degree units). Growing degree days (GGD) are calculated by summing for the period of interest the average daily temperature [(max + min)/2] minus a base temperature that is crop dependant (e.g. 32E for wheat and 50E for corn). GDDs can be obtained for a range of locations in ND from the NDAWN website (http://ndawn.ndsu.nodak.edu). Table 1 lists the growing degree accumulations for selected sites in ND for both wheat and corn for this year.

As mentioned previously, the early planted small grain crop has emerged and currently has between 2.0 and 2.5 leaves (see Table 1). Until the four leaf stage, small grain plants are initiating new leaves. The yield component of plants per given area is more or less fixed at this stage (some plants may die but no new plants are likely to emerge). The most important tillers develop during the 2 to 3.5 leaf stage of the main stem. Any stress during this time may hinder the development of these tillers and the adventitious roots associated with them. If they do not form at this time, they cannot develop later. The reproductive phase begins shortly after the 4 leaf stage. It is during the reproduction phase (4 leaf stage through to flowering) that the vast majority of the yield potential of the crop is established. Tiller numbers, spikelet per spike and grains per spikelet are all fixed during the reproductive phase. Not surprisingly, any stress during this stage can have a dramatic effect on yield. As mentioned previously, controlling the weather is not feasible, but some abiotic and biotic stresses during this period can be managed. Nitrogen stress should be eliminated through top dressing before the 6 leaf stage (more on that elsewhere in this issue). Similarly, weeds should be controlled in a timely manner so that they do no interfere with the growth and development of the crop at this stage.

Corn typically requires an accumulation of about 125 GDD from seeding before it emerges. As you can see from Table 1 we have some heat units to go before we reach 125 GDD throughout the state (assuming a 1 May planting date). During cool springs, corn can take between 28-35 days to emerge. Emergence is slowed when seeds are planted deep, in soils that are heavy and/or that have a heavy residue cover, and when soils are drier than optimum. Don�t get too concerned if emergence takes up to 30 days during a cool spring. Most seed treatments provide protection from insects and diseases for more than 45 days.

With the continuing rain, I am now becoming concerned that corn that has not already been planted might be planted too late. Corn yield can decline by 15% if planting is delayed from the 1^st to the 20^th of May. After the 20^th of May it is recommended that you switch from your full season hybrid to an earlier maturing one. In the many states corn borers cause more damage in late planted corn than in early planted corn, making the use of a BT hybrid a more profitable option for later plantings. There is no data, at least that I am aware of, that would indicate that later corn plantings suffer greater losses from stem borers in North Dakota. Nevertheless, it may be something for you to consider if you are faced with switching hybrids and planting late.

NDSU Extension Service, North Dakota State University of Agriculture and Applied Science, and U.S. Department of Agriculture cooperating. Sharon D. Anderson, Director, Fargo, North Dakota. Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. We offer our programs and facilities to all persons regardless of race, color, national origin, religion, sex, disability, age, Vietnam era veterans status, or sexual orientation; and are an equal opportunity employer.
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