Section 2 - Crop Development

Relative Maturity of Field Crops

Following is average days to physiological maturity of many crops grown in the Northern Plains. Early killing frost plus extreme high temperatures at flowering stages are the two factors most limiting yields of late planted crops. Time required for maturity varies with variety or hybrid, seeding date, geographic region, and available growing degree days. A shortage of growing degree days can increase days required for maturity. Corn, soybean, sunflower and millet are especially sensitive.

Tracking Growth Stages, Growing Degree Days

All grain plants follow the same general pattern of development, although the specific time interval between stages, the number of leaves and nodes on the main stem and the number of tillers will vary by variety, season, planting date and location. As well, the amount of growth for any variety is directly related to nutrient and moisture availability.

Still, the rate of growth development for any wheat variety is directly related to temperature (accumulated heat units), except under extremely dry conditions. Thus, by knowing the planting date for wheat, and by tracking weather data, one can predict growth development and plant stage. This helps growers make timely treatments to control weeds, top dress fertilizer, control diseases, and other management decisions.

The North Dakota Agricultural Weather Network (NDAWN) can help growers keep track of weather and growing degree days. On NDAWN’s Internet home page (http://ndawn.ndsu.nodak.edu) click on the “applications” link. There, you will find a number of applications for using NDAWN, including:

• Predicting Sclerotinia risk in canola

• Corn degree days

• Potato late blight severity

• Sugarbeet degree days,

growth stages, cercospora

• Sunflower degree days

• Wheat degree days, growth stages, disease forecasting, midge forecasting

• Crop water use

• Insect degree days

• Heating/cooling degree days

For wheat, the GDD information can be used for determining date of emergence and current growth stage. Current leaf stage provides information, for example, on when herbicides are needed and when the crop is too advanced for certain herbicides. If frost or wind damage causes loss of leaves, the GDD information provided by NDAWN would allow correct leaf staging in absence of some leaves. Correct growth staging also is important for fungicide decisions.

Consult with an agronomist, certified crop adviser, or county extension agent/educator for more background on growing staging crops, or about how to apply NDAWN information. NDSU has a publication online, “Identifying Leaf Stages in Small Grains,” at www.ag.ndsu.edu/pubs/plantsci/weeds/w564w.htm. The University of Minnesota publication “Growth and Development Guide for Spring Wheat” can be found online at www.extension.umn.edu/distribution/cropsystems/DC2547.html.

Effect of Environment on Growth,Development and Yield of Small Grains

The following describes how temperature and water stress impacts small grain development and yield at key growth stages.

Emergence to Four-Leaf Stage -- During the vegetative phase of development, from emergence to about the four-leaf stage, growth is directed towards new leaves and tillers. All leaves that will emerge on the main stem are initiated during this stage. Tillering begins at about the 2-leaf stage but tillers do not become visible until the 3rd to 4th leaf stage. The total number of leaves (typically 8) that will develop is primarily determined by the genetics of the variety and is rarely altered by the environment. The only yield component that is fixed at this stage of development is plants ft-2. Yield potential is generally not adversely affected during this phase except by severe moisture stress or very high temperatures.

Four-Leaf to Jointing -- At the four-leaf stage, the plant switches from vegetative to reproductive development as the growing point begins forming the spike. Shortly after the six-leaf stage the main stem begins to elongate (begins jointing). Spikelet numbers are fixed in this relatively short period of about 10 days between the four-leaf stage and jointing. Though tiller development can continue beyond this stage, most tillers that produce spikes that contribute to yield will form by the beginning of jointing. Drought stress and elevated temperatures can reduce the number of spikelets that develop and induce tiller mortality.

Jointing to Anthesis -- During the period from jointing to anthesis, tillers that cannot be supported by the plant die and the number of spikes per plant and the number of florets per spikelet become fixed. Most physiologists seem to agree that yield is most affected by stress during this phase. Any stress that will reduce the rate of photosynthesis (i.e. high temperatures, drought, foliar diseases, competition from weeds) will impact yield potential by reducing the number of tillers that survive and the number of florets that will be fertile. It is in the previous growth stage that most of the potential components of yield are developed, but it is during this growth stage the components that will actually contribute to yield are fixed.

Anthesis to Physiological Maturity -- After anthesis the number of kernels per plant is fairly well established, though some kernel abortion can occur early in the grain filling process. Any stress that will reduce the rate of photosynthesis can impact the weight of the kernel. High temperature and drought during this stage typically produces kernels with low seed and test weight

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