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Growth Staging Cereal Crops

Joel Ransom

May 28, 2003

The next few weeks are extremely important in determining the yield potential of cereal crops. Yield can be described as a function of the genetics of the crop, the environment and management practices. You can�t do a great deal about the environment, and now that decisions on which varieties/hybrids to plant have been made and the crop is in the ground you can�t do anything about the genetics. What remains is to ensure good and timely management in order to optimize the varieties planted with the prevailing environment. Timely application of management practices is critical to achieving high yields. Since crop growth and development is affected by the environment and by the variety or hybrid grown, the recommendations for most management practices for which timing is important (e.g. fertilizer topdressing and herbicide application timing, etc.) are based on crop growth stage, rather than calendar date. Therefore, being able to properly identify the growth stage of your cereal crop will be important to ensuring that management practices are applied at the appropriate time. In this article I will briefly review how to determine the growth stage of your cereal crops.

There are a number of different scales (i.e. Feekes, Haun and Zadok) that have been developed to classify the growth stages of small grains. These growth stage scales are commonly used by researchers when describing experimental methods and results in scientific publications but less so in communicating recommendations to farmers. The timing of management recommendations are most commonly based on leaf numbers or other visible characteristics of the plants. Therefore, in this article I will focus on how to assess these various characteristics and will not delve into the details of growth scales.

When growth staging your crop you should begin by obtaining a representative sample of plants from the field or part of the field of interest. To give you a good feel for an "average" plant, use ten plants selected at random away from the edges of the field. Remove any soil attached to the plant so that you are able to observe the roots and crown. Leaf stage is the most common physical feature used to describe early development of small grain crops. Leaf stage is defined by the number of leaves that have visible collars on the main stem. Care must be taken to ensure that the earliest leaves are included when counting. The first leaf is small and is frequently lost from the plant during normal growth. It has a characteristically blunt tip. Look for the sheath remnants at the crown of the plant if you suspect that the first leaf (or second for that matter) is missing. Count only the leaves on the main stem, which is the tallest and most leafy of the stems. Include only those leaves that have a collar. When staging plants include all leaves, even those that have been damaged by hail or frost. The total number of leaves that a plant will developed is more or less fixed for a given variety; leaves that are striped from the plant will not be replaced by additional new leaves.

Each tiller produced in addition to the main stem is numbered when it becomes visible. There are two types of tillers: those arising from a crown leaf axis and those arising from the coleoptiler node. Only tillers arising from a crown leaf axis are counted when staging. These tillers are also surrounded by a small membranous structure, called a prophyll, that is useful to distinguish axillary tillers from main stem tillers. When present there will only be one coleoptiler tiller.

Sometimes it is useful to be able to estimate or predict when a certain growth stage will be reached. Plant development is closely correlated to the accumulation of heat units or Growing Degree Days (GDD), much more so than calendar days. Based on plant emergence and historic temperature trends, you can fairly accurately predict when a crop will reach a certain developmental stage. Growing degree days are readily available for a number of locations in North Dakota using the NDAWN website (http://ndawn.ndsu.nodak.edu).

Wheat requires about 140 GDDs and barley about 100 GDDs to produce a leaf. The actual number of GGDs required can vary between varieties, but these values will give estimates that will be accurate enough for most applications. Be sure to use GGD that were calculated for small grains which use a base temperature of 32 degrees. Other base temperatures are used for corn and sunflower and certain pests.

As an example, if you wanted to know what stage your wheat crop would be in at the end of the week, you could estimate it by using either historical weather data or predicted weather data. Fargo accumulates about 29 small grain GGDs daily during the last week in May and 31 GGD per day during the first week of June. Using these data, you could expect wheat to produce 1.5 leaves during the last week of May and 1.6 leaves during the first week of June. Barley could be expected to produce 2 and 2.2 leaves per week during these same periods.

Early staging of corn is very similar to that of small grains. The above information regarding the selection of plants used in assessing growth stages applies to corn, though if you have uniform emergence you can probably get by with looking at fewer than 10 plants. Corn rarely produces tillers, so the vegetative staging focuses only on leaf numbers. Leaf stage of the corn plant is determined by counting the number of leaves with visible collars. The first leaf, which is often hard to find intact on the plant, is short and has a rounded tip. So the process is fairly straight forward, find the first leaf and count the leaves with collars.

In corn, management recommendations are frequently made based on the height of the plant (rather than growth stage). For example, certain herbicides can only be applied to corn less than 12 inches tall. The plant height in this case is measured from the base of the plant to the highest point that the leaves reach without stretching them out. Leaves tend to droop as they get larger and plant height during early growth is a measure of where the natural canopy of the crop reaches (not how high the upper most leaf extends if pulled straight).

The same principles described above for predicting the appearance of leaves in small grains also apply to predicting the appearance of leaves of corn. Corn growing degree days, however, are calculated using a different base temperature (50 degrees) than small grains. Corn requires about 100-125 corn GDD to emerge after planting. During early development (up to 10 leaves) leaves appear after about every 85 GDDs. Based on long term data, in Fargo we typically accumulate 12 GDD daily during the last week in May and 13 GGD daily during the first week in June. Using these data, you could expect corn to produce roughly 1 leaf per week during this two week period. You can find more on predicating growth stages using GDDs at http://www.agry.purdue.edu/ext/corn/news/articles.03/LeafStagePredict-0520.html.

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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North Dakota State University
NDSU Extension Service