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Dig Up Some Wheat Plants....Now!! (05/26/16)

It's important for farmers and agronomists to examine wheat plants, about 6 weeks after planting, because the plants can "tell" you a lot about their overall health, and lessons can be learned, if you know what you are looking for.

Dig Up Some Wheat Plants....Now!!

It's important for farmers and agronomists to examine wheat plants, about 6 weeks after planting, because the plants can "tell" you a lot about their overall health, and lessons can be learned, if you know what you are looking for.

The above-ground portions of a wheat plant consist of a main stem, and a variable number of tillers. A normal, healthy wheat plant, at the 4.5 to 5 leaf stage of the main stem, should have a T1 tiller and a T2 tiller. The T1 tiller arises from the base of leaf 1, and is initiated at the 2.5 leaf stage of the main stem. The T2 tiller arises from the base of leaf 2, and is initiated at the 3.5 leaf stage of the main stem (Figure 1). If the plant is suffering stress, at the 2.5 leaf stage of the main stem, the T1 tiller may not be initiated, and it will not initiate later. If the plant is suffering stress at the 3.5 leaf stage of the main stem, the T2 tiller may not be initiated, and it will not initiate later.  In other words, the presence or absence of T1 and T2 tillers can tell us a lot about the early-season health of a wheat crop. 

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There is seldom 100% initiation of T1 and T2 tillers in the field, but 90% is a reasonable goal. In other words, if you examine 10 wheat plants, there should be nine T1 tillers and nine T2 tillers. If that is achieved, that means that plant health was good during the early stages. The plants were probably planted at a reasonable seeding depth, the seedbed was good for seedling establishment, and nutrients like N and P were likely in good supply. If there isn't 90% initiation of T1 and T2 tillers, questions need to be asked, problems identified, and corrections made for next year. The T1 tiller is sometimes not initiated, due to planting too deep, or perhaps the seedbed was too hard, or due to N or P deficiency. It is easy to diagnose whether or not the crop was planted too deep.  The length of the "white zone," the distance between the seed piece and where the stem turns green, is a reliable measure of seeding depth, after the soil has settled (Figure 2). The T2 tiller is usually the most robust tiller on a wheat plant, and if it isn't formed, N or P deficiency is usually the cause (Figures 3 and 4), and tissue analyses might be appropriate. One exception to the prior sentence is for the variety Bolles, which does not seem to tiller fully at the T2 position, even when given generous rates of N and P.

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Understanding how to differentiate between main stem leaves and the tillers is also helpful in differentiating between N deficiency and S deficiency. Figure 3 shows a typical N deficiency, with the yellowing on the lowest leaves. Figure 5 shows a typical S deficiency, with the oldest parts (main stem leaves 1, 2, and 3) green, and the youngest parts (main stem leaves 4 and 5, and the T1 and T2 tiller) being yellow.

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So, get out there, dig up some wheat plants, and start looking for T1 and T2 tillers. There are lessons to be learned.

R. Jay Goos

NDSU Soil Science Professor

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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