Crop & Pest Report


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Grain Filling Concerns in Small Grains (07/25/19)

Most of the spring wheat in the state is now well into the grain filling stage, with some winter wheat approaching maturity.

Most of the spring wheat in the state is now wellplsc.3 into the grain filling stage, with some winter wheat approaching maturity. Wheat’s yield potential (spike numbers and potential kernels per spike) is largely fixed prior to heading, and for most of the state, conditions have been favorable for high yield potential development.

It is during the grain filling period, however, that this yield potential is realized. Most of the carbohydrates (85-90%) that fill the developing kernels are produced by the plant’s green tissue, the remainder is translocated from the stems and older leaves. The amount of photosynthate that can be moved to the kernel is dependent on the amount of green tissue actively photosynthesizing and the rate of photosynthesis minus any respiration. Cool temperatures during grain filling, particularly cool night temperatures favor greater availability of photosynthates and therefore higher kernel weights and yield. The above average night temperate during the first two weeks of July may have negatively impacted the yield of this year’s early planted crop. The current weather, however, is favorable towards yield, and will greatly benefit some of the later planted crops.

Another factor that has the potential to limit yields this year is Bacterial Leaf Streak (BLS). In regions of the state that have had wind-driven rains (these conditions favor infection of BLS), this disease has become severe, especially in varieties that are highly susceptible. In some fields that I have visited, there is very little green tissue remaining on the flag leave (see Figure 1). The amount of yield reduction that this foliar disease will cause depends on factors such as the timing of the infection, and its severity. I have seen some recent information that suggests between 20 and 40% of the carbohydrates moved to the kernels are produced by the tissues in the spike (glumes, awns and kernels themselves). The majority of the photosynthates must arise from the leaves (largely the flag leaf) and stem with an additional 10 to 15% of the carbohydrates being translocated from the stem. Therefore, early infections of BLS that burn most of the flag leaf have the potential of severely reducing grain yield. There is no practical means of controlling BLS in-season, but there is some level of genetic resistance available in a few cultivars. Certainly, if you are experiencing high levels of BLS infection this year and you are using a variety that is susceptible, consider using one with greater resistance in the future.


Joel Ransom

Extension Agronomist, Small Grains and Corn

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