September/
October 1998
University of Minnesota Small Grains Specialist
Library
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Prairie Grains is the
official publication of
the Minnesota
Association of
Wheat Growers,
North Dakota Grain
Growers Association,
South Dakota Wheat,
Inc., and the
Minnesota Barley
Growers Association.
The final analysis on this year's small grain harvest won't be complete until later this fall. It is apparent, however, that the Red River Valley will have better wheat yields and wheat quality despite the development of scab early in the season. Scab does not like dry, hot weather (temperatures over 85 degrees) hence, the heat helped to keep scab damage in check. Barley didn't seem to fare as well, however; tight industry standards and the presence of vomitoxin once again limited the acceptance of a lot of barley for malting.
This harvest brought a number of grower questions, including whether the use of fungicides paid off or not. A few of these questions and subsequent observations:
Did the fungicides control scab?
Yes, the fungicides, if applied on time, suppressed the incidence of scab. It did not eradicate it, but gave similar results to other years; as much as 50% less incidence of scab in the field. It is, however, good to remember that the fungicides were applied not only to suppress scab, but also to control other foliar diseases like tan spot, septoria, and powdery mildew. All of these diseases can cause substantial yield and quality losses as well. The fungicides gave excellent control for the above mentioned diseases. Since the scab outbreak in 1993, growers and crop scientists alike are learning more about the effective use of fungicides every crop season. Fungicide trials conducted by NDSU this summer will tell us more about the additional benefits of variations in application technology. You will hear others and me discussing results of these fungicide trials and other fungicide research work and comparisons in the off-season.
Does a fungicide delay ripening and slow dry-down?
No, a fungicide does not delay ripening or slow dry-down - instead it prevents premature senescence (plant maturity) because it keeps the plant healthy and free of diseases like tan spot or septoria. In other words, untreated fields mature faster because diseases have killed the plants. A fungicide-treated field will stay green a little longer, but the payoff is additional yield and quality.
I saw 60-bushel straw, but got only 40-bushel grain in the hopper!
There are two possible explanations for this observation. First, most of the initial infections of scab did not produce any kernels or very shriveled tombstones. These will blow out the back of the combine. Thus resulting in less bushels per acre. Secondly, remember that a lot of our newer varieties are taller wheat cultivars. In our search for more scab-resistant wheat varieties, we have turned away from semi-dwarf wheat cultivars like Wheaton, Norm or Marshall and have substituted them with tall wheat cultivars like Russ, Sharp, Forge, Gunner.
In crop physiology, we have something we call harvest index, which is basically the ratio of straw versus grain. It is the portion of the total above ground bio-mass that we keep (in this case the grain). The harvest index for many of the tall wheat is 50%. One of the reasons why semi-dwarfs are higher yielders is the fact that their harvest index is 55%. In other words, we have come accustomed to semi-dwarfs like Marshall and have a mental picture of the expected yield based on the way the crop looks like. A thick lush crop should yield more grain. Well, a tall wheat will produce more straw for less grain. We have to adjust our mental picture of what grain yield looks like.
Why is my swather covered with rust?
Well, maybe it needs a new coat of paint. Just kidding!! Actually, leaf rust was present in many fields later in the season. The reasons for that are twofold. First, a number of varieties are susceptible to a new family of leaf rust races. These so-called T-races are becoming more predominant and are virulent on some of our hard red spring wheat cultivars like 2375 and AC Barrie. This is not a reason to panic and switch away from those varieties. We have excellent control options and the chance of an epidemic early in the season are small enough. As the crops mature, a leaf rust infection will cause less yield loss (see Table 1). In addition, most varieties will start to show some low levels of infection later during the grain fill period as they approach physiological maturity. The resistance breaks down and the plants will become more susceptible to the disease. Since most of the dry matter already has accumulated, there is little effect on grain yield and quality.
Why did I have more wheat lodging?
The switch to taller varieties as discussed above is also contributing to more problems with lodging. Semi-dwarf wheat varieties generally have better straw strength and better resistance to lodging when compared to standard height wheats. It's as simple as tall trees catch more wind. Of course, there are differences between varieties for straw strength even if they are the same height. Some of our newer releases like Russ, Bacup, Forge, and Ingot have indeed very weak straw and tend to lodge a lot quicker. The early planting and cooler temps in May also allowed the crop to grow taller in comparison to previous years when the crop was planted two to four weeks later. n