Many reports of disease on the wheat crop have come in the past week. Crop Systems Educator Robert Bellm at the Edwardsville Extension Center and Dennis Epplin of the Mt. Vernon Extension Center both report take-all. Epplin also reported numerous other diseases, including barley yellow dwarf, leaf and glume blotch, and leaf rust. Omar Koester, Randolph Extension Unit, reports minimal head scab as well as take-all. That's a lot of take-all; why?|
Take-all is a foot and crown rot of wheat that becomes very obvious at heading. It is a somewhat dramatic name, but that is what the disease does: it takes all the grain. The soilborne fungus Gaeumannomyces graminis var. tritici causes take-all.
The most visible symptoms are the presence of circular patches in the field with prematurely white heads. The white heads are obvious because the rest of the crop is still green. As the season progresses, the heads are often colonized by secondary fungi that make the heads look sooty. The sootiness, of course, masks the bright white heads of the previously infected heads. Closer examination of the plants will reveal virtually sterile heads or heads with just a few shriveled kernels. Although take-all most typically occurs in patches, entire fields can also be affected.
White heads are not unique to take-all, so the roots and lower stem need to be examined to make a field diagnosis. Peel off the lower leaf sheaths to observe the base of the stem.
The base and roots near the crown will appear blackish. The coloration is due to the presence of the fungus just below the epidermis. Early in the infection or in less severe cases, the blackening may not be obvious and may require microscopic examination.
Several factors create a conducive environment for take-all to develop: high pH; low-fertility and lighter soils; and cool, wet weather. The fungus survives on many grass hosts; these grasses serve as a reservoir for the disease. Debris from previous wheat crops is also a source of infection.
Control will center on several management strategies. First, crop rotation: stay at least 2 years out of wheat. Control of grassy weeds, and volunteer wheat, is very important as well. From the fertility standpoint, a pH of 7.0 or above is very favorable to take-all, as well as applications of lime and nitrate fertilizers. Fertility patterns or sections of the field that have a different cropping history are usually quite evident with this disease.
Aim for an even balance of N, P, and K; high levels of N will lead to other disease such as powdery mildew.--Suzanne Bissonnette