This is the process by which residue is buried to enhance decomposition. Unfortunately, this practice has also resulted in substantial loss of soil over the years. We are not advocating a return to farming practices where fields are tilled on an annual basis, but some form of tillage is practical in some fields where pressure from soybean diseases is high.
Tillage can reduce the incidence of plant disease in two ways — by enhancing decomposition of soybean residue which limits survival of pathogens on the residue and by limiting the time that soil moisture levels are sufficiently high enough to favor pathogens that require free water. Phialophora gregata, which causes brown stem rot, is a residue-borne soybean pathogen. This fungus will survive on the residue on the soil surface for as long as it is there. When the residue is buried, other fungi and bacteria will decompose soybean stems and the Phialophora fungus will die due to starvation.
No-till fields take longer to warm and have a higher moisture-holding capacity than tilled fields. The longer the soils hold moisture, the greater the time that "water-loving" pathogens can infect plants. Phytophthora and Pythium both require free water in soil to form swimming zoospores that can infect soybean seeds and seedlings. The longer soils remain wet, the more disease will result from those pathogens. Previous studies have shown that mold-board plowing results in less disease, from Phytophthora and Pythium, than chisel plowing which in turn results in less disease than no-till.
Tillage can also enhance some diseases. For example, burying of sclerotia of Sclerotinia can enhance their survival. Recent studies have shown that leaving sclerotia on the soil surface the year previous to planting soybeans can lead to a reduction in the incidence of Sclerotinia white mold. The reason is that while the sclerotia are left near the soil surface, some will germinate to form apothecia and be subject to predation. If there is a non-host crop such as corn or wheat, the spores released from apothecia will not infect the rotation crops and sclerotia will no longer be viable in following years when soybeans are planted.
|
| Figure 7. Partially chiseled field ready to be tiled to improve drainage. |
Equipment used for tilling soil will aid in spreading pathogens within fields and from field to field. This is especially critical for soybean cyst nematode. Soybean cyst nematode is moved readily with soil.
Equipment that is caked with soil may also be carrying soybean cyst nematode. Sclerotinia is another good example of a pathogen that is moved by equipment, especially the sclerotia in harvested grain and by combines.
Back | Forward | Table of Contents
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-1868