Control Root Disease to Earn Extra Income

Proper crop rotations can boost wheat yields in western North Dakota by an average of 40 percent by controlling root diseases, research at the North Dakota State University Dickinson Research Extension Center shows.

Producers who grow wheat in continuous rotations of wheat, barley, and durum lose about 40 percent of their grain yield to root pathogens, according to Roger Ashley, NDSU Extension Service agronomist at the Center. In addition, quality (test weight and protein) is also affected adversely. Annual forage producers stand to loose up to a ton per acre in production.

Also contributing to potential root loss are management practices implemented by the producer and growing season conditions, Ashley confirmed.

Data collected during the past four growing seasons in western North Dakota show root disease is often difficult to diagnose. "Most pest problems are visible because they attack plant foliage or strike suddenly in confined areas but root pathogens begin nibbling away at the root system even before the plant emerges," Ashley said. "Symptoms develop gradually so the field appears ‘normal.’ It’s only when unfavorable weather for crop growth occurs that the damage from these pathogens becomes readily apparent."

In his demonstrations, Ashley used a soil fumigant to control soil borne pathogens in small areas within producers’ fields. Fumigation is not an economical means of controlling root disease for wheat producers, but it is a good research and demonstration tool that can be used to discover the effectiveness of crop rotations for controlling root disease.

Ashley applied the fumigant under tarp-covered plots for 48 hours and allowed it to penetrate the soil and control many of the harmful root pathogens. The cooperating producer then farmed through the plot area with normal farming procedures.

Crop development was more vigorous and rapid in the fumigated plots. "In continuous wheat fields we normally get a call from the producer about the time that the crop begins to head asking us what we used in the treated plots," Ashley said. "The difference is amazing."

Root and whole plant evaluations from fumigated and natural soil plots support producer observations. Continuous wheat rotations in fumigated soils have about twice as many crown roots and up to 150 percent more tillers per plant.

Ashley said a two-year break between wheat crops "does an effective job controlling root lesions, thus improving root and tiller development. We also see no differences in yield or quality between fumigated and natural soil plots in these rotations." He said non-host crops that do well in southwestern North Dakota include many of the broadleaf crops, corn, and oats.

The research conducted at the Dickinson center and on the farms of cooperating producers in the region shows wheat grown in a rotation every other year, such as in a wheat-fallow, wheat-pea, wheat-corn, or wheat-oat rotation, suffers a 22 to 25 percent yield loss because of root pathogens.

"We don’t see as great a difference between fumigated and natural soil plots in lesion, root and tiller counts, or yield in crop rotations where wheat is grown every other year but root pathogens are still taking a good portion of the yield," said Ashley.

In research, propagule counts--the number of infectious spores per unit of soil--have indicated that as the amount of time increases between wheat crops there are fewer fungal spores to infect the crop. Crop rotations where wheat, barley or durum is grown once every three or four years allows naturally occurring microbes to break down disease-causing fungal spores. Wheat, barley, and durum are all host to the same complex of root diseases.

Ashley suggested seed treatments can provide limited fungal root disease protection, but an integrated approach that includes crop rotation and seed treatments is much better.

He said broadleaf crops that work well in rotations are canola, sunflower, safflower, pea, lentil, garbanzo beans, flax, and alfalfa. He cautioned, "These crops must be put together in the right sequence if other disease and management problems are to be avoided."

He said corn, oat, millet, or sorghum must be included to reduce the risk of broadleaf crop diseases and diseases which impact wheat, barley or durum. Results suggest wheat followed by corn followed by a broadleaf crop before rotating back to wheat is a good combination. Long-term rotations can include alfalfa but producers should eliminate grassy weeds to obtain the maximum benefit in the control of root pathogens. Some grassy weeds are hosts for the same pathogens that attack wheat, barley, and durum.

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Source: Roger Ashley, (701) 483-2349, rashley@ndsuext.nodak.edu
Editor: Tom Jirik, (701) 231-9629, tjirik@ndsuext.nodak.edu

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