Dickinson Research Extension Center
1089 State Avenue
Dickinson, ND 58601
CROP ROTATIONS AND ROOT DISEASE
Roger Ashley, Area Extension
Marcia McMullen, Extension Plant Pathologist
Field demonstrations at eleven locations over a two year period have shown the impact of root diseases on yield and quality of dryland hard red spring wheat and durum in western North Dakota. These demonstrations also have shown the importance of rotations with non-host crops in reducing root disease pathogen levels. The video illustrates what producers observed at the Dickinson and Williston Research Extension Centers during the 1998 growing season. Results from these two sites, as well as from representative on-farm locations in western North Dakota, are used to depict what producers may observe when various crop rotations are used.
A soil fumigant was used in the demonstration to control disease causing fungi, allowing us to show side by side comparisons of the effect of root disease in the field. Soil fumigation is not an economical means of controlling root disease but was used as a tool to demonstrate the losses producers experience in the field and to demonstrate what producers can expect if adequate rotations to control root disease are used. Details on how this demonstration was conducted are available through your county extension agent or at the web site address: http://www.ag.ndsu.nodak.edu/dickinso/research/1997/rootdise.htm.
Significant differences in grain yield (Figure 1) were detected between fumigated and natural soil (non-fumigated) plots in a continuous durum wheat rotation at Hazen. The durum grain yield from the fumigated plots was 42% greater than from the natural soil plots. Continuous wheat grain yields from fumigated plots at Amidon and Beach in 1997 (data not shown) were 40% greater than from natural soil plots but with a rotational crop in the crop sequence, fumigated and natural soil plot yields were almost equal. At Dickinson, the difference between the fumigated and non-fumigated plot wheat grain yields in the wheat-oat-wheat-wheat (W-O-W-W) rotation was 36% (Figure 2). When two years of non-cereal crops were introduced into the rotation, mean fumigated plot wheat grain yields were seven percent greater than natural soil plot yields and significantly greater than W-O-W-W crop sequence. Oat is generally thought to not be a host or a poor host to many of the root pathogens that attack wheat. At Williston, grain yield difference between fumigated and non-fumigated plots in a continuous wheat rotation was 20% (data not shown). At two other sites where continuous wheat was grown and affected by very dry conditions (less than 12 inches of estimated available water) differences in grain yields between fumigated and natural soil plots were 20 to 25%. Cumulative water-use at Williston (Figure 3) was about nine inches from May 11 through August 3, with slightly higher water use in fumigated plots than in natural soil plots.
Crop rotations which included a two-year break in cereals proved to be nearly equal in grain yield to fumigated treatments in farm fields located at Beach and Amidon in 1998. Fumigated plot grain yields were 1.5% greater at Beach and 1.1 % less at Amidon than yields from natural soil plots (Figure 1). Grain protein content was nearly the same for fumigated and natural soil plots although fumigated plots under continuous wheat showed about a 1% protein bump over the natural soil plots at Hazen (Figure 4). Fumigation gave about a one pound increase in grain test weight at all three sites (Figure 5).
Head density in continuous wheat rotations was significantly greater for fumigated plots then natural soil plots (Figure 6 and 7). However, when crop rotations with a two-year break between cereal crops was analyzed, no significant differences were observed.
In addition to the root color noted in the video, subcrown internode ratings and Rhizoctonia lesion counts provide an indication of the severity of root disease. Subcrown internode ratings in fumigated plots and plots that had a two-year break from cereals were approximately one half of those ratings found in non-fumigated continuous wheat samples (data not shown). Rhizoctonia lesions were absent in both fumigated plots and in plots that included a two-year break from cereals, while all continuous wheat rotations exhibited some lesions of Rhizoctonia.
Implications of Demonstration
Root disease ratings were consistently lower in fumigated plots than non-fumigated plots when the field had a history of continuous wheat. When wheat or durum was grown in a continuous wheat rotation, grain yields were 36 to 42% less and quality factors were lower at most sites than in fumigated plots. When available water was less than 12 inches, grain yield differences between fumigated and non-fumigated was about 20%. When crop rotations included crops that are poor hosts to wheat root disease, wheat yield and quality was nearly the same for fumigated and non-fumigated plots.
Producers can expect reduced wheat and durum grain yields and quality when wheat or durum is grown in a continuous wheat, durum or barley rotation. Producers can also expect less straw returned to the soil by smaller and poorly tillered plants, typical of wheat with root disease. Less straw means less coverage, making soil more susceptible to water and wind erosion. This could eventually lead to a decline in soil health and productivity. Wheat plants with root disease are inefficient in utilizing water and nutrients, especially nitrogen. Also a crop with root disease can leave a wheat crop more vulnerable to weeds because diseased plants are less competitive.
Climatic conditions and crop rotations will affect the severity of disease. Dry conditions will reduce grain yield differences between fumigated and non-fumigated plots. This demonstration has shown that crop rotations which include non-host crops will reduce the impact that root disease has on wheat and durum yields.
Additional information on root disease can be found in the NDSU Extension Bulletin PP-785 (Revised), Root and Crown Rots of Small Grains.
The video tape is available from your North Dakota State University County Extension Agent or at the Dickinson Research Extension Center. The title of the video tape is "1999 Pesticide Recertification - Crop Rotation and Small Grain Root Disease" and is 16 minutes and 24 seconds.