Tillage and Fungicide Management of Foliar Diseases in a Spring Wheat Monoculture

Enthusiasm over conservation tillage in wheat (Triticum aestivum L.) monoculture has been tempered by concern about the carryover of foliar diseases on the surface residue. A 3‐yr study evaluated the effects of foliar diseases on wheat production with different methods of primary tillage and with fungicide control treatments. Plots with chisel plowing (2×) as the primary tillage had higher surface residue and higher foliar severity in the early growth stages compared with moldboard plowing or with moldboard plowing preceded by burning. Early season differences in severity between moldboard plowing treatments with and without burning were mostly insignificant. The effect of chisel plowing on early season foliar disease did not consistently carry over to late season foliar ratings. In 1991, chisel plowing resulted in the highest late‐season foliar disease as indicated by the area under disease progress curve (AUDPC). In 1992, there was no significant difference in AUDPC between tillage treatments, and in 1993, chisel plowed plots had the lowest AUDPC. In this study, yields were not significantly affected by any tillage‐related foliar disease effect. Foliar fungicides consistently reduced foliar severity, but in all 3 yr, the fungicide treatments were not economical at 1991–1993 market prices. Research Question Extensive acreages of spring wheat are planted on ground having wheat the previous' year. This practice increases foliar infection by certain wheat pathogens that have initial inoculum levels dependent upon the amount of surface residue from the previous crop. The impact of primary tillage on foliar disease severity and the use of foliar fungicides for managing foliar diseases under plow and chisel tillage were studied. Literature Summary The initiation of several wheat diseases has been closely linked to fungal inoculum overwintering in the crop residue. A trend toward conservation tillage, the popularity of air seeders, and the convenience of planting with a single pass have increased the importance of disease management. The potential influence of conservation practices on a synoptic scale upon foliar disease is a great concern. Crop rotation options currently have been limited for many farmers due to a lack of economically viable alternative crops and to farm program benefits that are maximized by maintaining a base acreage of wheat. High yield management systems require optimal fertility, seeding rate, and canopy necessary to maximize the genetic potential of the crop. The resulting microclimate may enhance conditions for production of fungal inoculum and disease development. Interactions of recrop residue and foliar diseases have been studied previously but limited information is available on the management decisions that optimize production of spring wheat under these conditions. Study Description The experiment was conducted for 3 yr at Langdon, ND. In each year, ‘Butte 86’ hard red spring wheat was planted on land cropped to ‘Sceptre’ durum wheat the preceding year. Fall tillage treatments included chisel plowing (2×), moldboard plowing, and moldboard plowing immediately preceded by burning the stubble. Subplot fungicide treatments were applied across each main plot tillage treatment. Mancozeb and tebuconazole fungicides were applied with varied timings and numbers of applications. Disease severity ratings during each growing season and harvest results were used to interpret management effects. Applied Questions Do tillage practices with higher residue on the surface result in greater foliar diseases associated with overwintering pathogens? Plots chiseled had significantly more residue on the ground surface than plots that were moldboard plowed or burned plus plowed. The chiseled plots had significantly greater foliar severity during the early part of the growing season. Consequently, higher residue tillage practices resulted in greater levels of infection due to the overwintering diseases. In this study, however, the effect of higher residue upon early season disease levels did not consistently carry over to the later growth stages of the crop. In 1991 and 1992 when tan spot was the predominant disease, the chiseled plots had greater areas under the disease progress curve (AUDPC) than the plowed plots. In 1993 when septoria blotch was the predominant disease and rainfall was above average, the chiseled plots had less AUDPC than the plowed plots. This suggests that carryover of recrop residue may be a greater concern for tan spot than for septoria blotch and growing season environment has a large impact on the effect of overwintered inoculum. What combination of tillage and fungicide alternatives most effectively support higher production levels in recrop situations? The differences in yield and test weight among tillage treatments were mostly nonsignificant. Similarly, the differences in yield and test weight among fungicide treatments were too small to be economical. Therefore, although differences in amount of disease were found, no tillage or fungicide practice was clearly advantageous in this 3‐yr study. These results may not necessarily hold true for other cultivars or environments. The cultivar Butte 86 is susceptible to tan spot and septoria blotch but it is also early maturing, which may help the grain to mature faster with minimal loss in yield or test weight.