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Effects of previous crop residues and tillage practices on Fusarium head blight (FHB) of wheat were examined. Fusarium head blight was monitored in plots of the FHB-susceptible spring wheat cultivar Norm following crops of corn, wheat, and soybeans in 1995, 1996, and 1997. Moldboard plow, chisel plow, and no-till treatments were imposed perpendicular to crop strips to establish a range of residue levels in each of the previous crop residues. Fusarium head blight incidence and severity were greatest when wheat followed corn and least when wheat followed soybeans. Incidence and severity were lower in moldboard plowed plots than in either chisel plowed or no-till plots, although differences among chisel plow and no-till treatments were not apparent. Yields of wheat were approximately 15% lower in plots where wheat followed corn or wheat than in wheat following soybeans and were 10% greater in moldboard plowed plots than in either chisel plowed or no-till treatments. The deoxynivalenol (DON) content of harvested grain was significantly correlated with FHB incidence and severity. The DON level in wheat following soybeans, averaged across tillage treatments, was 25% lower than in wheat following wheat and 50% of the level in wheat following corn. These findings suggest that changes in regional tillage practices, principally the move toward conservation tillage and reduced-till systems, contributed to the recent FHB epidemics in the Upper Midwest. Because differences in the type and quantity of crop residues in small plots affected disease development, it is likely that local sources of inoculum, such as those within a grower's field, contribute directly to the inoculum load and disease potential. The implication of these findings is that selection of cultural practices aimed to reduce inoculum-borne residues will assist in the control of FHB.

Benomyl and tebuconazole reduced head blight incidence, head blight severity, and the percentage of visually scabby kernels (VSK) in harvested grain when applied to the susceptible spring wheat cv. Norm at anthesis. Deoxynivalenol (DON) concentration was also reduced. Fungicide treatment increased head weight, test weight, thousand kernel weight, and yield. Fludioxonil reduced certain parameters associated with the disease in barley, including incidence, severity, and deoxynivalenol concentration, while increasing the percentage of plump kernels and yield. In vitro, isolates of Fusarium graminearum were sensitive to fludioxonil, benomyl, tebuconazole, and mancozeb (concentrations that give 50% growth inhibition of 7.4 × 10-3, 3.5 × 10-1,9.9 × 10-1, and 7.3 mg a.i./liter, respectively). No evidence for insensitivity (resistance) was found. Prospects for chemical control of Fusarium head blight (FHB), however, remain limited. The repeatability of assessment methods used in evaluating host response to fungicides and to the damage caused by F. graminearum is discussed. Disease incidence, disease severity, VSK, and DON were identified as key variables that best measure the effects of FHB.

Recent epidemics of Fusarium head blight (FHB) severely damaged the hard red spring wheat and barley crops in Minnesota. Samples of commercial grain were analyzed in 1993 and 1994 to determine the effects of FHB on several quality parameters. Wheat test weight (TW) averaged 832 kg m-3 (55.4 lb/bu), thousand kernel weight (TKW) averaged 27.4 g, and the proportion of visually scabby kernels (VSK) averaged 11.0%. Deoxynivalenol (DON) was detected in 493 of 500 samples (98.6%). The mean concentration was 8.3 μg/g (range = 0.0 to 44.7 μg/g). Scab in wheat could rapidly be estimated using easy-to-prepare visual comparison standards. Scores of percent VSK were correlated with DON concentration at r = 0.897 and 0.908 in 1993 and 1994, respectively. TW and TKW were less effective estimators of DON (r = -0.622 and -0.550, respectively). DON was detected in 100 of 100 six-row barley samples collected during the survey and averaged 10.4 μg/g (range = 0.5 to 39.7 μg/g). DON concentration in barley could not be effectively estimated with grading parameters including TW, TKW, percent plump kernels, or a visual index of kernel discoloration. In 28 samples of oats, DON averaged 1.4 μg/g (range = 0.0 to 6.4 μg/g). Nivalenol was not detected in any of the 628 samples analyzed during the two-year study.

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