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Nitrogen and Tillage Effects on Wheat Leaf Spot Diseases in the Northern Great Plains

^a USDA-ARS, Northern Great Plains Research Lab., Box 0459, Mandan, ND 58554-0459
^b USDA-ARS, 2150 Centre Ave., Bldg. D, Suite 100, Fort Collins, CO 80526-8119

View larger version (17K): [in this window] [in a new window]   Fig. 1. Growing season precipitation from April through August, 1984 to 1996. Averages for 13 and 120 yr are included for comparison.

View larger version (28K): [in this window] [in a new window]   Fig. 2. The percentage of wheat leaves infected with Pyrenophora tritici-repentis (PTR, cause of tan spot), and Phaeosphaeria nodorum (PN, cause of Stagonospora nodorum blotch), major components of a leaf spot disease complex on wheat.

View larger version (23K): [in this window] [in a new window]   Fig. 3. Effect of N fertilization (kg N ha–1) on leaf spot disease severity on spring wheat after sunflower, averaged over tillage and cultivar. Treatments with different letters for a particular date are significantly different (P 0.05). Asterisk (*) indicates significant N x tillage interaction; FL = flagleaf, uppermost leaf; FL-1 = first leaf below the flagleaf.

View larger version (22K): [in this window] [in a new window]   Fig. 4. Effect of N fertilization (kg ha–1) on leaf spot disease severity on winter wheat after spring wheat, averaged across tillage and cultivar. Treatments with different letters for a particular date are significantly different (P 0.05). Asterisk (*) indicates significant N x tillage interaction; FL = flagleaf, uppermost leaf; FL-1 = first leaf below the flagleaf.

View larger version (19K): [in this window] [in a new window]   Fig. 5. Examples of significant N (kg ha–1) x tillage interactions for leaf spot disease severity on spring wheat (SWA) after sunflower (Fig. 3) and winter wheat (WWA) after spring wheat (Fig. 4), averaged across cultivars. CT = conventional till, MT = minimum till, and NT = no-till.