Management practices to minimize tan spot in a continuous wheat rotation
In the central United States, practices that maintain residue in wheat (Tritricum aestivum L.) often lead to yield losses from tan spot (Pyrenophora tritici-repentis) infections. Tillage, fungicides, N fertility, and resistant varieties may reduce tan spot severity. Studies were conducted over five location-years to determine wheat yields and tan spot severity across three residue levels (no-till, reduced till, and burned) and cultivar susceptibility to tan spot. Nitrogen fertilizer and fungicide treatments were also evaluated for their influence on tan spot severity and wheat yields. Tan spot severity ranged from 12 to 64%, based on leaf ratings at anthesis across four environments when second year wheat was no-till planted. Removing previous crop residue by burning or tillage, host plant resistance and fungicide applications reduced tan spot severity across four environments 49, 30, 58, and 93%, respectively. Severities were higher with the susceptible cultivar when planted no-till and with no fungicides applied. Fungicide applications on the susceptible cultivar improved yields 14%, compared with only a 3% in the resistant cultivar. Under a severe tan spot infection, fungicide applications improved yields 34% for the susceptible cultivar and 10% resistant cultivar. Fungicide applications had no effect in three of the five environments. Burning and tillage increased yields 11 and 2% compared with no-till, respectively. Kernel weight was the most commonly affected yield component because tan spot infections affect flag leaf health during grain fill. These results suggest that it may be possible to develop no-till rotations with wheat following wheat without significant risk to producers.