Studies on the Fungicidal Control of Septoria Leaf Blotch of Wheat

A number of fungicides were screened for the control of septoria leaf blotch of wheat from 1984 to 1987 at Holetta Research Center. Rate, spray frequency and interaction between promising fungicides and cultivars have been studied. Propiconazole, chlorothalonil, flutriafol and fentinacetate + maneb restricted the disease spread, reduced disease severity and number of pycnidia on flag leaves of susceptible cultivars. Seed weight and yield were increased by more than 50 percent. Two applications at half rate (0.5 lt ha-1) of propiconazole and flutriafol, early (when symptom appeared) and late (3 weeks after the first spray), and one application at full rate (1.0 lt ha-1) of the same products at about heading, and in addition, two application (early and late) of chlorothalonil (1.125 kg a.i. ha-1) have similarly and significantly reduced the disease and increased both seed weight and yield of a susceptible cultivar laketch-8156. Five fortnightly sprays (starting at the on-set of the disease) of fentinacetate + maneb (0.1 percent) were required to achieve the same level of control. The effect of these fungicides was less when a resistant cultivar (Enkoy) or a moderately susceptible cultivar (Dashen) were sprayed. On the other hand, spraying a susceptible cultivar like Laketch-8156 with the fungicides had significantly controlled the disease and increased seed weight and yield by about 40 and 60 percent, respectively. The result indicates that spraying a cultivar with some moderate or high resistance for the control of septoria leaf blotch per-se may not be necessary. However, if one has to spray wheat fields for the control of stripe and leaf rusts, the broad spectrum fungicides, such as propiconazole and flutriafol, may as well be used for the control of septoria leaf blotch as these diseases often occur together at different severity levels depending upon the cultivar and environmental factors