USE OF FUNGICIDES, BICARBONATE SALTS, AND FILM-FORMING POLYMERS TO SUPPRESS POWDERY MILDEW OF FLAX.

An outdoor pot experiment was conducted in 1999 and 2000 growing seasons to evaluate foliar application of a diverse group of compounds for control of flax powdery mildew. The tested compounds were a sulpher fungicide (That Flowable Sulphur), three ergosterol biosynthesis inhibitors (Bayfidan, Bayleton, and Rubigan), three bicarbonate salts (salts of sodium, potassium, and ammonium), and two film-farming polymers (Nu-Film and Super-Film). Disease intensity variable (disease incidence and disease severity) and yield (straw and seed) were used as criteria for judging efficiencies of the compounds in controlling the disease. The findings of the present study demonstrate that sterol biosynthesis inhibitors in particular Bayfidan were the best performaring compounds in controlling the disease. This superiority was attributed to the following reasons: first, they were the only compounds, which significantly reduced disease incidence after the second spray in 1999. Second, they were the most effective compounds in reducing disease incidence after the second spray in 2000. Third, they were the most effective compounds in reducing disease severity after the second spray in 1999. Fourth, they showed high efficiencies in reducing disease severity after the second spray in 2000. Fifth, they gave considerable increases in straw and seed yield each year. In some cases, bicarbonates and film-forming polymers were as effective as or even more effective than fungicidal chemicals in controlling the disease and increasing yield; however, bicarbonates and film-forming polymers had two drawbacks: first, they showed inconsistent performance in controlling the disease compared to the fungicidal chemicals. Second, when they were effective, they mostly showed lower efficiencies in reducing disease incidence and disease severity. Significant negative correlations between powdery mildew intensity variables and yield were observed each year particularly in case of cultivar Giza 7. Three regression models, derived from stepwise multiple regression analysis, were constructed for each year to predict straw and seed yield. These models showed that yield differences observed were due largely to the disease which accounted for 56.23 to 88.18% and 49.31 to 74.28% of the explained (model) variation in straw and seed yield, respectively.