All aboveground parts of the wheat plan can be affected, but the premature bleaching of heads is the most striking symptom. The pathogen can affect yields in a matter of days, leaving farmers no time to act. Head infections during the flowering stage result in no grain production. However, infection at the grain filling stage results in small, shriveled and discolored grains. Two types of lesions are visible on older leaves: in mild cases, black specks and large eye-shaped lesions with light gray centers and darker margins. Severely infected leaves, in turn, are characterized by the presence of black specks and small brown spots with black margin and sometimes a chlorotic halo. Symptoms on the ear closely resemble and could easily be mistaken for Fusarium head blight.
The symptoms are caused by the fungi Magnaporthe oryzae, which can survive on seeds and crop residues. Besides wheat, this species has diversified and adapted to infect important crops such as barley and rice as well as a number of other plants. This makes crop rotation rather ineffective to control it. Most wheat varieties currently grown are susceptible to this disease. During ear emergence and grain filling stages, warm temperatures and (18-30°C) relative humidity above 80% can result in severe damage and sometimes the devastation of the crop within a week.
To date, there is no evidence of biological control of M. oryzae in the field. However, in rice, seed treatment and foliar spray with formulations of Pseudomonas fluorescens effectively controls blast disease and increases the grain yield.
Always consider an integrated approach with preventive measures together with biological treatments if available. Elevated precipitation of prolonged exposition to dew during the flowering or grain filling stages is a strong driver of wheat blast. Check weather forecast for rain/ dew before the application of systemic fungicides as a preventive measure. Regardless, fungicides typically provide only a partial defense. Apply solutions containing active ingredients trifloxystrobin + tebuconazole before rain or dew at flowering stage. Do not use chemicals with the same mode of action each year as this can lead to resistance.