Spot blotch and tan spot of wheat in Paraguay
1998
Viedma, L.Q. de | Kohli, M.M. (Ministerio de Agricultura y Ganaderia, (Uruguay). Centro Regional de Investigacion Agricola)
Historically wheat has not been a traditional crop in Paraguay. With the significant increase in soybean production over the last two decades, the area of wheat during the winter has also increased. However, high temperatures and humidity are favorable for severe disease epidemics, especially of rusts, powdery mildew, and foliar and head blight of wheat. These diseases are limiting factors for stable wheat production in the country. Foliar blight is caused by spot blotch (Bipolaris sorokiniana) and tan spot (Dreschlera tritici- repentis), which are two very important wheat diseases. Spot blotch, combined with other diseases, was responsible for a grain yield reduction of almost 70 percent in the mid 1970s, while tan spot has recently become important. Increase in tan spot prevalence is primarily associated with the increase in cropping area under zero tillage cultivation. An integrated disease management strategy has been implemented to reduce losses caused by the diseases. The national germplasm development program has been successful in releasing commercial varieties including IAN 8, IAN 9, Itapua 35, and Itapua 40 that allow only moderate infection levels. Seeding these varieties every third or fourth year on oat or vetch stubble has significantly reduced infection levels; however, in a year of severe disease, chemical control is essential. Chemical control of black point in grain, caused by B. sorokiniana, has been successfully achieved using iprodione, guazatine, or triadimenol fungicides at a rate of 200 g/100 kg seed. Foliar applications of systemic fungicides such as tebuconazole, propiconazole, flutriafol, ciproconazole, fluzilazole, epoxiconazole, and metaconazole, applied between heading and grain filling stages, have achieved cost effective disease control. Under severe disease levels, a double application of fungicide can result in a grain yield increase of 38-61 percent.
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