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Disease Detection and Losses

Yield Losses Caused By Fungal Foliar Wheat Pathogens in Brazil. Wilmar Corio da Luz, Research plant pathologist, Centro Nacional de Pesquisa de Trigo, Caixa Postal 569, 99100, Passo Fundo, RS, Brazil; Phytopathology 74:1403-1407. Accepted for publication 6 June 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-1403.

In 1981- 1982, field experiments were performed at the National Wheat Research Center, Passo Fundo, Rio Grande do Sul, Brazil, to estimate the yield losses due to fungal foliar diseases of wheat. Selective and broad-spectrum fungicides were applied, individually and in combinations to control one or more specific diseases. Results indicated that leaf rust and spot blotch caused the greatest economic losses in wheat. In 1982, leaf rust reduced the yield of wheat cultivars CNT 10 and Nobre by 20 and 18%, respectively. Cochliobolus sativus was the most prevalent leaf spot pathogen, causing yield losses of 19 and 14% in CNT 10 and Nobre, respectively. These diseases did not cause yield reductions on either cultivar in 1981. In 1981, powdery mildew reduced the yield ~8% on cultivar CNT 10 but did not reduce the yield of Nobre. In 1982, powdery mildew had no effect on yield and the combined reduction in yield due to scab and glume blotch was 8% on each of the two cultivars. In 1981, the combined reduction was 10% on cultivar CNT 10. Leptosphaeria nodorum caused some infection on leaves in both years of study. No other fungal leaf disease affected plants in the plots to any appreciable extent. The multiple fungal foliar diseases reduced yields about 19 and 32% in 1981 and 48 and 40% in 1982 on cultivars CNT 10 and Nobre, respectively. The total wheat loss was greater in 1982 due to higher disease severity favored by wet periods and high temperatures.