Yield losses to maize streak disease andBusseola fusca(Lepidoptera: Noctuidae), and economic benefits of streak‐resistant maize to small farmers in Zaïre

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Abstract
Results of two seasons of on‐farm trials are reported. In 1986/87 yield losses to maize streak disease were 6.5–8.9 kg/ha for each additional 1% increase in incidence of infected plants. In fertilized plots losses to borers ranged from 9.1 to 13.6 kg of maize/ha for each 1% increase in incidence of borer‐attacked plants; in unfertilized plots losses were insignificant. When different parameters of yield loss to streak disease were compared, incidence × symptom severity was more highly correlated with loss than either incidence or severity alone, but the difference was slight, and data on incidence were more easily collected. Sampling of young plants (< 8 weeks old) proved superior to sampling of older plants (> 8 weeks old). Increases in disease incidence and severity and in borer infestation rates were characterized. In 1987/88 the streak‐resistant variety Babungo‐3 generally out‐yielded the local variety and showed lower streak incidence and symptom severity. The average farm family must apply fertilizer in order to meet its food requirements. A dose of 50 kg/ha (N‐P‐K) on the local variety would permit the family to satisfy its own grain requirements and produce a marketable surplus of 600 kg. The same dose applied to Babungo‐3 would give a marketable surplus of 1100 kg.