Relationship between Climatic Variables during Early Flowering of Sorghum and the Incidence of Sugary Disease caused by Sphacelia sorghi

The relationship between sugary disease incidence and six climatic variables during the early stages of flowering was determined in field trials conducted over three seasons. Daily maximum temperature was highly significantly correlated with sugray disease incidence and accounted for 83 % of the variation observed in disease incidence. The critical period for infection was limited to 5 days after commencement of pollen shed. Deviations from the temperature × sugary disease model occurred in late flowering plots. These were correlated with low temperatures during the 2 weeks prior to pollen shed and, thus, possibly, a reduction in pollen vigour.