Effect of fungicides on germination of Albugo candida oospores in vitro and on the foliar phase of the white rust disease’

An wspore germination technique was used to study the effectiveness of 27 fungicides, including some systemic ones, in inhibiting germination at various stages. Among the chemicals tested, Mersil, PMA10, and Panogen, each at a concentration of 500 ppm active ingredient, inhibited germination about 75%. Of the nonmercurial compounds, mancozeb and ethazole were the best giving about 60% inhibition. Several compounds were tested in the growth chamber for controlling the foliar phase of the disease. Application of either chlorothalonil or mancozeb. at 250 or 500 ppm, respectively, 6 hr before inoculation plus a week after inoculation controlled the disease effectively. However, sprayings of either fungicide 24 hr after inoculation plus a week later were not effective. Two foliar sprayings of chlorothalonil in June significantly reduced both foliar and systemic infections in the field. However, in view of the growth room studies on successful initiation of systemic infections, a third application at the time of flowering is also advised. More studies are required to determine when sprays should be applied for maximum disease control.