Soybean rust: symptoms, etiology and chemical control

Soybean rust: symptoms, etiology and chemical control

Pantnagar G. B. Pant University of Agriculture & Technology India

1973

53p. : tables

M.Sc. (Plant Pathology)

SB608.S7S51

Soybean rust caused by Phakopsora pachyrhizi is one of the most destructive fungal diseases of soybeans causing serious yield losses. Studies on symptomatology morphology, pathogenicity, survival of the fungus, and suitable control measure of the disease were conducted. Field trials during Kharif of 1971 using variety Bragg. Showed that all aerial plant parts including leaves, stem, petioles and pods were infected. Uredia were round to oval in shape measuring 63-168 x 46-92 microns in size with an average of 112 x 72 microns and are accompanied with paraphyses. Plants of all ages were equally susceptible to this disease. The incubation period was 10-14 days. Uredospores germinated between 20-30 C, with the optimum being 25 C. Normal germination occurred at 20, 25 and 30 C. Uredospores did not germinate at or below 10 C and above 30 C if continuously exposed. However, spores pre-exposed at 5 C for a minimum of 6 hours germinated when they were transferred and held even at 10 and 35 C. Pre-exposure at 35 C for 6 hours or more killed the spores. Darkness favoured germination. Uredospores lost their ability to germinate within 96 hours after detachement from plants. Dithane M-45 and Dithane Z-78 were best at controlling the disease followed by Brestanol. Plantvax was ineffective. Sandovit and Teepol inhibited uredospore germination. Sandovit was found to be compatible with all of the fungicides tested. Tenac was not found to be compatible with any of these fungicides. Nufilm-17 and Teepol were found to be compatible with most of the fungicides tested while Tween-80 only with Dithane Z-78 and Brestan. Nufilm-17 and Tween-80 showed synergistic effects when used with Dithane Z-78. Zineb with Nufilm-17 or Tween-80 would possibly result in the best control. [AS/THH/GLH]

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