Response of Rhizoctonia solani and Binucleate Rhizoctonia to Five Fungicides and Control of Pocket Rot of Table Beets with Foliar Sprays. GILBERTO OLAYA, Graduate Research Assistant, Cornell University, NYSAES, Geneva, NY 14456. GEORGE S. ABAWI, Professor, Department of Plant Pathology, and JOHN BARNARD, Computer Services, Cornell University, NYSAES, Geneva, NY 14456. Plant Dis. 78:1033-1037. Accepted for publication 20 July 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1033.

The response of 107 isolates of Rhizoctonia solani AG 2-1, 2-2, 4, and 5, and binucleate Rhizoctonia collected from roots, petioles, and leaf tissues of table beets, as well as directly from hymenia of Thanalephorus cucumeris, were tested in vitro for sensitivity against five fungicides (benomyl, iprodione, pencycuron, tolclofos-methyl, and fludioxonil [CGA-I73506]) each at four different concentrations. The growth of the isolates was inhibited by fludioxonil and tolclofosmethyl at 1 Μg a.i./ml and iprodione at 10 ?g a.i./ml, but the isolates varied considerably in sensitivity to pencycuron and benomyl even at 100 Μg a.i./ml. Benomyl, iprodione, tolclofos-methyl, and fludioxonil were evaluated for control of disease under field conditions. Table beets were inoculated with soil infested with three highly virulent isolates of R. solani. In 1991, one spray of each of these fungicides at a rate of 2.2 kg formulated product per hectare was applied before or after inoculation with R. solani. The experiment was repeated in 1992, except that a second spray was applied 2 wk after the first spray. In both years, all fungicide applications significantly (P < 0.01) reduced the number of infected roots. In 1991, fludioxonil applied before the inoculation of R. solani reduced the incidence of infected roots from 21.8 to 3.8% and was the most effective treatment. In 1992, one spray before inoculation or two sprays (one before inoculation and the second 2 wk later) of fludioxonil reduced the incidence of infected roots from 14.6 to 1.2 and 0.7%, respectively. Fungicide applications made before inoculation with R. solani were more effective than those made after inoculation (I day later). In the field, fungicides should be applied before the first cultivation, at which time a considerable amount of R. solani infested soil is thrown on the beet plants.

Keyword(s): Beta vulgaris, chemical control, root rot.