Pesticidal and nutritional predisposition of creeping bentgrass (Agrostis palustris Huds.) to large brown patch (Rhizoctonia solani Kühn)

Influence of selected herbicides and fungicides, under two nitrogen levels (147 kg/ha and 686 kg/ha), on susceptibility of Penncross creeping bentgrass (Agrostis palustris Huds.) to the large brown patch disease (Rhizoctonia solaniKühn) was investigated. Determinations included pesticide effects on foliage color, stand density, overall quality appearance, and bentgrass susceptibility to other pathogenic fungi.

A significant increase in R. solani incidence resulted from individual treatments of DCPA (dimethyl tetrachloroterephthalate) under low N conditions, and benomyl [methyl 1-(butylcarbamoyl)-2- benzimidazolecarbamate] under low and high N conditions.

Pesticide combinations resulting in increased R. solani incidence were benomyl x bensulide [0,0-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzene-sulfonamide], benomyl x DCPA, benomyl x oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropyloxyphenyl)- δ²-1,3,4-oxadiazolin-5-one], and triadimefon [1-(4- chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-yl)-2-butanone] X bensulide, triadimefon x DCPA, and triadimefon x oxadiazon, all under low and high N.

Pesticides implicated in reduction of bentgrass color were chlorothalonil (tetrachloroisophthalonitrile), triadimefon, and oxadiazon under low N, and benomyl, chlorothalonil, triadimefon, and oxadiazon under high N. Pesticide combinations resulting in loss of bentgrass green color were oxadiazon in combination with each fungicide under low N. Benomyl and chlorothalonil each in combination with all three herbicides, and triadimefon in combination with oxadiazon caused loss of bentgrass green color.

Pesticides reducing bentgrass stand density were bensulide, DCPA, and oxadiazon under high N. Chlorothalonil in combination with bensulide and with oxadiazon reduced bentgrass stand.

Benomyl, DCPA, and oxadiazon treatments under low N resulted in a significant increase in dollar spot. Pesticide combinations involved with increased dollar spot were benomyl x oxadiazon, chlorothalonil x bensulide, chlorothalonil x oxadiazon, and triadimefon in combination with each herbicide. Benomyl and triadimefon, in combination with each herbicide, resulted in increased dollar spot under high N.