Field studies evaluated the effect of brown patch control on preemergence herbicide efficacy in tall fescue. Pendimethalin (1.7 followed by [fb] 1.7; 3.4 kg ai/ha), prodiamine (0.7 fb 0.6; 1.3 kg ai/ha), and oxadiazon (2.2 fb 2.2; 4.5 kg/ha), applied sequentially and as a single application, were evaluated for smooth crabgrass control with and without the use of azoxystrobin, a fungicide that controls brown patch. Azoxystrobin suppressed brown patch and increased smooth crabgrass control with pendimethalin in both years. This enhanced efficacy with azoxystrobin was attributed to improved tall fescue turf density and thus increased competition between this turf species and smooth crabgrass. Longer soil-residual herbicides such as oxadiazon and prodiamine provided high levels of smooth crabgrass control (often >90%). With the exception of oxadiazon at 4.5 kg ai/ha in 2000, smooth crabgrass control with oxadiazon and prodiamine was unaffected by the use of azoxystrobin.
Nomenclature: Azoxystrobin, methyl (E)-2-((6-(2-cyanophenoxy)-4-pyrimidinyl)oxy)-alpha-(methoxymethylene)benzeneacetate; oxadiazon; pendimethalin; prodiamine; smooth crabgrass, Digitaria ischaemum Schreb. ex. Schweig. #3 DIGIS; tall fescue, Festuca arundinacea Schreb. # FESAR ‘Ky 31’.
Additional index words: Soil persistence.
Abbreviations: fb, followed by; PRE, preemergence.
