Chemical Suppression of Gloeotinia temulenta Apothecia in Field Plots of Lolium perenne

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Abstract
Formation of apothecia of G. temulenta (cause of blind seed disease) was suppressed by 1-4(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl)-2-butanone (triadimefon); .alpha.-(2-chlorophenyl)-.alpha.-(4-fluorophenyl)-5-pyrimidinemethanol (nuarimol); and .alpha.-(2-chlorophenyl)-.alpha.-(4-chlorophenyl)-5-pyrimidinemethanol) each at less than 0.4 mg active ingredient (a.i.)/92 cm2 applied once over cold-conditioned, infected seeds of L. perenne (pseudosclerotia) at the soil surface in plastic pots. In field plots of L. perenne ''Linn'', triadimefon and fenarimol both gave complete control at 1.12 kg/ha after 1 application as a soil-surface drench. Triadimefon and nuarimol applied once in a spray or in a granular formulation gave poor to incomplete control. Apparently, the leaf canopy in the field interfered because these chemicals gave excellent control in concurrent pot tests at field rates. Apothecium formation was prevented by sodium azide at 12 and 16 mg/92 cm2 soil surface in greenhouse pot tests; 8 mg gave nearly complete control. In field plots, sodium azide applied 29 April, at 11.2 kg/ha exerted complete control that lasted through the anthesis period 1-15 June. When applied 11 May, sodium azide gave 75% control at 11.21 kg, 99% control at 16.8 kg and complete control at 22.4 kg/ha. Incomplete control resulted from applications on 14 April. Sodium azide provides the 1st case of control of blind seed disease by a chemical applied with conventional equipment in field plots. Control was achieved by suppression of apothecia.

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