Area-of-Influence of Herbicide Granules

Abstract

The area influenced by individual herbicide granules was determined by rating control of weeds planted in fixed patterns around granules. The area of foxtail millet [Setaria italica(L.) Beauv.] controlled by alachlor [2-chloro-2′,6′diethyl-N-(methoxymethyl) acetanilide] was larger than the area of velvetleaf (Abutilon theophrastiMedic.) controlled by atrazine [2-chloro-4(ethylamino)-6-(isopropylamino)-s-triazine]. Control was most consistent when granules and seeds were near the same depth and was most variable when granules were on the soil surface. Control of foxtail millet with alachlor increased with increasing soil moisture, with decreasing granule depth, and with increasing seed depth. At low soil moisture, control of velvetleaf with surface-applied atrazine was better with simulated rain than with subirrigation. When soil moisture was high and atrazine granules were placed 1-cm deep, control was better with subirrigation. The area-of-influence, or the control (y) as function of distance (x) from granule, was described by y = 10e-A(x-B)2. The radius-of-control (ROC), defined as the radius of the circular area around a granule within which weeds are effectively controlled, was estimated from this relationship.