A side effect of chlorthiamid and dichlobenil herbicides

Abstract

SUMMARY2,6‐Dichlorobenzamide (BAM) induced leaf margin chlorosis (LMC) on the leaves of kale seedlings and apple trees when applied to the roots. The leaf symptoms were similar to those sometimes seen after use of the herbicides chlorthiamid and dichlobenil. BAM was deposited mainly in the margin of the leaf to which BAM was transported via the transpiration stream. BAM appeared to be the causative agent of chlorosis although hydroxy derivatives of BAM were also present in the leaf. Factors possibly responsible for the variations in the occurrence and in the intensity of LMC are discussed.

Phytotoxicity of Soil-Incorporated 2,6-Dichloro-Benzonitrile to Clonal Apple Rootstocks1

“…Considering the overall effect of dichlobenil, however, the rootstocks responded differently (Table 3). The rootstocks differed significantly in shoot growth, with EM VII producing transpiration stream, these same workers (11) postulated that those environmental factors which increase transpiration are likely to enhance LMY. This postulation may explain why LMY developed in 1971 and not in 1970.…”

“…In 1966, the herbicide 2,6-dichlobenzonitrile (dichlobenil) received registration by the Pesticide Regulation Div., USDA for weed control in fruit tree nurseries and in established plantings of fruit trees. Despite the reported tolerance of fruit trees to dichlobenil (10,16,17,19), yellowing of the leaf margins (LMY) and leaf-tip burn were frequently observed following its use (7,10,11,13). More severe damage is expressed as interveinal blotches of yellowed tissue and marginal necrosis.…”

“…Dichlobenil does not move readily in soil and is generally found in the upper 6 inches of soil (2 ,4 , 15). Nevertheless, the presence of LMY in established plantings of fruit trees indicates that sufficient amounts of dichlobenil or its metabolites (11) enter the tree roots to cause foliar symptoms of phytotoxicity. Because roots are sensitive to dichlobenil (3 ,9 , 14), the present study was undertaken to determine the phytotoxicity of soil-incorporated treatments to EM VII, EM IX and MM 106 clonal apple rootstocks.…”

Effects of repeated application of dichlobenil in a commercial apple orchard

“…It has been shown that this major metabolite of dichlobenil is resistant to further breakdown and appears to be the end product of the herbicide degradation in soil (Verloop, 1972). Leach et al (1971) reported that 2,6-dichlorobenzamide is water soluble and is moved readily by soil water. The accumulation of this major breakdown product under eastern Ontario conditions may suggest that due to the insufficient rainfall in this area the material is not leached away from the root zone.…”

“…The occurrence of leaf margin chlorosis due to the use of dichlobenil as a soil-applied selective herbicide varies in accordance with geographical location and climatic conditions (Verloop, 1972). The leaf chlorosis varies from year to year (Verloop, 1972), probably due to soil conditions when dichlobenil is metabolized to 2,6-dichlorobenzamide, the causative agent of the leaf yellowing (Leach et al, 1971).…”