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

Abstract

Shoot growth and fresh wt of greenhouse-grown EM VII clonal apple rootstocks in 1970 were reduced by 1.5 ppm soil-incorporated dichlobenil. Concentrations of 6.0 ppm and higher prevented growth. No leaf margin yellowing (LMY) was observed in 1970, but in 1971 it occurred following placement of 3 clonal rootstocks outdoors. EM VII produced the most shoot growth and EM IX the least. EM IX produced the least fresh wt increase, while those of EM VII and MM 106 were equivalent. EM VII had more LMY than the other 2 rootstocks. The responses of the 3 rootstocks to several concn of dichlobenil were similar. Dichlobenil concn of 0.2 and 0.4 ppm increased fresh wt, largely due to stimulation of root growth. Concentrations of 0.8 ppm and more of dichlobenil suppressed growth.

Response of ‘McIntosh’ Apple Trees to Annual Applications of 2,6-Dichlorobenzonitrile (Dichlobenil)1

“…It should be noted that these data are for trees in soil of 6.6% organic matter which is higher than many soils planted to orchards in eastern United States (6,9,15). It may be that trees in soils of lower organic matter might be more adversely affected by these rates of dichlobenil, since it is well known that organic matter adsorbs herbicides and makes them less available to plant roots.…”

“…Although greenhouse studies have shown that dichlobenil will adversely affect growth of fruit trees (15,19), similar findings in field studies with recommended or excessive rates are limited (9). Leach et al (13) explained the absence of deleterious effects of LMY on the basis that leaves have the ability to compensate for some loss of effective leaf area.…”

“…Leach et al (13) explained the absence of deleterious effects of LMY on the basis that leaves have the ability to compensate for some loss of effective leaf area. Growth restriction, however, could result from root sensitivity to dichlobenil (3,15,16).…”