Residues of two fungicides (dodine and fenarimol) and two insecticide/acaricides (amitraz and formetanate) on pear (Pyrus communis L.) leaves were reduced by over-tree sprinkler irrigation applied 24 or 72 hours after pesticide treatment. The difference in residue persistence following over-tree irrigation applied at 24 vs. 72 hours after pesticide treatment was significant only for fenarimol. Residues on leaves from nonirrigated trees at 96 hours post-treatment had declined 24% to 57% from initial levels. Over-tree irrigation further reduced residues by 14% to 47%. For all compounds except dodine, foliar residues measured at 96 hours post-treatment were reduced from initial levels to a greater extent by factors other than over-tree irrigation. Chemical names used: dodecylguanidine monoacetate (dodine); α-(2-chlorophenyl)-α-(4-chlorophenyl)-5-pyrimidinemethanol (fenarimol); N'-(2,4-dimethylphenyl) -N-[[(2,4-dimethylphenyl) imino]methyl] -N-methylmethanimidamide (amitraz); N,N-dimethyl -N'-[3[[(methylamino) carbonyl]oxy]phenyl]methanimidamide (formetanate).
David Sugar and P.H. Westigard
R.J. Hilton, H. Riedl and P.H. Westigard
Handgun treatments of abamectin and oil applied between mid-June and late August caused distinct epidermal rings where drops of spray liquid dried on the surface of pear fruit (Pyrus communis L.). The severity of epidermal injury was related to the concentration of oil in the abamectin spray mixture (abamectin applied without oil caused no fruit damage). Of six pear cultivars tested, `Anjou' was most susceptible to injury, followed by `Cornice' and `Bartlett'. `Sensation Red Bartlett', `Bosc', and `Seckel' showed little or no phytotoxicity symptoms from abamectin and oil treatments with oil concentrations from 0.125% to 2.0% (v/v). On sensitive cultivars, the concentration of oil should not exceed 0.25% (v/v) when combined with abamectin to reduce the risk of epidermal injury. Oil at 0.25% provides for adequate leaf penetration of abamectin and results in commercially acceptable spider mite (Tetranychus urticae Koch) control. Chemical names used: avermectin B1 (abamectin).