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S.V. Overton, L.D. Moore, and O.K. Miller

Ultrastructural observations were made of leaves of apple (Malus domestics Borkh. cv. Red Delicious) 12, 24, and 72 hours following a single foliar application of the sterol-inhibiting fungicide bitertanol. Thylakoids of chloroplasts from treated leaves were swollen and irregular and chloroplasts had lost their integrity within 12 hours after treatment. Occasionally, mitochondria looked washed out, although no other changes in membrane or organelle structures were observed. Within 24 to 72 hours, moreover, thylakoids of chloroplasts from treated leaves returned to a state similar to that of the controls. However, the numbers of starch granules in the chloroplasts of treated leaves appeared to increase throughout the 72 hours and remained somewhat higher than levels in controls. Thus, bitertanol does not appear to have a lasting effect on apple leaves. Chemical name used: ß-([1,1′-biplenyl]-4-yloxy)-α-(1,1-dimethylethyl)-1H-1,2,4-trizole-1-ethanol (bitertanol).

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Alan R. Biggs

The proportion of spurs blooming on `McIntosh' apples (Malus domestica Borkh.) was reduced significantly in 1986 and 1988, but not in 1987, following seasonal programs of six bitertanol or flusilazole treatments applied at two and three rates, respectively. The fungicides were not associated with any visible phytotoxic effect nor was shoot length reduced by any fungicide treatment. In two of three experiments conducted in May and June 1986, transpiration was reduced by the low rate of flusilazole and the high rate of bitertanol relative to both the captan and nonsprayed trees. In all three experiments, flusilazole at 1.4 g a.i./100 liter was associated with transiently reduced transpiration rates, lasting a minimum of 48 hours, relative to the nonsprayed control. Fungicides affected the diffusive resistance of apple leaves in all three experiments; however, there were no consistent treatment effects on diffusive resistance among the three experiments.

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Gonzalo Morales-Salazar, Jose P. Morales-Payan, and Bielinski M. Santos

The effect of three plant growth retardants, bitertanol, tradimefon, and hexaconazole, on short-term vine regrowth of pruned `Arabe' grape (Vitis vinifera) was studied in field experiments conducted in the Dominican Republic. Individual soil drench treatments of the three retardants were applied to adult pruned `Arabe' grape plants at rates 0, 0.25, 0.50, 0.75 and 1.00 g active ingredient per plant. Three weeks after treatment, bitertanol did not have a significant effect on vegetative growth, whereas triadimefon and hexaconazole caused significant reductions on vine regrowth. The effect of triadimefon as a growth retardant was stronger than that of hexaconazole, as described by regression equations Y = 30.88 - 25.68X for triadimefon, and Y = 32.9 - 15.2X for hexaconazole.