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P.L. Sholberg and A.P. Gaunce

Acetic acid (AA) as a vapor at low concentrations was effective in preventing fruit decay by postharvest fungi. Fumigation with 2.7 or 5.4 mg AA/liter in air at 2 and 20C reduced germination of Botrytis cinerea Pers. and Penicillium expansum Link conidia to zero after they had been dried on 0.5-cm square pieces of dialysis tubing. Decay of `Golden Delicious', `Red Delicious', and `Spartan' apples (Malus domestica Borkh.) inoculated with 20 μl drops of conidia of B. cinerea (1.0 × 105 conidia/ml) or P. expansum (1.0 × 106 conidia/ml) was prevented by fumigating with 2.0 and 2.7 mg AA/liter, respectively. Tomatoes (Lycopersicon esculentum Mill.), grapes (Vitis vinifera L.), and kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang et R. Ferguson var. deliciosa] inoculated with B. cinerea or navel oranges (Citrus sinensis L.) inoculated with P. italicum Wehmer did not decay when fumigated with 2.0 mg AA/liter at 5C. AA fumigation at low temperatures (1 and 5C) with 2.0 or 4.0 mg AA/liter prevented decay of `Spartan' and `Red Delicious' apples and `Anjou' pears (Pyrus communis L.) inoculated with B. cinerea and P. expansum, respectively. `Spartan' apples immersed in a suspension of P. expansum conidia (1.4 × 105 conidia/ml) and fumigated with 2.7 mg AA/liter at 5C had an average of 0.7 lesions per fruit compared to 6.1 for nontreated fruit. Increasing the relative humidity from 17% to 98% increased the effectiveness of AA fumigation at 5 and 20C. At the concentrations used in our trials, AA had no apparent phytotoxic effects on the fruit. The potential for commercial fumigation with AA to control postharvest decay of fruit and vegetables appears promising.

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A.L. Moyls, P.L. Sholberg, and A.P. Gaunce

A fumigation technique using brief exposure of fruit to a low concentration of acetic acid vapor was combined with modified-atmosphere packaging to reduce storage rots and increase shelf life of grapes (Vitis vinifera L.) and strawberries (Fragaria ×ananassa Duch.) by two or three times normal values. Both commodities were inoculated with spores of Botrytis cinerea Pers. before fumigation with acetic acid, packaging, and storage at lowered O2 levels. Fumigation with acetic acid at 8.0 mg·L–1 followed by modified-atmosphere packaging for 74 days at 0 °C reduced the percentage of rotted grapes from 94% to 2%. Strawberries fumigated with acetic acid at 5.4 mg·L–1 were free of decay compared to 89% rotted for the control fruit stored for 14 days at 5 °C.

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M. Meheriuk, A.P. Gaunce, and V.A. Dyck

`Golden Delicious', `Delicious', and `Spartan' apples (Malus domestics Borkh.) showed a high, moderate, and low tolerance, respectively, to methyl bromide fumigation. Incidence of external and internal disorders increased, in most instances, with longer storage periods after fumigation treatments and with longer exposure times to the fumigant. Dips in diphenylamine before fumigation reduced, but did not prevent, disorders. Fumigation had little effect on firmness and no effect on soluble solids content or titratable acidity. Methyl bromide concentrations with a low risk of disorder development were 32 to 64 g·m-3 for `Golden Delicious', 32 to 48 g·m-3 for `Delicious', and 32 g·m-3 for `Spartan', all at 10C for 2 hours.

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A.G. Reynolds, D.A. Wardle, A.C. Cottrell, and A.P. Gaunce

Paclobutrazol (PB) was sprayed on hedged `Riesling' (Vitis vinifera L.) vines at one of five concentrations (0, 1000, 2000, 3000, or 4000 mg·liter-1) as single annual applications over 3 years (1987-89). Observations were made on growth, yield, and fruit composition during the years of application and 1 year thereafter (1990) to test carryover effects. PB had no effect on vine vigor, expressed as weight of cane prunings, during the three application years, but reduced vine vigor linearly with concentration in 1990. Yield was reduced by PB in the first 2 years of the trial, while in one season cluster weight and berries per cluster were also reduced. °Brix was increased by PB during all 3 years of application; titratable acidity was reduced and pH increased in the first year of application. PB sprays significantly reduced lateral shoot length, mean leaf size on both main and lateral shoots, and total leaf area on main and lateral shoots. Winter injury to buds, cordons, and trunks was also reduced with increasing PB level. Residues of PB in fruit in the first year of application ranged from 9 μg·kg-1 at the 0-m·gliter-1 level to 638 μg·kg-1 at the 4000-mg·liter-1 level. PB shows promise as a viticultural tool for advancement of fruit maturity, with possible additional benefits such as improved vine winter hardiness. Chemical name used β -[(4-chlorophenyl) methyl]-α -dimethylethyl)-1-H-1,2,4-triazole-l-ethanol (paclobutrazol, PB).

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Andrew G. Reynolds, A.C. Cottrell, D.A. Wardle, and A.P. Gaunce

`Okanagan Riesling' (Vitis spp. parentage unknown) vine trunks treated in 1984 with three levels of NM (0, 10,000, and 20,000 mg·liter-1) and three levels of paclobutrazol (PB; 0, 250, and 500 mg·liter-1, in white latex paint were subjected to a reapplication in June 1987 at the same rates of NAA and at 0, 1000, and 2000 mg PB/liter. Linear reductions in suckers per vine were observed with increasing NAA concentration but not PB. Yield and clusters per vine were reduced by PB in the season following retreatment (1988), while berry weight was increased by NAA in 1987. Titratable acidity was increased by NAA in 1988, and pH was highest that season with PB at 1000 mg·liter-1 . No PB was detected in fruit tissue in 1987, but NAA levels of 2.4 and 2.0 μg·kg-1 were detected in clusters sampled from the 10,000- and 20,000-mg·liter -1 treatments, respectively. Chemical names used: l-naphthaleneacetic acid (NAA); β-1[(4-chlorophenyl)methy]-α-1 (l,l-dimethylethyl)-1H-l,2,4-triazole-l-ethanol (paclobutrazol).