Articles
FRUIT RUSSETTING AND TREE TOXICITY SYMPTOMS ASSOCIATED WITH COPPER TREATMENTS OF GRANNY SMITH APPLE TREES (MALUS SYLVESTRIS MILL.)
Article number
489_98
Pages
565 – 572
Language
Abstract
Control of fire blight on apple trees often requires multiple applications of the antibiotic streptomycin sulfate.
This practice has led to antibiotic resistance in the pathogen Erwinia amylovora. Effective alternatives that could be used in rotation with the antibiotic would help in preventing resistance.
Copper bactericides would be useful if bloom or fruit development stages could be identified that are not subject to fruit russetting.
Granny Smith apples trees were treated with 113 or 454 g/3.8 l cupric hydroxide (50% metallic copper) once each at pink bud, full bloom, petal fall, weekly for 5 weeks afterwards, and every week.
Control trees were similarly sprayed with water or left untreated.
On each date and just before each treatment 50 fruit were tagged on each tree.
At harvest these and 100 randomly selected fruit were collected from each tree and fruit russetting evaluated.
Russetting was minimal (less than 20% of fruit affected) in 1991 and no fruit from any treatment were culls.
In 1992, among fruit treated once at bloom more than 60% were russetted and up to 55% were culls.
Russetting was negligible in post bloom treatments and the water controls.
Among fruit treated every week nearly all were russetted and 50 to 80% were culls.
In both years there were more scarred fruit in trees treated with the 454 than 113 g rate and in those treated every week than only once.
Rain did not fall during the experiments in either year.
Trees treated the 7th or 8th week or every week developed toxicity symptoms including poor growth, small fruit, sparse canopy, shoot dieback and general weakness.
Internal copper content of leaves taken from affected trees was greater (20 to 45 ppm) than from healthy trees (5 to 12 ppm).
This practice has led to antibiotic resistance in the pathogen Erwinia amylovora. Effective alternatives that could be used in rotation with the antibiotic would help in preventing resistance.
Copper bactericides would be useful if bloom or fruit development stages could be identified that are not subject to fruit russetting.
Granny Smith apples trees were treated with 113 or 454 g/3.8 l cupric hydroxide (50% metallic copper) once each at pink bud, full bloom, petal fall, weekly for 5 weeks afterwards, and every week.
Control trees were similarly sprayed with water or left untreated.
On each date and just before each treatment 50 fruit were tagged on each tree.
At harvest these and 100 randomly selected fruit were collected from each tree and fruit russetting evaluated.
Russetting was minimal (less than 20% of fruit affected) in 1991 and no fruit from any treatment were culls.
In 1992, among fruit treated once at bloom more than 60% were russetted and up to 55% were culls.
Russetting was negligible in post bloom treatments and the water controls.
Among fruit treated every week nearly all were russetted and 50 to 80% were culls.
In both years there were more scarred fruit in trees treated with the 454 than 113 g rate and in those treated every week than only once.
Rain did not fall during the experiments in either year.
Trees treated the 7th or 8th week or every week developed toxicity symptoms including poor growth, small fruit, sparse canopy, shoot dieback and general weakness.
Internal copper content of leaves taken from affected trees was greater (20 to 45 ppm) than from healthy trees (5 to 12 ppm).
Publication
Authors
B.L. Teviotdale, M. Viveros
Keywords
Malus sylvestris, Erwinia amylovora, fire blight
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