Date of Award

1989

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Lowell L. Black

Abstract

Surveys of strawberry (Fragaria x ananassa Duch.) summer nursery beds and production fields in Louisiana from 1986-1989 indicated that anthracnose crown rot (ACR) incited by Colletotrichum fragariae Brooks limited both plant and fruit production on most farms. Pathogen-free production plants were provided to growers in the strawberry growing region of southeast Louisiana for establishment of summer nursery beds. The pathogen-free strawberry plants remained free of ACR in summer nursery beds separated from beds with locally grown transplants. Infield spread of ACR was rapid in summer nursery beds, but there was no evidence of disease spread in production fields. To assay nursery plants for ACR, sample lots of plants were potted and held at 27-30 C for 6 wk to observe for development of the wilting symptoms of ACR. The results of this grow-out assay were predictive of the ACR-incidence that could occur in production fields established with those nursery plants. Fungicides were tested in vitro using fungicide-impregnated paper disk assays to determine their activity against a benomyl-resistant isolate of C. fragariae. Fungicides causing fungal growth inhibition at 100 ppm and above included captafol, CGA-453, and chlorothalonil and those causing inhibition at 1000 ppm and above included flusilazol, propiconazole, fenarimol, diniconazole, captan and TPTH. When compared by mean levels of inhibition over all rates, the seven most effective fungicides ranked in descending order were propiconazole, flusilazol, myclobutanil, fenarimol, CGA-453, chlorothalonil, and captafol. In the 1986 field test, captafol was the only fungicide tested that suppressed the disease. In 1987 and 1988 field tests, propiconazole, myclobutanil, flusilazol and CGA-453 alone or in combination with chlorothalonil significantly reduced the incidence of ACR. Data are present from 1988 and 1989 field evaluations on the efficacy of fungicides alone or in various combinations for strawberry fruit rot control. A tank mixture of benomyl + captan was effective against gray mold, stem end rot, and anthracnose. Captan was the only fungicide tested that was effective against anthracnose. Vinclozolin and iprodione were effective against gray mold.

Pages

85

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