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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #69934


item Kremer, Robert

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Agricultural and horticultural production enterprises require prudent use of chemicals to control many pests that can adversely affect yields and quality of cultivated plants. In situations where a chemical is used continuously because it had performed reliably over the years in controlling a specific pest, a shift in the soil biology or plant response to the chemical may occur resulting in actual damages due to "overuse" of the same chemical. This type of situation was apparent for many ornamental plant enterprises in which a particular fungicide was used continuously over a period of several years. For example, leatherleaf fern (the fern used in many flower arrangements) consistently produced distorted and off-color fronds (leaves), which were of low-quality grade and of low value. We found that where the fungicide was used continuously, high concentrations of soil bacteria that detrimentally affected plant growth developed in the leatherleaf fern root zone. The fungicide, applied repeatedly during the growing season, apparently selected a segment of soil organisms that actually attacked the plants and adversely affected product quality. This information will be useful in developing pest management systems with several chemical, biological and cultural options available, decreasing reliance on a limited number of pest control chemicals, and reducing severe shifts in the composition of the natural soil organism populations.

Technical Abstract: Reduced frond production as well as foliar disorders and root damage to leatherleaf fern (Rumohra adiantiformis [Forst.] Ching) coincided with the widespread use of Benlate fungicide in grower operations. These symptoms could not be explained by environmental conditions or the presence of new pathogens. The objective of this study was to examine the effects of Benlate at labeled rates on frond production, root morphology, and soil an rhizosphere microbial characteristics of leatherleaf ferns. A separate experiment was conducted by adding Benlate at the labeled drench rate to previously untreated soil to evaluate the promotion of soil bacterial populations. Benlate was applied to leatherleaf fern plants in the greenhouse at labeled foliar and drench rates for 17 months. Fronds were harvested during the last nine months. Roots of the ferns were examined using electron microscopy after final harvest. Rhizosphere bacteria were evaluated for composition and bioassayed for potential phytotoxic activity Ferns receiving Benlate applied as a drench yielded 38% less marketable fronds than those receiving no Benlate. All Benlate treatments reduced root hairs and disrupted root surfaces of ferns. High proportions of rhizosphere bacteria that were detrimental to plant growth were associated with Benlate-treated plants. Promotion of detrimental bacteria by Benlate was verified in soil receiving the chemical under controlled conditions. Results indicate that Benlate can potentially reduce yields of leatherleaf ferns directly by contact with root surfaces or by promoting deleterious bacteria in the rhizosphere.