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Title: Field evaluation of microbiological control agents on Eurasian watermilfoil
Authors: University of Massachusetts at Amherst. Department of Environmental Sciences.
Aquatic Plant Control Research Program (U.S.)
Gunner, Haim B., 1924-
Limpa-Amara, Yuthana.
Weilerstein, Philip J.
Keywords: Aquatic plants
Aquatic weed control
Biological control
Eurasian watermilfoil
Myriophyllum spicatum
Issue Date: Feb-1988
Publisher: Environmental Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Technical Report
Abstract: Control of Myriophyllum spicatum L., as previously reported, was based on the multiple effects achieved by the fungus Mycoleptodiscus terrestris and selected bacterial isolates with strong pectinolytic abilities and the capacity to exercise a hormonelike stress effect on the plants. Enriched media were adopted for growth of the fungus and bacterial inoculants. This reduced incubation time to 72 hr for the fungus and to 48 hr for the bacterium. These changes in inoculum growth procedures were reflected in the subsequent change in the pattern of M. spicatum decline after exposure to the control agents: from the appearance of isolated necrotic areas to generalized systemic decline and the ultimate disintegration of the plant. The most rapid and devastating response to the organisms grown in these new media was observed in the laboratory when the inoculated plants were maintained in jars. This reflected the sustained high concentration of the inoculum and isolation from environmental effects. In pool experiments, the most significant result obtained was the restriction in biomass after treatment with M. terrestris, either alone or in combination with the bacterium Isolate P-8. These data were further validated by the appearance of the treated plants: greater tissue decay, separation of stem from root, and scarcity of new tips. In the pool setting, the application of the bacterium alone again resulted in increased internodal length. There was also a slight delay in the growth cycle as evidenced by the appearance of the plant and the number of growing tips. However, there was no significant difference in biomass between untreated controls and bacteria-treated pools. Thus, bacterial action must be considered capable of enhancing fungal lethality, but not of exercising a lethal effect by itself. This is supported by the biomass data in which joint fungal-bacterial treatment resulted in the greatest decline in biomass. The most encouraging dimension of this work was the recent extension to a field setting, in Stockbridge Bowl in western Massachusetts, and the demonstration that an explicit decline in M. spicatum could be achieved by the application of these organisms. In the course of the field experiments, unequivocal results were obtained that show: (A.) Where sustained contact between microbial inoculum and plant was achieved, plant kill followed. (B.) Symptoms of kill were systemic; leaves and stem tissue appeared bleached and chlorotic. (C.) Bleached tissue subsequently decomposed and disintegrated. That biomass figures did not appear to reflect these changes may be adduced to be a consequence of the difficulties in sequestering plants within the designated quadrant areas and the subsequent uncertainty in harvesting. At this time there may have been a loss of decayed material from the quadrant or the intrusion of new material rooted outside the treated area. In general there was a significant drop in biomass in the 12 weeks of the experiment in all quadrants (treated and control), which reflected seasonal decline. This seasonal change may also have served to mask any biomass difference that could have resulted from treatment with the microbial control agents. One may hypothesize that the pectinolytic organisms are primary decomposers, releasing nutrients and, by pitting the plant surface, providing additional ecosites for plant-associated microorganisms. This, in turn, is reflected by an increase in the numbers of these populations and the evidence of their action. The results of these initial field tests on the control of M. spicatum by the application of plant-derived microorganisms provide grounds to pursue the development of this approach as a practical control strategy. The results reported herein represent the findings of our most recent work (1984-1985) and are part of an ongoing series of studies, initiated in 1980, on the microbiological control of Eurasian watermilfoil. Beginning with laboratory studies and proceeding to pool-scale trials, the current work includes our first attempt to control Eurasian watermilfoil in a natural setting. The results provide an encouraging perspective for this microbial, ecosystem-compatible technique for the control of the aquatic weed.
Appears in Collections:Technical Report

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