Date of Award

5-2007

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Botany and Plant Pathology

Advisor

Seanna Annis

Second Committee Member

David H. Lambert

Third Committee Member

John M. Smagula

Abstract

Mummy berry disease, caused by the fungus Monilinia vaccinii-corymbosi, is the predominant lowbush blueberry disease in Maine. Chemical fungicides can control mummy berry, but organic growers may only burn or mulch fields to control disease. Correct treatment application timing in relation to leaf bud development and mummy berry germination is essential for controlling primary infection. Organic biological controls were tested in randomized complete block design experiments at one organically managed and three conventionally managed fields over two years. The treatments tested in 2005 were two aerated and two non-aerated compost teas (diluted 1:3 with water), Plant Shield (Trichoderma harzianum formulation; Bioworks), and Sonata (Bacillus pumilus formulation; AgraQuest). The 2006 treatments tested were undiluted aerated compost tea, Sonata, Serenade (B. subtilis formulation; AgraQuest), Trilogy (Neem formulation; Certis USA), and BioLink (garlic adjuvant; Westbridge Ag Products). In 2006, BioLink was added to the other four treatments as an adjuvant, and a water treatment was applied in both years as a control. Disease incidence was measured as percent of stems infected. Yield was the weight of harvested berries from a hand raked strip in each plot. Bacterial and filamentous fungal colony forming units (CFU) present on leaf surfaces before and after treatment applications were correlated to the incidence of mummy berry disease. Three centimeters of peat mulch was applied in 2006 to inhibit germination of apothecia from M. vaccinii-corymbosi mummified fruit. Adjuvants were tested in greenhouse studies before BioLink was used in 2006 field applications. Leaves sprayed with Plant Shield and plated with M. vaccinii-corymbosi significantly suppressed mycelial growth compared to control leaves. Plant Shield was not effective at lowering mummy berry blight incidence when applied in field experiments. Leaves from Sonata and Serenade plots often had significantly more bacterial CFU present than other treatments throughout the season, but neither significantly lowered disease incidence. Serenade showed some affect on mummy berry disease, with lower mean disease incidence than both water and untreated controls in both fields. The diluted and undiluted aerated and non-aerated compost teas in 2005 and 2006 did not significantly lower mummy berry disease incidence compared to the control plots at any of the field sites. There was no direct correlation between the total number of bacteria and filamentous fungi present on the treated leaf surfaces and disease incidence. The BioLink adjuvant added to the treatments did not alter retention of microorganisms on leaf surfaces, and the BioLink and Trilogy treatments had no effect on disease incidence. Peat mulch applied before leaf bud break in one field significantly suppressed disease by 41% compared to the control, but had no effect on disease at the other field. None of the treatments significantly affected yield when compared to the controls. There is potential to lower mummy berry disease incidence on lowbush blueberry using organically certifiable controls. Our preliminary studies indicate that peat mulch and Serenade should be reexamined for disease control.

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