Compost Extracts and the Biological Control of Foliar Plant Disease

• 1993 annual report

[Note to online version: The report for this project includes graphical figures that could not be included here. The regional SARE office will mail a hard copy of the entire report at your request. Just contact North Central SARE at (402) 472-7081 or ncrsare@unl.edu.] Aqueous extracts of anaerobically fermented spent mushroom substrate (SMS) were applied during the growing seasons of 1993, 1994, and 1995 to apple trees at two locations (university experimental orchard and commercial orchard) for control of the apple scab disease caused by the fungus Venturia inaequalis. Extracts significantly reduced the disease but were not as effective as a fungicide sprayed at the same intervals. Evaluation of the extract potency, based on laboratory assays for inhibition of germination of the pathogen's spores, suggested that the major active principle was a small, heat-stable, non-protein metabolite produced by microorganisms in the compost. In studies conducted on various composts to examine the effect of compost sample size (50 to 5,000 grams) on the precision of estimates of extract potency, we found that samples of at least 500 g were needed to avoid large errors related to sample heterogeneity and efficacy. Experiments to test the effects of aging and storage conditions (indoors vs outdoors) of compost on efficacy of extracts showed that the effects of these factors vary with compost and may be negligible or significant. Similarly, storage conditions of extracts (5 months at 24°C, 4°C, or -20°C) influenced efficacy of extracts from one source tested but not the other.

i)To test water extracts of composts for seasonal and overwintering control of the apple scab disease.

ii)To determine mechanism of action as direct vs. indirect, and microbiologically-based or chemically-based.

iii)To determine how mass of compost samples for bioassays relates to predictability and reproducibility of assay results.

iv)To determine optimal formulation of compost or compost extract for storage.