Sessions - Disease Suppression


Disease Suppression and Microbial Communities of Potting Mixes Amended with Biowaste Compost


BLOK, WIM J. (1), Coenen, Trudie CM (1), Pijl, Agata S. (2), Termorshuizen, Aad J. (1)


(1) Biological Farming Systems Group, Wageningen University, Marijkeweg 22, 6709 PG Wageningen, the Netherlands (2) NIOO-Centre for Terrestrial Ecology, P.O. Box 40, 6666 ZG Heteren, The Netherlands


Dutch biowaste compost, produced from separately collected organic household waste, is often applied to agricultural land as an efficient and inexpensive way to increase organic matter levels. Previous studies have shown that biowaste compost has the potential to provide significant disease suppression especially to peat-based potting mixes where as much as 20 vol.% of compost can be added. This disease suppression is, however, currently still largely unpredictable. To be able to effectively use biowaste compost in disease management, we aim to identify key factors that determine the level and persistence of disease suppression, which will enable us to select or produce batches of suitable compost. Nine batches of biowaste compost were collected from commercial composting facilities and tested directly after collection and again after a storage period of 4-6 months. Potting mixes of light Sphagnum peat with 20 vol.% compost were characterized microbiologically and physico-chemically and their disease suppressiveness was evaluated in greenhouse bioassays at 20C for the combinations Pythium ultimum cucumber, Phytophthora cinnamomi-lupin and Rhizoctonia solani-carrot. Disease suppression varied considerably between the nine compost batches, was age-dependent and differed per pathogen. Suppression of P. cinnamomi was strongly correlated (R(&2)=72%) with general microbial activity measured as basal respiration (g CO(2)/ ml potting mix / hr). The basal respiration of the potting mix explained 36% of the disease suppression of P. ultimum but was not correlated with suppression of R. solani. Denaturing gradient gel electrophoresis analysis of PCR-amplified SSU rRNA genes, followed by sequence analysis of excised bands, was used to characterize the microflora of composts and potting mixes. Differences in composition of the bacterial and fungal microflora in relation to differences in disease suppression will be discussed.


Compost-Induced Suppression of Turfgrass Diseases




(1) Dept. Plant Pathology, The Ohio State Univ., Columbus, and (2) Dept. Plant Pathology, Cornell Univ., Ithaca, NY, USA


Composted materials and humic substances have long been used by the turfgrass industry as soil conditioners and organic fertilizers.  Until the1940's, composts served as one of the principal sources of fertilizer used on golf courses and athletic fields.  The utilization of composts declined dramatically, however, with the advent of synthetic, urea-based fertilizers, and organic fertilizers such as Milorganite which offered more consistent and predictive nutrient release characteristics.  After nearly 60 years of heavy reliance on chemical inputs, we find ourselves in the midst of a resurgence in the use of organic matter amendments and topdressings for managing high quality turfgrass.  This resurgence is in part fueled by an increase in the diversion of solid wastes from surface waters and landfills, concerns over urban sprawl and an intense desire by the public to develop more environmentally-sound waste utilization and pest/disease management methods.   Recent research on the use of composts on turfgrass has focused on the suppression of turfgrass diseases, the potential for reducing fungicide and fertilizer inputs, and the effects of composts on the physical, chemical and microbiological properties of soils.  The specific claims of this session are to provide an overview of the nature of turfgrass diseases and how organic matter amendments and topdressing applications may be used to promote healthy turfgrass and suppress the development of disease. Emphasis will be placed on the disease suppressive properties of composts used by the turfgrass industry.


Suppressive Effects On Soil Borne Diseases of Yard Waste Composts in Organic Horticulture


CHRISTIAN BRUNS, Christian Schüler


Department of Ecological Agriculture, University of Kassel, Germany, Germany


The considerable number of reports about suppressive effects of composts on soil borne plant pathogens covers biowaste and yard waste composts originating from source separated organic kitchen and garden refuse. We compared suppressive effects of yard waste- (YWC), biogenic waste- (BWC) and cattle manure compost (CMC). Both, the amendment of Pythium ultimum inoculated sterilised sand and nonsterilised growing media with YWC and BWC resulted in a significantly increased fresh matter yield and a reduction of the disease incidence by 30 to 50 % with several hosts. CMC showed such effects only occasionally. Therefore, in a current research project YWC is produced on commercial composting plants according to a fixed composting system. Peat batches of german or baltic origin are amended with YWC up to 40 % (v/v) and used by organic horticulturists involved in the project. The suppression of several pathogens (P. ultimum, Phytophthora cinnamomi, Fusarium spp.) by YWC amended media was successful in both standard bioassays and under practical conditions with Euphorbia pulcherima, Pelargonium peltatum, Chamaecyparis lawsonianae and a number of herbs serving as hosts. Reduction of disease incidence ranged from 30 to 80 % in treatments with a strong disease severity of approx. 70 to 90 %. From both, the literature and our own research it was shown that suppressive effects of composts are mainly related to biological features as demonstrated by gamma-irradiated composts, higher counts of antagonistic bacteria, cellulose degrading fungi in YWC and BWC than in CMC or fungistatic effects induced by YWC and BWC. Evaluating the three composts for their microbial activity there was no correlation with the suppression of P. ultimum. Calculating a specific activity (unit microbial activity per unit microbial biomass), however, resulted in a correlation to suppressive effects (r = 0,742**). YWC and BWC had high specific activities whereas the specific activity of CMC was low. There are indications that microbial communities of YWC and BWC have a greater competitive potential for easily available substrates, i.e. root exudates than those of CMC.


The Effects of Compost Tea On Golf Course Greens Turf and Soil On


Blair, Marney (1), CONFORTI, CHRISTA (1), Hutchins, Kevin (2), Koch, Jean (1).


(1)The Presidio Trust, (2) Arnold Palmer Golf Management Company, USA


Pest management on golf courses has traditionally included regular fungicide applications to the greens. Many of these fungicides have the potential to harm wildlife, humans, or move into groundwater. In an attempt to reduce the need for fungicides and improve the overall health of turf and soil, the Presidio Golf Course conducted a field trial to evaluate the effects of compost tea applications on golf course greens under real-world conditions. Greens were sprayed at a rate of one gallon of compost tea per 1000 square feet for twelve months. Applications occurred weekly during times of high disease pressure, and bi-weekly during times of moderate or low disease pressure. Turf was evaluated for color, density, overall quality, thatch depth, root length, mycorrhizal root colonization, and disease, insect, and weed incidence. Soil was tested for pH, carbon dioxide level, oxygen level, turf nutrient levels, and bacterial and fungal biomass. Turf treated with compost tea had longer root length, less disease, and higher density than untreated turf. Treated turf did not differ from untreated turf in color, overall quality, thatch depth, soil pH, soil carbon dioxide, soil oxygen, insect and weed incidence, soil nutrient levels, soil bacterial biomass, soil fungal biomass, or mycorrhizal root colonization. Compost tea has become an integral part of Presidio Golf Course pest management and the overall turf maintenance program. Further trials are needed to evaluate various application rates and application methods to determine the potential effects of compost tea on golf course soils.


Effects of Compost Extract On Disease Suppresion and Growth of  Potato




Team Project INCO-RTD/DNRST, Guinea


Valley of Timbi has 970 mm of annual rainfall  where potatoes are the principal crop and it is an important zone for the more output potatoes in Fouta Djallon. There are numerous constraints to its production. Among the major constraints is the presence of pests and diseases. However its yield per area unit  has remained very low. One of very important factor is potatoes's susceptibility to a devastating diseases caused by  early blight, late blight and bacterial wilt . Thus there is a great need to protect the crop by using news strategies to implement conventional control measures involving compost extract. The purpose of this communication is to determine the effects of compost extract on the suppression of early blight, late blight and bacterial wilt on grown potatoes. Trial were conducted at up to agronomic center station of Bareng. Six treatments were studied  including: control (nil), compost extract from four or eight days with five  or ten applications, and  Benlate. This strategy  indicates that three diseases were likely to become established within the trial  as early blight, late blight and bacterial wilt. According to the results, trials with  compost extract from four days with ten applications have provided highest yield( 8,83 tha-1 )more than  compost extract  from eight days with five application . However  compost extract from four days with five application have been less damage (0,77 tha-1) of tubers. During vegetative period, disease had  been significantly difference in comparison with control. In early blight  case, area with  compost extract  from eight days with ten applications has been less infestation (0,14 %) compared with control (4,46%). In late blight case, trial with  compost extract  from eight days With ten application have given higher infestation (3,16 %). With  bacterial wilt case, area with  compost extract  from eight days with ten application had provided low infestation (33,37%), trial with Benlate had too higher infestation (76, 57%). In storage period,  compost extract from 4 days with 5 applications gave less damage to the tubers (414g) in comparison with the control treatment (622g).


Compost-Induced Disease Suppression and Growth Enhancement in Vegetable Crops.


S. A. MILLER(1), H. A. J. Hoitink(1) and M. D. Kleinhenz(2)


(1)Dept. of Plant Pathology, (2) Dept. of Horticulture and Crop Sciences, The Ohio State University-OARDC, Wooster, OH USA 44691., USA


Vegetable crops are subject to numerous environmental stresses and foliar and fruit diseases that reduce yield and quality.  The effects of compost amendment on disease suppression and yield were assessed in both conventional and organic systems.  Bacterial spot, caused by Xanthomonas spp., was significantly reduced in compost-amended tomatoes in both greenhouse and field evaluations, when disease pressure was high.  Anthracnose fruit rot, caused by Colletotrichum coccodes, was suppressed in organic but not conventionally-produced tomatoes under environmental conditions favorable to disease development.  Organic tomato yield was higher in compost-amended than non-amended soil.  One or two years of compost amendment did not increase conventional tomato yield. Initial evidence from studying the effects of multiple seasons of compost amendment on disease suppression and plant growth and yield in conventionally-produced tomatoes and peppers indicates that compost amendment may lead to shifts in biomass accumulation and partitioning, especially under low moisture and high temperature stress.


Soil Organic Matter and Plant Disease Suppression in Field Agricultural Systems.




Dept. of Horticulture, Oregon State University, USA


This paper will summarize the literature on soil organic matter mediated suppression of root and foliar diseases caused by bacterial and fungal pathogens in field agricultural systems.  The discussion will include: 1) mechanisms involved in soil organic matter-mediated disease suppression, including soil biological (e.g. competition, antibiosis, hyperparasitism, and induced resistance), chemical (e.g. nutrient availability), and physical (e.g. porosity, plant available water) properties; 2) soil organic matter source, including green manures and raw and composted organic wastes; and 3) soil organic matter quality (e.g. decomposition level).


Evaluation of Composted Agricultural Wastes As Alternatives for Plant Disease Control


(1)TRILLAS,M.I., (2)Aviles, M., (2)Ordovas, J., (3)Bello, A., (4)Tello, J.


(1)Universitat de Barcelona, Facultat de Biologia, (2)Universidad de Sevilla, Escuela Universitaria Ingenieria Tecnica Agricola (3)CSIC. Centro de Ciencias Medioambientales, (4) Universidad de Almeria., Spain


The natural suppressive effects of composts prepared from tree barks and some municipal solid wastes against plant diseases caused by soil-borne plant pathogens are well established.  Little is known, however, about such effects of composts prepared from by-products of the plant oil, rice, cork, grape, cotton and mushroom industries.  In Spain, the agricultural industry generates per year about 10 x 105 of wastes form the oil industry, 32 x 104 from the wine industry, 15 x 104 of worn out mushroom compost, 4.5 x 104 or rice husks, 1.8 x 104 from industrial cork wastes and about 2.9x104t from cotton fiber.  Moreover, in 1998 Spain was the fourth country in the world, after U.S.A., Japan and Italy, in the consumption of methyl bromide (MeBr) with a total of 419 t, applied as a fumigant to around 8988 ha of cultivated soil, mainly to strawberry (33%), cucumber (29%), ornamentals (9%) and cucurbitaceae(9%) fields.  As a member of the EU, Spain should reduce these levels by 2005, with a gradual retreat of 60% in 2001, 75% in 2003.  MeBr is used to control Fusarium oxysporum, Phytophthora spp. and Verticillium spp. and the root-knot nematode Meloidogyne spp.  For the control of these diseases and interregional project was initiated to test the feasibility of suppressive composts as alternatives. We have established that composted cork effectively suppresses Verticillium wilt and Rhizoctonia damping off disease and slightly reduces Fusarium wilt, which is also controlled by composted grape residues.  Root know disease caused by Meloidogyne spp. was suppressed through soil incorporation of 50-100 ha-1 of diverse agricultural industry residues, with a C/N between 8-20.  Results are discussed from the viewpoint of microbial and chemical properties of the materials.  Composts of various organic waste materials show