U.S.EPA
Methyl Bromide Alternative Case Study
Part of EPA 430-R-97-030, 10 Case Studies, Volume 3
September 1997

Disease Suppressive Compost as an Alternative to Methyl Bromide

Disease suppressive compost can be an effective and viable alternative to methyl bromide use in some nursery production systems, and when used in combination with integrated pest management practices. Disease suppressive compost also has potential for replacing methyl bromide use in the production of fruit and vegetable crops. Diseases that have been shown to be effectively suppressed by compost use include those caused by Fusarium, Phytophthora, Pythium, and Rhizoctonia solani. In addition to suppressing the spread of disease at nurseries and in field crops, disease suppressive compost mixes provide nutrients and organic matter, thereby eliminating or reducing the need for fertilizer additions or use of expensive peat mixes. Compost can also create soil which allows for better water transmission, thereby decreasing the potential for disease development. Use of compost is particularly valuable as a way to utilize what would often be considered waste products: tree barks, municipal solid waste components, green wastes, peanut hulls, and sewage sludge. While compost generally does not contain toxic or potentially harmful substances, it is critical that compost made from sewage sludge and related municipal or animal waste must undergo testing on a regular basis, and its use carefully monitored to ensure that it will not pose any risks to human health or environmental quality. However, in general, disease suppressive compost does not require any special care during use and handling, and therefore eliminates the need for the re-entry period necessary when using methyl bromide.

While the use of disease suppressive compost as a pest control tool is theoretically sound, the science is still new and not clearly understood. It should be noted that most greenhouse operations do not have the equipment necessary to fully adopt this technology. In addition, large-scale field operations may not give consistent results, as a number of factors (including the amount of compost necessary to suppress disease) need additional research.

Disease suppressive compost is available to a limited extent, and is currently in use in some greenhouses and nurseries in the United States. Several companies sell disease suppressive compost growing media mixes that already include necessary fertilizers and wetting agents. These mixes have virtually eradicated the use of expensive fungicide drenches and fumigants like methyl bromide in the greenhouses and nurseries which are using these materials. Research is currently being conducted to determine the specific interactions that make compost effective and to determine its usefulness in field applications.

Although there are currently no standards regulating the manufacture of disease suppressive compost, the process by which it is made and the inoculations some mixes receive have been shown to be critical to their effectiveness against certain pathogens. For disease suppressive composts to be marketed as natural pesticides, the U.S. Environmental Protection Agency is requiring that they be registered and undergo health and safety testing (Segall 1995). In addition, compost sources tend to be extemely variable with regard to beneficial microorganism abundance, pathogen presence, and salinity.

Development of Disease Suppressive Compost

There are three main phases in the production of compost. The first phase occurs during the first few days when temperatures rise and sugars and other easily biodegradable substances are consumed. Over the next several weeks, in the second phase, the temperature range increases and cellulose and other less biodegradable substances, pathogens, and some biocontrol agents are destroyed. In the third phase, temperatures and decomposition rates decline as the supply of readily biodegradable substances becomes limited. The drop in temperature allows for microorganisms (e.g. Bacillus, Enterobacter, Flavobacterium balustinum, Pseudomonas, and Streptomyces) to recolonize the compost's interior layers, thereby creating the natural suppressiveness.

There are two primary mechanisms by which the colonies of biocontrol organisms in compost combat disease: general suppression and specific suppression. General suppression occurs when a high-microbial activity environment is created in which the germination of pathogen propagules is inhibited. Specific suppression involves the action of a specific microbial agent in suppressing a specific pathogen. This can be achieved by inoculating the compost with the desired microbial agent (Hoitink 1993).

To ensure that compost will provide the required suppressive qualities, it has been determined that the composting process must be carefully monitored (Hoitink 1991 and 1993, Hoitink and Grebus 1994). Heat levels and anaerobic conditions must be maintained throughout the composting cycle and the compost should be allowed to mature properly before use. Studies have shown that immature compost is generally not as effective as mature compost at suppressing disease (Quarles and Grossman 1995). Assays currently exist that allow the compost to be monitored and evaluated for its disease suppressive capabilities. In addition, some states, most notably Georgia are taking steps to regulate the compost industry by creating standards that all compost manufacturers must meet in order to ensure the quality and performance of their compost.

Research Findings

The discovery that compost can be naturally disease suppressive was made when some nurseries began using composted wood wastes in an effort to reduce their use of expensive and increasingly scarce peat. As a result, plants grown in the composted mixes showed more vigorous growth and Phytophthora appeared to be suppressed (Hoitink and Grebus 1994). These findings triggered formal research that further showed the effectiveness of disease suppressive compost as a viable replacement for methyl bromide and other fungicides. Composted mixes that have been shown to have disease suppressive qualities include those based on tree barks, green wastes, and sewage sludge (Quarles and Grossman 1995).

Because disease suppressive compost growing media has been found to be a viable alternative to chemical fungicides (methyl bromide) at nurseries, extensive research is now being conducted to determine whether or not disease suppressive composts can also replace fungicide use in field fruit and vegetable crops. Preliminary research is already showing that this is a reasonable possibility. Some of the findings in this area are summarized below:

Cost of Disease Suppressive Compost

Costs associated with growing plants in nurseries are attributable to the purchase of growing media, fertilizer, wetting agents, fungicides and herbicides, including methyl bromide, and to labor. Using disease suppressive compost generally reduces fertilizer inputs and often results in a reduction in labor costs due to the elimination of labor needed to utilize fumigants and the subsequent elimination of a re-entry period in which workers must wait to have access to a fumigated field or area. Therefore, the primary difference in cost between use of disease suppressive composts versus other growing media is the cost of the material itself. Fumigated container media range in cost from $18 to $60 per cubic yard plus the cost of methyl bromide which is $1.64 per cubic yard (Asgrow 1995, Great Lakes 1995). A cubic yard of disease suppressive compost growing media costs approximately $38 per cubic yard. Cost information is summarized in Table 1. Manufacturers of disease suppressive compost are attempting to ensure that their products are approximately equal or less in cost to other growing media that require fumigation (Southern Importers Inc 1996).

Table 1. Comparison of Costs Among Container Media Used at Nurseries



Composted Mix Uncomposted Bark Mix Uncomposted Peat Mix
Typical price per cu.yd. $30 $12 $56
Plus:

Fertilizer

Methyl bromide

Lime

Shrinkage



$6

$0

$0

$2 (6%)



$10

$1.64

$1

$4 (30%)



$6

$1.64

$0

$14 (25%)

Actual cost per cu. yd. $38.00 $28.64 $77.64

Sources: BioComp 1996, Asgrow 1995, Great Lakes 1995.


Costs associated with using disease suppressive composts in field applications include the cost of the compost plus costs resulting from implementation of integrated pest management and other low-input organic practices. Studies by Gliessman et al. (1990, 1994, 1996) compare conventional and organic methods to grow strawberries. The conventional method includes using methyl bromide to fumigate the soil. The organic method includes using compost in combination with integrated pest management approaches to take the place of the methyl bromide. Results from this study to date show that organic yields relative to conventional yields of strawberries were 39 percent lower in the first year, 30 percent in the second year, and 28 percent in the third year (Gliessman et al. 1996).


References

Anonymous. Urban yard waste benefits orchard. California Agriculture 1995, 49(5), 4.

Asgrow Agricultural Supply, Collier County, FL, personal communication, 1995.

BioComp, Inc., Edenton, NC, unpublished materials, 1996.

Gliessman, S.R.; Swezey, S.L.; Allison, J.; Chochran, J.; Farrel, J.; Kluson, R.; Rosado-May, F.; Werner, M. Strawberry production systems during conversion to organic management. California Agriculture 1990, 44(4), 4-7.

Gliessman, S.R.; Werner, M.R.; Swezey, S.L.; Caswell, E.; Cochran, J.; Rosado-May, F. Conversion to organic strawberry management changes ecological processes. California Agriculture 1996, 50(1), 24-31.

Gliessman, S.R.; Werner, M.R.; Swezey, S.L.; Caswell, E.; Cochran, J.; Rosado-May, F. Conversion to an organic strawberry production system in coastal central California: a comparative study"; study by the Agroecology Program, University of California: Santa Cruz, CA, 1994.

Great Lakes Chemical Corporation. Product specimen label. Great Lakes Chemical Corporation, West Lafayette, IN., 1995.

Hoitink, H.A.J. Compost can suppress soil-borne disease in container media. American Nurseryman 1993, pp 91-94.

Hoitink, H.A.J.; Grebus, M.E. In Composting Source Separated Organics; Plant Disease Control; J.G. Press: Emmaus, PA., 1994; pp 204-209.

Hoitink, H.A.J. Status of compost-amended potting mixes naturally suppressive to soilborne diseases of floricultural crops. Plant Disease 1991, 75(9), 869-873.

Kim, K.D.; Nemec, S.; Mussen, G. "Effects of composts and soil amendments on soil microflora and Phytophthora stem rot of pepper"; Indian River Research and Education Center: Fort Pierce, FL, 1996.

Logsdon, G. Using compost for plant disease control. BioCycle 1993, pp 33-36.

Quarles, W.; Grossman, J. Alternatives to methyl bromide in nurseries--disease suppressive media. The IPM Practitioner 1995, 17 (8), 25-37.

Segall, L. Marketing compost as a pest control product. BioCycle 1995, pp 65-67.

Southern Importers, Inc., Greensboro, NC, unpublished results, 1996.

Please note that this publication discusses specific proprietary products and pest control methods. Some of these alternatives are now commercially available, while others are in an advanced stage of development. In all cases, the information presented does not constitute a recommendation or an endorsement of these products or methods by the Environmental Protection Agency (EPA) or other involved parties. Neither should the absence of an item or pest control method necessarily be interpreted as EPA disapproval.

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