By Michelle Grabowski
What is ASD?
Anaerobic soil disinfestation (ASD) is a disease management strategy used to reduce or eliminate soil borne plant pathogens from agricultural soils. Despite its complicated name, ASD is a relatively simple process.
By adding carbon (a food source) and water (to fill pores in the soil), ASD harnesses the power of naturally occurring soil microorganisms to temporarily create conditions within the soil that are toxic to plant pathogens. The procedure was developed to provide an alternative management strategy to soil fumigation.
Here is a quick summary of the procedure:
- A carbon source (i.e. molasses or wheat bran purchased from a feed store) is worked into the soil to a depth of 6 to 8 inches.
- The soil is irrigated until it is completely saturated to the same depth. Ponding of water should occur. This will take several hours.
- Soil is covered with plastic. The plastic covering needs to be completely sealed at the edges and must remain in place for 3 to 5 weeks.
- The soil needs to be consistently 85 F or greater while the plastic is in place to be effective. In Minnesota this means that the procedure needs to take place during the growing season. Most growers choose spring or fall to allow time for a crop during the primary part of the growing season.
Ohio State University has a great publication describing the steps for anaerobic soil disinfestation in detail.
What types of diseases is ASD a useful management tool for?
In both fruit and vegetable production, a number of different soil borne plant pathogens can result in root rot, poor growth, plant wilt, and death. Soil borne pathogens include fungi, bacteria, and nematodes. These types of pathogens often build up in the soil over multiple years of production, especially if crop rotation is not used. Research in other states shows that ASD is successful in eliminating the fungi Verticillium dahliae (wilt) and Fusarium oxysporum (wilt, root and crown rot), the water molds Pythium spp. (root rot) and Phytophthora capsici (root rot and wilt), bacteria like Agrobacterium tumefaciens (crown gall), and root knot nematode (Meloidogyne incognita) from soil.
How does ASD work?
There appear to be multiple factors at work in ASD. Agricultural soils naturally have small pores filled with oxygen. When these are filled with water, the soil turns anaerobic (no oxygen available) and the microorganisms in the soil change dramatically. Most plant pathogens are not well adapted to these low oxygen conditions and die or have reduced growth. There is an increase in the number of bacteria that thrive in anaerobic conditions. As these bacteria consume the carbon source without oxygen, they release volatile organic compounds, including alcohols, organic acids, and organic sulfides all of which contribute to the suppression of plant pathogens. Some of these new microorganism are believed to be antagonistic to plant pathogens as well.
Testing ASD in Minnesota
In 2018, we tested ASD on two sites with known disease problems.Click here to see more...
One site had a history of Verticillium wilt, a soilborne fungus that infects a number of fruit and vegetable crops, resulting in wilt and death of the plant. The other site had clubroot, caused by a long lived pathogen (related to slime molds) that causes the roots of cole crops to become swollen and distorted.