Enzymatic Soil Treatments


“Hi. Have you an enzymatic product used to treat soil for growing tomatoes to prevent wilt diseases? THanks. ~D.”

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Thank you for the email.  I’m sorry, but we do not carry any enzymatic products for soil treatments.

There is some buzz in the horticultural world about treating the soil around tomatoes with enzymatic products like Kefir, a milk-based product that has a grainy texture and is a combination of bacteria and yeasts in a yogurt-like mixture of proteinslipids, and sugars. The thought behind using this is kind of like putting your plant on probiotics – Kefir contains a species of yeast called Torula sp. and Saccharomyces sp.  When Kefir curds are incorporated into the root zone of the plant, the inclusion of the enzymes from the Torula ‘bulk up’ the production of erythritol in the plant (erythritol is a storage compound found in the roots of a plant).  Essentially, it makes the roots more robust and better functioning.  As for the Saccharomyces, enzymes from this yeast allow for a reorganization of amino acids in the root tissues, and it is thought that this alteration may strengthen the roots of a plant to combat various bacterial and fungal pathogens.

However, there are three problems with treatments like this.  The first is that most enzymatic additions to the soil degrade in the heat of summer.  They prefer soil temperatures of 68 to about 90 degrees.  Depending on the color and composition of the soil, the temperature of the soil in the summer months may exceed this.  The second thing is that there hasn’t been a lot of university or field research done on these in terms of control for wilts in any plant.  And third, enzymatic treatments are very temperamental when it comes to other organic products you may be using in your garden, like copper or other pesticides (chemical or organic).

As an organic gardener, the main wilt diseases I worry about with my tomatoes are Fusarium and Verticillium.  The best way to combat these problems (and others in the process) are to incorporate the five following methods:

–Select resistant varieties. Using varieties that have more disease resistance will aid in the plant being healthy and less prone to various other diseases.

Suppress diseases. A soil is considered suppressive when, in spite of favorable conditions for disease to occur, a pathogen either cannot become established, establishes but produces no disease, or establishes and produces disease for a short time and then declines.    Among the most beneficial root-inhabiting organisms, mycorrhizal fungi can cover plant roots, forming what is known as a fungal mat. The mycorrhizal fungi protect plant roots from diseases in several ways:

–By providing a physical barrier to the invading pathogen.

–By providing antagonistic chemicals that work as antibiotics and toxins against pathogenic organisms

–By competing with the pathogen for available resources.

–By increasing the nutrient-uptake ability of plant roots. For example, improved phosphorus uptake in the host plant has commonly been associated with mychorrhizal fungi. When plants are not deprived of nutrients, they are better able to tolerate or resist disease-causing organisms.

–By changing the amount and type of plant root exudates. Pathogens dependent on certain exudates will be at a disadvantage as the exudates change.

–Crop rotation. Avoiding disease buildup is probably the most widely emphasized benefit of crop rotation in vegetable production. Many diseases build up in the soil when the same crop is grown in the same field year after year. Rotation to a non-susceptible crop can help break this cycle by reducing pathogen levels. To be effective, rotations must be carefully planned. Since diseases usually attack plants related to each other, it is helpful to group vegetable rotations by family—e.g., solanacious, alliums, cole crops, cucurbits. The susceptible crop, related plants, and alternate host plants for the disease must be kept out of the field during the rotation period. Since plant pathogens persist in the soil for different lengths of time, the length of the rotation will vary with the disease being managed. To effectively plan a crop rotation, it is essential to know what crops are affected by what disease organisms.

In most cases, crop rotation effectively controls those pathogens that survive in soil or on crop residue. Crop rotation will not help control diseases that can survive long periods in the soil without a host—Fusarium, for example. Rotation, by itself, is only effective on pathogens that can overwinter in the field or be introduced on infected seeds or transplants. Of course, disease-free transplants or seed should be used in combination with crop rotation. The period of time between susceptible crops is highly variable, depending on the disease. Three years without tomatoes or other related crops (potato, tomatillo, eggplant, petunia, ground cherry, huckleberries, peppers) is needed to avoid various wilts.

Organic and Nutritional Enhancements. Soil pH, calcium level, nitrogen form, and the availability of nutrients can all play major roles in disease management. Adequate crop nutrition makes plants more tolerant of or resistant to disease. Also, the nutrient status of the soil and the use of particular fertilizers and amendments can have significant impacts on the pathogen’s environment.  For example, a direct correlation between adequate calcium levels, and/or higher pH, and decreasing levels of Fusarium wilt occurrence has been established for a number of crops, including tomatoes.

Nitrate forms of nitrogen fertilizer may suppress Fusarium wilt of tomato, while the ammonia form increases disease severity. The nitrate form tends to make the root zone less acidic. Basically, the beneficial effects of high pH are lost by using acidifying ammonium nitrogen. Tomato studies have shown that use of nitrate nitrogen in soil with an already high pH results in even better wilt control.

Potassium fertility is also associated with disease management. Inadequate potash levels can lead to susceptibility to Verticillium wilt.  High potassium levels also retard Fusarium in tomatoes.

–Compost.  Compost is effective because it fosters a more diverse soil environment in which a myriad of soil organisms exist. Compost acts as a food source and shelter for the antagonists that compete with plant pathogens, for those organisms that prey on and parasitize pathogens, and for those beneficials that produce antibiotics. Root rots caused by Pythium and Phytophthora are generally suppressed by the high numbers and diversity of beneficial microbes found in the compost. Such beneficials prevent the germination of spores and infection of plants growing on the amended soil. To get more reliable results from compost, the compost itself needs to be stable and of consistent quality.

It has become evident that a “one size fits all” approach to composting used in disease management will not work. Depending on feed stock, inoculum, and composting process, composts have different characteristics affecting disease management potential. For example, high carbon to nitrogen ratio (C:N) tree bark compost generally works well to suppress Fusarium wilts in tomatoes. With lower C:N ratio composts, Fusarium wilts may become more severe as a result of the excess nitrogen, which favors Fusarium. Compost from manure typically has a low C:N ratio.

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© Mertie Mae Botanics LLC and Horticulture Talk!, 2009. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Mertie Mae Botanics LLC and Horticulture Talk! with appropriate and specific direction to the original content.

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