Herbicide Damage in The Garden Part 3

Welcome to part three of our series on Herbicide Damage in the Garden. In this episode we will answer the questions...What Now? What do you do if herbicides have been found in your soil? Welcome to the growing zone. In episode 2 we walked you through how to diagnose herbicide damage. If herbicides have been confirmed to be present in your garden soil, either through professional diagnosis, bioassay or laboratory testing, you have a few options to consider. In this episode we will learn methods you can consider using if you have herbicide residuals from growth regulating type herbicides in your garden soil. Depending on your individual situation and the extent of the situation, relocating the garden or removal of the soil may be the best option. While removal of the soil can involve lots of labor, time, and money, it may be best, especially if the soil contains high levels of herbicides. What should you do with the removed soil? Each situation will vary, and the quantity of soil will help determine the best way to handle it. Contact your local County Extension agent for some advice. Another option to consider is to plant a cover crop in the area using a plant species that is not susceptible to the herbicide, then cut, remove and destroy this plan material after it has matured. These plants will help absorb some of the herbicide in the soil and may also increase microbial activity. The increased microbial activity will increase the rate of chemical breakdown. It may take several years of repeat cover crop usage on the site before the herbicide levels in the soil decrease. Some examples of cover crops to consider are wheat, rye, oats, or millet. Make sure to harvest the cover crop before it goes to seed. Remember that the plant material will contain certain levels of the herbicide that is in the soil, so don't compost the plant material or feed it to livestock that you plan to use the manure from in your garden or to animals you are currently milking. Contact your local county extension office or local waste authority for suggestions on disposal of the cover crop plant material. A third option in healthy soils with adequate microbial action, is to consider frequent tillage and irrigation to aid in the microbial degradation of the herbicide in the soil. Microbes in the soil need moisture and aerobic conditions to survive. Tillage improves the oxygenation within the soil that microbes need and improves photo-degradation due to the increased sun exposure. A final option that has been suggested is to use activated charcoal to absorb the herbicide in the soil. Activated charcoal may be broadcast across the area followed by tillage and irrigation. Suggested rates range from about 100 to 400 pounds of activated charcoal per acre or about 2.3 to 9.2 pounds per thousand square feet. Another option, especially for smaller areas is to make a slurry with the charcoal, which is then incorporated into the soil. Suggested rates are 1 pound of charcoal per gallon of water for the slurry. Make sure to read and follow the label instructions. There are a few other factors which may cause herbicides to persist longer in soil. First, soils with a high pH. High pH tends to slow down microbial degradation, however, chemical degradation can speed it up. Second, soils with high organic matter will significantly decrease the movement of the herbicide out of the garden. Finally, herbicides can also persist longer in areas of low moisture and sunlight such as in a high tunnel or greenhouse. Ample moisture and sun are important to breaking down the chemical. Be aware of the ways herbicides can unintentionally end up in your garden and take the necessary steps to prevent it. Be sure to ask questions of all the suppliers of soil, soil amendments and mulch that you use. Do a bioassay of all top soil and compost before adding it to your garden, or send a soil or compost sample to a laboratory for testing. If you find herbicides in your garden there are a few things you can do to limit the impact of that herbicide, although prevention is the best course of action. Check out Episode one for more information on how herbicides end up in your garden, or episode two where we discuss how to diagnose herbicide presence. And, of course, contact your local county extension office for more information and assistance.