In the Garden:
Upper South
February, 2006
Regional Report

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2030

Inoculating the soil with a mycorrhizal product not only helps the plant survive transplant shock, it also improves growth and pest resistance.

The Frontiers of Pest Control

We all have the perfect garden at this time of year, at least in our mind's eye. There are no bugs, no mildew or other fungus with which to contend. Yet no matter how much we may wish it otherwise, they will appear again, decimating melons, attacking roses, and defiling whatever else seems an appropriate luncheon host. So, in the spirit of preparedness, now is the time to assemble an arsenal of defenses, instead of waiting until the height of summer.

Any gardener who cares about the environment and their own personal heath and that of their family will appreciate the ever-increasing number of alternatives to synthetic chemicals that are available. The difficulty is in understanding what they do, how they work, and what to choose.

Biological Agents
Biological agents contain living microbes, either bacteria or fungi, that suppress the disease pathogen. The mode of activity may be by producing a substance that inhibits growth of the pest, seeks and destroys the pest, or increases the plant's natural defenses. A major benefit of biological agents is that they have specific targets, which limits their toxicity to humans and the environment.

The products most widely available to gardeners utilize Bacillus subtilis for control of fungal diseases. Rhapsody, Serenade, and Sonata are trade names for these biofungicides. There are also products used by commercial growers that utilize a fungus to control diseases such as root rot. More of these will become available to home gardeners in the future.

The key to using biological agents is to remember that they are living entities that need a suitable environment in order to grow and survive, and that they often need time to become established. They are best used as a preventative.

Biologically Rational Materials
Also known as biorational chemicals, these are materials derived from natural sources, including botanicals, microbial compounds, and minerals. Botanicals, such as neem oil, ground sesame plant, or pyrethum, originate from plants. Microbial compounds, such as Bacillus thuringiensis, or Bt, are collected from bacteria and fungi and are detrimental to other microbes. Minerals mined from the earth or minimally processed, such as sulfur, copper compounds, diatomaceous earth, hydrogen peroxide, kaolin clay, or bicarbonates, are also used as pest-control agents.

Biorational chemicals often work as quickly as synthetic chemicals, but are possibly less likely to result in pest resistance. Usually biorational chemicals degrade more quickly in the environment. In order to use them effectively, it's important to understand both the mode of action of the materials as well as the pest to be controlled.

Plant-Incorporated Protectants
Plants themselves can respond to attacks by insects and diseases by activating an array of natural defense compounds that can inhibit disease or reduce insect feeding. When certain compounds are absorbed by the leaves or roots into the plants, this resistance can be increased. The DNA of the treated plants is not altered, just the resistance level. Incorporation of plant protectants takes time and is best used as a preventative before the pest is seen. Generally, there is very low toxicity to humans, non-target organisms, soil, and groundwater.

Some compounds induce resistance in plants when applied to the foliage, such as salicylic acid, potassium phosphate, a water solution of NPK fertilizer, and certain plant or microbial extracts. For example, a product called Messenger contains as the active ingredient a protein called harpin, which is one of a class of proteins produced in nature by certain bacterial plant pathogens. The harpin protein elicits a complex natural defense mechanism in plants, making them resistant to a wide range of fungal, bacterial, and viral diseases, and even some insects.

The addition of mature compost to soil or potting mixes has been shown to induce a resistance response in above-ground parts of some plants, but the response varies greatly. Commercially available compost teas, applied either as a soil drench or sprayed on foliage, have also shown benefits. Although neither of these practices deals with specific pests, the overall improved growth of the plants leads to improved resistance.

Mycorrhizal inoculants are fungi that form a synergistic relationship with plant roots, helping the plant to better absorb nutrients, improve growth, and be better able to survive pest attacks. Microbials used for soil diseases have also shown above-ground plant parts to be more resistant to pests.

The bottom line is that while some of these biological controls have proven effectiveness, others will take years for us to understand and use most effectively. Plus, they are not always easy to find locally and will often have to be ordered through catalogs. Time and your own research and experimentation will be needed. Still, it's exciting to see that more and more universities and companies are addressing a concern for health and the environment and that we have the option of using them.


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