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Stabilizing Crop-Protectant Microbes for On-Seed Application

Microbes can offer targeted protection against agricultural pests—if they survive manufacturing, storage and planting. New proprietary encapsulation methods from Battelle may soon help to stabilize microbial bioformulations used in on-seed coatings.

Biopesticides offer some significant advantages over traditional synthetic chemistries. Because they are targeted to specific pests, they generally have fewer unwanted ecological effects than broad-spectrum synthetics. They also offer promising new options to control pests that have developed resistance to chemical formulations. However, biopesticides still make up only a tiny portion of the overall agrichemical market. In large part this is due to the difficulties of stabilizing the living microbial organisms, which can vary by strain. The microbes used in biopesticides must be alive at the point in the plant’s lifecycle when the targeted pest emerges. For seed protectant formulations, that means they must survive the process of applying the product to the seeds, the time spent in transit and storage, and the planting process.

Existing seed protectant products are applied on the seed. They may contain microbial and synthetic components, which work together synergistically to protect the seed and emerging plant from nematodes, insects, fungi and other pests found in the environment. Unlike synthetic chemicals, some microbes are able to colonize the plant so that their mode of action and protection becomes integrated with the root system of the plant. However, many microbes are sensitive to changes in temperature, moisture content or pH, or to the presence of other agrochemicals.

Battelle has developed an encapsulation technique that encases the living microbes in tiny polymer microcapsules. The encapsulated microbes are applied directly on the seed using the same methods agricultural and manufacturing companies already use to apply synthetic chemicals or traditional bioformulations. The capsules can be designed to open in response to different environmental triggers such as water, pH, temperature or the presence of other bacteria in the soil.

By adjusting the trigger used to open the microcapsule, researchers can time the delivery of the living microbes to the right time in the plant’s life cycle. For example, some kinds of pests in the soil may start to emerge as temperatures rise. A temperature-dependent microcapsule would release the protective microbes at the same time. Other microcapsules may be triggered by the soil pH or the first heavy rain, again releasing microbes at the point where they are needed.

Encapsulation processes can be created for a wide variety of microbes, including bacteria, viruses or fungi. The protective coating around the microbes allows them to remain shelf-stable for a longer period of time and survive a broader range of environmental conditions. It also allows the microbes to be combined with synthetic chemicals in a single application, keeping microbes separated from the chemical until they are released. Lab tests show that the encapsulated microbes can stay shelf-stable for six months or longer without a significant loss in efficacy. This increased stabilization will help to make biologics a viable and economical solution for a broader range of applications.