Microbes against microbes

Biological control, or biocontrol in plant pathology refers to the use of beneficial microbes to prevent disease development. In this article, we will provide guidelines on how to use microbial-biofungicides for the control of root rot and damping off in greenhouse-grown vegetables.

Apply biofungicides as preventive, not curative.

Beneficial microbes control pathogens by directly feeding on them, producing chemicals that inhibit pathogen growth, competing for resources, or inducing plant resistance. Beneficial microbes need to establish to multiply and reduce pathogen populations. For this reason, we should always apply microbial biofungicides as a preventive measure. Some biofungicides require multiple applications over time to ensure a steady population of beneficial microorganisms in the growing media or nutrient solution.

Match the product to the crop and the target pathogen.

Microbes interact with specific microbes and adapt to some plants better than others. Products are labeled for specific crops and pathogens. In Table 1, we provide a summary of the microbial biofungicides that are available for root rot of greenhouse-grown vegetables. Use the information in this table to match the product to the problem you are interested in preventing.

Graphic: Rosa Raudales

Conduct your own trials.

In our trials, we have observed that some biofungicides reduce plant growth, even in the absence of plant pathogens. These differences were only evident when we compared side-to-side plants with and without the biocontrol. We highly recommend that you perform in-house trials before applying any new product and that you always test the product next to untreated plants.

We tested the efficacy of Companion, RootShield Plus WP, and Triathlon BA for control of Pythium root rot in microgreens. We must note that in our trials we expose plants to higher disease pressure than what you would observe in commercial farms. Kale ‘Red Russian’ was not susceptible to Pythium spp. and grew evenly across all treatments. Arugula (Fig. 1), mustard, and radish plants infected with Pythium spp. were visibly smaller than non-infected plants. The results from this replicated experiment indicated that the under high disease pressure Triathlon BA protected this group of plants species from Pythium root rot.

Grahpic: Rosa Raudales

Apply the products in the right place at the right time.

Growers can apply biofungicides for control of root rot drench, dip trays, spray, via chemigation, or by using growing media with biopesticides. Companion, Actinovate SP, and RootShield are specifically labeled for use in hydroponic systems. Anecdotally, we have observed that some products are not compatible with systems with fine emitters, like the hydroponic nutrient film technique (NFT) or other fine emitters. When some products are dissolved, they form a thick foam that clogs the irrigation components. This is another reason why we recommend that you start small and test before widely adopting a practice.

Don’t forget the cultural practices.

The efficacy of biofungicides can only be achieved when combined with proper cultural practices. The efficacy of these products depends on the survival of the beneficial organisms. The shelf life of microbial biofungicides is shorter than chemical products. Therefore, proper storage and use of fresh product is essential to provide the right dose of treatment. Avoid product rotation with fungicides or bactericides that can affect the populations of beneficial microbes.

Maintain a strong sanitation program and good overall plant health. For example, high temperatures and low oxygen in the root zone are conducive to root rot development. Growers can prevent disease development by avoiding overwatering in container production and increasing aeration of the nutrient solution in hydroponics.

Biofungicides, similar to beneficial insects, will only work in an integrated crop management program. Growers can achieve efficacy of control when they integrate other cultural practices and proper management of the beneficial microbes.

Rosa is an assistant professor at the University of Connecticut (rosa.raudales@uconn.edu) with a M.S. in Plant Pathology and a Ph.D. in Horticulture. Cora is a graduate student in horticulture at the University of Connecticut.

Acknowledgements. This project is supported, in part, by The Connecticut Department of Agriculture via the Specialty Crop Block Grant Project# AG151260.

Disclaimer: Reference herein to any specific commercial products by trade name does not necessarily constitute or imply its endorsement, recommendation, or favoring by the University of Connecticut. The data presented here shall not be used for advertising or product endorsement purposes.