How to identify and manage nostoc in nurseries and greenhouses – Part 2

Identifying nostoc early in container production can help growers develop an effective weed control plan. Part 2 discusses the management strategies of nostoc.

Green, mossy-looking substance on a gravel covered ground.
Photo 1. Visible mats of nostoc growing on gravels in container nursery. Photo by Debalina Saha, MSU Horticulture.

Part 1 of this article series focused on the biology and identification of nostoc in container nursery and greenhouse ornamental production. Nostoc is a genus of cyanobacteria or blue green algae that can proliferate in almost any environment. Colonies of nostoc are made of long filamentous chains, or strands of cells that continue to elongate without separating and can go on to form visible mats on the surface (Photo 1). Nostoc can be a helpful organism in some situations when looking at nutrient levels and soil moisture content. Although it is true that nostoc contributes nutrients to the soil, it is also responsible for using those resources to increase its own presence. The possible overgrowth of nostoc can also lead to competition for light and moisture as well in greenhouses and nursery production sites, depending on the specific morphology of the plant in relation to the growth of nostoc. Contamination of greenhouses and nursery floors can also create large areas of very slippery biomass that pose a safety hazard for growers, workers and, potentially, clientele.

For greenhouses or other nursery sites that sell ornamental or agricultural plants for which aesthetics affect the use or sale of the product, a heavily nostoc colonized crop of plants can result from significant financial loss. Hence in this second part, we will be discussing the management strategies of nostoc.


Managing nostoc with nonchemical methods

Proper sanitation practices can deter the growth of nostoc before it begins. Examples of precautions include using separate tools for each site or sanitizing them before use at a different location. Common sanitizers or disinfectants such as 10% sodium hypochlorite (household bleach) solution, 70% alcohol, hydrogen dioxide and quaternary ammonium compounds can be used for cleaning and sanitizing tools. Caution should also be taken by the plant handlers to keep personal equipment like boots and gloves clean and free from any possible residues or contaminants.

According to “Biology and management of Nostoc (Cyanobacteria) in nurseries and greenhouses” by Laughinghouse et. al, reducing overhead irrigation and improving drainage is important to control nostoc. In nurseries and greenhouses, nostoc can be removed for short term by physically removing them which includes raking or allowing the area to dry or using blowers to blow out of the production areas.

Managing nostoc with chemical methods

Pelargonic acid (Scythe) has been shown to be extremely effective at killing nostoc colonies and preventing their regrowth for three to seven weeks after application. However, this is a broad-spectrum herbicide that is highly toxic to nursery and greenhouse crops, so it should be used very carefully, according to “The continuing battle against nasty Nostoc” by Jennifer Parke. Studies at the University of Florida have found that certain chemicals are more or less effective depending on the surface nostoc is growing on. Hydrogen peroxide plus peroxyacetic acid (i.e., Zerotol 2.0) was more effective at controlling nostoc on gravel and pelargonic acid (i.e., Scythe) was more effective on plastic, while sodium carbonate peroxyhydrate (i.e., TerraCyte PRO) and generic bleach were effective on both.

Finally, copper sulfate should be avoided. Control studies have not been consistent and more importantly, it is not registered for ground application and may cause severe damage to surrounding ecosystems, according to “Biology and management of Nostoc (Cyanobacteria) in nurseries and greenhouses” by Laughinghouse et. al. Because nostoc can consist of several species of cyanobacteria, results may vary with the above listed chemicals. It is recommended to test a smaller area before making a widespread application. Never apply these chemicals over the top of the desired plants as severe injury can occur. It is also highly recommended to read the manufacturer’s label carefully before applying the chemicals.

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