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Keeping Your Greenhouses Clean in Springtime -- Make Your Best Effort

Thu, Mar 14th, 2019, created by Nick Flax
Now that we are in mid-March, bench space and hanging basket lines are filling up rapidly around the U.S. The "organized chaos" of spring bedding-plant season is a familiar feeling for greenhouse growers, but this time of year is typically when greenhouse cleanliness starts to fall by the wayside. This happens to the best of us, but it is vital to manage both our crops AND our production environments. With crop density at a seasonal high and plant material coming in from offsite, this time of year is often when pest and disease pressures jump, weeds pop up, and algae blooms grow in abundance.

Plant disease incidences tend to increase in frequency or worsen in severity, and infestations are often prolonged when greenhouse sanitation is neglected. Fallen foliage and flowers serve as suitable hosts for a variety of plant pathogens, and should be cleaned up regularly in order to curb disease pressure. For example, back in February, one of my e-Gro colleagues, Jean Williams-Woodward, warned growers to be on the lookout for Botrytis, and provided excellent management solutions (e-Gro Alert Vol. 8.10). She noted that “gray mold” can spread via infected plant debris on floors, under benches, and even in trash cans, and that sanitation is an important part of managing this disease. 

Similarly, weeds or old plants that you held over from last season can harbor pests and pathogen vectors. Consider managing weeds in- and outside your greenhouse preemptively, and pitching old material prior to the busy season as a way to start clean. However, if you see weeds in the greenhouse or popping up outside of an open louver while doing a walk-through, take a few seconds to pull them and properly dispose of them. Another scenario that I see with relative frequency is when growers keep old back-week plug trays, beat-up liners, or past-prime finished material in an attempt to clean it up and sell it later. Resist the temptation to do this! You will likely be better off removing these plants before pests and diseases that they may be harboring can compromise your other crops.

Algae also tends to start showing up on floors and under benches this time of year. Once houses are full, relative humidity is high, and plants are being watered and/or fertigated frequently, algae will thrive. Aside from being a slipping hazard, algae blooms serve as a reservoir for pests like shore flies. While plant material is being shuffled around, falling debris can accumulate under benches and block floor drains. This often leads to algae proliferation, and a noticeable increase in shore fly population. Removing debris under benches and around drains regularly can help combat this. Alternatively, algae can also come in on plug material like begonias, dracaena, and other bedding plants that are typically grown under moist conditions and have long plug production cycles. If substrate moisture and watering practices are not managed appropriately, algae caking can occur on the substrate surface. This ultimately will attract shore flies to your crops and necessitate control measures being taken. If algae in your greenhouses is a perennial problem, growing plants “drier” maybe a 3-for-1 strategy worth investigating to simultaneously reduce algae on your floors, in your crops, and manage pests like shore flies.

Cleaning up plant debris, pulling weeds, and managing algae may seem like low-priority tasks during the busiest part of the spring, but these few simple actions can go a long way in helping manage pest and disease pressure throughout the season. I have heard growers say that cleaning before the end of May is a waste of valuable time, but I challenge that assertion! Think of maintaining greenhouse cleanliness as a core component of your Integrated Pest Management efforts, and not as a chore that can wait until the end of the season.



About the Author:

Nick Flax

Commercial Horticulture Educator, Penn State Extension

Nick Flax is a Commercial Horticulture Educator with Penn State Extension, based in Doylestown, PA. His background is in greenhouse crop physiology, with an emphasis on plug production, annual bedding-plant production, seasonal potted crops, and container-crop production using biocontainers. Nick has industry experience in wholesale young- and finished-plant production, retail floriculture, and has a strong background in pest and disease management, biological IPM, and controlled-environment crop research.

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