Weeds in the greenhouse: More than unsightly
Keeping your greenhouse free of weeds is an essential part of producing high quality plants while minimizing insects and diseases.
Besides being unsightly, weeds can pose serious problems in the greenhouse (Photo 1). Weeds have the potential to serve as a reservoir of insects, including aphids, whiteflies and thrips. In addition, some weeds can also become infected with common greenhouse viruses, including impatiens necrotic spot virus or tomato spotted wilt virus, and these weeds do not always show the virus symptoms. If a virus is present in the weeds, thrips or aphids can potentially spread this virus from the weeds to susceptible greenhouse crops.
Photo 1. Weeds under greenhouse bench.
So, how do you manage weeds? The best management tool is prevention. Screens placed over greenhouse vents can be used to prevent many weed seeds from entering the greenhouse. Use a reputable supplier of media or plants to ensure they are not sources of weed seeds. Using a physical barrier (like weed block fabric) on greenhouse floors will aid in preventing weed establishment (Photo 2). Do not cover the weed barrier with gravel, as spilled media will be harder to clean up and will provide a great place for weeds to establish. Make sure you keep weeds under control outside of the greenhouse, too, to additionally prevent those seeds from coming in the greenhouse.
Photo 2. Weed barrier.
If prevention is not enough, consider hand-weeding rather than using an herbicide in the greenhouse, as some herbicides can volatilize and cause damage to desirable crops months after the herbicide was applied. If you choose to use an herbicide, it is best to do so when the greenhouse is empty and always make sure the herbicide is labeled for use in greenhouses. Use caution when spraying herbicides outside the greenhouse, as spray may drift inside the greenhouse. Symptoms of herbicide injury include discolored, thickened or stunted leaves.