Southwest Michigan greenhouse situation report – February 2019

Avoid late-season pest problems with careful scouting and sanitation practices.

Marigold production in a greenhouse
Marigold production in a Michigan commercial greenhouse. Photo by Jeremy Jubenville, MSU Extension.

It's fair to say that the weather during February 2019 has been something of a roller-coaster ride. Significant fluctuation in temperatures have brought record highs and record lows to some areas of southwest Michigan. While we would normally characterize February as a month of ice and snow, these last four weeks show a pattern of unseasonably warm weather broken up by a few days of sub-freezing conditions. As of this writing, the average daily high temperature in the Kalamazoo area for the month of February is just under 35 degrees Fahrenheit (via Michigan State University's Kalamazoo Enviroweather station) with an accumulated 52 degree-days above freezing.

Spring crop status

The work pace has picked up dramatically over the last two to three weeks. The make-shift poly walls that some growers use to separate warm production space from the rest of the facility are slowly coming down as floors and benches start to get full. Not every grower propagates their own material, however, so mid- to late February is right about the time those greenhouses start to transplant plugs into hanging baskets, mixed planters and other finishing containers. With Mother's Day less than 11 weeks away (can you believe it?!), our busiest time is upon us!


Fungal and bacterial disease pressure continues to be low in southwest Michigan. Even with all the requisite humidity and moisture present during propagation, our growers are doing a great job of keeping opportunistic pathogens at bay. One thing we've noticed, however, is the regular appearance of tospoviruses such as impatiens spotted necrotic virus (INSV) in carryover plants. Plants that remain in production areas year-round are at an increased risk for acquiring insect-vectored diseases.

Tospoviruses have a broad host range, occur naturally in our environment, and are vectored by thrips. It's easy to imagine how an infection could happen during warmer months when greenhouses are open to the outside world. All it takes is for an infected thrips to fly in and feed on a plant.

Symptoms can take a while to become obvious, so it's worth the time to examine any pet plants or carryovers for disease symptoms on a regular basis. Catching a problem early could save an entire crop. For more information on plant viruses, check out some of these excellent MSU Extension and e-GRO articles:


Thrips pressure remains average to below-average throughout much of the area. Even though outside temperatures have been above freezing, they're still low enough to provide significant suppression of insect populations. That's not going to last very long, though. Prevention is the most economical pest management strategy, so we should do our best to eliminate inside sources of pests (and diseases) by removing any weeds that have recently sprouted. Removing a single female thrips from a greenhouse can easily prevent thousands of her descendants from feeding on our beautiful crops.

Whiteflies continue to be found on ‘Black and Blue’ Salvia. At this point in the season, it's more likely to be the greenhouse whitefly (Trialeurodes vaporariorum), but a Bemisia infestation is still a possibility. Correct species identification is important in biological control. Don't hesitate to contact a member of the MSU Extension floriculture team if you need help with identification. We’re happy to help!

Outside of a couple of isolated infestations, aphid pressure has been almost non-existent. February weather all but precludes local environmental sources, so be sure to carefully inspect incoming plant material. Common hosts include peppers, eggplant, Ipomoea, Sprengeri, dracaena spikes, Salvia and Fuchsia.

Spider mite sightings have been reported on just about every species we might expect. Some recent finds include infestations on Buddleia (common), Cordyline (very common) and some mint (also common). Broad mites have now been found on Scaevola and we're still finding them on Reiger Begonia, Torenia and Thunbergia. Check out the January situation report to see what plant species were infested last month. If you think you might have broad mites, but aren't sure (because they're so stinking small), don't hesitate to contact me. Early detection can be the difference between shipping the crop on time or tossing it all in the dumpster.

Conventional management product suggestions for all pests mentioned in this article can be found in the “Greenhouse Pest Management with Insecticides” sheet for 2019.

Thanks to Mark Crossley of West Michigan IPM for sharing his time and expertise.

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