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Pest pressure

The plants in the greenhouse of the University of Minnesota Conservatory, all 3000 of them, are now well into the growing season. The sap is rising and new growth is bursting up the stems. All this tender new plant material is a feast for plant-eating insects. Mealybugs, scale insects, thrips, and other species are multiplying in numbers by the day. If not kept in check, the result would be withering leaves from the insects, and sooty black mold which thrives on their poop. To combat these many critters there are tools to reduce, but never eliminate, their numbers.

Today, my chore as a volunteer at the greenhouse is to use a simple soap solution and a sharp spray of water to physically knock the insects off from the surfaces of the leaves. It took me about 3 hours to treat one bench of plants; there are approximately two-dozen benches in the collection, spread across 4 different climate-controlled rooms. Especially in the growing season, it takes dedicated persistent effort to keep the bugs under control.

Synthetic chemicals are an attractive choice for controlling the insects, but eventually the bugs develop resistance to the chemicals. It is better to spread natural biologic predators to control the insects feeding on plants. This biologic control helps, but it is not enough. Physical methods are also needed to reduce the pest pressure.

While I spent the hours spraying insects off from plants, I noted this lovely blossom on a vine from South Africa: Gloriosa superba, or glory lily. It is highly toxic if ingested, but small quantities have been used in folk medicines - all parts of the plant are particularly effective as an emetic.

Gloriosa superba, or glory lily. Used in Africa as a medicine, but can be highly toxic.


From the bench on the left all plants had to be individually washed with soap and a sharp spray of  water.




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