Biological Control in a College Greenhouse

The Humboldt State University (Calif.) greenhouses consist of a 9,000 square foot house that houses our teaching collection of more than 1,000 species of plants from over 180 families and a 2,500 square foot house used for laboratory projects, and faculty and graduate student research projects. We have the normal array of horticultural pests to control together with the need to have maximum student access to the collection. Pest control using chemicals brought on complaints when the facility had to be closed one day a week for pesticide application. If your plant taxonomy lab fell on that day tough luck. We also had lots of negative comments from students about the chemical smell in the greenhouse as well as questions about safety, environmental ethics, etc.

I stopped using chemical pesticides in 1983 and have relied on biological, cultural and physical control, with major emphasis on biological control, since then. Why? To put it bluntly, chemical controls didn't work. Biological controls have worked and at far less cost in money, staff time and health, etc. We've had complete control of greenhouse whitefly, once our major pest problem, with Encarsia formosa and E. pergandiella since 1983 at a total cost of $15!

Soft scales (black, hemispherical, soft brown) are an occasional curiosity, usually seen only when ants protect them from control by Metaphycus helvolus and unidentified volunteer parasites. Cottony-cushion scale infest our few Citrus and Acacia specimens. We obtained vedalia beetle from a researcher years ago, but it didn't establish. Now we hand pick about twice a year and get adequate control.

Citrophilus mealybug is well controlled by a volunteer parasite. Citrus mealybug is partially controlled by Leptomastix dactylopii, which does not overwinter well in our greenhouses and is hard to find commercially, and by physical methods (water blast, hand picking). Longtailed mealybug is my current challenge. We're using Cryptolaemus (mealybug destroyer) with fair to adequate control (varies by plant species) on cycads and water blasting with adequate results on ferns. The several promising parasites of longtail mealies don't seem to be available commercially so we are going begging to researchers.

Twospotted spider mites are also of minor concern. Some years I have to introduce predatory mites (Phytoseiulus persimilis and Galendromus occidentalis), some years physical/cultural controls (water "blasting," humidity control) are enough.

Greenhouse thrips control is satisfactory with Thripobius semileuteus if I remember to monitor and move populations of parasites into isolated thrips infestations somebody please teach those critters to fly!

Bean aphid can be a problem on some plants in spring and fall, but pruning, hand control, and a volunteer parasite usually give adequate control. If not, I use an inundative release of ladybugs. The several other species of aphid we encounter are easily controlled by water blasting and volunteer parasites.

Several species of lepidopteran larvae give us problems if we don't keep on top of them with Trichogramma releases, Bt sprays, and hand picking.

I'm sure there are others that I have forgotten about but that's one of the benefits of BC!

- William C. Lancaster, Greenhouse Manager, Department of Biological Sciences, Humboldt State University, Arcata, CA 95521


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