A few weeks ago, I reported on the poinsettias that the University of Rhode Island Master Gardeners are growing for sale in early December. Despite assaults from the above-mentioned (and common) greenhouse pests, the poinsettias are thriving. Many of the plants are showing bract color, and some are even boasting cyathia (the actual flowers).
The Master Gardeners employ integrated pest management (IPM) in the greenhouse, and for those of us who volunteer there, it’s always interesting and educational to see what’s being used each year. I like to imagine the ongoing war – on a very tiny scale – between the pests and the organisms we enlist to control them.
Here are the weapons in the IPM arsenal this season:
Gnatrol: this is a larvacide, added to water to control fungus gnats, which, like whiteflies, often occur whenever you water the plants from the top. The active ingredient in Gnatrol is Bacillus thuringiensis israelensis (Bti). To control adult gnats, we use sticky traps. A daily (and time-consuming!) fluffing of the soil in each pot also helps fight them.
Aphid Parasite Aphidius colemani: Aphidius colemani is a small parasitic wasp that lays its eggs in aphids. The eggs hatch inside and the larvae spin cocoons, which swell the aphid’s body. The adult wasps then exit the aphids’ bodies, leaving behind hard brown shells called “aphid mummies.” Aphidius colemani is a very good flyer and is able to locate small colonies or even individual aphids! Gross, but effective.
Whitefly Parasite Encarsia Formosa: Encarsia formosa is a tiny wasp that attacks whiteflies. Adult female Encarsia kill whitefly scales in two ways: by puncturing and feeding on pupae, or laying their eggs in pupae (each female may produce 30-500 eggs during her lifespan). Encarsia eggs hatch into tiny larvae, which cause the whitefly pupae to turn black as the young wasps mature.
These wasps arrive on small cards, which are hung amid the plants throughout the greenhouse. The cards are replaced every couple of weeks. It’s cool to look at them through a magnifying glass, because you can see the wasps moving around.
Eretmocerus eremicus: another small wasp that parasitizes and host-feeds on silverleaf whitefly larvae. This is a valuable tool for controlling silverleaf whitefly, because it is more tolerant of higher temperatures and pesticide residues.
With less than two months to go before our big sale, the “points” are looking good, thanks to the efforts of Master Gardeners – and an army of tiny insects.