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I Didn’t Know That!

By Martha Kirk, Colorado Master Gardener

Biocontrols Lend a Helping Hand

Biocontrols can be a secret weapon for fighting weeds. The Palisade Insectary grows and offers to the public insects and fungi to combat pervasive garden weeds. The effect is not instant as with a pesticide, but weed populations can be reduced significantly over time. Studies show that Canada Thistle infestations have been reduced from 45% to 100% with a rust fungus (Puccinia punctiformis). It is applied to the base of the plant in the fall and spreads to other thistle infecting the root system.

Left, Rust on Canada Thistle, Photo: Joel Price, Oregon Department of Agriculture,
Right, Bindweed gall mite damage, Photo: Bob Hammon, Colorado State University,

Field bindweed can be combated with the bindweed gall mite, Aceria malherbae. The mite forms a gall on new growth, distorting the leaves and stunting the plant. In some cases, flowering is reduced. Bindweed mites are not meant for residential lawns that are watered. Apply infected stems in the spring or fall when active growth occurs. Find a fresh stem and wrap it around an infected stem to secure it. In the winter, mites move to the roots, feeding on them and further weakening the plant.

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