Learn About Whitehall Bio Control: 6/14/2023

The Whitehall Biological Weed Control Project (Whitehall Project) is part of the Jefferson County Weed District. Jill Allen is the Jefferson County Weed Coordinator. Todd Breitenfeldt is the Whitehall Project Coordinator. The Assistant Coordinator is Brynna Wolfe and the crew members are Lexi Stratton, Reed Zander, Austin Bonnet, and Izaya Howlett.

This week we are collecting Dalmatian toadflax stem boring weevils (a weevil is a beetle with a long snout) in the Missoula area. We give these releases to landowners who have this weed on their land. Dalmatian toadflax is scattered in the south end of Jefferson County but fairly widespread in the north end. Therefore, most of these releases will be going to the north end of the County.

We will also have a few releases of the yellow toadflax root boring weevils available. Yellow toadflax is related to Dalmatian toadflax but has thinner, less waxy leaves. In our area, it is more rare and scattered than Dalmatian toadflax. Both toadflaxes have yellow, snap dragon-like flowers.

We will also have some Russian knapweed insects available sporadically throughout the summer. The next insect we will be collecting is the leafy spurge flea beetles (several species) in late June or early July. For all these insects, feel free to call and get on the list - Todd: 406-498-5236 or Brynna: 406-202-2393. Please call during normal business hours.

Now for some information about Whitetop or hoary cress (Lepidium draba). Whitetop is a rhizomatous (rhizomes are underground stems) perennial flowering plant that is native to western Asia and southeastern Europe. It is a Montana State-designated noxious weed. It has flat to slightly domed clusters of white flowers on the top of the stem (thus the common name whitetop). It probably came as a contaminant in seeds brought over from Europe in the early 1900s. It now occurs in most of the lower-48 states and is also a problem in Australia. It happens to be all over the Whitehall area and is flowering now. I sometimes joke that we should rename Whitehall "Whitetop, Montana" for the month that Whitetop is blooming all around town. It spreads via seeds and rhizomes/roots.

It is easy to kill with specific herbicides (please call Jill Allen about that) but, we unfortunately do not yet have an available biological control agent to release on this weed. There is one agent, a mite, that has been approved for release in Montana and has been established at a few release sites. This mite is almost microscopic and deforms the flowers, so few seeds are produced thus slowing the plants spread. It does not, however, kill the plant. We should receive these mites for release in this area in a few years as their numbers in Montana hopefully increase.

Mowing whitetop helps but does not kill it. Hand pulling knocks it back but even a small root fragment can regrow into a new plant. Be sure and bag/throw away all the plants you pull. Burning and tilling/plowing are also not very effective. We encourage you to try any or all of these control methods. Never move soil that could have whitetop root fragments or seeds in it.

Be proactive about the noxious weeds on your land!