Learn About Whitehall Bio Control: 6/28/2023

Because of the continued cool, wet weather, we are continuing to collect the Dalmatian toadflax stem boring weevil Mencius janthiniformis. We have requests for over 70 releases and have only been able to collect 10 releases so far. We will be trying to collect more this week as the weather warms. Wish us luck! It is very heartening to see how much damage these skinny little black weevils are doing to Dalmatian toadflax along the I-90 corridor in the Missoula area and along the 1-15 corridor between Helena and Boulder.

We were able to collect four releases of the yellow toadflax stem mining weevil Mecinus janthinus, some at our insectary at the high school track, and are really enjoying how much they damage this nasty/pretty little yellow-flowered plant where they are well established. These releases went into southern Jefferson County and Silverbow County.

We also will be collecting the leafy spurge flea beetles Aphthona spp. (several species) next week through mid-July. Although most of you landowners have these fine little spurge killers, we are accepting requests for releases. They are out as adults now so please monitor to see if you have them before requesting a release. We will be glad to explain or show you how to monitor them on your land. Feel free to call Todd at 406-498-5236 or Brynna at 406-202-2393 during normal business hours.

A weed to watch out for is called yellow starthistle (Centaurea solstitialis). This noxious weed is designated 1A by the State of Montana. It is not present in the state but occurs in neighboring states. Occasionally seeds are transported into Montana by accident and infestations occur. These are eradicated quickly, and the site is monitored for several years. If you see this weed, report it to your County Weed Coordinator!

This weed is toxic to horses and can cause a fatal nervous disorder called chewing disease with no known treatment. The flowers look like other knapweeds but are yellow with long sharp spines. It forms a dandelion-like rosette (ring of leaves) with lobed leaf margins. The stems are winged and branched. The plant is a winter annual meaning it usually germinates in the fall and matures the following summer. It reproduces only via seeds that can remain viable for 3-10 years in the soil seed bank. One plant can produce tens of thousands of seeds. It forms very dense stands that are almost a monoculture (all one type of plant).

The spines can be painful to humans, wildlife, and livestock. When I was in Utah teaching a biological control class to teachers, we collected the yellowstar thistle seed head weevil that had been released there for biocontrol and the spines gave me an itchy rash on my hands and arms. In Montana, we only release biocontrol agents on weeds that we have given up trying to completely eradicate (such as leafy spurge and Dalmatian toadflax) so this weevil is not used in Montana. As mentioned above, we have so far successfully kept this nasty plant out of Montana! So, keep your eyes open for this dastardly invader!