Weed Control 2007

Leafy Spurge

In 2004, 2005 and 2006, we released varieties of bugs to attack three specific noxious weeds: Leafy Spurge, Musk Thistle and Canada Thistle. Leafy spurge is one of the hardest to control, as it is difficult to kill with herbicides and it spreads easily. Gary has marked 7 leafy spurge outbreaks on our property with a GPS system and is checking the sites periodically to track the progress of spurge spread or control. One part of the monitoring process is to take panoramic pictures of two sites where we do not use any other controls (e.g., herbicides) so we can compare them year to year.

Another part of the process is to visit the sites and try to identify insects that are attacking the weeds. This year, we identified colonies of 3 of the 4 varieties we have released specific to leafy spurge. There are additional varieties of insects released by others over the years that have found their way to our area. It will take 5 or more years to determine if our new varieties are able to control the weed.

Finally, we use herbicides on 3 spurge sites near the Carriage House and Main House in hopes of not having to look at noxious weeds from our windows. While spraying does seem to have reduced the density (plants per square meter), spurge still spreads through its deep and extensive root system. Thus, the infested areas still increase in size.

(click on pictures to view larger version)

This gall caused by Spurgia Esulae inhibits seed production and weakens the spurge plant.

Oberea Erythrocephala admiring her work (note broken stem). This insect lays an egg in the stem and the larvae eat the plant from the inside.

Aphthona Nigriscutis adults feed on leafy spurge foliage and flowers; larvae feed on roots.

We found this caterpillar in 2004. This insect was released in Bridger Canyon decades ago, but it does not thrive well enough to be a factor.

Click beetle found on spurge plant. It must be lost since this beetle doesn't attack the plant.

Eggs laid by Hyles Euphorbiae (spurge hawkmoth) on a spurge plant. These will turn into caterpillars like the ones pictured at far left.

More Weeds

We also released Trichosirocalus Horridus and Rhinocyllus Conicus for Musk Thistle. We recently observed these in their mating frenzy on newly sprouted plants. They have really helped control this weed. Rhinocyllus Conicus is especially satisfying, since we can take people on hikes, spot a thistle, break open the flower and show how larvae have eaten the seeds.

Releases of Urophora Cardui and Ceutorhynchus Litura for Canada Thistle has helped a bit, but the plant is difficult to control since it propagates through its root system as well as by seeds.

The remaining noxious weed we would like to control is Hound's Tongue, but there are no insects approved for release in the United States. Some insects have been approved and released in Canada, so perhaps they will eventually find their way here. Gary takes frequent hikes with a backpack sprayer along game trails to kill hound's tongue. Since the seeds spread primarily by attaching themselves to animal's fur, game trails are prime areas to pick up or drop off seeds.

We use herbicides to control these three weeds in disturbed areas (mostly along the driveway and the construction site). We hope the insects can take care of the rest of the thistles.