Learn About Whitehall Bio Control: 7/3/2024

Another nasty noxious weed is houndstongue (Cynoglossum officinale). It seems our North American attempts to control this weed are becoming a somewhat sensational secret success story! Let's describe the weed first.

Houndstongue is a biannual (grows for two years) plant. In the first year, the seed sprouts and grows a basal rosette (a ring of leaves near the ground) and a deep tap root. During the second season, the plant uses the energy and nutrients stored in the carrot-shaped tap root to grow leaves and then bolt (quickly grow tall flowering stems), flower, and produce seeds.

The leaves are rough and somewhat hairy. They can be 4-12 inches long and 1-3 inches wide. The leaves become progressively smaller as you move up the stem. Some people say they resemble a hound's tongue, thus the plant's name. The hairy stems can be 1-4 feet tall.

The flowers occur in clusters at the ends of the stems. They are dull reddish-purple to burgundy, about ¼ inch wide, and have five rounded lobes. Each flower produces four nutlets; each nutlet contains one seed. The surface of these nasty nutlets is covered with barbed hooks that tangle in fur and clothing and aid in seed dispersal. This seed dispersal strategy is good for the plant but a pain for us! I have spent hours and hours combing these obnoxious seeds out of my dogs and horses... These nutlets can greatly decrease the value of sheep's wool if present. Each houndstongue plant can produce 200-2,000+ seeds. These seeds can stay viable in the soil seed bank for 2-3 years.

Houndstongue plants contain pyrrolizidine alkaloids that stop the production of liver cells. They are toxic to cattle, horses, goats, and other livestock. Dead, dried plants, however, can safely be consumed by livestock in hay. The plant can also cause dermatitis in some humans. So, it is just a "generally fairly noxious" darn weed!

Most Montana state-designated noxious weeds are invaders from other continents, and houndstongue comes from Eurasia. Researchers have surveyed the insects that feed on houndstongue in Eurasia and located a candidate bioagent insect called Mogulones crucifer, the houndstongue root weevil. This insect underwent the usual intensive testing to see if importing as a biological control agent was safe. Canada approved it for release, whereas the United States did not. The US didn't approve this insect because it has the potential to spill over (feed on) several native threatened and endangered species of Boraginaceae plants related to houndstongue that occur in the lower 48 states but do not occur in Canada.

This insect was released in Canada in 1997 and has been a resounding success in many houndstongue infestations, greatly reducing the density of this nasty plant! This small weevil is a strong flyer and has dispersed (or been moved by people illegally) into northern Washington, Idaho, and Montana. The Whitehall Project crew has found them throughout southern Jefferson County, from Homestake Pass to Waterloo, Cardwell, and Milligan Canyon. They are greatly reducing the density of houndstongue at all these locations!

Because the houndstongue root weevil is not approved in the United States, the Whitehall Project crew does not collect and redistribute them. The insects seem to be moving about Montana rapidly enough on their own. I observed them almost completely clear houndstongue off a heavily-infested 3-acre pasture (where I sometimes kept my horses) in just three years! I am impressed by this insect.

Mogulones crucifer adult weevils are round, about ¼ inch long, black/brown with a white cross pattern on their back (thus the name "crucifer.") Their feeding creates small circular/oval holes in the plant leaves, making it look like someone shot the plant with a shotgun. The weevils can lay eggs three times during their 1–2-year lifetime. Adults who emerge in summer can lay some eggs in early fall. The overwintering adults can then lay up to 180 eggs in the spring. And they then may live long enough to lay some more eggs the next fall.

The larvae soon hatch and feed within the plant's tap roots. The larvae create tunnels within the root filled with dark brown frass (insect droppings and chewed plant parts). Mature larvae pupate in the soil. Larval feeding throughout the summer weakens or kills the plant. If most of the houndstongue plants in an infestation are killed or prevented from flowering by the weevils for several years, the infestation is mostly wiped out - as the seeds in the soil seed bank only stay viable for 2-3 years.

The "sensational secret success" of these weevils in our area is a real conundrum. They are approved in Canada but not in the good old USA, even though they are very successful in Canada.

Mogulones have moved (or have been moved) into WA, ID, and Montana and have also been very successful in controlling houndstongue. Since the insect could possibly spill over and damage some threatened and endangered native US borages, they may never be approved here. However, they are here, are spreading over a wide area, and are very effective. I have never seen another insect bioagent have such rapid and profound success! For now, we watch and happily observe houndstongue rapidly decreasing in many areas in Montana. No more pickn'-and-flickn' these nasty little nutlets! Hummm...