Learn About Whitehall Bio Control: 7/31/2024

It's Cypho Season! The Whitehall Project is soon going to start collecting spotted knapweed root boring weevils (Cyphocleonus achates). These weevils are starting to emerge from the roots as collectable adults. This is a bit earlier than usual because of the hot weather we have been having.

Spotted knapweed is a short-lived perennial plant with a tap root. If you hand pull it and get most of the root you will kill it. Wear gloves and a long-sleeved shirt when pulling knapweed. Always bag and dispose of the plant after you pull it. Pull your share on every outing! The plant first grows a basal rosette (ring of leaves) and then bolts (shoots up flowering stems) to produce purple flowers for most of the summer.

We have 4 seedhead feeders (two small weevils and two small flies) that eat the seeds and lower seed production 40-60%. These 4 insects are strong fliers and are established throughout Montana. We also have a root boring moth that is well established in most of the state. The moth damages the plant but does not usually kill it.

However, the best insect for killing lots of knapweed plants is the spotted knapweed root boring weevil mentioned above. We call them Cypho (pronounced sifo with a long "i" and a long "o"). These weevils do not fly and can disperse about 70 meters/year from a release site. Therefore, we try to release them about every 1/4th mile or quarter section. Since we have been releasing them for 25 years, we are finding them at most (but not all) locations we monitor throughout SW Montana. In many areas they are greatly decreasing the density of spotted knapweed!

Cypho lay their eggs in the root crown (top of the root) in August and September.

The larvae soon hatch and bore (eat their way) into the root. They slowly grow all fall, winter and spring within the root causing major damage to the plant. They pupate in early July and emerge as adults again in late July/August to do it all again. The exit hole they make in the root often finishes off the weakened plant by letting in all kinds of soil bacteria and fungi that can kill the plant root.

Cypho are good-sized weevils (beetles with long snouts) and need a plant with a tap root that has about the diameter of a dime or larger to develop. When we make a release, it often takes 2-4 years before many of the larger knapweed plants die. Then many of the seeds from the soil seed bank (knapweed seeds stay viable in the soil for up to 14 years) sprout. This often causes the site to look worse than before as there are more plants per square meter. However, the plants are much smaller and produce many less seeds per square meter. Over the next 5-7 years most of the knapweed plants are killed by the weevils and the seedhead feeders mentioned above destroy most of the seeds so, the knapweed on the site just slowly disappears.

Remember, the weevils will not kill ALL your knapweed. If they were to kill it all in their native Eurasian habitat, they would have gone extinct. Therefore, they just knock the weed population way back enough that the plant becomes just another pretty flower scattered about a bit, and not much of a problem. That is how we are going to have to learn to live with spotted knapweed... As we monitor throughout the area, we are seeing larger and larger swaths where the insects have greatly lowered the density of knapweed to tolerable levels. This makes for many happy landowners!

If you want a release of these superb weevils to help control your knapweed, feel free to call Todd: 406-498-5236 or Ava: 310-237-3353 during normal business hours, please. They will be available through the thirrd week of August.

Remember, the time to manage your noxious weeds is NOW! Make a plan and stick with it.