The tiny insects are combating the “Worst Weeds In the West.”
Most of us who spend time in the outdoors are annoyed on occasion by insects. Bees and wasps are at the top of the list of the most disliked and unwanted, especially when they bother us at the picnic table. But sometimes we just need to leave these creatures alone.
Navajo State Park in southwest Colorado is famous for great boating, fishing and camping; but soon it could be renowned for its wasps. Oh, they’re good wasps, about the size of sesame seeds, not the kind that pester us in the campground.
The gall wasps like to set up house inside the stems of the invasive Russian knapweed. Like many non-native plants, Russian knapweed crowds out native vegetation. It can quickly take over pastures and is poisonous to horses. “It’s one of the worst weeds in the West,” explained Sonya Daly of the Colorado Department of Agriculture’s Biological Pest Control Program.
On a small plot of land on the east side of the park, biocontrol specialists are developing a stem gall wasp nursery site. The insectary has been working on using stem gall wasps for natural weed control since 2013. They are very host-specific and will not attack Spotted or Diffuse Knapweed or agricultural crops.
In the spring of 2019, Daly released 200 wasps at a plot on the east side of Navajo State Park which has Russian knapweed infestations. The insects feed within the stems of the plant and eventually impact plant health. “We’ll most likely never eradicate Russian knapweed with using this biocontrol agent; but we can impact the overall plants’ health to hopefully decrease its seedbank by using the wasps,” Daly said. “We want to establish nurseries in every county in the state.”
The Colorado Department of Agriculture currently collects, rears and releases about 20 different species of biological control agents for use against both weeds and insect pests. The “host specific” insects will not damage native vegetation or agricultural crops.