Navajo State Park in southwest Colorado is famous for great boating, fishing and camping; but soon it could be renowned for its wasps.
Not the kind that pester you at picnics; but a much smaller sesame seed-sized wasp that sets up house inside the stems of Russian knapweed and helps to control the invasive weed. On a small plot of land on the east side of the park, biocontrol specialists from the Colorado Department of Agriculture are developing a stem gall wasp nursery site. Like many non-native plants, Russian knapweed crowds out native vegetation, can quickly take over pastures, and is poisonous to horses.
“It’s one of the worst weeds in the West,” explained Sonya Daly. She works for the agriculture department’s Biological Pest Control Program that is based at the Palisade Insectary and is part of the Conservation Services Division. The Palisade Insectary celebrated its 75th anniversary on August 14.
The Insectary has been working on using stem gall wasps for natural weed control since 2013. The Russian knapweed biocontrol agents are very host specific and will not attack Spotted or Diffuse Knapweed or agricultural crops. After receiving several hundred gall wasps from the USDA in 2018, Insectary staffers placed them in numerous locations throughout Colorado to start nurseries. Eventually, the Insectary hopes to collect thousands of wasp galls every year from those sites.
After receiving the wasp, Daly started contacting weed control specialists at every county in the state to tell them about the natural biological control method. When she contacted Ethan Proud, weed and pest supervisor for Archuleta County, he suggested releasing wasps at Navajo State Park which has Russian knapweed infestations.
In the spring of 2019, Daly released 200 wasps at a plot on the east side of the park. The insects feed within the stems of the plant and eventually impact plant health. Daly surveyed the test plot recently and found the wasps to be well established in the knapweed. By 2022, the Colorado Department of Agriculture, Colorado Parks and Wildlife and Archuleta County hope to collect the wasp galls and distribute them to other land managers and property owners.
“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.”
Using biological controls like insects to control invasive species cuts down on the use of pesticides and helps landowners and land managers save money by reducing their need to buy expensive chemicals. 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.
Archuleta County is also using host-specific mites from the Insectary to battle field bindweed. Proud is collecting mites from Navajo State Park and distributing them to other private and public land managers.
Navajo State Park Manager Brian Sandy is looking forward to holding a bug-giveaway event at the park for area residents.
“Weeds are a problem on the state park just like they are a problem on farms and ranches,” Sandy said. “We want to be good neighbors, we can cut down on our use of chemicals and we hope to become a source for the community.”
For more information about biological controls, go to the Colorado State Insectary website at https://www.colorado.gov/agconservation/biocontrol.
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