Leafy Spurge Control with Flea Beetles
Leafy spurge is a long-lived perennial weed that has proven to be difficult to control. Often times a combination of chemical, cultural and biological control methods are needed to successfully decline a leafy spurge population. Flea beetles have been a successful biological control agent for helping aid in the control of leafy spurge. The first flea beetles were released and established in 1988 near Valley City. By 1996, flea beetles had become established in just about every county in North Dakota.
Adult leafy spurge flea beetles typically emerge mid-June, feed on the foliage, mate and then lay eggs. Adult beetles favor cool, wet conditions and typically are active for about 1.5 to two months during the summer. A dry, hot summer will shorten the amount of time the adults are active. Larvae will emerge from the eggs throughout the summer and undergo three instars before becoming adults. Larvae feed on both the filamentous roots and the root crown and overwinter on the roots. Although the adult beetles do feed on the plant foliage, leafy spurge sustains the most damage from flea beetles larvae feeding on the roots.
Leafy spurge flea beetles are typically collected and redistributed in mid-June to early July. This year the emergence has been delayed due to the cool spring. The sunflower total accumulated growing degree days (AGDD) tool the NDAWN website (ndawn.ndsu.nodak.edu) can be used as a guide to determine when to begin scouting and collecting adult flea beetles. Scouting for flea beetles should begin when 1000 sunflower AGDD have accumulated. As of today, June 27th, we are at about 965 GDD at the Dazey and Fingal NDAWN station locations.
The best time to collect flea beetles for redistribution is between 10 am and 3 pm, when the temperature is greater than 70°F, there is little wind and the skies are generally sunny. Once collected, flea beetles should be transported in paper bags or containers with some leafy spurge to feed on and should be kept cool and out of the sun. Do not use plastic containers because moisture condensation can drown the insects. Flea beetles can also be obtained by contacting the Barnes County Weed Control Officer, Jamen Windish.
At least 1,000 beetles should be released per location for successful establishment. A successful establishment is considered when 50 or more flea beetles are collected in five sweeps the summer following the release. It can take up to three to five years for a leafy spurge population to fully establish. For more information, contact the Barnes County Extension office at 701845-8528 or e-mail Alicia at alicia.harstad@ndsu.edu.