What is Leafy Spurge?
Leafy spurge, Euphorbia virgata, is a perennial, colony-forming, invasive plant that originates from central Europe. It was brought to the U.S. accidentally multiple times throughout the 1800s and as of 2005, it has invaded over 4.6 million acres of land. Leafy spurge invasion in the U.S. was long attributed erroneously to Euphorbia esula, a very closely related species also native to Europe.
How to Identify Leafy Spurge
The most distinguishable characteristic of leafy spurge is the white latex sap that will ooze from the stems when broken or cut. The best time to look for leafy spurge is May-June when bright, chartreuse-yellow, clustered flower bracts tinge the colonies and landscape yellow. Leafy spurge is typically 1 to 3 feet tall with smooth bluish-green stems and lance-shaped leaves. It may occur in almost every environment but is typically found in dry meadows, grasslands, and along waterways and roads. It is an especially common contaminant of alfalfa and hay.
Effects of Leafy Spurge
Invasion by leafy spurge costs millions of dollars in lost productivity of grazing and forage-producing land. The root system of leafy spurge may spread over 30 feet into the soil which helps the plant outcompete natives for water and nutrients. Prolific seed production, up to 140 seeds per stem, also helps leafy spurge spread quickly. The seeds may be ejected up to 15 feet away from the plants. Stem densities of leafy spurge have been reported as high as 1,000 stems per square meter which can easily crowd out native vegetation and reduce the biodiversity of insects and animals. Cattle and horses avoid grazing leafy spurge and may be injured by ingestion of the caustic sap. Humans can also be injured by the sap so care must be taken when working around leafy spurge. The large root system readily recovers from disturbance, making mechanical control difficult. Control with herbicide is costly, takes several years of application, and has broad environmental impacts.
Beginning in 1989, six species of flea beetles from the genus Aphthona were released in Colorado. These include A. flava (1989), A. nigriscutis (1989), A. lacertosa (1993), A. czwalinae (1993), A. cyparissiae (1991) and A. abdominalis (1996). All have established populations except for A. abdominalis. Adult flea beetles feed on the leaves of leafy spurge while the larvae feed on the root system. These flea beetles have become established at field insectary sites across Colorado and can be collected in large numbers to be redistributed.
Life Stages of the Flea Beetles
Adult leafy spurge flea beetles emerge in the spring and early summer to feed and mate. After mating, female flea beetles lay their eggs near the root crown of leafy spurge plants. Each female can lay over 200 eggs during their 45-65 day adult lifespan. The larvae hatch from the eggs, burrow into the soil, and begin to feed on the root system. When finished feeding the larvae will pupate within the root where they hibernate until spring or early summer and then emerge as an adult. One generation is produced per year.
Flea Beetle Damage & Identification
The 1 - 5mm, shiny brown or black adult flea beetles may be found on leafy spurge plants from mid-May to mid-August. As they feed, they create characteristic “shotgun” like holes in the leaves. At high densities, the adults may completely defoliate the leafy spurge leaving only ragged stems. They will jump when disturbed and are most active during the hottest parts of the day. Since they are so active and small it may be hard to observe them on the plants and it is usually easiest to use an insect net to sweep the plants and confirm their presence or absence. It is very difficult to distinguish between the different brown-colored species adults and the two black-colored species adults in the field and typically a mix of species is present. When very high larval populations are present underground the only indication will be gray patches of stunted and malformed dead leafy spurge stems.
- Will Apthona spp. kill leafy spurge?
Leafy spurge flea beetles do kill leafy spurge plants. The primary means of mortality is through the larval feeding on the roots which reduces root energy stores and decreases nutrient uptake. The feeding damage can also open the plant up to infections from soil pathogens.
- Will flea beetles attack other plants?
Leafy spurge flea beetles may very rarely feed on other spurge plants in the Euphorbia genus but are unable to complete their life cycle on any plant other than leafy spurge.
- How long will it take to control leafy spurge?
Control of leafy spurge is highly correlated with flea beetle density. With high-density populations of flea beetles, up to 95% reduction of spurge has been observed in three to five years post-release. The largest effect is one year after release in the immediate area around the release location.
- What is the best release site?
The ideal release site for leafy spurge flea beetles are colonies of leafy spurge with one to three feet of space between plants, coarse well-drained, and semi-exposed soil, and south, west, or east-facing slopes. Long periods of water-logged soil will drown the developing larvae. Vegetation that is too thick makes it difficult for the beetles to lay eggs on the root crowns or move through the plant colony.
- When is the best time to release flea beetles?
Aphthona spp. emerge from the soil in late May and the typical season to field collect, ship, and release these agents is June through July.
- Can I spray leafy spurge with herbicide?
Herbicide in combination with the leafy spurge beetles may work better than either control method alone. Herbicide applications may be used to open up the canopy of a dense leafy spurge colony to allow the better establishment of the beetles and may also reduce the nutrient stores in the roots faster by removing the above-ground plant growth. Herbicide should only be applied during the times of the year when adults are not above ground breeding and laying eggs. Typically, early spring (before mid-May) and late fall (after mid-August) are appropriate times.
- Is there a charge?
Yes, the flea beetles are $30.00 per release of approximately 1000 adults.