Learn About Whitehall Bio Control: 6/26/2024

We are into summer now, and the weeds are showing their ugly or pretty heads. The Whitehall Biological Weed Control Project is finished with whitetop flower mites, yellow toadflax stem-boring weevils, and Dalmatian toadflax stem-boring weevils. Next, we will be monitoring for and collecting/releasing leafy spurge flea beetles and the red-headed leafy spurge root/stem-boring beetle.

Leafy spurge is a deep-rooted perennial plant invader from Eurasia. It has a latex-filled milky white sap that can irritate humans' skin and eyes. Cattle and horses generally do not eat it; sheep and goats will. Because of the deep roots, hand pulling, burning, and mowing do not work to control it. Herbicides, intensive cultivation, and biological control can be effective. The plant has small green flowers with yellowish bracts (modified leaves that protect the flower and may also have color to attract pollinators) that can be mistaken for flower petals. The 1-3-foot-tall stems have narrow alternate leaves with smooth margins.

We have been releasing spurge insects since the 1990s and have them established in most spurge patches in Jefferson County and the surrounding counties. The leafy spurge flea beetles (Aphthona spp. – there are several species approved for release, and we release a mix of these species) are small brown or black beetles with jumping back legs like a flea or grasshopper. The adults are coming out now and can severely damage the plant by leaf feeding if in high numbers. They scatter their eggs on the soil surface around the base of the weed. The larvae soon hatch, burrow into the soil, and feed on leafy spurge roots. Larvae do the most damage to the plant. They over-winter underground and emerge as adults in late spring/early summer to do it all again. They generally work quite well on dry sites. Unfortunately, the larvae drown in wet and heavily irrigated sites where leafy spurge can flourish, so we see spurge along creeks, canals, and ponds. You may also see rings of healthy spurge plants around ant piles as ants chaise the adult flea beetles away and prey heavily on flea beetle eggs before the larvae can hatch and burrow away to safety. Remember, these bioagents will not eradicate the weed (if they did so, they would have become extinct in Eurasia, where they co-evolved with the weed). They hopefully knock spurge back to tolerable levels.

The red-headed leafy spurge stem/root boring beetle (Oberea erythrocephala) emerges as adults in spring and early summer. They lay their eggs on the stem, often killing that stem. The larvae bore (feed within) into the stem and root crown and overwinter there. The larvae do the most damage to the host weed. They emerge as adults the following season to do it all again. These beetles are strong fliers dispersed throughout our area, so we no longer distribute them.

We are finding that over time, the density of leafy spurge has greatly decreased on dry sites. We seem to have an ongoing cycle where the spurge increases, and then the insects respond by increasing again and knocking the spurge back over several years. This cycle keeps spurge at a much lower density level than before the bioagents were released. It seems that this is what we will have to live with over time.

We are having a hard time finding good places to collect these insects in useful numbers for distribution as the large, heavy patches of leafy spurge of the past that produced high insect numbers have crashed (are mostly gone). We will collect some insects for folks that need releases, however we will monitor your sites before we release them to see if you have them already. If you do have the flea beetles in good numbers, we will not release more, as that would be a waste of resources. Feel free to call us during normal business hours to discuss your weed problem and the possibility of monitoring and releasing on your property. Call Project Coordinator Todd Breitenfeldt at 406-498-5236 or MCC AmeriCorp volunteer Ava at 301-237-3353. The time to get after your weeds is NOW!