BY BLAINE BUG CREW
One of the earliest and most aggressive noxious weed invaders in Blaine County is leafy spurge. This plant starts early, and is in its full glory during the hottest days of summer. It is critical with this plant to act early, identify it, and develop a plan of attack before it has a chance to get established and eventually go to seed in mid to late summer. Here is what you need to know.
Leafy spurge is a deep-rooted, aggressive, persistent perennial that reproduces vegetatively and by seed. Plants have an extensive root system that grows horizontally and is capable of reaching depths up to 20 feet. Stems are thickly clustered and are narrow. Alternate leaves exude a milky latex when damaged. The flowers are small and yellow-green and are enclosed in showy yellow-green bracts. Seeds are oblong and occur in clusters of three. When seeds are dry, the capsules shatter and spread the seeds are as far as 15 feet from the plant. Leafy spurge is commonly found in grassland and rangeland habitats, but is also capable of invading forests and riparian areas, displacing native vegetation.
Our stem-boring moth is called Oberea. Adult OBER have red heads, black eyes, and slender bodies, with antennae that are nearly as long as the body. Males emerge several days before females and both sexes are sexually immature for two weeks before they start mating. Females often girdle the upper part of the stem, gnaw a hole into the stem above the girdle, and deposit an egg into the hole from the end of June to mid-July. Each female can produce approximately 60 eggs during her lifetime. Larvae hatch 10 days after eggs are laid and feed in leafy spurge stems on the pith, tunneling downward to the root where they remain during the winter. Mined stems dry, wilt and do not produce flowers or seed. Crown and root feeding reduces the plant’s root reserves and allows pathogenic fungi to enter infested leafy spurge roots. OBER prefers moist areas with trees and can survive subfreezing winter temperatures. Some research suggests that this agent may be biotype-specific, only attacking certain biotypes of leafy spurge.
Leafy spurge is a formidable foe for both homeowners and professionals. It is key to identify a new invasion early to have the best chance to gain control and keep your property free from this very invasive plant. If you have more questions on control options for this plant, please contact the Blaine County Weed Department at (208) 788-5543.
