Euphorbia Esula - As An Invasive Plant

As An Invasive Plant

Leafy spurge was transported to the United States possibly as a seed impurity in the early 19th century. First recorded from Massachusetts in 1827, leafy spurge spread quickly and reached North Dakota within about 80 years. It now occurs across much of the northern U.S., with the most extensive infestations reported for Montana, North Dakota, Nebraska, South Dakota, and Wyoming. It has been identified as a serious weed on a number of national parks and on reserves of The Nature Conservancy in eleven northern states. It is now classified as an invasive species by the United States Department of Agriculture. It was first recorded in Alberta, Canada in 1933 and is also naturalised in parts of South America.

It displaces native vegetation in prairie habitats and fields through shading and by usurping available water and nutrients and through plant toxins that prevent the growth of other plants underneath it. It is an aggressive invader and, once present, can completely overtake large areas of open land. It is toxic as well.

Because of its persistent nature and ability to regenerate from small pieces of root, leafy spurge is extremely difficult to eradicate. Biological control offers a highly promising management tactic for leafy spurge. Goats, apparently able to graze on the plant without ill effect, have been used on rail trails in Idaho to clear leafy spurge from the trail shoulders. The U.S. Department of Agriculture has shown success using six European insects that feed on leafy spurge. These include a stem and root-boring beetle (Oberea erythrocephala), five root-mining flea beetles (Aphthona spp.), and a shoot-tip gall midge (Spurgia esulae). Large scale field-rearing and release programs are carried out cooperatively by federal and state officials in many northern states. The results are not as immediate as when herbicides are used but, if pesticide use is kept to a minimum, large numbers of these insects build up within a few years and have shown impressive results.

Several systemic herbicides have been found to be effective if applied in June, when the flowers and seeds are developing, or in early-to-mid-September, when the plants are moving nutrients downward into the roots. Preliminary research suggests that chemical treatment in the fall followed by a spring burn to reduce seed germination may be an effective strategy for reducing leafy spurge infestations. Multiple treatments are necessary every year for several years, making leafy spurge control an extremely expensive undertaking. If left uncontrolled for a single year, leafy spurge can reinfest rapidly. Prescribed burning, in conjunction with herbicides, may also be effective.