Leafy Spurge (Euphorbia esula L.)
Growth: Leafy spurge is an erect perennial plant growing from deep creeping underground rootstocks. Quick to emerge in the spring, it can reach heights of one metre (three ft.). All parts of the plant contain a milky white sap.
Leaves: Numerous simple, linear shaped leaves are alternately arranged on the lower stem.
Stems: A few scattered hairs are found near the top of the otherwise smooth stems.
Flowers: A whorl of leaves is located at the base of the inflorescence. The inflorescence is a cluster (umbel) of small inconspicuous yellow-green flowers and a pair of bracts surround each flower cluster. Flowering occurs late June through July. Occasionally under good growing conditions following a mild winter flowering may begin as early as May.
Seeds: The seeds, grey green, yellow or brown in colour, usually have a yellow bump near the base. Three seeds are found per capsule.
Roots: The creeping roots are red in colour and woody. They are covered with a thick bark which enables them to resist decay. New plants will develop from the numerous root buds.
By both seed and creeping roots. Since it can reproduce from root fragments up to one metre (three ft.) deep in the soil, control is difficult. Seed production is low - approximately 140 seeds per plant. Seeds are ejected from the capsules when ripe. Brown, grey-brown, grey and mottled seeds are able to germinate, but seeds that are reddish brown to orange and yellow are not viable.
Leafy spurge is aggressive in undisturbed areas such as pastures and roadsides, especially on sandy and marginal soils, and is considered a severe perennial weed in the Northern Great Plains of the United States and prairie provinces on untilled non-cropland sites. There is some evidence in recent years of leafy spurge establishing in low-disturbance direct seeded annual crop fields.
In Canada leafy spurge infestations increase yearly. The extensive creeping root system stores ample food reserves which aid root buds in establishing new plants. The roots can remain viable for years.. The sticky latex prevents grazing by many animals. Literature reports that the carrying capacity of pasture land will drop to near zero with more than 80 per cent leafy spurge cover, since cattle refuse to graze among spurge plants.
The toxic property found in the latex of leafy spurge when taken internally can cause scours, weakness, and occasionally even death. External contact can result in dermatitis and even blistering in animals and people. It has been reported that horses that walk through freshly mowed areas of leafy spurge will develop blisters and lose the hair above their hooves.
Sheep may consume up to 60 per cent of their diet as leafy spurge and goats may consume up to 90 per cent of their diet as spurge without ill effects, making them candidates for integrated control of leafy spurge. Cattle and horses learn to avoid eating the growing plants. Most animals will eat leafy spurge plants found in hay.
Leafy spurge does not tolerate frequent disturbance, and is therefore rarely a problem in annual crops.
Many weed managers have adopted a strategy of "early detection and eradication" of new infestations in combination with "containment and Integrated Control" of established stands in order to prevent the spread of invasive weeds such as leafy spurge.
Eradication of well-established stands is impractical if not impossible, but eradication of new infestations by intensive herbicide treatment is possible and part of an effective strategy to prevent spread of the weed.
Once populations are well established and eradication becomes impractical or cost prohibitive on a large scale, management priorities switch to containment and integrated control.
Containment requires that a perimeter boundary be established and maintained so that any plants emerging outside of the containment zone are quickly eradicated using similar herbicide techniques to the eradication priority. Within the containment zone, integrated management methods, such as biological control, sheep grazing, mowing, burning, etc., are used together to reduce the impact of the weed on the contained area. This general strategy can be applied to many other invasive plants.
Several biological control agents have been screened and released in North America for the suppression of leafy spurge.
The Apthona sp. flea beetle has been the most successful. There have been three species of Apthona that have been introduced, each with their own habitat requirements:
- The black dot (brown body),
- The brown dot (brown body), and
- The black (bodied) beetles.
They are progressively adapted from hot, dry, sandy sites (black dot beetle) through to warm, moister, loamy soils with increasing amounts of soil cover (black beetle). Excessive cover will impede the effectiveness of even the black beetle.
Other methods used in conjunction with beetles should avoid their vulnerable egg laying period from early June to late July. Unfortunately this is also the optimum time to apply most herbicide used for leafy spurge control.
Sheep and goats have been used in programs to try to control leafy spurge by browsing. On pasture land, close grazing with sheep will give good control. Sheep will graze the spurge ahead of the grass if the spurge plants are young. Removal of the sheep from these areas, even after many years of grazing, will result in recovery of the leafy spurge infestation within a season.
Burning can open up densely covered soil to allow access by either beetles or herbicide, but can increase the germination of spurge seedlings as well.