Spotted spurge: A common weed of container production in nurseries and greenhouses
Euphorbia maculata (or Chamaesyce maculata) also known as spotted spurge or spotted sandmat, is a common broadleaf weed in container production in nurseries and greenhouses. It is an herbaceous, summer annual, low-growing, weed in the plant family Euphorbiaceae, having spotted leaves. It has small (less than 0.5 inches long) linear or egg-shaped leaves arranged in opposite pairs. It has a prostrate growth habit with stems growing up to 2 feet and not more than a few inches high. There is often a dark spot in the center of leaf. Individual plants tend to form a mat, along the soil surface, with branches growing outwards from a central growth point in roughly radial patterns.
Spotted spurge has reddish-colored branched stems that have fine hairs (Fig 1). Broken or punctured stems secrete a milky-white, sticky sap that is poisonous and can irritate skin and eyes. Leaves have a short petiole, are arranged in opposite pairs, and are unequal. Leaves are small, oblong, dark green with purple spots in the center (on more than 95% of leaves), hairy, smooth, or finely toothed, mostly rounded at tips, and measure about one inch. Under ideal conditions, plants begin to flower just one month after germination. Plants are monoecious, producing tiny, white, and pink flowers in the leaf axils. Flowers consist of only stamens and hairy pistils, having white to pink petaloid (Petal like) appendages, and are grouped in cup-like structures, known as cyathia. The flowers may start producing fruits and seeds one month after flowering under ideal conditions. Reproduction of spotted spurge occurs via seeds. Under ideal conditions, plants can produce seeds prolifically with approximately 500 seeds per square foot. Generally, plants produce thousands of seeds that may germinate immediately (for seeds produced in summer) or remain dormant in the soil during winter in order to give rise to plants in the following spring or summer (for seeds produced in late summer or fall). Seeds buried deeper than ½ inch do not germinate due to the absence of light.Scouting for spurge is important for control and growers need to remove weeds at early stages when infestations begin. Growers need to check that planting material is free from any weed infestation and planting should be done in a weed-free substrate. Hand weeding or mechanical tilling can be followed to remove spurge plants before they set seed. Workers must wear gloves during hand weeding as the plant sap is a skin irritant. Walking through spurge mats should be avoided to control seed spread. Growers must also avoid raking of uprooted or mature spurge plants across the soil surface and dead spurge plants should be disposed carefully. Tools must be cleaned or washed off to remove any spurge seeds. Shady conditions inhibit seed germination of spotted spurge. Irrigation systems must be in proper working order to avoid unwanted wet areas that promote spurge infestations. Mulching with organic materials such as shredded bark, compost, or straw up to two inches depth in nursery containers can also suppress seed germination. For chemical control, products containing oryzalin, prodiamine, dithiopyr, pendimethalin, isoxaben or trifluralin can be used for preemergence control and products containing combinations of 2,4-D, MCPP, dicamba and/or fluroxypyr can be used for postemergence control of spotted spurge outside the greenhouse condition. These herbicides cannot be used inside the greenhouse or any other enclosed structures as they can cause severe phytotoxicity by vapor formation inside the greenhouse condition. So, growers are recommended to follow the nonchemical practices for spotted spurge control inside the greenhouse or any enclosed structures.
Debalina SahaAssistant Professor, Michigan State University
Debalina Saha is an Assistant Professor of ornamental weed management in the Department of Horticulture at Michigan State University. She has an appointment in research, teaching, and extension. Debalina provides statewide weed identification and management recommendations for ornamental plant production in greenhouses, nurseries, landscapes, and Christmas tree production. The primary goal of her research program is to improve upon current weed control practices and develop new effective methods of weed control using an integrated approach that involves both chemical and non-chemical strategies.