Taking an environmentally sensitive approach to pest management


Integrated Pest & Crop Management



AUTHOR

Kevin Bradley
University of Missouri
Division of Plant Sciences
(573) 882-4039
bradleyke@missouri.edu

Weed of the Month: Toothed Spurge (Euphorbia dentata)

Kevin Bradley
University of Missouri
(573) 882-4039
bradleyke@missouri.edu

Published: July 23, 2014

Toothed spurge is one species that has been found with increasing frequency in Missouri soybean fields in recent years.

Toothed spurge, Euphorbia dentata, is a summer annual that is native to the eastern United States and Mexico. The plant is also referred to as wild poinsettia but this common name is more properly suited to a close relative of toothed spurge, Euphorbia heterophylla. Wild poinsettia (Euphorbia heterophylla) is a very common weed throughout much of Central America and now also occurs in the southern U.S. from Florida to California, but I have not personally encountered it in Missouri yet. Toothed spurge is one weed that I have seen more of over the past several years in Missouri cropping systems. I would not consider it a common weed yet by any means, but one that has increased in prevalence over the past several seasons, especially in Missouri soybean fields. Toothed spurge can also be found in pastures, along roadsides, and in other non-crop areas.

Toothed spurge has leaves that are elliptic to ovate in outline and exude a milky sap when broken.

Toothed spurge can reach up to 2 feet in height and has stems that are light green to reddish green with short hairs. The leaves can be either opposite or alternately arranged along the stem and are from ¾ to 3 inches in length and up to 1 inch in width. The leaves are elliptic to ovate in outline with toothed margins. Leaves occur sparsely along the lower stems but are bunched or whorled near the upper portions of the plants. The upper leaf surfaces are dark green and without hairs, while the lower leaf surfaces are light to medium green and can have short hairs along the veins. The leaves and stems emit a white milky sap when broken. This milky latex sap is poisonous and can produce blisters and dermatitis in humans, cattle, and horses, and can also cause blindness if it comes in direct contact with the eye. The stems terminate in a flat-topped cluster of flowers. Each cluster consists of a mixture of flowers and immature fruits. The flowers are without petals or sepals and are yellow, pink, or white. Toothed spurge typically blooms in mid-summer and the blooming period lasts for about 1 month. After blooming, the flowers are replaced with 3-lobed nodding fruits. The fruits can become light red to purple with maturity. Each fruit contains 3 seeds that are oval in shape and dark brown to black in color. The roots consist of a taproot with a fibrous root system.

A young toothed spurge plant.

Toothed spurge is tolerant to normal use rates of glyphosate, which is more than likely the reason why we have seen more of it in Missouri cropping systems in recent years. The appearance of toothed spurge is an example of a weed shift, which is what occurs when producers rely predominantly on one herbicide or one weed management system to meet all their weed control needs. After continuous application of the same herbicide, in this case glyphosate for post-emergence weed control, species that are naturally tolerant of that herbicide are most likely to appear in that cropping system and become more prevalent. Also, toothed spurge does not typically emerge until later in the season, and in this way “escapes” the residual effects of many pre-emergence residual herbicide treatments.

Unfortunately, there is little information available on the control of toothed spurge in corn and soybeans. What little information I have found indicates that in corn, atrazine and isoxaflutole (Balance Pro, Balance Flexx) provide good pre-emergence control, while dicamba (Banvel, Clarity, Status, Distinct, etc.), glufosinate (Liberty), and a tank-mix of bromoxynil (Buctril) plus atrazine can provide good post-emergence control. In soybean, flumioxazin products (Valor, Fierce, Envive, etc.) have good pre-emergence activity, while lactofen (Cobra, Phoenix) and a tank-mix of imazethapyr (Pursuit) plus bentazon (Basagran) have been shown to provide good post-emergence control. Liberty in Liberty Link soybean is also an option. In both corn and soybean, a single post-emergence application of glyphosate will likely only provide about 50 to 60% control of toothed spurge. Although it is unlikely that complete control will ever be achieved with glyphosate, control can be increased to approximately 70 or 80% with two applications of glyphosate, but toothed spurge seed production will almost certainly still occur.

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REVISED: September 30, 2015