Controlling spiny emex in maize and wheat

This tough weed should be eradicated as soon as possible after it emerges.

Spiny emex ( Rumex hypogaeus) is a decumbent or semi-erect annual plant that can grow densely and reach up to 60cm in height. The leaves and stems appear vivid green from seedling stage. The leaves are simple, arranged either alternately or in small bundles, egg-shaped (ovoid) to oblong, and up to 8cm long and 5cm wide.

The flowers are green and in axillary bundles, but not particularly prominent. The fruits are large, triangular and clearly visible on the plant between the leaves. Each seed has three indentations on each side and three strong, sharp, spreading thorns.

Spiny emex is widespread in Southern Africa and threatens both winter and summer rainfall areas. It has spread rapidly to dryland maize and can be a problem where wheat is irrigated.

Control

Various pre- and post-emergence herbicides are registered for the control of spiny emex in maize and wheat ( see Tables 1 and 2).

Administer a pre-emergence herbicide in the soil during planting or within four days after planting. Pre-emergence herbicides require sufficient soil moisture to become active and work effectively, so irrigate the soil accordingly.

Administer a post-emergence herbicide after the weeds and/or crops have emerged.

Follow the instructions and prescriptions on the label of each product. A post-emergence herbicide should preferably be mixed with an additive that promotes herbicide penetration; see the label for instructions.

Spiny emex is often a difficult weed to eliminate. To control it effectively, apply the herbicide when the weed is between the twoand six-leaf stage. The more fully grown the plant, the less effective the herbicide will be.

Although not an important weed in wheat production of the Free State, spiny emex is distributed widely in the Western Cape production areas. Because resistance to herbicides has not yet been reported, broad leaf herbicides are still used with success.

Shallow cultivation can lessen the occurrence of spiny emex.

Note: The control options mentioned here are merely guidelines. Check with your extension officer before applying any chemical.

• Source: grainsa.co.za/control-of-weeds-inmaize-and-wheat-part-1-spiny-emex.