Control of weeds in maize and wheat – Part 1: Spiny Emex

Category: WEED SERIES

Scientific name: Emex australis
Afrikaans name: Kaapse dubbeltjie
English name: Spiny Emex, Three-cornered Jack, Devil’s thorn

Short description

Decumbent to semi-erect annual plants, up to 60 cm high when growing densely. Leaves and stems appear vivid green from seedling stage. Leaves are simple, alternately arranged or arranged in small bundles, egg-shaped (ovoid) to oblong, up to 8 cm long and 5 cm wide.

Flowers are green, in axillary bundles, but not very prominent. Fruits are big, triangular and clearly visible on the plant between the leaves. It has three indentations on each side and three strong, sharp, spreading thorns that can cause a lot of discomfort for humans and animals. Seeds are produced all year round.

Distribution

Spiny Emex is widespread in southern Africa and can be a problem weed in both winter and summer rainfall areas. It is rapidly distributing to dry land maize and can be a problem where wheat is being irrigated.

Control

Chemically
Various pre- and post-emergence herbicides are registered for the control of Spiny Emex in maize and wheat (Table 1 and Table 2). Pre-emergence herbicides are administered in the soil during planting or within four days after planting. Sufficient soil moisture is necessary to activate pre-emergence herbicides in the soil and to provide effective control. Post-emergence herbicides are administered after emergence of the weed and/or crop.

Follow the specific instructions and prescriptions on the label of each product. For effective control post-emergence herbicides should preferably be mixed with an additive that promotes the penetration of the herbicide. See label for instructions.

Spiny Emex can be a tough weed and should be controlled as soon as possible post-emergence. The optimum time is between two to six leaf stages of the weed. The bigger the plant, the less effective the herbicide will be.

Although this weed is not an important weed in wheat production of the Free State, it is distributed freely in the Western Cape production areas. Because resistance to herbicides has not yet been reported for this weed, broad leaf herbicides are still used with success. Always take into consideration resistance and do not use herbicides against which there already are resistance. Always contact a reliable chemical advisor before using any chemicals to ensure the correct dose and specifications on the label are adhered to.

TABLE 1: Herbicides registered to control Spiny Emex in maize.

Active ingredient	Formula	Time of application
atrazine/sulcotrione	300/125 g/litre	Pre-emergence or early post-emergence of the weed
bromoxynil	225 g/litre 400 g/litre 450 g/litre 500 g/litre	Post-emergence of weed between four or six leaf growth stage
dicamba/topramezone	160/50 g/litre	Early post-emergence before six leaf stage. Apply in tank mixture with atrazine or atrazine/terbuthylazine
flumetsulam	800 g/kg	Pre-emergence apply in tank mixture with metolachlor or s-metolachlor
linuron	500 g/litre	Pre-emergence or only directed post-emergence application between row crops when weed is 35 to 50 cm tall
metribuzin	480 g/litre	Post-emergence between the four to six leaf stage of the weed
topramezone	336 g/litre	Early post-emergence before six leaf stage. Apply in tank mixture with atrazine or atrazine/terbuthylazine

TABLE 2: Herbicides registered to control Spiny Emex in wheat.

Active ingredient	Formula	Time of application
2,4-D/dicamba	240/80 g/litre	Post-emergence between two to six leaf growth stage
bromoxynil	225 g/litre 400 g/litre 450 g/litre 500 g/litre	Post-emergence, weed fully emerged, but not older than three leaf stage
bromoxynil/pyrasulfotole	210/37,5 g/litre	Post-emergence, weeds fully germinated and between four to six leaf stage
carfentrazone-ethyl/metsulfuron-methyl	400/100 g/kg	Post-emergence, when weed is between two to six leaf stage
carfentrazone-ethyl	400 g/kg	Post-emergence, when weed is between two to six leaf stage
chloorsulfuroon	750 g/kg	Post-emergence, when weed is between two to six leaf stage
chlorsulfuron/metsulfuron-methyl/tribenuron-methyl	119/79/222 g/kg	Post emergence of weed, when crop is between four to six leaf stage
florasulam/flumetsulam	75/100 g/litre	Post emergence of weed, between four to six leaf growth stage
iodosulfuron-methyl sodium/mefenpyr-diethyl	50/150 g/kg	Post-emergence, weed fully germinated. Apply when crop is between growth stages seven and thirteen
iodosulfuron-methyl sodium/metsulfuron-methyl/mefenpyr-diethyl	30/30/90 g/kg	Post-emergence, weed fully germinated and when the crop reached four leaf stage
metsulfuron-methyl/thifensulfuron-methyl	68/680 g/kg	Post-emergence, when weed is between four to five leaf stages
metsulfuron-methyl/tribenuron-methyl	80/300 g/kg	Post-emergence, when weed is between two to six leaf stages
metsulfuron-methyl	200 g/kg 500 g/kg 600 g/kg	Post-emergence, apply when crop is in the three to five leaf stage Post-emergence, when weed is between two to six leaf stages and crop between three to five leaf stages
prosulfocarb	800 g/litre	Pre-emergence, apply in tank mixture with trifluralin en triasulfuron
prosulfuron	750 g/kg	Post-emergence when weed is between two to six leaf stages
pyroxsulam	45 g/liter	Post-emergence when weed is between two to six leaf stage
sulfosulfuron	750 g/kg	Post-emergence when weed is between one to four leaf stages
thifensulfuron-methyl	750 g/kg	Post-emergence, when weed is between four to five leaf stages
triasulfuron	750 g/kg	Pre-emergence applied during planting

Cultivation
Shallow cultivation can lessen the amount of Spiny Emex.

Contact the writers at elbe.hugo@syngenta.com (Elbe Hugo) and deweth@arc.agric.za (Hestia Nienaber).