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

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    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/sulcotrione300/125 g/litrePre-emergence or early post-emergence of the weed
    bromoxynil225 g/litre

    400 g/litre

    450 g/litre

    500 g/litre
    Post-emergence of weed between four or six leaf growth stage
    dicamba/topramezone160/50 g/litre
    Early post-emergence before six leaf stage. Apply in tank mixture with atrazine or atrazine/terbuthylazine
    flumetsulam800 g/kg
    Pre-emergence apply in tank mixture with metolachlor or s-metolachlor
    linuron500 g/litrePre-emergence or only directed post-emergence application between row crops when weed is 35 to 50 cm tall
    metribuzin480 g/litrePost-emergence between the four to six leaf stage of the weed
    topramezone336 g/litreEarly 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/dicamba240/80 g/litrePost-emergence between two to six leaf growth stage
    bromoxynil225 g/litre

    400 g/litre

    450 g/litre

    500 g/litre
    Post-emergence, weed fully emerged, but not older than three leaf stage
    bromoxynil/pyrasulfotole210/37,5 g/litre

    Post-emergence, weeds fully germinated and between four to six leaf stage
    carfentrazone-ethyl/metsulfuron-methyl400/100 g/kg

    Post-emergence, when weed is between two to six leaf stage
    carfentrazone-ethyl400 g/kg

    Post-emergence, when weed is between two to six leaf stage
    chloorsulfuroon750 g/kg

    Post-emergence, when weed is between two to six leaf stage
    chlorsulfuron/metsulfuron-methyl/tribenuron-methyl119/79/222 g/kgPost emergence of weed, when crop is between four to six leaf stage

    florasulam/flumetsulam75/100 g/litrePost emergence of weed, between four to six leaf growth stage

    iodosulfuron-methyl sodium/mefenpyr-diethyl50/150 g/kg

    Post-emergence, weed fully germinated. Apply when crop is between growth stages seven and thirteen

    iodosulfuron-methyl sodium/metsulfuron-methyl/mefenpyr-diethyl30/30/90 g/kgPost-emergence, weed fully germinated and when the crop reached four leaf stage
    metsulfuron-methyl/thifensulfuron-methyl68/680 g/kg

    Post-emergence, when weed is between four to five leaf stages
    metsulfuron-methyl/tribenuron-methyl80/300 g/kg

    Post-emergence, when weed is between two to six leaf stages
    metsulfuron-methyl200 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
    prosulfocarb800 g/litre

    Pre-emergence, apply in tank mixture with trifluralin en triasulfuron
    prosulfuron750 g/kg


    Post-emergence when weed is between two to six leaf stages
    pyroxsulam45 g/literPost-emergence when weed is between two to six leaf stages
    sulfosulfuron750 g/kg

    Post-emergence when weed is between one to four leaf stages
    thifensulfuron-methyl750 g/kg

    Post-emergence, when weed is between four to five leaf stages
    triasulfuron750 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).