Control of weeds in maize and wheat – Part 5: Amaranthus hybridus (Common pigweed, Cape pigweed, redshank)

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    Seedling.
    Adult plant.

    Spikelets and seed.

    Flower spike.

     

    Scientific name: Amaranthus hybridus
    Afrikaans name: Gewone misbredie
    English name: Common pigweed

    Short description

    Common pigweed is an erect, multi-branched, hairless, annual herbaceous plant. It can grow up to 90 cm long, but much higher in suptropical conditions. The stems are green to brown and sometimes it is redly tinged and strongly ribbed. The leaves ae simple, alternately arranged and broad lancet shaped. It can be up to 6 cm long and 3 cm wide. The margins of the leaves can be entire and the veins are more distinct on the lower surface of the leaf. Leaf stalks can sometimes be as long as 5 cm. Flowers are borne in dense terminal and axillary spikes and are unisexual, with male flowers at the top of the spike and the more numerous female flowers at the bottom. The flowers are straw-coloured. Fruits of common pigweed are small bladder-like fruits, that are dehisced by lids. The seeds are small, shiny, dark brown to black and lens-shaped.

    Distribution

    Common pigweed is one of the most abundant and widely distributed broadleaved weeds of cultivated fields in southern Africa. Common pigweed occur in both summer- and winterrainfall areas of South Africa.

    Control

    Cultivation
    Common pigweed is easy to control with shallow cultivation when the weed is still in the seedling stage.

    Chemical
    Various pre- and post-emergence broadleaf herbicides can be used to control common pigweed effectively (Tables 1 and 2).

    TABLE 1: Broadleaved herbicides registered for use on maize for the control of common pigweed.

    Active ingredient Formula Time of application
    2,4-D480 g/litrePre-emergence application five to six days after plant. Post-emergence when crop is 30 cm tall, otherwise use drop-arms for directed spray
    2,4-D/dicamba240/80 g/litrePost-emergence when weeds are actively growing, five to six leaf stage
    acetochlor/atrazine/simazine160/165/165 g/litrePre-emergence with or just after planting
    acetochlor/atrazine/terbuthylazine125/187,5/87,5 g/litre

    150/225/225 g/litre

    200/150/150 g/litre

    250/225/225 g/litre

    350/175/175 g/litre
    Pre-emergence with plant or within three days after planting. Early post-emergence, not later than four leaf stage of the weed
    atrazine500 g/litre

    900 g/kg
    Pre-emergence on well-prepared seedbed

    Early post-emergence, two leaf stage of the weed
    atrazine/cyanazine

    167/333 g/litre

    250/250 g/litre
    Pre-emergence or early post-emergence
    atrazine/mesotrione/s-metolachlor

    208,5/26,8/208,5 g/litre
    Pre-emergence application
    atrazine/metazachlor/terbuthylazine

    210/60/210 g/litre

    Pre-emergence, within three days after planting. Can be followed-up with an early post-emergence application
    atrazine/metolachlor

    300/300 g/litrePre-emergence application within three days after planting

    atrazine/metolachlor/terbuthylazine

    174/252/174 g/litrePre-emergence or early post-emergence, before weed reaches four leaf stage
    atrazine/s-metolachlor

    370/290 g/litrePre-emergence application just after planting
    atrazine/s-metolachlor/terbuthylazine

    262,5/175/262,5 g/litrePre-emergence application
    atrazine/sulcotrione

    300/125 g/litrePre- or early post-emergence application
    atrazine/terbuthylazine

    250/250 g/litre

    270/270 g/litre

    300/300 g/litre

    450/450 g/kg
    Pre-emergence or post-emergence before four leaf stage of the weed
    atrazine/terbutryn

    250/250 g/litrePre-emergence with planting or just after planting
    bendioxide480 g/litrePost-emergence application
    bromoxynil225 g/litre

    400 g/litre

    450 g/litre

    500 g/litre
    Post-emergence, four to six leaf stage of the weed
    bromoxynil/terbuthylazine150/333 g/litrePost-emergence
    dicamba480 g/litre

    700 g/kg

    Post-emergence, before crop reaches 30 cm
    dicamba/tropamezone160/50 g/litreEarly post-emergence, before six leaf stage, use in tank mixture with atrazine or atrazine/terbuthylazine
    EPTC720 g/kg

    200 g/litre
    Pre-plant, incorporated into soil,consult product label
    flumetsulam800 g/kgPre-emergence, use in tank mixture with metolachlor or s-metolachlor
    flumetsulam/s-metolachlor

    20/630 g/litreApplied with planting or within three days after plant
    glyphosate/mesotrione/s-metolachlor250/25/250 g/litrePost-emergence, only on glyphosate tolerant cultivars
    halosulfuron750 g/kgPost-emergence
    linuron500 g/litrePost-emergence as a directed spray, when weeds are between 50 cm - 75 cm tall and crops are between 35 cm - 50 cm tall
    MCPA400 g/litre

    700 g/kg
    Pre-emergence, within five to six days after plant. Post-emergence till crop is 30 cm tall
    mesotrione480 g/litrePre- or post-emergence. Use only in tank mixture with atrazine, atrazine/terbuthylazine or s-metolachlor
    mesotrione/s-metolachlor83,3/416,7Pre-emergence

    s-metolachlor/terbuthylazine102,8/497,2 g/litre

    312,5/187,5 g/litre
    Pre-emergence

    Pre-emergence, in tank mixture with mesotrione
    metribuzine480 g/litrePost-emergence, between four to six leaf stage of weed, in tank mixture with 2,4-D or bromoxynil
    pyraflufen-ethyl20 g/litrePost-emergence, when weed is between two to four leaf stage. Use only in tank mixture with MCPA or bromoxynil
    tembotrione/isoxadifen-ethyl420/120 g/litrePost-emergence in tank mixture with atrazine
    terbuthylazine500 g/litrePost-emergence application with 2,4-D/dicamba

    trifluralin480 g/litrePre-plant application

    tropamezone336 g/litreEarly post-emergence, before six leaf stage, use in tank mixture with atrazine or atrazine/terbuthylazine

    Table 2: Broadleaved herbicides registered for the control of common pigweed in wheat.

    Active ingredient Formula Time of application
    2,4-D480 g/litreApply at growth stage seven to 13 of the wheat
    2,4-DB400 g/litreUndersowed lucerne in grain crops, wheat must be between leaf stage five and full tillering, READ THE LABEL
    2,4-D/dicamba240/80 g/litreApply at growth stage seven to 13 of the wheat
    bendioxide480 g/litre

    Apply on young, actively growing weeds
    bromoxynil225 g/litre

    400 g/litre

    450 g/litre

    500 g/litre
    Weeds must be fully germinated, but not older than six leaf stage. Wheat seedlings should be between the three leaf and end of booting stage
    chlorsulfuron/metsulfuron-methyl375/300 g/kgWeed in leaf stage three to four
    dicamba700 g/kgOnly to be used in a tank mix with Enhancer (10 - 12 g) + Reaper (10 g) + adjuvant
    halosulfuron750 g/kg
    In mixtures (see label)
    fluroxypyr/triclopyr

    240/120 g/litreWeed in leaf stage two to eight
    MCPA400 g/litre

    700 g/kg
    Apply at growth stage seven to 13 of the wheat
    pyraflufen-ethyl20 g/litrePost-emergence, when weed is between two to four leaf stage. Use only in tank mixture with MCPA or bromoxyni
    trifluralin480 g/litreBefore planting

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