Weed identification
Dicotyledons (most broad-leaf weeds) and monocotyledons (e.g. grasses) are the two main plant types. Weed grouping has a significant impact on the potential for management. The more closely related a weed is to the host crop, the harder it will be to manage.
Table: Weed and crop family groupings (Monocotyledons - 'M')
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Family
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Weed examples
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Related crops
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Apiaceae
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Slender celery (Ciclospermum leptophyllum)
Australian carrot (Daucus glochidiatus)
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celery, carrot, parsley
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Amaranthaceae
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amaranthus (Amaranthus spp.)
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Chinese amaranthus
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Asteraceae
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billygoat weed (Ageratum spp.)
sowthistle (Sonchus oleraceus)
cobbler's pegs (Bidens pilosa)
fleabanes (Conyza spp.)
parthenium (Parthenium hysterophorus)
potato weed (Galinsoga parviflora)
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lettuce, artichokes
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Brassicaceae
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wild turnip (Brassica tournefortii)
wild radish (Raphanus raphanistrum)
turnip weed (Rapistrum rugosum)
shepherd's purse (Capsella bursa-pastoris) peppercress (Lepidium spp.)
lesser swinecress (Coronopus didymus)
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cabbage, cauliflower, broccoli, brussels sprouts, Chinese cabbage
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Chenopodiaceae
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Fat hen (Chenopodium spp.)
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beetroot
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Convulvulaceae
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bell vine (Ipomoea plebia)
bindweed (Convolvulus erubescens)
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sweetpotato
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Euphorbiaceae
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caster oil plant (Riccinus communis)
caustic creeper (Euphorbia drummondii)
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cassava
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Fabaceae
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rattlepod (Crotalaria spp.)
vetch (Vicia monantha)
medics (Medicago spp.)
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peas, beans
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Liliaceae
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onion weed (Nothoscordum gracile)
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onion, garlic
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Malvaceae
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small-flowered mallow (Malva parviflora)
sida (Sida spp.) bladder ketmia (Hibiscus trionum) anoda weed (Anoda cristata)
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okra, rosella, cotton
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Solanaceae
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apple of Peru (Nicandra physalodes)
nightshades (Solanum spp.)
thornapples (Datura spp.)
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tomato, potato, capsicum, eggplant
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Crop rotation:
Crop rotation is the programmed succession of different crops during a period of time in the same plot or field. It is a key control method to reduce weed infestation in vegetables. Crop rotation was considered for a long time to be a basic practice for obtaining healthy crops and good yields. At present, however, crop rotation is gaining interest and is of value in the context of integrated crop management. Classically, crop rotations are applied as follows:
- Alternating crops with a different type of vegetation: leaf crops (lettuce, spinach, cole), root crops (carrots, potatoes, radish), bulb crops (leeks, onion, garlic), fruit crops (squash, pepper, melon).
- Alternating grass and dicots, such as maize and vegetables.
- Alternating different crop cycles: winter cereals and summer vegetables.
- Avoiding succeeding crops of the same family: Apiaceae (celery, carrots), Solanaceae (potato, tomato).
- Alternating poor- (carrot, onion) and high-weed competitors (maize, potato).
- Avoiding problematic weeds in specific crops (e.g. Malvaceae in celery or carrots, parasitic and perennials in general).
Examples of crop rotations are as follow (Zaragoza et al. 1994):
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· In temperate regions:
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Pepper - onion - winter cereal
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Melon - beans - spinach – tomato
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Tomato - cereal – fallow
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Lettuce - tomato – cauliflower
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Potato - beans - cole - tomato- carrots
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Melon - artichoke (x 2) - beans - red beet - wheat - cole
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· In tropical regions:
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Tomato - okra - green bean
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Sweet potato - maize - mung bean
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Introducing a fallow in the rotation is essential for the control difficult weeds (e.g. perennials), cleaning the field with appropriate tillage or using a broad-spectrum herbicide. It is also important to avoid the emission of weed seeds or other propagules.
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