The common bean does not compete well with weeds because it grows slower compared to most weeds and can thus suffer from successive flushes of weeds, causing significant yield losses.
A weed is any plant growing in a wrong place, usually considered undesirable. Weeds compete with the crop of interest for growth factors including nutrients, moisture and space, and may completely suppress the crop if uncontrolled. Besides, they harbour pests and diseases which can significantly reduce yields.
Common Bean Weeds
A wide range of weeds grow in a bean crop garden. These include the following;
Broadleaf weeds | Grass weeds |
| Pig weed (Amaranthus spp) | Crab grass (Digitaria spp) |
| Sow thistle (Sonchus oleraceae) | Barnyard grass (Echinochloa crusgalli) |
| Mexican marigold (Tagetes minuta) | Nutsedge (Cyperus spp) |
| Devil’s thorn (Emex australis) | Wild oat (Avena fatua) |
| Thorn apple (Datura stramonium) | Johnson grass (Sorghum halepense) |
| Macdonald’s eye (Galinsoga parviflora) | Bermuda grass (Cynodon dactylon) |
| Black jack (Bidens pilosa) | Star grass (Cynodon spp) |
| Nightshade (Solanum nigrum) | Guinea grass (Panicum spp) |
| Oxalis (Oxalis spp) | Goose grass (Eleusine indica) |
Why is proper weed control important?
Weed management is extremely important because;
- Weeds greatly reduce crop yield as well as its general performance.
- They harbor pests and diseases.
- They directly compete with plants for growth factors like sunlight, water, nutrients, space. This makes the plants weak and susceptible to attack by pathogens.
- Some are parasitic, others are harmful when eaten by livestock and humans.
- Generally, plants in wrong places look ugly.
- Some weeds can damage the crop by producing toxic substances
- They cause harvesting problems, especially those that develop late in the crop season
What is the benefit of early/timely weed control?
Weed control is critical early in the season because;
- It eliminates competition for light, nutrients and moisture, giving the crop the opportunity to establish well.
- It protects the palatability and nutritional potential of the crop
- It substantially curtails opportunities for pests’ establishment in the crop
- Young weeds are easier to control, e.g., they absorb and translocate herbicides better
- Weeding can be less effective in times of drought stress, which mostly occurs at later dates of the season
Management & Control
To obtain high and quality yields, proper weed management is essential. Several methods are employed, which include;
Chemical method
This method involves the use of herbicides. This method is highly preferred because;
- It is fast and easy
- There is no mechanical damage to the crop.
- It is cost effective
- Weeds with similar morphological factors with crop are effectively controlled.
The following herbicides are recommended for use in controlling bean weeds;
Catapult® 480SL (Glyphosate – isopropyl ammonium 480g/L)
It is a broad spectrum non-selective herbicide with enhanced systemic activity, which controls post-emergence broadleaf and grass weeds. It is recommended for use before planting, usually during land preparation.
Application rate; 200 ml/20L
Hotline® 450 SC (Linuron 450g/L)
This is a broad spectrum selective herbicide which controls pre-emergence and post-emergence weeds in in carrots, coriander, beans, baby corn, maize and potatoes. It is recommended for use 2-3 days after sowing.
Application rate; 50ml/20L
Bentagran Top® 240EC (Bentazone 150g/L + Fomesafen 70g/L+ Quizalofop-p-ethyl 20 g/L)
This is a broad spectrum selective herbicide which controls annual weeds in bean fields. It is recommended for use when the crop is at 2-5 leaf stage.
Application rate; 50 ml/20L
Forester® 150 EC (Fluazifop – p – butyl 150 g/L)
This is a highly active systemic and selective herbicide which controls most annual and perennial grass weeds in broadleaf crops, including beans, groundnuts, cotton, tobacco, tomatoes, peppers, cucurbits, brassicas and other vegetable crops. It is recommended for use as an early post-emergence to young active growing weeds, preferably at 3-4 leaf stage.
Application rate; 50-75 ml/20L
Mechanical method
This involves the removal of weeds using tools and implements like Jembes, hoes, among others. It should be done carefully in order to prevent mechanical damages to the crop.
Cultural method
The cultural practices which help in weed management include the following;
- Planting early maturing bean varieties
- Using clean bean seeds that are free from weed seeds
- Using irrigation water that is free from weed seeds
- Mulching
- Crop rotation
- Adopting a closer row spacing
- Hand pulling/uprooting the weeds
- Early planting
Remarks
- It is advisable to mix the herbicide with Integra® 3 ml/20L, an adjuvant which improves the efficacy of the chemical by acting as a sticker, spreader and penetrant.
- Herbicides should be diluted with clean water.
- An integrated weed management strategy is highly encouraged.
