Smooth pigweed (Amaranthus hybridus) has become a major weed of vegetables and row crops throughout the world. A Weed being defined a plant growing where it is not wanted and whose negative effects on cultivated crops outweighs its economic importance. They are herbaceous annuals belonging to family Amarantaceae. Smooth pigweeds are tall, erect to bushy plants with simple oval, Diamond shaped with alternate leaves. They are broadleaved plants. They have dense inflorescence flower clusters comprised of many small green flowers, set seeds and die within the frost free growing season. It’s commonly known as ‘Muchicha’ in Swahili.
Distribution of Amaranthus hybridus.
It is widespread in tropics and sub-tropical regions of the world and widely distributed to humid to sub-humid areas in Kenya as a weed. They are native to parts of North and Central America. Crop cultivation and human commerce has opened new niches hence colonisation of Agricultural ecosystems throughout America, Europe, Asia and Africa.
Ecological and Environmental Requirements of Amaranthus Hybridus
They require an altitude of 900-2600m above the sea level. Prefers shallow loam soils. The seed require adequate soil moisture and good soil contact to absorb moisture and germinate. More deeply buried seeds remains dormant but viable for many years and germinate upon being brought to the surface through cultivation. It is adapted to different soils Sandy, loamy, alkaline and saline soils but prefer soil P. H of between 6.0 – 7.5. They also prefer different climatic conditions varying from cool, warm, humid and dry environments hence colonisation of different parts of the world.
In Kenya, it is very common weed in western parts of Kenya though it is evenly distributed in almost all parts of the country.
Adaptations of Amaranthus Hybridus to Its Survival
It survives in different environmental conditions ranging from hot weather and tolerating drought. This anables the weed to colonise different crops growing in different environmental conditions.
Responds well to nutrients especially nitrates. This ensures faster growth hence high competition for nutrients with crops.
It is adapted to avoid shading due to rapid stem elongation. This ensures faster growth hence can compete for light with crops having the competitive ability.
They produce large amounts of seeds. These ensures faster propagation as compared to the crops.
They have many methods of dispersal such as;
- Flood water
- Tillage tools
- Tractor tyres
- Soil clinging on footwear
This ensure there is always a chance of their dispersal hence colonisation of many farms.
They have multiple dormancy mechanisms so that seeds produced in a given season germinate at different times over next year. This ensures survival of the weed hence difficult to eradicate it.
Mostly erect. Therefore, overtops short crops such as brocolli and snap peas blocking light hence poor photosynthesis for the crops.
They have C4 photosynthetic pathways which confers an ability to grow rapidly at high temperatures and high light intensity and compete aggressively with crops for nutrients, light and water hence weakening the crops.
Negative Effects of Amaranthus Hybridus to Crops
Amaranthus hybridus hosts pest nematodes (Meloidogyne app) and many vegetable pathogens such as those causing early blight in potatoes and tomatoes (Alternaria solani), Lettuce rot (Sclerotinia sclerotiorum), and southern blight (Sclerotium rolfsii). Viral pathogens such as Cucumber Mosaic Virus can also be transmitted by Amaranthus hybridus.
Competes with crops for nutrients, water and light hence weakening the crops and lowering their yields.
Contaminates crop yields with their seeds hence lowering the produce quality.
Increases cost of production of crops since it is capital intensive as well as Labour intensive to control the weed.
It blocks irrigation channels.
Greenlife Solutions for the Control of Smooth Pigweed (Amaranthus Hybridus)
Greenlife Crop Protection has many approaches to eradicate the weed depending on the crop the weed is growing alongside since the weed can be found growing in different crop fields such as in maize, onions, carrots, beans among many other crops.
During Land Preparation for crop cultivation (non-cropped land) use:
- WEMBE 200 SL A non-selective post emergence herbicide, to clear Annual and perennial grasses and broad leaved (smooth pigweed) weeds and any other weed in the field including difficult weeds. Use during Land preparation to clear all weeds.
Rate of use: 3.0Litres per Hectare (300ml in 20L)
- CATAPULT 480 SL Is a non-selective Post emergence herbicide which controls Annual and perennial grasses and broad leaved (smooth pigweed) weeds. Use CATAPULT 480 SL during Land Preparation to clear all weeds.
Rate of Use: 2.0Litres per Hectare (200ml in 20L)
- HURRICANE 200% SL Is a non-selective post emergence herbicide, used to control Annual grasses and broad leaved (Smooth pigweed) weeds on Maize, Sweet corn, Baby corn and sugarcane. Apply between rows when crops are above waist high.
Rate of Use: 1.5Litres per Hectare (150ml in 20L)
- BENTAGRAN TOP 240 EC Is a selective Early Post Emergence herbicide which controls Annual grasses and broad leaved (Smooth pigweed) weeds on Common beans and French beans, Should be applied when weeds(Smooth pigweed) are actively growing.
Rate of Use: 0.5Litres per Hectare (50ml in 20L)