Senna obtusifolia (L.) H.S.Irwin & Barneby

Code

Growth form

Biological cycle

Habitat

Northern Cameroon: Senna obtusifolia is observed throughout the rainy season, although its frequency and abundance are higher in the beginning of the crop cycle than in the middle or end of the cycle. Germination takes place in the month of May following the first significant rains. Following each cultural operation (plowing, weeding, ridging), a new phase of germination occurs lasting 2-4 weeks. Flowering begins in late July-early August and ends in late September. Fruiting takes place from August to November, until the plant dries out early in the dry season. In the absence of weeding, the complete development cycle occurs in 12 or 13 weeks. In the case of individuals from later emergence, flowering and fruiting is delayed, but the development cycle is shortened to 8 or 9 weeks. Seed production is so low because it is produced by plants of weak development.
Mayotte : Senna obtusifolia flowers from March to August and fruits from May to September.

Senna obtusifolia usually grows as a pasture weed but sometimes found along roads and in disturbed areas in rain forest. In West Africa it occurs in open areas along roadsides, grasslands and cultivated fields, common near settlements, and in waste areas. It could probably thrive in disturbed areas of prairies.

S. obtusifolia is a ruderal species (along roads and irrigation canals, around the villages or cattle yards) and common weed of crops in plots where the soil is still fertile (cell cultures in floodplains, depressions and terraces).
 
Northern Cameroon: Senna obtusifolia is a characteristic species of the Sudano-Sahelian regions, where the annual rainfall is less than 1100 mm.
Mayotte: Senna obtusifolia is an exotic species but not frequent, and naturalized in secondarized environments such as wastelands, crops, ditches, or urban areas, mainly in the center part of the island.
West Indies: Although Senna obtusifolia is an undemanding species in terms of soil quality, it is characteristic of areas with low rainfall (less than 1100 mm) and therefore becomes less frequent in wetter areas.

Toxicity

Senna obtusifolia is toxic for cows if eaten in large quantities.

Local harmfulness
 
Benin: Senna obtusifolia is rare and scarce in paddy fields.
Burkina Faso: Rare and scarce
Northern Cameroon: Senna obtusifolia is present in over 60% of the cultivated plots in Sudano-Sahelian region. However in more humid regions, where annual rainfall exceeds 1300 mm, the frequency of occurrence is very low (7%). It does not have any preference for any significant soil provided that it drains well. It is common and abundant on fersialitic soils, ferruginous soils of dunes and on alluvial, but it is uncommon in Vertisols because of their poor drainage. This is a very common weed in traditional farming systems, neither using herbicides nor fertilizers thus soil preparation before planting is superficial or non-existent. In these culture systems, sorghum is the dominant culture. S. obtusifolia is typically a regional weed.
Ivory Coast: Frequent and scarce.
Ghana: Rare and scarce.
Kenya: Frequent but not abundant
Mayotte: S. obtusifolia is a weed that is not frequent (2% of cultivated plots), it grows especially in vegetable crops.
Nigeria: Rare and scarce.
Uganda: Rare and scarce.
West Indies: Senna obtusifolia is a low pest species present in all crops. It can become locally abundant when conditions are favourable.

Global control

Senna obtusifolia is very difficult to control with cultivation usually spreading rather than controlling this weed. Hand pulling is difficult because of its long curved taproot. Slashing reduces vigour and if combined with other management measures such as restricted grazing and soil fertility augmentation, can bring this plant under control. A variety of herbicides can be used to control S. obtusifolia. Their success depends upon environmental conditions. When using any herbicide always read the label first and follow all instructions and safety requirements. If in doubt consult an expert.


General guidelines for weed management in lowland rice, consult

For weeding Advice broadleaf annual weeds of irrigated rice and lowland in Africa, visit
 
Local control
 
Madagascar: Generally, Senna obtusifolia is slightly troublesome in crops. Pulling manually is difficult because of the strong taproot system. Controllable with oxadiazon preemergence and 2,4-D and / or glyphosate postemergence on young plants. Tolerant to most herbicides in the adult stage (also sensitive to dicamba postemergence, product not available in Madagascar).

Herbarium pictures ReCOLNAT: https://explore.recolnat.org/search/botanique/simplequery=Senna%2520obtusifolia