Mexica Marigold (Tagetes minuta) is an erect woody annual herb usually 0.5m-2m tall with strongly odorous foliage. The taproots are usually short and tapering, and surrounded by fibrous and roots which form mycornhizal associations .Its stem are typically erected, woody, and grooved or ridged. Initially green but often maturing to brownish or reddish.
They are usually branched only in the upperparts, unless broken or cut off near the base. Its leaves occur in opposite pairs on the main stem and usually singly on the laterals. Leaves are 5-20cm long slightly glossy-green and are pinnately compound with 4-6 pairs of pinnae opposite below and alternate or opposite above. Leaflets are narrow lanceolate sharp toothed and 2-4 cm along
Underside of the leaves bears a number of small punctuate orange multicellular glands which exclude a licorice-like atom when raptured gland occurs beside the midribs and towards the margins of each leaflets and may also be found in the stem and involucre bracts. Scented panicle-like inflorescence consist of 20- 80 narrow cylindrical flower heads.
Heads are small 10-15mm long and 3-4 mm in diameter surrounded by 4- 5 fused involucre bracts and dotted with glands not sprinting apart at maturity. Seedlings have apogeal germination. Slender, often reddish. Hypocotyls are 1.0-1.5 cm along and end in elongate cotyledons about 1cm long which are often reddish below. The first pair of leaves are deeply decided into 3 segment with large terminal lobe and have irregularly toothed edge.
Mexican marigold originated in South America, and has been deliberately distributed across the tropics, subtropics and several temperate countries as ornamental medicinal or perfume pant as well as accidentally as a weed. In Kenya was first recorded as an Allen weeds during the 1920s.
It was originally restricted to the higher altitude, but has since spread to lower altitude, but has since spread to lower altitude a results of increasing agricultural activities. Was also introduced in California USA to control root-knot nematodes in orchards, but had since become an invasive weed.
Ecological requirements of the weeds
Mexican marigold is capable of rapid growth and seeds production (about 29,000) seeds per plants, enabling it to invade ephemeral habitats which provide at least seasonally a medium to high temperature, ample water, light and nutrients and minimal competition from perennial plants. Grows in moist and areas, from sea legal to reasonable altitude in the tropics ad subtropics and soil PHs ranging from 4.3 to 6.6.
Thrives under high nutrients and high soil moisture connections. The weed tolerant low rainfall. It’s commonly found along streams and river banks. It can colonize waste areas, neglected range land and also poorly managed fields.
Disadvantages of Mexican Marigold
- Its acts alternative host that harbor pest, diseases and other micro-organisms.
- Compete with the crop for water, soil, nutrients, light and space .This leads to reduction in crop yields.
- Its leaves allopathic residues in the soil .The roots exude polyacetylene derivatives which delays germination and reduces the yields of crop in the soil previously infested with the species.
- It’s a fast growing annual weeds which compete with crop and interferes with their management or harvest.
- It increases the cost of production.
- When the seeds of Mexican marigold mix with the produce lowers the quality.
- Adaptation of Mexican marigold weeds to various environmental conditions.
- The plant is propagated by seeds which germinate over a period of 48 hours.
- Seeds do not require light for germination, however they respond to it positively, so that germination only occurs from seeds from seeds near the soil surface and most seedling emerge from depth of less than 6mm.
- They produces enormous quality of seeds.
- They have the capacity to withstand adverse conditions in the fields because they can modify their seeds production and growth according to availability of moisture and temperature.
- They can germinate under adverse soil moisture condition.
- They have short period of plant growth generally grow at fast rate and produces seeds earlier than most of the crop.
- The seeds can remain viable in the soil for a long period without missing their viability.
- In maize plantation, wheat and rice, Agromine860SL 100ml/20l, Clampdown480SL 200ml/20l non selective herbicide. For clearing all weeds before planting.
- In carrots, Hotline450SC 50ml/20l.
- In onions, Commander240EC 50ml/20l.