The Mexica Marigold, scientifically known as Tagetes minuta, is a tall erect annual herb with woody characteristics. It typically reaches a height of 0.5m-2m and has foliage that emits a strong odor. The plant has short and tapering taproots that are surrounded by fibrous roots, forming mycorrhizal associations. The stem of the plant is usually upright, woody, and grooved or ridged. While initially green, the stem often matures to a brownish or reddish color.
Branching in the Mexica Marigold primarily occurs in the upper parts of the plant, unless there is damage or cutting near the base. The leaves are arranged in opposite pairs on the main stem and usually singly on the lateral branches. They measure 5-20cm in length, have a slightly glossy-green appearance, and are pinnately compound with 4-6 pairs of pinnae positioned opposite below and alternate or opposite above. The leaflets are narrow lanceolate in shape, sharply toothed, and approximately 2-4cm long.
On the underside of the leaves, there are several small punctuate orange multicellular glands. When these glands are ruptured, they release a licorice-like aroma. The glands are present beside the midribs and towards the margins of each leaflet, and they may also be found in the stem and involucre bracts. The plant produces scented panicle-like inflorescences consisting of 20-80 narrow cylindrical flower heads. The heads are small, measuring 10-15mm in length and 3-4mm in diameter. They are surrounded by 4-5 fused involucre bracts and are dotted with glands that do not separate when mature.
Mexica Marigold seedlings have apogeal germination. The hypocotyls, which are slender and often reddish, measure 1.0-1.5cm in length and end in elongated cotyledons approximately 1cm long. The cotyledons often have a reddish coloration below. The first pair of leaves are deeply divided into three segments, with a large terminal lobe and irregularly toothed edges.
The Mexican marigold has its origins in South America and has been intentionally introduced to various regions across the tropics, subtropics, and several temperate countries for its ornamental, medicinal, and perfume properties. However, it has also unintentionally spread as a weed. In Kenya, it was initially documented as an alien weed during the 1920s.
Initially, the Mexican marigold was limited to higher altitudes, but over time it has expanded its range to lower altitudes due to increased agricultural activities. Additionally, it was introduced to California, USA, with the purpose of controlling root-knot nematodes in orchards. Unfortunately, it has since become an invasive weed in that region.
Ecological requirements of the weeds
The Mexican marigold possesses the ability to undergo rapid growth and produce a large number of seeds, approximately 29,000 seeds per plant. This characteristic enables it to invade ephemeral habitats that offer favorable conditions such as medium to high temperatures, abundant water, sufficient light, and nutrients, while experiencing minimal competition from perennial plants. The plant thrives in moist areas, ranging from coastal regions to moderate altitudes in the tropics and subtropics, and can adapt to soil pH levels between 4.3 and 6.6.
Mexican marigold flourishes in environments with high nutrient availability and ample soil moisture. It is capable of withstanding low rainfall conditions, making it particularly tolerant to arid conditions. Commonly, it is found growing along streams and river banks. Furthermore, it can colonize waste areas, neglected rangelands, and poorly managed fields, taking advantage of disturbed or less cultivated spaces.
Disadvantages of Mexican Marigold
- Acts as an alternative host, harboring pests, diseases, and other microorganisms.
- Competes with crops for water, soil, nutrients, light, and space, leading to reduced crop yields.
- Leaves allopathic residues in the soil, as the roots release polyacetylene derivatives. This can delay germination and reduce crop yields in soil previously infested with the species.
- It is a fast-growing annual weed that competes with crops and interferes with their management or harvest.
- Increases the cost of production.
- When the seeds of Mexican Marigold mix with the produce, it lowers the quality.
- The Mexican Marigold weed adapts to various environmental conditions.
- The plant is propagated by seeds that can germinate within 48 hours.
- The seeds do not require light for germination, but they respond positively to it. Germination typically occurs from seeds near the soil surface, with most seedlings emerging from depths of less than 6mm.
- Mexican Marigold plants produce a large quantity of seeds.
- They have the capacity to withstand adverse field conditions by adjusting their seed production and growth according to moisture and temperature availability.
- They can germinate even under unfavorable soil moisture conditions.
- Mexican Marigold has a short period of plant growth, growing at a fast rate and producing seeds earlier than most crops.
- The seeds can remain viable in the soil for a long period without losing their ability to germinate.
GREENLIFE SOLUTIONS FOR THE CONTROL OF MEXICAN MARIGOLD
CATAPULT 480 SL: CATAPULT 480 SL is a non-selective post-emergence herbicide designed to control both annual and perennial grasses as well as broad-leaved weeds, including Mexican marigold. It is recommended for use during land preparation to effectively clear all types of weeds. The suggested rate of use is 2.0 liters per hectare, which can be diluted to 250ml in 20 liters of water.
WEMBE 200 SL: WEMBE 200 SL is a non-selective post-emergence herbicide that targets annual and perennial grasses and broad-leaved weeds, including tough ones like purslane and oxalis. It is particularly useful during land preparation to eliminate all types of weeds. For tougher weeds, the recommended rate of use is 3.0 liters per hectare, which can be diluted to 300ml in 20 liters of water.
GOVERNOR 580 SE: GOVERNOR 580 SE is a selective herbicide suitable for pre- and early post-emergence use. It effectively controls annual grasses and broad-leaved weeds, including Mexican marigold, in crops such as maize, sweet corn, baby corn, and sugarcane. It is important to apply this herbicide when the soil is well-moistened for pre-emergence use. For early post-emergence application, ensure that the weeds are actively growing. The recommended rate of use is 2.5 liters per hectare, which can be diluted to 250ml in 20 liters of water.
COMMANDER 240 EC: COMMANDER 240 EC is a selective herbicide designed for specific crops. For onion family crops such as onions and garlic, it is applied as an early post-emergence or post-transplant herbicide, 2-10 days after transplanting. For brassica family crops like cabbages and broccoli, it is used as a pre-emergence or pre-transplant herbicide, applied two days before transplanting on a well-prepared bed. It effectively controls annual grasses and broad-leaved weeds, including Mexican marigold. The rate of use for this herbicide is 1.0 liter per hectare, which can be diluted to 50ml in 20 liters of water.