Family: Orobanchaceae
Common name: Denseflower witchweed, Agya, Denseflower Striga
Denseflower witchweed is a notorious weed very commonly seen in India especially in higher elevations. They are primarily known for its parasitic nature that affects agricultural crops. These plants can cause significant damage to rice, maize, sorghum, and sugarcane.
Plant characteristics
The plants are very small, only growing to a height of 20-30 cm with hairy stems and leaves. Stems are erect with thin, long leaves which are about 1-1.5 cm long.
Flowers of Denseflower witchweed are small, white, and tubular with a prominent calyx-cup holding the flower and long green bracts arising from the base of the calyx.
The flowers have 3 distinct petals on one end, and one broader petal on the other end which is notched in the middle. The flowers are borne at the tips of the stems in dense clusters giving the plant its name ‘densiflora’.
Once pollinated, these flowers produce small, capsule-like fruits that contain numerous seeds. A single plant can produce hundreds of seeds, which are then spread by wind, water, small animals, and even by humans through their clothing, crop bags, machinery, or implements.
Parasitic nature of Denseflower witchweeds
Denseflower witchweeds can cause a lot of harm in agricutural land because of their parasitic nature. The seeds remain dormant in soil for a long time until they find a a host plant root that it can attach itself to.
Certain chemicals triggered by the roots will cause Denseflower witchweed seeds to start germinating by attaching themselves to the host root. A small swelling forms at the place where these seeds attach themselves to the host roots.
Denseflower witchweed seeds are capable of producing chemicals that can dissolve the outer covering and penetrate the host roots, drawing nutrition from them through structures called haustoria.
Once the Denseflower witchweed plant grows, the host plant will wither and die. It is difficult to figure out the attack since most of the activity happens underground. By the time the Witchweed is noticed, it would already be established in the host root.
How to control these weeds
The methods used to control them are crop rotation so that Witchweeds will not find their host plants all the time, mechanical removal, and quarantine of affected land. A method called trap cropping is also used, which involves planting crops that will induce the Witchweed seeds to germinate, but will not allow them to attach themselves to the roots.
As soon as a new plant is noticed, it has to be removed from the soil before flowering and fruiting.
Propagation is through seeds.
Photographed at: Nandi hills area, Bangalore
