Pearl millet affected by Striga
Striga is a very important weed in pearl millet cultivation. Unlike other weeds, which compete for water and nutrients Striga, as a root parasite, literally sucks the life out of pearl millet plants. In doing so, growth is stunted and yields are greatly reduced.
Striga infested pearl millet field
Striga has been given the common name of "witchweed" because of attaching to the roots and robbing the host of water and nutrients.
White flowered Striga
There are different species of Striga. The Striga found in India is most often has white flowers. But, Striga plants with yellow, pink or purple flowers are also common.
Pink flowered striga Mauve flowered striga Red flowered striga
Small Striga seeds
compared to sorghum
Depending upon the extent of infestation, 30-60% of reduction in grain yield can occur. Striga infestation is most severe in low moisture and low fertility soils. Thousands of very small seeds are produced by a single plant of Striga. These seeds can remain dormant but viable for many years.
Striga plants emerge from the soil adjacent to pearl millet plants and produce many upright green stems with pink to white flowers.
Flowering can begin within 2 weeks and seeds begin to mature 2-4 weeks later. The seed capsules (Fig.) may contain 400-500 seeds and a single plant may produce 20,000 seeds. Mature seeds are dispersed by wind, rainwater, cultivation, soil on tools, or even grazing and manure fertilization.
Control measures: Physical control: Hand pulling at too early stage may break the shoot and reduce the rapid growth. Sparse infestation should be hand pulled shortly before flowering to prevent build up of seed. Such hand pulling should continue through to harvest and beyond so long as flowering is occurring.
Cultural control: It has been noted that pearl millet plant shading can restrict Striga growth when generous soil fertilizer is applied. In areas of high rainfall, factors such as high plant populations, recommended fertility levels, and good weed control encourage lush crop growth and shading in spite of Striga parasitism. This is not feasible in moisture stressed rainfed areas. Crop rotation should be practiced with trap crops which stimulate Striga seeds to germinate without themselves being parasitized. Crops claimed to be effective include: cotton, sunflower, groundnut, castor, dolichos bean, and linseed. Unfortunately once a severe infestation has developed, it may take many years to reduce Striga population in the field to non-damaging level.
Chemical control: As Striga is a broadleaf plant, pre-plant herbicides such as Atrazine, Goal, and Flex show some effect though not efficient enough to be justified. Post-emergence use of 2,4-D is effective when sprayed on the Striga leaves. Though low in cost, pearl millet is vulnerable to stalk twisting and lodging if 2,4-D is sprayed into the leaf whorl. Spraying should only be done by trained labor and cautioned to the hazards.
Control measures: In summary, control of Striga infestation is difficult and requires an integrated approach. Non-host crops must be rotated (for two years in heavily infested fields) with pearl millet varieties.
Following good practices will help reducing striga effect in pearl millet crop:
plant populations and fertility adjusted for soil moisture availability to maximize shading,
weeding and Striga control through hand pulling and perhaps limited 2,4-D spraying, and finally
care not to spread seeds of Striga though fodder, manure or contaminated soil on tillage tools.
Submitted by kiran yadav on Wed, 14/03/2012 - 11:50