SAMUEL MWITA

By SAMUEL MWITA
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Striga is a parasitic weed that threatens the livelihoods of thousands of rural households in western Kenya.

The weed is devastatingly prolific, with a single plant producing up to 200,000 tiny, sticky seeds, which can remain viable in the soil for over 20 years.

Spread by wind, water, humans, animals and farm implements, striga seeds germinate only when they sense germination stimulants from a potential host crop, after which the parasite sucks nourishment from the victim.

Striga infestation causes significant yield losses of 20-100 per cent in maize, forcing some farmers to give up cultivating the crop entirely.

But there is hope through Imazapyr-resistant (IR) maize technology for striga control, which is a promising step in managing this noxious weed in the affected areas.

The IR technology has two components: (i) Herbicide resistant maize seed, which can be coated with the chemical without affecting the growth of the maize plant.

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(ii) Herbicide (Imazapyr) coating, where the cover kills sprouting striga seedlings as they attempt to attach themselves to the maize roots, protecting the crop and reducing the weed’s seed bank in the soil.

As the maize seeds germinate, they take in the herbicide. The germinated maize then produces a chemical which induces germination of the striga weed, but as the striga seedlings attach themselves to the roots of the maize to draw nutrients, they are killed by the herbicide.

For effective control, there is need to combine this technology with good agronomic practices such as planting crops in alternating sequence or leaving infested field.

SEEDS DEVELOPED TO OVERCOME STRIGA

Rotation with non-host crops further breaks addition of striga seed into the soil and improves soil fertility, some rotation crops produce allelopathic exudates that reduce the effects of striga weed.

Heavy infestation of striga is an indication of soil deficient of minerals salts, especially nitrogen and phosphorous.

Thus, addition of nitrogenous fertiliser especially from ammonium source leads to significant reduction in striga numbers.

In addition, farmers should combine this technology with intercropping IR maize with legumes though care should be taken while handling the legume seed after planting IR maize since the herbicide is detrimental to legume seeds.

Legume crops used in intercropping improve the fertility of the soil and covers soils helping smother weeds.

Intercropping is a potentially viable, low-cost technology, which assists farmers to address the two important and interrelated problems of low soil fertility and striga menace.

The use of this technology has resulted to renewed hope for farmers living under the perceived curse of striga.

They have begun opening up previously abandoned land since using the IR maize seeds reduces the striga seed bank in the soil, greatly cutting the threat posed by the weed to maize farming and farmers’ livelihoods.

H528-IR (Kenya Seed Company) and FRC425-IR (Fresco Seed Company) are some of the seeds developed to overcome striga.

They retail from Sh360 to Sh500 per 2kg packet and are available in agro shops in striga prone areas.
While planting the IR seed varieties, there are precautions to take.

First, use gloves while handling the seed and second, do not plant IR seed in the same hole with the other seed for those intercropping since the herbicide will kill the legume seeds

Lastly, wash hands before handling the other seeds.

Mwita is based at the Department of Crops, Horticulture and Soils, Egerton University.

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