When to weed
In general, the earlier the better. Small, young and tender weeds are easier to uproot or
cut than older, tougher weeds. Also the root system of the crops that are being weeded
are less disturbed.
Small weeds are also less likely to re-grow after they have been uprooted and left on
the soil surface, and they have less time in which to damage the crop by removing
nutrients etc.
Obviously it is a good idea to uproot weeds before they have developed, and
released, their seed.
Striga—“ Witchweed”
More information is available online in the IDRC Archive publication “Controlling the
Striga is a parasitic plant weed that can devastate crops and cause 80% or more loss
of yield in sorghum, maize, rice, millet, sugarcane and other crops. It is found in many
parts of Africa, Asia, India, North America and Australia. The weed penetrates the roots
of flowering plants, mainly of the cereal family, and digests the root system of its host.
In some parts of Ethiopia it is known as Harama Hazabe (“Weed from Hell”).
There are about 60 species of Striga, of which Striga lutea is the most important.
Striga can badly affect the following: sorghum, maize, rice, wheat, oats, rye, pearl
millet, finger millet, Italian millet, teosinte (Euchlaena mexicana) and sugarcane.
One species, S. gesneroides, is sometimes found in Africa and Asia and unlike other
Striga species can parasitise tobacco, several legumes and some species of Ipomoea.
Striga is an annual, each plant producing up to 500,000 very tiny seeds (0.0045 g)
which can remain viable in the soil for up to 20 years. Normally the seed will only
germinate when a susceptible crop is grown in the same soil.
Alas this is virtually impossible, and the spread of this weed can normally only be
limited to some extent, by using a combination of the following methods:
- Crop rotation of 15 years or more without growing a susceptible crop. In the
rotation trap crops are grown such as cowpeas, soybean, field peas, groundnuts,
sesame, sunflower or sunn-hemp (good in poor, sandy soil); these trap crops
stimulate the Striga seed to germinate but are not themselves seriously damaged.
The Striga plants must then be destroyed before they set seed. Sometimes the trap
crop itself is ploughed in together with the Striga, before it sets seed. - The increased use of fertilisers may have some effect, but unfortunately this also
tends to increase the vigour of Striga. - Wider plant spacing of some crops may help them to withstand Striga infestation.
- Careful hand weeding before Striga sets seed can be done in small areas; weeding
should be repeated several times every season. - Some herbicides such as phenoxy and benzoic acids, 2,4-D, ametryne and atrazine
can give good control in some crops if the soil and weather conditions are
favourable.
89
deeply, nor to produce a saucer-like depression around each tree, unless this is a
deliberate form of micro-catchment to catch rainwater.
Controlling Striga
GROWING FOOD – THE FOOD PRODUCTION HANDBOOK
Noxious Weed Striga” and elsewhere.