How maize farmers can control striga

Striga infested maize garden. Photo / Courtesy

What you need to know:

  • Despite its numerous importance, maize productivity is being constrained by a number of factors including abiotic factors of which soil nitrogen and drought stresses are most common. 

Maize is one of the important crops grown by farmers serving as source of food as well as a reliable source of income.

Despite its numerous importance, maize productivity is being constrained by a number of factors including abiotic factors of which soil nitrogen and drought stresses are most common.  There are also biotic factors which include pests and disease infestation and above all weeds constituting of none parasitic weeds such as coach grass (Digitaria scalarum) and commelina benghalensis and parasitic weed mainly striga (S.Hermonthica).

Background

Striga also known as witch weed is a parasitic weed which infests roots of the host plant especially cereals belonging to grass family. It survives by siphoning water and nutrients required for its growth from host plants such as maize, rice, millet and sorghum among others thereby causing stunting and wilting of the host plants.

Striga infestation has affected the productivity of cereal crops in farmer fields mainly maize but it is also prevalent in sorghum, millet and rice farms in the eastern parts of Uganda and western parts of Kenya. Experts say the weed is one of the major constraints in maize productivity and have devised ways for farmers to deal with it.

Weed management

Dr Charles Lwanga, a senior research officer at the National Crops Resources Research Institute (NaCRRI), with a team of scientists from Kenya have been carrying out research on striga weed since 2013. Dr Lwanga explains that the weed has posed a serious challenge to farmers growing cereal crops in some parts of East Africa.

In the case of Uganda, the incidence is severe in the districts of Bugiri, Iganga, Kaliro, Kamuli, Namutumba, Tororo, Busia, Butalejja, Moyo, Kitgum, Amuru, Masindi, Kasese, Kamwenge and Kumi

Detecting striga

In a training manual about striga management in maize farms in Uganda, published by Dr Geoffrey Asea, the director of NaCRRI, it is stated that striga is characterised by bright green stems and pink or purple leaves depending on the species.  According to Dr Asea, most devastating striga species include hermonthica and S. asiatica.

Since striga seeds are tiny, they can easily be carried on different items including shoes, clothes, field tools, livestock and run off water. However, the major way of spreading is during preparation of the land for planting maize or any other cereal crop.

Striga control measures

There are a number of measures farmers must apply in eliminating striga infestation in their farms and these include reducing the seed bank in the soil. A striga plant can produce 50,000 seeds which remain viable in the soil for between 10 and 20 years.

Farmers can control this by planting Imazapyr resistant herbicide treated maize seeds.

Dr Asea and team acknowledge maize hybrid varieties such as LongeH7 have been coated with the required herbicide to cause resistance.  Currently, Imazapyr resistant maize seed is being promoted under the trade name Striga Away Maize seed and it has different local names such as Kayongo- GO in Uganda, Ua Kayongo in Kenya and Komesha Kiduha in Tanzania

Farmers are advised to follow the right practices including observing spacing of 0.75m by 0.50m by 0.30m when planting one seed per hole. Ensure the soils are moist during planting and the growing shoot will appear yellowish meaning the herbicide has been absorbed.

The advantage is that the herbicide will deplete the striga seed bank in the soil making the farm striga free.

Push pull technology

The other measure is the adoption of push pull technology which involves intercropping maize with desmodium in addition to planting napier grass at the borders.

Desmodium produces secondary metabolism in its roots which exhibits chemical effects on the striga and this reduces the seed bank in the soil. It is advantageous because the push pull technology will increase availability of nitrogen in the soil making it fertile.

Pests and diseases

Apart from striga weed being a major challenge in maize farming, there is biotic stress with the major disease being leaf blight, grey leaf spot, maize streak virus and maize lethal necrosis. Dr Asea and team bred maize varieties which are tolerant to these diseases which, farmers can access from certified seed companies.

Other challenges are pests with the major one being maize stem borer, termites and maize weevils which, destroy the crop at farm level and stored grains. These can be controlled using appropriate pesticides and using the right storage material as a measure of post-harvest handling.

About striga

• It is a parasitic weed that affects cereal crops, especially maize and sorghum, in many parts of Africa. It can also affect other grass-like plants, such as finger millet, rice, sugar cane, Sudan grass and Napier grass. • Two types of Striga are found in Africa: Striga hermonthica grows up to one metre tall, with pinkish flowers. Striga asiatica is shorter, growing to just 30 cm tall, with reddish flowers. • Striga seeds can lie in the soil for a long time up to 15 years,  germinating only when a cereal crop is planted.  Striga can only grow by attaching itself to the roots of a grass-like plant, most commonly maize and sorghum.

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