Researchers develop new maize varieties to tackle Striga weed

A field trial contrasting Striga infested maize alongside the varieties that are resistant to the weed. PHOTO BY AATF

One of Uganda’s major challenges to cereals farming is Striga or witch-weed which causes up to 100 per cent crop-loss in highest-infestation areas. But soon, there will be more effective control when a new method, the Imazapyr Resistant (IR) hybrid maize, matures this year.

Striga is a parasitic weed that severely hampers productivity of staple crops such as maize, sorghum, millet and upland rice in Sub-Saharan Africa. It survives by siphoning off water and nutrients from host crops, for its own growth.

IR involves treating seeds of the cereal crop with IR herbicide, which keeps off Striga from growing on roots where it positions itself.

Dr Godfrey Asea, the director, National Crops Resources Research (NaCRRI)-Namulonge, says preliminary results from the research are promising.

In its IR research project, NaCRRI is collaborating with the International Maize and Wheat Improvement Centre (CIMMYT).
“Hybrid maize variety has to be resistant to the herbicide that once the chemical (Imazapyr) is coated on its seed, the maize survives while striga dies before it can damage the host plant,” Asea explained.

“But the most effective approach for farmers is an integrated system that entails push-pull, intercropping with legumes, seed-coating with herbicide.”

Push-pull technology is intercropping maize with Desmodium and Napier grass at the borders. This has been proven to effectively control Striga and stem borers.

“The IR solution comes out at the end of 2016 when we shall apply for release to the ministry of Agriculture,” added Dr Asea, who previously headed NaCRRI’s Cereals Research Programme.

Charles Kasozi Lwanga, an officer in the cereals research programme, points out that various maize hybrids including Longe7H have been converted for resistance against Imazapyr. “Several promising IR maize hybrids are being selected with the hope of selecting superior ones for release and commercial production.”

Farmer’s experience
Currently, IR maize is being promoted under the trade name of “StrigAway” maize; but it has different local names such as Kayongo-GO in Uganda, Ua Kayongo in Kenya and Komesha Kiduha in Tanzania.

“On-farm use of IR maize technology enables farmers to increase harvests from a paltry average of 500 kilogrammes per hectare [kg/ha] to over 1,500 kg/ha,” says Kasozi.

Probably, the only disadvantage of IR is there is no seed recycling as the farmer has to buy IR maize seed every season. Also, since the seed is coated with herbicide, it should be handled with care to avoid hazards.

Kaleb Titia Kamure, a farmer in Katrini Sub-county in Arua District, who has suffered losses due to Striga infestation, confirms it is a serious challenge to cereal farmers.
“I lost sorghum and maize in Arua District where it is widely prevalent. In the Lugbara language, we call it “ava” meaning master/dangerous weed. It is notorious and frustrating to us here,” Kamure says.

He, however, observes that where root crops especially cassava grows and in wetland areas, Striga does not germinate.
Other crops affected by Striga in Uganda are sugarcane and elephant grass.

Kamure who mainly engages in growing upland and wetland rice, adds that where he grows wetland rice in Uriama Sub-county, the Striga problem does not emerge.

“This season I have intercropped maize with cowpeas. These being legumes, it will help control Striga,” he says adding that rice farmers in Nebbi, have also devised a method of Striga control using biological methods.

According to the Nairobi-based African Agricultural Technology Foundation (AATF), Striga infests as much as 40 million hectares of smallholder farmland in Sub-Sahara Africa and causes yield losses ranging from 20–80 per cent and even total crop failure in severe cases.
AATF is collaborating in a public-private partnership on Striga control in maize in Africa.

Partnerships
Meanwhile, in Kenya and Tanzania—where Striga is worse than Uganda—AATF is collaborating with two seed companies— Freshco Seeds in Kenya and Tanseed International—which it has provided seed-treater machines to boost IR maize seed processing.
The seed-treaters, which were installed and launched in September 2014 have brought efficiency in coating maize seed with the Imazapyr herbicide.

“They will reduce time taken to coat the seed, increase accuracy, uniformity and drying, factors that will enhance the effectiveness of the herbicide-coated maize seed to control Striga,” reads a statement by AATF. “The end result will be quality seed in desired quantities for smallholder farmers in the two countries.”

Prior to the intervention, the two companies used manually operated treaters that made the seed coating time consuming and resulted in unevenly coated seed.

The new seed-treaters have capacity to coat three tonnes of seed per hour while the fabricated manually driven treater takes a day to coat about one tonne of seed.

Use of the treaters will enhance access to quality seed by smallholder farmers and enhance maize production.
During the same period, Kenya Seed Company joined the efforts to fight the weed in Kenya by launching its StrigAway IR maize variety H528, which was marketed to farmers for the first time in 2014. Freshco Seeds also sold its variety FRC425 IR for the second season.

What is Striga

The most common type is Striga hermonthica, which is endemic in the eastern, western, Northern and north-western regions while Striga asiatica is mainly in the northern parts.
The areas hardest-hit include Tororo, Busia, Teso, Northern Uganda, West Nile and Bwera in Kasese, close to the DR Congo border.

Some of these regions also suffer from the virulent maize lethal necrosis (MLN) viral disease combining three viruses that attack maize mainly in eastern Uganda.
Striga causes serious damage to its host crop before emerging from the soil by producing phytotoxins, which are harmful to the host crop.

Upon attachment to host roots, it withdraws photosynthate, minerals and water, resulting in characteristic “witch” appearance of the host crop manifested by stunting, withering and eventual death.