Frequently Asked Questions on Striga and the IR maize

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What is Striga?
Striga is a parasitic weed that attacks c ereal crops, retarding plant growth, resulting in stunted and withered plants.

Are there diff erent types of Striga?
There are several species of Striga. In cereals, only two species are of economic importance. These are the purple-fl owered Striga hermonthica and redfl owered Striga asiatica. Striga hermonthica is the most destructive.

Which crops are susceptible to Striga infestation?
Striga infests cereal crops such as maize, millet, sorghum, upland rice and napier fi elds throughout Sub-Saharan Africa.

How does Striga damage the cereal crop?
Striga attaches itself to the roots of host plants and siphons the nutrients and water intended for plant growth. This stunts and discolours the plant, fi nally causing it to wither resulting in grain yield losses. Striga is most damaging to the crop before emerging from the soil. Early signs of Striga attacks are folded leaves and wilting even where there is suffi cient soil moisture. Some crops act as trap crops or false hosts. They stimulate the Striga seeds to germinate. However, the Striga seedling cannot successfully attach to the trap crops in order to feed and hence it dies.

What are the other names of Striga?
Striga is also known as witchweed because of the twisted discoloured growth of aff ected plants. In west Kenya, farmers’ refer to it as Kayongo (Luo), Oluyongo (Luhya), and Imoto (Teso). In Tanzania it is known as Kiduha in Kiswahili.

Which conditions encourage Striga to fl ourish?
Striga infestations fl ourish in conditions characterised by low soil fertility, and mono-cropping with cereals.

How does Striga spread?
Striga seeds are very small and are mainly spread through the use of contaminated seed and equipment, surface run-off , eroded soil, wind, animals and people. Uprooted Striga plants should be burned otherwise the weed easily spreads to other farms. Seeds may remain dormant in the soil for 15–20 years.

What is the impact of Striga infestation on maize production?
In Sub-Saharan Africa, Striga causes yield losses of between 30% and 100%, worth USD 1 billion and aff ect livelihoods of about 100 million people. Studies show 76% of farmland in west Kenya – about 210,000 hectares – is infested with Striga. What this means is that a farmer whose crop is attacked by Striga could lose a whole crop and any harvests would not be suffi cient to feed the family and contribute to the family’s livelihood.

What are the available Striga control methods?

Striga control methods have been researched in Africa for over 50 years with a focus on agronomic practices such as uprooting and burning Striga plants before fl owering, fi eld sanitation (use of Striga-free planting material and clean tools), crop rotation, intercropping, organic matter usage, improved fallows and pushpull system, host plant resistance (use of Striga-tolerant maize germplasm) and the application of herbicide.

A new Striga control technology known as Imazapyr resistant maize (IR maize) has been developed by scientists at the International Maize and Wheat Improvement Center (CIMMYT), Weizmann Institute of Science, Kenya Agricultural Research Institute (KARI) and BASF, the Chemical Company. The Imazapyr resistant herbicide-coated maize seed kills Striga before it damages the crop and is being promoted under the trade name StrigAway® maize but has different local names such as Ua Kayongo in Kenya and Komesha Kiduha in Tanzania.

Then why does Striga infestation persist?
Striga-infested areas have developed very high levels of long-lived Striga seeds in the soil with only some breaking dormancy each season when stimulated by germinating crops and conducive environmental conditions. Available control methods have not been widely adopted by farmers probably due to limited knowledge of the Striga lifecycle, lack of land for crop rotation, and because their benefi ts accrue over the long term. Herbicide applications are also expensive and ineff ective since the crop is already damaged before Striga emerges.

What is the IR maize technology all about?
IR maize or StrigAway maize technology comprises two main elements – a herbicide- resistant maize seed and imazapyr, a systemic imidazolinone herbicide. The herbicide-resistant maize is coated with low doses of the herbicide, about 30g imazapyr per hectare, to control Striga. As the StrigAway maize germinates, it absorbs some of the herbicide used in coating it. The germinating maize stimulates Striga to germinate and as it attaches to the maize root, it is killed before it can cause any damage. Herbicide that is not absorbed by the maize plant diff uses into the soil and kills Striga seeds that have not germinated.

How does StrigAway maize control the spread of Striga?
The StrigAway seed coating acts at the time of Striga attachment to the maize root. Striga seed attempting to attach to germinating mize seed is killed and the herbicide prevents the attachment of the Striga on the maize plant. The herbicide also kills Striga seeds that have not germinated in the soil surrounding the maize seedling. The StrigAway maize technology, therefore, decreases the level of Striga in the farm through direct attacks on the Striga plants and seeds. The maize fi eld can virtually be clear of Striga throughout the season.

How is herbicide resistance acquired in maize?
The resistance is derived from a naturally occurring gene in maize originally identifi ed by BASF and made available to CIMMYT.

Is the StrigAway maize technology available to farmers?
The technology is available in Kenya and Tanzania and is currently being tried in farmers’ fi elds in Uganda and Ethiopia. In southern Africa, evaluation is being conducted in Malawi, Zambia, Zimbabwe, Lesotho and Swaziland. This is being done through the joint eff orts of CIMMYT, AATF, BASF, NGOs, agricultural extension, the national agricultural research institutes and seed companies such as Kenya Seed Company and Western Seed Company in Kenya, Tanseed in Tanzania and Nalweyo Seed Company (NASECO) in Uganda.

What is the increase in maize yield when using StrigAway hybrid maize?
Extensive on-farm testing of ordinary maize and the new hybrid on farmers’ fi elds under Striga infestation found that the hybrid maize yields were three (3) times those of ordinary maize. Apart from its Striga control qualities, StrigAway maize has other advantages that include resistance to maize streak virus and Turcicum, thus reducing the problems that aff ect maize production.

Is StrigAway maize therefore the best technology in controlling Striga?
It’s one of the methods of controlling Striga that can be used by farmers. For long-term control of Striga, farmers are advised to combine StrigAway maize with other Striga management methods, such as uprooting, burning Striga plants before fl owering, fi eld sanitation, crop rotation, intercropping, organic matter use, improved fallows and push-pull system MBILI planted with groundnut, golden gram, soybean or lablab and Striga-tolerant maize germplasm. What has been noted, however, is the quick action on Striga by StrigAway maize and the immediate increase in maize yields.

Do farmers need to take precautions when handling StrigAway maize?
StrigAway maize is planted and managed in the same way that farmers currently grow their maize. As is recommended with all commercially available maize seed coated with insecticide and fungicide, farmers should wash their hands after handling the maize. They should not handle other seed before they wash off the imazapyr herbicide as this may aff ect germination of the other crops. StrigAway maize can be intercropped with legumes, but the two must not be planted in the same hole, as the herbicide is likely to aff ect the legume seed. Instructions on handling of the treated seed should be provided to farmers enclosed with packaged seeds.

Does StrigAway maize have residual eff ects where it is grown?
No. The amount of herbicide is minuscule and is completely broken down in the soil 2–3 months after planting.

Can StrigAway maize be grown in a fi eld not infested with Striga?
Yes. It will grow and perform just like any other improved maize variety but the farmer will not have the benefi t of the seed dressing without the presence of Striga.

Where can farmers fi nd StrigAway maize seed?
StrigAway hybrid seed is commercially available to farmers in Kenya and Tanzania. In Kenya, the seed is available through Western Seed Company and agro-dealers in the Striga infested areas of western Kenya and in Tanzania through Tanseed International Ltd. New StrigAway maize varieties will be available in future from other seed companies in the region.

Is the StrigAway maize genetically modified?
No. As mentioned above, the technology relies on herbicide resistance that was derived from a naturally occurring gene in maize originally identifi ed by BASF and made available to CIMMYT. Plant breeders at CIMMYT in collaboration with Weizmann Institute of Science, Israel and KARI with funding from Rockefeller Foundation later incorporated the IR-gene into African maize varieties and adapted it for agro-ecological regions in Africa where Striga is endemic.

Where can one obtain more information on StrigAway maize?
Information can be obtained from CIMMYT, BASF, AATF, KARI, Forum for Organic Resource Management and Agricultural Technologies (FORMAT), We RATE, Kenya Seed Company, Western Seed Company, Tanseed International (Tanzania), Uganda National Crop Resources Research Institute-National Agricultural Research Organisation (NACRRI-NARO) and Ethiopian Institute of Agricultural Research (EIAR).

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