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Push-Pull Technology For The Control Of Stem Borers And Striga Weed In Maize Crop

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By Dr Jolly Kabirizi

Over 50% of the total population in Uganda live with chronic hunger and malnutrition; this number could probably increase given its projected rate of population growth. Hence there is a need to increase food security in the country; one solution is through increased agricultural productivity that delivers increased food availability and rural income.

Maize is the most important cereal crop in Uganda providing over 40% of the calories consumed in both rural and urban areas. Farmers rely on maize for food, fodder and as a cash crop. Small scale farmers who constitute the bulk (80%) of the rural poor also account for the largest share of maize production.

Maize crop is grown in every part of the country and a direct source of livelihood to over 2 million households, over 1,000 traders/merchants and over 600 millers. Increasingly, maize has become a major non-traditional export cash crop particularly benefiting smallholder farmers. In 2020, maize production for Uganda increased to about 2,750 thousand tonnes from about 286,000 tonnes in 1980.

Challenges to production of maize in Uganda

Low productivity is one of the biggest challenges facing Uganda’s maize industry. Low maize productivity is linked to human, technical and socio-economic factors, and in the dominant smallholder sector to a virtual absence of improved maize varieties, use of unimproved agronomic and post-harvest technologies; high cost of inputs such as fertilizers and pesticides; lack of irrigation facilities, poor soils, pests such as stemborers and parasitic weeds such as striga.

Methods that embrace the application of herbicides, insecticides and inorganic fertilisers are environmentally unfriendly and unaffordable to most farmers, whereas crop rotation, uprooting strigaweeds, organic fertilizers and natural enemies, although affordable, often result in insufficient levels of control.

Additionally, control of stemborers using insecticides is often ineffective as the chemicals fail to reach deep inside the plant stems where the larvae reside; similarly use of herbicides against strigacan be ineffective.

Stemborers

Stemborers are of greatest importance as pests of maize in Uganda, but they also attack other cereal crops such as sorghum, millet and sugarcane. Damage is caused by larvae which first feed on young leaves, but soon enter into the stems. During early stage of the crop growth larvae may kill the growing points resulting in dead hearts.

Striga weed

Striga (witchweed) is a parasitic weed that attacks and significantly reduces the yields of maize, sorghum, millet, and sugarcane throughout sub-Saharan Africa. Low cost management methods such as hand weeding, short crop rotations, trap cropping, or conventional bio-control have not been effective.

Striga weed

Maize yield losses caused by stemborers can reach as high as 80% and by strigaweeds between 30 and 100%, and both are aggravated by low soil fertility. Where both pests occur simultaneously, farmers often lose their entire crop. These losses, which amount to approximately $7,000m annually in Sub-Saharan Africa, mostly affect subsistence farmers resulting in high levels of food insecurity, malnutrition and poverty.

Push-pull technology for the control of stemborers and striga weed

A ‘Push-pull’ strategy was developed by International Centre for Insect Physiology and Ecology (ICIPE), Kenya and its collaborators for the control of stemborers and striga weed in resource-poor maize farming systems. This technology controls both stemborers and striga and improves soil fertility. The National Crops Resources Research Institute (NaCRRI), Namulonge introduced the “Push-pull technology” into Uganda in 2001.

Push-pull technology involves intercropping maize (or other cereal crops) and Silver or Green

leaf desmodium (e.g. Desmodium uncinatum), with napier (elephant) grass (Pennisetum

purpureum) or Brachiaria (Brachiaria cultivar mulato II) grass planted as a border crop. The

forage legume is planted between maize rows.

The desmodium produces volatile chemicals, which repel the stemborer moths from the

maize (‘push’) while those released by Napier grass attract female moths (‘pull’) to lay eggs.

Desmodium roots produce chemicals which stimulate Striga seed germination, and others

which inhibit their attachment to maize roots (suicidal germination), thereby reducing Striga

seed bank. Desmodium also provides a good soil cover, controls weeds (decreases labour for

weeding) and improves soil fertility through nitrogen fixation. Both plants provide quality

fodder for livestock. Therefore, farmers using ‘push–pull’ technology for pest control not only

reap three harvests (maize, napier grass and desmodium); they also dramatically reduce the

devastating effects of the parasitic weed striga through the effects of desmodium.

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