Margaret Seur weeding her maize crops at Mukutani Irrigation scheme in Mukutani village ,Baringo south. [Kipsang Joseph, Standard]

Yield losses in maize is mainly caused by completion with weeds. Weed infestation is a severe problem in early part of the growing season. This is because of the slow growth and wide row spacing. Weeds compete with maize crop for light, nutrients, space, and moisture. This affects the morphology and phenology of crop, reduces yield, and damages the quality of grains. Additionally, high weed infestation increases the cost of cultivation, lowers value of land, and reduces the returns of maize farmers.

To realise favourable yields form maize, proper weed management is necessary. The recommended best practice is that an integrated approach to weed management is adopted. This involves a combination of cultural, mechanical, biological, genetic, and chemical methods. This is because no single method can provide complete weed control.

Cultural Control

Research has shown that weeds that emerge after four weeks of crop establishment have less impact on the yield; therefore, early-season weed control is extremely important for good yield. it is important to establish a uniform plantation at recommended plant density. Ensure that that the crop is protected from stress resulting from insect and disease attack.  Use of cover crops is another example of cultural control of weeds. Cover crops can be used for to protect smother weeds. Also it protects the soil from erosion and improves soil structure. Intercropping maize with a leguminous plant called mucuna has be reported to reduce weed infestation by 30 to 60 percent.  The plant produces a large biomass and can provide a ground cover that effectively controls weeds which compete with crops for water, nutrients and light. Once it dries up it forms a dense layer of plant material that prevents germination of weed seed leading to a clean seed bed.

Mechanical Weed Control

Tillage is the most common method of mechanical weed control and it done before planting or after planting in rows. Tilling land before planting kills the weeds present before planting and gives the crop a good start to compete with weeds during the early stages of growth. Field cultivators and discs are commonly used by farmers, and they are highly effective for controlling weed seedlings if used properly. The in-row cultivation is used to remove weeds after the crop has been planted.

Flame Weeding

Flaming controls weeds primarily by rupturing the cell membranes that dries the tissue. Propane burners can generate combustion temperatures up to 1900℃, which raises the temperature of the exposed plant tissues rapidly. An increase of temperature above 50℃ inside the plant cells can result in the coagulation of membrane proteins leading to loss of the membrane integrity. Consequently, flamed weeds would die or their competitive ability against the crop would be severely reduced. The susceptibility of plants to flame largely depends on their heat avoidance, heat tolerance, or both.

Chemical Weed Control

Use of herbicides is the most important method of weed control in maize. Though not adopted by most farmers, it is effective and economical in controlling weeds in maize. Herbicides can be applied at different time intervals, such as before the crop is planted (pre-plant), after the crop is planted but before emergence (pre-emergence), and after crop emergence (post-emergence). The choice of herbicide application timing depends on many factors and varies from farmer to farmer and field to field.

Pre-plant herbicides are used to early growing annual weeds. Foliar active herbicides, such as glyphosate, 2,4-dichlorophenoxyacetic acid (2,4-D) are the most common applied herbicides. While this may provide a clean seedbed at planting and crop emergence, the longevity of weed control is likely to be shortened significantly.