Efficacy of weed control: Ensuring successful cultivation of crops

By Bob Aston

Adopting an Integrated weed management helps to ensure successful cultivation of crops. Speaking during a Training of Trainers (TOT) workshop convened by the Agricultural Sector Development Support Programme (ASDSP) on February 22-23, 2016 at the Agricultural Machinery Services (AMS) Hall in Nyahururu, Mr. Lincoln Njiru, Laikipia County Crops officer said that lack of a weed control plan leads to low production.

Mr. Lincoln Njiru emphasizing a point during the training

He said that weed control during the first four to eight weeks after planting is crucial, because weeds compete vigorously with the crop for nutrients and water during this period.

“The first critical requirement for effective weed control is correct weed identification. Weeds have special characteristics that tend to put them in the category of unwanted plants,” said Mr. Njiru.

He said that weeds have special characteristics that tend to put them in the category of unwanted plants as they can withstand adverse conditions in the field and can germinate under adverse soil moisture condition.

In addition, weed seeds remain viable for longer period without losing their viability and they have a short period of plant growth.

“Weeds that emerge at the time of crop germination or within a few days of crop emergence cause greater yield loss than weeds emerging later in the growing season,” said Mr. Njiru.

He urged farmers to adopt integrated weed management, as it reduces weed interference with the crop while maintaining acceptable crop yields.

Integrated weed management approach ensures selection of adapted variety or hybrid seeds with good early season vigor and appropriate disease and pest resistance. He urged farmers to ensure weed free farm through cultural, mechanical, biological, or chemical management.

Cultural weed control entails early weeding, proper inter cropping, crop rotation, use of cover crops, improved soil fertility and reduced environmental stress including pests and disease management.

Mechanical weed controls involves pre-plant tillage, in row cultivation, and flaming weed control by use of propane burners to kill the weeds by denaturing the proteins in the cell membranes hence desiccating them.

Biological control entails reuniting weeds with their natural enemies, although it is important that they do not become pests themselves. Example is use of turkeys in fruit orchards, commercial bio-herbicides, and tick berry against couch grass.

Chemical weed control involves use of pre-emergence and post-emergence herbicides. Use of more than one herbicide usually ensures a season long weed control.

“ High weed infestation increases the cost of cultivation, lowers value of land, reduces the returns of maize producers, reduce yield, make harvesting difficult, and lowers the quality of grains,” said Mr. Njiru.

One of the participants contributing to a discussion

He said that some harmful effects of weeds include loss of agricultural produce; reduced crop yields as weeds compete with crops for water, soil, nutrients, light and space; some like witch weeds are parasitic to maize; and some act as alternative hosts that harbor insects, pests, diseases and other micro-organisms.

Other harmful effects of weeds include reduction of quality of marketable agricultural produce, and release into the soil inhibitors of poisonous substances that may be harmful to the crop plants, human beings, and livestock by some weeds.

He said that some annual maize weeds include black jack, gallant soldier, double thorn, wandering Jew, marigolds, saw thistle, spiny pigweed, and jimson weed. Perennial maize weeds include couch grass, nut grass, Johnsons grass, star grass, and field bindweed.

He noted that despite the many harmful effect of weeds, some are beneficial as they help conserve soil moisture and prevent erosion, and can be valuable indicators of growing conditions in a field like water levels, compaction, and PH.

In addition, presence of weed cover may be a factor in increasing effectiveness of biological control of pests and reducing pest damage.