Weed management crucial for optimum yields

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RECENT rains received in most parts of the country have renewed hope for a decent harvest in the 2023/24 cropping season.

This follows the weakening of the El Niño weather phenomenon, which was expected to cause severe drought in Southern Africa, including Zimbabwe.

While the rains have seen an improvement in the condition of crops and livestock, they have triggered a menacing weed problem. This calls for farmers to adopt proper integrated weed management practices to save their crop and obtain optimum yields.

Farmers risk losing up to 80 percent of their potential yield if they fail to effectively deal with the weed menace, especially in the first 10 weeks after germination.

Weeds are unwanted plants that compete for sunlight, water and nutrients with crops. They can be distinguished according to habitat, origin, degree of harm, among many other characteristics, with the most common being the plant morphology and lifespan of weeds.

The lifespan of weeds means their classification using the time or duration in which they complete their lifecyle — for example, annual, biennial and perennial weeds.

Plant morphology is the physical appearance of plants. There are broad-leaf weeds — which have wider leaf structures, like the bonongwe (pigweed/ amaranthus thunbergia) — and narrow-leaf weeds, which include grasses and nodes.

Owing to climate change, the weed problem is becoming serious.

One of the lesser-known consequences of climate change is its impact on weeds, which can have far-reaching consequences on yield. As global temperatures continue to rise, this is leading to extended seasons, which, in turn, lead to an increase in weed populations.

Warmer temperatures can also enable weeds to reproduce more quickly, making it difficult for farmers to manage their spread.

Consequently, farmers are required to respond by adopting the most effective weed management techniques to save their crop. Some agronomists believe farmers can lose more than half of their potential yield if they fail to deal with weeds. Effective weed management is essential for maintaining plant health and ensuring sustainable farming. It involves a combination of traditional, mechanical, biological and chemical control methods tailored to specific weed species and the cropping system in question.

Mechanical weed management This involves the removal of weeds or disrupting their growth using tools and machines. The most common mechanical control methods include hand-pulling, hoeing, mowing, tilling and mulching. Even though this method is labour-intensive, it can be effective in managing weeds, especially in areas where other methods are not feasible.

Traditional weed management This involves incorporation of practices that create conditions that are unfavourable for weed growth while promoting the growth of preferred crops.

These methods include crop rotation, intercropping, planting competitive crop varieties, adjusting planting dates, among others. By manipulating the growing environment, these traditional methods suppress weed populations. Such methods should be accompanied by others to be effective.

Biological weed management

Chemical weed management Involves the use of herbicides to selectively target and control weeds.

Herbicides are formulated to interfere with specific processes in plants, leading to their growth inhibition or death.

However, the use of herbicides requires careful consideration as some weeds can become resistant. They can also impact on the environment and non-target organisms.

Farmers are encouraged to adopt integrated weed management practices, where several control tactics are combined in a coordinated and sustainable manner to achieve effective weed suppression while minimising environmental impact.

Such practices consider specific cropping systems and factors such as weed biology, ecology and economic considerations.

Integrated weed management, also referred to as integrated weed control, is an approach that integrates both chemical and non-chemical practices to control weeds.