Don’t let weeds destroy your crop and profit

October 2025

EARLY WEED CONTROL IN SUMMER CROPS IS EXTREMELY IMPORTANT AS WEEDS LOWER CROP YIELDS BY COMPETING FOR SOIL MOISTURE, NUTRIENTS, SPACE AND SUNLIGHT. GOOD WEED CONTROL MANAGEMENT IN SUMMER CROPS IS THEREFORE ESSENTIAL FOR THE PRODUCTION OF HIGH-YIELDING AND PROFITABLE CROPS. FOR HIGH-COST AND HIGH-VALUE IRRIGATED CROPS, COMPETITION FOR LIGHT AND NUTRIENTS IS EVEN MORE IMPORTANT.

Weeds are one of the most significant problems farmers face. It can seriously harm a crop and are especially difficult to control during the hot summer months, when it grows quickly and the weather helps it to thrive.

The best time to control weeds is in the early stages of their development, when they are still small and weak. Unfortunately, due to poor time management and planning, farmers sometimes miss this window. It then leaves the difficult task of trying to keep weeds under control when they are growing at full force and at their strongest.

Although it is more challenging to manage weeds at this time, it still has to be done. Weed control is a constant job, and staying on top of it can lead to better harvests and higher yields. It is extremely important not to let weeds take over.

HOW WEEDS AFFECT YOUR YIELD AND PROFITABILITY
Crop production, particularly under dryland conditions in South Africa, presents numerous challenges and risks that need to be managed. Weed control and crop care make up a significant part of this.

Yield losses caused by weeds can vary enormously – from an almost minor yield loss to the complete loss of a crop. Farmers must aim to reduce weed numbers and then maintain control with an ongoing control programme throughout the season.

Due to low rainfall and uneven distribution of rain during the growing season, poor weed control can drastically increase the economic impact on crops. Weeds in the young stage of the crops can easily take up to 60% of the crops’ yield, and without weed control, it can be even more.

Crops must be able to benefit maximally from the nutrients naturally in the soil and from the fertilisers applied during planting, to develop strong roots that will result in a hardy, strong plant. If the small seedlings are forced to share these nutrients with young weeds, especially invasive and strangling grasses, it will never yield what it is supposed to.

Weeds can also restrict the essential amount of sunlight that is required by the planted crop, especially in the early growth stages. Additionally, some weeds act as hosts to various insects and disease pests. It is vital to learn which weeds will grow rapidly and significantly impact the potential planned crop yield.

Don’t be fooled by the height or size of the weed, compared to the height or size of the crop planted. A young maize plant may seem healthy and stand tall in comparison to the surrounding weeds, but if it has to compete for food, its growth has undoubtedly been compromised.

It is essential to control a potentially harmful infection, either before or after planting, timeously to prevent a significant economic loss.

WEED CONTROL
The best time to control weeds is early in its development cycle, when it is at its weakest. When weeds are left too long, it becomes more resilient, which makes it much harder to kill. Weeds also have a much higher nutrient and moisture intake when it is young and actively growing – therefore, when farmers spray at this time, its intake of chemicals will also be higher, giving the best results.

Weed control must start with pre-season practices and even as far back as during the previous growing season, when weeds should not be allowed to form seed. If at all possible, ploughing should be done in the winter for maximum moisture control or at the least disking should be done in the early spring to control these early germinating weeds.

Another good way of controlling the early spring weeds is to have a good sprayer set with the correct nozzles and then to apply a good quality herbicide such as Roundup.

Good crop rotation systems, rotating herbicides and combining both chemical and non-chemical weed control methods are all methods that can be used. It is also essential to control weeds along fences, contour banks, waterways, irrigation channels and other non-cropping areas.

The control of weeds post-emergence is critical. It is a big mistake to neglect weed control practices and risk sacrificing as much as 20% of the potential crop at this stage of plant development.

Weeds also cause harvest problems. It influences the plant in a way that reduces the actual quality of the grain. Weed-seed contamination of grain can result in your harvest being downgraded, and your fields will experience a re-infestation, which will negatively influence the next crop.

Many spray programmes are available for genetically modified and normal crops that can be applied before planting, during planting and after planting. Keep in mind that the correct spray procedures must also be used in both a no-till system and a conventional crop production system. Always consult your herbicide supplier or agent before undertaking any programme you have in mind.

SCOUTING FOR WEEDS
Scouting is defined as a process of exploring to gain information. In this instance, the information gained concerning the specific weed problems on your farm will enable a relevant weed control programme to be developed and implemented.

Scouting for pests or weeds is usually carried out by walking through the lands in a zigzag or M pattern, and assessing and counting the various weeds found in a square metre steel square placed on the ground, for example, every 50 m or 100 m. The idea is to create a random but representative picture of the intensity and prevalence of the problem weeds.

The scouting and monitoring should take place during the period between crops, before planting, and in maize production at the 4th to 5th leaf stage, at a stage when annual broadleaf and grass weeds are less than 38 mm tall.

Remember that weed infestations at the edge of a land may not represent the population of weeds found within the land. Sample carefully and objectively, and consider the size of the land when deciding on the number of points where measurements are taken. A rule of thumb would be to do each 25 ha separately.

CONCLUSION
As the use of herbicides is an expensive exercise when the total cost of each spraying operation is taken into account, it is vital to assess the problem in time accurately. The increasing problem of herbicide resistance must be taken into account. Many farmers are returning to mechanical weed control, combined with the optimum application of chemicals, to reduce the overall cost of weed control, but within the context of realising profitable yields on their farms.

References
https://www.grainsa.co.za/be-a-winner-in-the-war-against-weeds
https://www.grainsa.co.za/early-weed-removal-is-important
https://www.grainsa.co.za/scout-and-control-weeds-before-and-after-planting
https://www.grainsa.co.za/weed-control-is-essential-for-crop-health

Publication: October 2025

Section: Pula/Imvula

Author: COMPILED BY THE PULA EDITORIAL TEAM

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