Weed control is a high-risk, and often complicated, activity. When developing a weed control strategy, there are several important aspects the farmer should keep in mind. Always keep track of the environment. During the growing season there may be things like very high temperatures or strong winds. The best the farmer can do is to be aware of possible changes and to plan accordingly.
The conditions are mostly:
■ Temperature (heat or cold).
■ Rain or the lack of rain.
■ Humidity (amount of water vapour in the atmosphere or the absence of atmospheric moisture when conditions are very hot and dry).
■ Wind.
■ Dust on the surface of leaves caused by a combination of drought and wind.
KNOW YOUR WEEDS
■ A good knowledge of the weeds in your fields helps with weed control.
■ Identify the common names of weeds and write them down as part of your record-keeping.
■ Accurate identification of weeds that occur in the current growing season will help with the right herbicide selection for the coming season.
CHOOSE THE RIGHT HERBICIDE
■ Knowing the names of the weeds you plan to control means you can make the right choice when selecting expensive herbicides.
■ On the label of each herbicide, you will find tables clearly indicating the common names of weeds controlled by that specific herbicide.
■ The more accurate your list of expected weeds, the better your chances of choosing the most suitable product. When practicing post-emergence control, apply herbicides early as the outer layers of the (weed) plants become thicker and waxier, and may be covered with hairlike structures as the plant grows and matures. This makes it more difficult for the herbicide to penetrate and be effective as a weed killer.
In many cases, herbicide labels refer to the concept of early post-emergence control rather than post-emergence control only. Post-emergence control should happen at an early stage when weeds are still young and vulnerable. For example, on the Basgran label (a post-emergence herbicide manufactured by BASF with the active ingredient Bendioxide) the leaf stage and its relation to rate of application (dosage) is indicated on one of its tables and shows that weeds should be controlled at an early stage.
The table above shows examples from the Basagran label, indicating the leaf stages at which certain weeds should be controlled, and the higher rate of application that might be needed, depending on the leaf stage.
BOOM SPRAYER CARE
Neglected and ineffective boom sprayers are unfortunately still in use on many farms. If you want to win the war on weeds, keep your sprayer in good condition, ready to spray. Calibrate it correctly and do not spoil the mix. Use clean water in the spray tank when preparing the mixture. Sometimes water contains minerals with a negative effect on certain herbicides, so it is a good idea to test the water quality at a laboratory.
BOOM SPRAYER CHECKLIST
■ The pump and the inlet filter should be in good working condition.
■ The tank (with at least a 600 litre capacity) should have a proper agitator spray head to ensure thorough mixing.
■ Pipelines should not have any leakages.
■ Clean filters.
■ Use the right spray nozzles for the task.
■ For effective cover the nozzles should be of the same kind, equally spaced, and well directed on the boom.
■ The tank lid filter must be clean to keep dust and dirt out of the tank.
■ The pressure meter should be in good working condition.
■ The PTO shaft, linking the tractor to the sprayer, should be in good working condition with a proper safety shield.
■ A strong, straight boom-bar, set at the correct height, is important as it carries the pipeline and the nozzles.
Contact the Grain Crops & Small Grains Institute (018 299 6253) or Kefiloe Manthata (ManthataK@arc.agric.za).
