Importance of weed control during summer months

December 2016

Weeds are the farmer’s biggest enemy and are the single biggest threat to a farmer’s potential crop. Controlling weeds can be a huge challenge especially during the summer months from November to January when they are in their most vigorous growth stages and when climatic conditions are favourable.

The best time to control weeds is in the early stages of their development when they are still weak and fragile, early in the summer months. Unfortunately, due to poor time management and planning we do not always get this right.

This leaves us the arduous task of trying to keep weeds under control when they are growing at full force and at their strongest. It may be harder to manage weeds at this time, but we still need to do it! It is crucially important to not let the weeds get ahead of us. It is an ongoing task which we need to stick at in order to reap the benefits of good yields during harvest time.

Best time to control weeds
We need to always remember that the best time to control weeds is early in their life when they are at their weakest. When we leave a weed too long it becomes more resilient which makes it much harder to kill. Weeds also have a much higher nutrient and moisture intake when they are young and actively growing, therefore when we spray at this time their intake of chemical will also be higher giving us the best results.

Weed control strategies during the summer months
As farmers we have two tools at our disposal to try and keep weeds under control. These are chemical weed control and mechanical weed control. Our management practices will determine which one of these we make use of the most. For example, if you follow no tillage practices on your farm then you will rely solely on chemical control. Whereas in a conventional system you will make use of both.

The ideal scenario when using no tillage practices would be to control all young weeds early on in the summer by using a broad based product which kills on contact. This can be done in conjunction with a pre-emergent herbicide which will give you longer lasting results. Many farmers however prefer to do these applications independently as the ideal conditions for control is clear warm
weather.

For pre-emergent application the desired conditions are cool drizzly weather which assists the chemical to absorb into the sub-soil which gives the best results. Post planting one would do another application of herbicide as one wants to give the young seedlings the best chance to get ahead with no competition. When maize is in the growing stage, one should continually be assessing the crop
for weeds. If there is evidence of weeds one should perform another application. There will be a constant threat of weeds until the point where the crop can provide good basal cover of the soil. Once this occurs there will be a lack of sunlight penetrating to the ground reducing the number of weeds germinating.

In a conventional system, farmers usually plant into a well prepared, clean seed bed. The seed bed would have been prepared soon after the first rains. Many conventional farmers will go just ahead of the planter with a scarifying cultivator or vibroflex so that there are no weeds at planting time. Just after planting they will spray the crop with a pre-emergent herbicide. Once the crop has emerged, one would perform another mechanical weed control in conjunction with a top dressing application by using a cultivator which is configured to clean in between the crop rows and which is set up with fertiliser bins. This can only be done to a certain point until the maize is too tall.

Ideal conditions for chemical application
Always remember that when spraying contact chemicals, that the ideal conditions are warm, calm clear conditions. The weeds should be actively growing to achieve the best results. Make sure that the spray is set up correctly and that there is little to no wind in order to limit spray drift. When spraying pre-emergent chemicals, the ideal conditions are calm and drizzly weather conditions. This will aid the chemicals to be absorbed into the soil where it can effectively inhibit the germination process of the weeds.

Weeds can have a devastating effect on the potential yield of your crop. Farmers should always be assessing their fields for weeds. Nothing can perform well when there is adverse competition. This is why we as farmers need to do all that we can to limit the impacts of weeds on our crops. Our success will be determined by our ability to plan ahead and our diligence in assessing the conditions of our fields and the actions that we take to maintain them.

Article submitted by Gavin Mathews, Bachelor in Environmental Management. For more information, send an email to gavmat@gmail.com.

Publication: December 2016

Section: Pula/Imvula