Sustainable Methods of Managing Weeds in Dryland Farming – Part 1

Article: Matshediso Motshabi

As the season for ploughing approaches, let’s prepare our farmland by managing weeds sustainably throughout their entire growth cycle. In fact, weeds are a recurring issue because they reduce crop yield by competing with the plants for water, nutrients, and sunlight. Weeds are typically controlled mechanically, by using herbicides, and by manual removal. However, heavy use of machinery to remove weeds worsens soil erosion, which reduces soil fertility. Herbicides have negative effects on our agro-ecosystems as well, particularly when they are applied for an extended period of time and contaminate the soil and groundwater. They also leave behind residues on the harvest we eat that can lead to chronic diseases in consumers. Herbicide resistance develops as a result of repeated overuse, which also throws ecosystems out of balance.

The best strategy for managing weed infestations as part of regenerative agriculture is through prevention. Prior to sowing, check seeds for any weed residues, make sure clean equipment is used when tilling land, implementing strict phytosanitary measures like not entering your farmland with clothing from the outside to prevent carryover of weed seeds into your farm land, routine inspection of your farm for any strange weed seedlings, and destroying such weeds by deep cultivation and uprooting their roots. The vegetative parts and propagules from the infestation site should be identified, and these areas should be destroyed to completely suppress weed growth. This method is particularly effective for noxious weeds like the invasive Cyperus, Striga, Cynodon, Saccharum, amongst other species. Making preparations for the upcoming dryland cropping season is crucial if you want to reduce the prevalence of noxious weeds. In this follow-up, we shall discuss about prevalent weeds in Botswana and how to manage them.

Cynodon dactylon; Bermuda grass/ Couch grass; Motlhwa

Bermuda grass tolerates drought quite well, but it grows best when irrigated or rainfed. Most Batswana farmers dislike cultural methods because they consider them as laborious, but they are the most effective way to manage it. This includes regularly raking to get rid of its vegetative parts (rhizomes and stolons). The remaining Bermuda grass will, however, reappear if irrigated or when it rains. To bring the majority of shoots to the surface, a single, deep cultivation between 20 -30 cm is effective. If the soil is moist, avoid cultivation because that’s when it spreads rapidly. It is crucial to thoroughly clean the field after deep cultivation to avoid the germination of vegetative parts since deep cultivation splits the stems into segments, each of which grows into a new plant. While drying and cultivating can effectively kill rhizomes and established plants, they do not kill seeds in the soil, and seeds have long periods of dormancy. Surrounding the farmland with tall trees and shrubs to increase shade is another cultural method of controlling Bermuda grass. This weed needs uninterrupted sunlight for optimum growth, so shaded areas of the farmland prevent it from expanding exponentially. Additionally, cover crops can be planted to effectively control it. No bare land will exist for its vegetative components to grow.

Bermuda grass can be managed using polythene sheets for mulching. Water the weed-infested area before covering it with a thick, black polythene sheet and leave it for six to eight weeks before summer ploughing. By preventing sunlight from reaching the weed’s vegetative parts, the plant ends up choking, and eventually, increases soil temperature to kill its vegetative parts and the dormant seeds. Another name for this technique is soil solarization. Kenya, the United Kingdom, and other nations have tested and approved this method; the findings show that there was no incidence of Bermuda grass for at least two cropping seasons. However, it is not a good idea to mulch with organic materials as they create favorable conditions for weed growth. For soil solarization to be effective, please make sure there won’t be any rain for at least two months.

Using of chemicals for control is common, but as weeds tend to develop herbicide resistance, rendering this method ineffective. Sethoxydim (Grass Getter), Fluazifop (Fusilade, Ornamec, and Grass-B-Gon), or Clethodim (Envoy) are effective grass- selective herbicides. The ideal time to use a grass-selective herbicide is early spring. For instance, first application should be made in the first weeks of September when the new Bermuda grass growth is less than 15 cm long. Three weeks later, before the regrowth reaches 15 cm once more, repeat the application. Throughout spring and summer, additional regrowth applications might be required. Bermuda grass is best controlled when it is actively growing, has a large amount of leaf surface, is not drought stressed, is not dusty, and has not been harmed by insects.

In order to completely eradicate Bermuda grass, it is crucial to consistently treat regrowth, which is the stage at which it is most vulnerable. However, the total amount of herbicide used per year per area is found on the label of each product. As aforementioned, DO NOT overdose or over apply herbicides. FMB