Weeds compete with the tree for available moisture, nutrients and oxygen in the soil. Weed competition is reduced by regular mowing or by spraying with herbicides. Although numerous herbicides are used on olives overseas, only glyphosate and fluazifop (both post-emergence) are currently registered for use on olives in South Africa.
Chemical weed killers have to be used with care since the long term effects on tree performance and the environment have not been determined.. In an organic farming system a relatively thick mulch layer of high lignin material in the tree row helps suppress weed growth and stimulates beneficial fine root development.