Controlling weed development during the onion crop cycle is essential to obtain high yields and marketable products. Onions do not compete well with weeds: they are slow growing and can suffer from successive flushes of weeds; they have narrow upright leaves which do not shade out weeds that emerge in the rows. For most crops it is often possible to choose between mechanical or chemical control. But with onions, the plant and crop characteristics make mechanical solutions difficult to use after planting:
- They are shallow rooted, which makes cultivation difficult because it might prune the roots. Mechanical cultivation for example must be avoided when onions begin to bulb.
- The crop is planted at high densities which leaves no room for mechanical cultivation in the rows. Hand weeding is used in some countries but is very time consuming.
Moreover, the selection of herbicides is often limited because of legislation (different from one country to another), efficiency, effects on onion plants (serious damage risk) and price. It is therefore essential to built an integrated weed management program, combining cultural practices and herbicides. It is defined according to each situation. This page displays some basic information on such programs.