Weeds

Weeds play a big part in sweet corn production. In general, the cost of controlling weeds is substantial and economic production without weed control is virtually impossible. In NZ where the soil weed seed banks and the weed populations are high, competition from uncontrolled weeds can result in substantial yield losses. Recently, the availability of new post-emergence herbicides has made it easier to manage some problem weeds in sweet corn. Weeds decrease crop yields through competition for nutrients, water and light. Like many crops, sweet corn suffers the worst weed competition in the early stages of growth. This is mainly because the young plant grows slowly during the first 10 to 12 weeks. Sweet corn is less vigorous and much less competitive than maize. The common warm-zone grasses, like summer grass, barnyard grass and smooth witchgrass, are serious competitors. The composition of the weed flora can vary widely between fields and between different growing regions. It is usually influenced by the site history. The list includes a large number of both annual and perennial species. However, weed populations are often so high that usually only a few species dominate at any one time. Our maritime climate encourages sequential emergence of weeds well into the summer. These factors highlight only some of the rather special problems faced by sweet corn growers in NZ which are somewhat different from the large maize and sweet corn growing areas of the world. In the following sections we provide brief information on major weeds of sweet corn in NZ and the main weed control options available currently, and describe the major challenges of weed control in maize and sweet corn in recent years.