Field evaluation and selection of winter wheat for competitiveness against weeds

The evaluation of new varieties in relation weed suppression should consider characteristics such as growth habit, speed of early development and tillering ability. Weed suppression cannot be attributed to a single characteristic. Instead the interaction between a series of desirable characteristics has been shown to be important, with varieties compensating for weakness in certain characteristics with strengths in others. Generally, a high season-long crop ground cover is important. The balance between different characteristics for weed suppression will determine the value of the variety for early, late and season-long weed control, and for the climatic zone. Selection for general growth habits is based on understanding the role of different characteristics in weed competition. These habits will be of value under different soil and cropping conditions or locations in Organic Farming. Defined growth habits are: (1) The continuous planophile habit which has a clear advantage for weed suppression over the erectophile type at a given plant or shoot population density. (2) The early season erectophile to late season planophile habit is a good model when crop establishment is high. (3) The early planophile to late erectophile habit can compensate more for lower crop establishment than the early erectophiles. (4) A continuous erectophile habit is only beneficial when weed levels are low, crop establishment is sufficiently high or crop row widths are very narrow.