Italian Rye-grass is about twice as competitive as black-grass on an individual plant basis and five rye-grass plants/m2 typically causes a yield loss of 5% in cereals.
Crop losses of up to 89% have been recorded at high infestations. Rye-grass also tillers more profusely than Black-grass; each plant commonly producing over 20 heads and 5,000 seeds. As a result populations can build up very rapidly.
- A weed density that causes a 5% yield loss is often used as a threshold value at which herbicidal control is justified to prevent unacceptable loss. For rye-grass in winter wheat this is, on average, 5 plants/m2.
- Because of the risk of higher yield losses, the potential for rapid population increase and the difficulty of assessing weed densities on a field scale, applying herbicides to control rye-grass at much lower densities is advised – at less than 1 plants/m2 in high risk situations.