The relation between time of sowing of cereals and cereal cyst nematode (Heterodera avenae Woll.)

Abstract

Many juveniles of Heterodera avenae Woll. were hatchable in April but hatching was inhibited by lack of water. Number of knots (infestations) per susceptible wheat plant in 1981 increased from less than 40 at the initial sowing in mid-May to a maximum of almost 80 in mid June sowings; in 1982, the maximum (80 knots/plant) was recorded at the initial sowing in late April. Loss in yield of grain of wheat and barley was minimal in crops sown in mid-May but rapidly increased to a maximum in crops sown in late May/early June, the optimum time of sowing for yield. This maximum loss changed little in crops sown up till early August and varied with the tolerance of the cultivar from 520 to 880 kg/ha. Early or late sowings reduced potential yield. Females with eggs first appeared on the roots 90 days (late July) after sowing, indicating that fallows to prevent reproduction of the nematode should begin in early August. Maximum numbers of females (16lplant) occurred in sowings at the optimum time for yield (late May/early June) and decreased in later sowings. Resistance in the host reduced numbers of females but applications of ethylene dibromide rarely did.