Measuring yield loss in cereals caused by root lesion nematodes (Pratylenchus neglectus and P-thornei) with and without nematicide

Yield loss caused by root lesion nematodes (Pratylenchus neglectus and P. thornei) was measured using the nematicide aldicarb (Temik 150G(TM)) or by correlating yield with initial or final nematode densities. In 1996, rotation trials (1 P. neglectus and 1 P. thornei) were established with susceptible and moderately resistant wheat varieties and resistant barley and triticale varieties. An intolerant oat variety (cv. Echidna) was planted over all plots in 1997. Nematode densities were 90% (P. neglectus) or 95% (P. thornei) lower in oat plots following the resistant triticale (cv. Tahara) relative to the susceptible wheat (cv. Machete). In 1997, a significant, negative correlation between both initial and final nematode density and yield was obtained. In wheat variety trials (3 sites) in 1997, a significant, negative correlation was also obtained between mean variety yield and mean final P. neglectus density or mean P. neglectus multiplication rate. Yield loss of up to 20% was calculated from the regression. In all trials, cereal varieties that were more resistant were also more tolerant. In 1996, aldicarb rate trials (1 P. neglectus and 1 P. thornei) were established to assess the affect of rate and timing of aldicarb application on yield of 2 susceptible/intolerant wheat varieties (cvv. Machete and Janz). Lower rates of aldicarb (less than or equal to 1.5 kg a.i./ha) gave inconsistent nematode control and did not significantly increase yield. Rates greater than or equal to 2.5 kg a.i./ha reduced nematode densities by 70-90%, resulting in up to 23% greater yield for Machete. The magnitude of yield loss caused by P. neglectus or P. thornei determined with or without nematicide was similar between trials.