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Summary. The root lesion nematodes Pratylenchus neglectus andP. thornei occur throughout the cereal cropping areas of South Australia. In 1996, field trials on the Eyre Peninsula of South Australia were assessed to determine the relationship between density of nematodes within field plots in early October and harvested grain yield of 9 wheat varieties. The Pratylenchus species present was either P. neglectus (at Streaky Bay, Minnipa and Kalanbi) or P. thornei (at Nunjikompita). Absence of other major yield limiting factors at these sites in 1996 enabled determination of the relationship between nematode population and wheat yield. There was a significant, negative correlation between mean yield and nematode populations for the 9 varieties at 3 of the sites (P<0.01 for Streaky Bay and Nunjikompita; P<0.05 for Minnipa). Root lesion nematodes were responsible for 56–74% of the observed varietal differences in yield at these sites. The tolerant variety Excalibur yielded 19% (Streaky Bay), 23% (Minnipa) or 33% (Nunjikompita) more than the intolerant variety Spear, and Excalibur resulted in 69, 63 or 66% fewer nematodes, respectively, than in plots of Spear. Although nematode populations could not be assessed at the Kalanbi site, varietal yield relations were similar to the other sites, with Excalibur yielding 18% more than Spear. The 9 varieties were ranked for both resistance and tolerance to the 2 nematode species.

Fungal diseases are the major constraint on canola (Brassica napus) production in Australia and worldwide. Blackleg (caused by Leptosphaeria maculans) and Sclerotinia stem rot (Sclerotinia sclerotiorum) are the predominant diseases limiting production but, with increased intensification of production, other diseases previously considered of minor importance and sporadic may be increasing in prevalence. We report on the incidence and severity of four 'minor' diseases of canola in Australia: white leaf spot (caused by Pseudocercosporella capsellae), downy mildew (Peronospora parasitica), Alternaria leaf and pod spot (Alternaria brassicae) and powdery mildew (Erysiphe cruciferarum). Diseases were monitored at more than 30 sites across Australia from 2013 to 2015. Regions were identified in which specific diseases are a consistent problem, such as white leaf spot in Hamilton in Victoria. In these regions, control strategies to minimise disease may be required. Varietal differences were observed for some diseases suggesting that resistance to these pathogens is already present in Australian advanced breeding material. Lastly, fungicide applications were shown to control some diseases such as white leaf spot.

Yield loss caused by root lesion nematodes (Pratylenchus neglectus and P. thornei) was measured using the nematicide aldicarb (Temik 150GTM) 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 (≤1.5 kg a.i./ha) gave inconsistent nematode control and did not significantly increase yield. Rates ≥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.