Effects of carbathiin and thiram with propiconazole and aldicarb on grain yield, and on incidence of root rot, leaf blotch, and root lesion nematode in spring wheat

Grain yields of spring wheat (Triticum aestivum cv. Belvedere) in experimen tal plots were increased by an average of 50% over three years when carbath iin and thiram were applied at 0.55 g a.i. kg(-1) of seed to control seedli ng disease, propiconazole was applied at 125 g a.i. ha(-1) to control leaf diseases, and aldicarb was broadcast and incorporated into soil at 2.24 kg a.i. ha(-1) to suppress nematodes. The 3-y average hectolitre wt and 1000-k ernel dry wt were also increased by the treatments. The analyses of varianc e indicated that the effects of the fungicides and aldicarb treatments were additive and not interacting. The analyses of covariance showed that the s ignificant treatment effects on grain yield and hectolitre wt were reduced to insignificance when the variables nematodes g(-1) of total root and kg(- 1) of soil obtained 1 day before harvest, were used as covariates. The 3-y average incidence of common root rot, incited by Cochliobolus sativus, was not suppressed by the fungicide treatments. Based on 3-y averages, root rot ratings increased from 30.4% at Zadoks Growth Stage (ZGS) 30-32 in July to 49.7% at ZGS 70-72 in the first half of September. Leaf disease, incited p rimarily by Stagonospora nodorum, was reduced by the fungicide treatments. Aldicarb reduced the population levels of the root lesion nematode Pratylen chus penetrans in soil, in the total root system, and in seminal and crown roots. The population densities of root lesion nematodes were about five ti mes higher in seminal roots than in crown roots. There were two significant (P less than or equal to 0.05) positive correlations between fungal and ne matode data in 1988: the incidence of leaf disease obtained in late July, a nd the average incidence of root rot obtained at ZGS 30-32, 55-60, and 70-7 2 were correlated with the number of nematodes in the total root system in late September. There were no other significant relationships (Pi 0.05) bet ween the incidences of root rot or foliar disease and numbers of root lesio n nematodes in soil or roots. We conclude that root lesion nematodes, as we ll as fungal pathogens, cause significant yield losses in spring wheat in e astern Canada.