Population estimates of cereal cyst nematode and response of wheat to granular nematicides

Abstract

Response of vegetative growth and grain yield of wheat Triticum aestivum cv. Condor to the control of cereal cyst nematode Heterodera avenae by nematicides applied with the seed, in the drill row was assessed in twenty field trials. These trials were conducted in 1978 on three soil types near Coonalpyn, South Australia. Aldicarb was used at all sites and fosthietan and terbufos at four sites. Significant grain yield increases to aldicarb were obtained at 12 sites while yields were increased by the three nematicides at three sites. Numbers of eggs of H. avenae were determined in soil taken in January 1978, and these counts showed that all sites were infested over the range 0.03-8.5 eggs/g soil. Plant assays of the soils assessed the reduction in the length of seminal root axes (range 0-45%) and the severity of the root knotting caused by H. avenae. The egg densities in the soil, reduction in the length of the seminal root axes and disease ratings in the plant assay were highly correlated with each other (r = 0.75; P< 0.001 to 0.91, P< 0.001). These variables were not significantly correlated with grain yield increase due to aldicarb on the two major wheat soils studied, although a correlation, explaining 32-42% of the increase, existed when all sites were considered. A mathematical model based on cropping history and an estimated annual hatch of eggs of H. avenae failed to show a relation between these variables and the yield increase from nematicide. H. avenae caused severe disease and yield loss on calcareous loams and red duplex soils but had only minimal effects at the sites on siliceous sands.

Crops and Pasture Rotations at Coonalpyn, South Australia: Effects on Nutrients in Wheat and Barley

“…The sown pastures were not legume dominant, being only of little better quality than the volunteer pastures (KING 1984). As a result they provided little extra soil nitrogen, disease control or growth of following crops.…”

“…tritici and R. solani (following grassy pasture in the rotation) and from low disease treatments in the crop rotation experiment reported by KING (1984). The mean wheat and barley yields A complete description of the treatments and general management of the crop rotation experiment may be found in KING (1984). Briefly, the experiment was undertaken from 1976 to 1979 and was located near Coonalpyn in the Upper South East of South Australia on a red duplex soil (Dr. 2.23, Northcote 1971).…”

“…tritici (Walker) and Rhizoctonia bare patch {Rhizoctonia solani Kuhn.) in all cereal districts of South Australia (ROVIRA 1976, SIMON and Rov-iRA 1982, KiNGet al 1982, KING 1984.…”

“…In this paper the nutrient contents of wheat and barley are compared under heavy attack from G. graminis var. tritici and R. solani (following grassy pasture in the rotation) and from low disease treatments in the crop rotation experiment reported by KING (1984). The mean wheat and barley yields A complete description of the treatments and general management of the crop rotation experiment may be found in KING (1984).…”

Cyst Nematodes

“…Apart from the seed dressings already mentioned, these are seed furrow treatments of EDB 3.7 1 ha-1 , terbufos 4 kg ha-1 , aldicarb 2 kg ha-1 or carbofuran 1.1 1 ha-1 • Increases of 30% or more in wheat yields following these treatments are common (Brown, 1984a). However, King et al (1982) showed that grain yield increases due to aldicarb which were statistically significant in 12 of 20 field experiments, could not be correlated with nematode egg density in the soil, length of seminal root axes, or severity of 'knotting' of the roots due to nematode attack. An ultra-low-volume applicator was developed for the application of small volumes of liquid nematicides in the seed furrows during sowing (Gurner et al, 1980), Using this equipment, small volumes of EDB or dichloropropene similarly applied did not improve the yield of susceptible oats in sandy loam infested with H. avenae in England, probably because of phytotoxicity, whereas 1.5 kg oxamyl ha-1 in the seed furrows greatly increased oat grain yield (Whitehead et al, 1982).…”