Effect of glyphosate application to grass weeds on levels of Gaeumannomyces graminis var. tritici inoculum
S.L. BithellA,C, R.C. ButlerA, A. MckayB and M.G. CromeyA
A New Zealand Institute for Plant & Food Research Limited, Private Bag 4704, Christchurch 8140, New Zealand.
B SARDI, GPO Box 397, Adelaide, South Australia 5001, Australia.
C Present address: Department of Regional Development, Primary Industries and Fisheries and Resources, GPO Box 3000, Darwin, NT 0801, Australia.
The cereal pathogen Gaeumannomyces graminis var. tritici (Ggt) that causes the disease take-all infects Elytrigia repens (couch) and a number of other grass weed species. Soil Ggt DNA levels 14 months after couch had been planted into a naturally Ggt infected site, in which Bromus willdenowii (prairie grass) was also present, indicated that the presence of couch maintained rather than increased Ggt levels.Following an early glyphosate applicationsoil Ggt levels increased three and eight fold, one and two months respectively after application (86 days before wheat sowing) to plots with couch present. A later glyphosate application (38 days before wheat sowing) also resulted in rapid increases in Ggt inoculum levels in plots with couch and to a lesser extent in plots without couch. Results confirm that couch is an important host of Ggt with more roots per wheat plant infected, more plants infected and a greater take-all severity in plots with couch present. Early or late glyphosate applications did not affect subsequent levels of take-all in wheat. Prairie grass seedlings were also identified as a significant Ggt inoculum source, but this effect was independent of glyphosate and couch treatments. Overall, increases in Ggt inoculum levels following glyphosate application are large and relatively rapid. Ggt inoculum associated with couch rhizomes is persistent. Finally, very early glyphosate applications will be required to allow time for the break down of couch rhizomes and decline in Ggt inoculum levels thus reducing the risk of take-all in subsequent wheat crops.
Key words: Gaeumannomyces graminis var. tritici, take-all, inoculum, couch, Elytrigia repens, Prairie grass, Bromus willdenowii, glyphosate, grass weeds.
Plant Protection Quarterly (2009) 24 (4) 161-167.