Treatment and Control of Stem Rust

Stem rust cannot be cured once a plant is badly infected, so farmers focus on preventing infection and slowing its spread.Resistant varieties. Plant breeders cross wheat with varieties or wild relatives carrying resistance genes (named Sr genes, for example Sr31). This is the cheapest and most effective method. However, the fungus evolves: mutation or recombination can produce a new race that the resistance gene no longer recognises, as happened when Ug99 overcame Sr31. Breeders now combine (stack) several resistance genes in one variety, because it is much less likely that the fungus will overcome all of them at once.Fungicides. Chemicals such as triazoles can be sprayed when rust is detected or forecast. They protect the crop, but they are expensive, must be applied at the right time and repeated, and the fungus can evolve resistance to them. Many farmers in poorer countries cannot afford them.Removing the alternate host. From 1918 a campaign in the USA destroyed millions of barberry bushes near wheat fields. This removed the sexual stage, reducing the spores released in spring and the production of new races.Cultural methods. Destroying crop stubble and self-sown (volunteer) wheat removes places where the fungus survives between crops. Early-maturing varieties can be harvested before rust builds up.Surveillance. Monitoring spores and new races lets scientists warn farmers and breeders early.