Danish farmers will need to keep their eyes open for new emerging plant diseases as global warming creates climate changes in Denmark.

- Agriculture must adjust to new plant diseases due to climate changes. We will also see marked changes in the importance of plant diseases that we are already familiar with, says senior scientist Mogens Støvring Hovmøller from the Department of Integrated Pest Management at the Faculty of Agricultural Sciences, University of Aarhus.

Some of the problems can be prevented by changing crop rotation and choosing resistant varieties. This presupposes that there will be ongoing monitoring of the traits of ”new” as well as “old” plant diseases. Such monitoring is a prerequisite for plant breeders developing new varieties with the right traits for resistance, giving farmers access to updated information on disease resistance in the varieties that they intend to grow.

Under the present climate conditions and crop distribution, fungal diseases cause a great deal of loss, particularly in cereals, potatoes and vegetables. There are several factors that can affect the prevalence of plant diseases in susceptible varieties. Weather conditions in the growing season are especially important, while the weather in the previous season can have an indirect impact with regard to accumulation of infectious material in the soil or on overwintering alive plants.

This was exactly what happened with the heavy attacks of rust fungi in most cereal species in Denmark in 2007. In the fall of 2006 a very high level of infection of a wide range of rust fungi was built up in cereals and grass due to an unusually warm autumn. It was followed by a mild winter that allowed the rust fungi to overwinter in great numbers.

- The increased risk of plant diseases can lead to an increased requirement for treatment with pesticides, but not necessarily. There is a close relationship between the incidence of disease and weather, varieties, resistance, traits in the infectious fungi and cropping system. It is therefore quite difficult to predict the future importance of the individual plant disease. There is also the direct effect on the crops and crop composition, explains Mogens Støvring Hovmøller.

Generally, high humidity in the growing season will increase problems with many foliar diseases, whereas dry conditions in the summer months will decrease the problems. Experience with the heavy attacks of wheat brown rust in 2007 illustrates that changes can occur with extremely short notice. With regard to potato blight, the scientists expect that it will develop earlier while warm and dry summers will shorten the blight season.

- All in all, we expect that problems with potato blight will increase, says Mogens Støvring Hovmøller.

Apart from that, the individual disease may be able to adapt to climate change. This subject has only been slightly investigated.

- How, how quickly and with what effect the individual disease can adapt is a sort of dark horse. One example is wheat yellow rust which until recently was regarded as a plant disease related to cool and humid growing conditions. Since 2000 it has spread to warm areas in the south and east of USA and Western Australia where it was previously either absent or of no importance. This shows that the nature of a particular plant disease may change extremely rapidly, says the senior scientist.

For further information please contact: Senior scientist Mogens Støvring Hovmøller, Department of Integrated Pest Management, Faculty of Agricultural Sciences, University of Aarhus, telephone: +45 8999 3661, e-mail: Mogens.Hovmoller@agrsci.dk