Climate Change – What Will Happen to Weeds and Diseases?

Much attention has focused on what plants will be able to grow where as the effects of climate change are felt. A key factor that plays into that analysis is what effect climate change will have on diseases and weeds.Two new papers in CAB Reviews look at those two elements and show that that the picture is a complex and sometimes surprising one.

Sukumar Chakraborty (from CSIRO Plant Industry) and co-authors note that modelling experiments suggest that the range of key pathogenic fungi may shift significantly towards the poles as a result of global warming. The impacts of raised CO2 and temperature together are more difficult to estimate, as raised CO2 may increase the vigour of some trees and crops. From certain studies it seems that C3 plants, such as cereals, may suffer from increased numbers of pathogens with increased CO2, while C4 plants (most other crops and trees) may not. Chakraborty and colleagues write that minor changes in climate can tip the balance in favour of an exotic species, and the same may be true of disease outbreaks. Import risk analysis will need to take into account changes in the risks of establishment of pests and pathogens as the climate alters.

Examining the 12 most serious weeds, Xianshong Wang (from Indiana University-Purdue University Indianapolis) and Jacqueline Mohan (from the University of Georgia) suggest the competitiveness of weeds at higher temperatures and CO2 levels may be affected greatly by water availability. Most of the weeds will be expected to be boosted by rising temperatures. Field bindweed may become a more serious weed in drier regions, while it may be outcompeted in well-watered soils. Purple nutsedge may suffer because of expected reductions in moisture and rising soil nitrogen.

Wang and Mohan point out that the move to biofuels may exacerbate some of the projected weed problems: “Altered land use and the unforeseen consequences of energy plants may have a greater impact on the seriousness and injuriousness of weeds and weed-crop interactions than the effects of other global environmental changes, including rising CO2, global warming and more frequent and severe droughts.”

Effects of global environmental changes on weeds by Xianzhong Wang, J.E .Mohan
CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2008, 3, No. 067, 20 pp.

Impacts of global change on diseases of agricultural crops and forest trees by S. Chakraborty, J .Luck, G. Hollaway, A. Freeman, R. Norton, K.A. Garrett, K. Percy, A. Hopkins, C. Davis, D.F. Karnosky
CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2008, 3, No. 054, 15 pp.

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