16 November 2001

Climate change set to raise weed control stakes

By Charles Abel

CLIMATE change is upon us and it has implications for weed control.

But it is most likely to affect UK farms by changing the opportunities for weed control rather than making a big change to the relationship between weeds and crops.

That is the message from research presented by a number of scientists at this weeks British Crop Protection Conference in Brighton.

Over the next 50 years climate change is set to bring warmer, wetter autumns and winters, longer growing seasons and drier summers.

A study led by David Harris of ADAS Boxworth shows such climate change may benefit some aspects of farming, because of longer growing seasons. But there may be significant consequences for weed growth and control both in the spring and autumn, particularly on heavy land farms.

The longer growing season could mean an earlier start for spring weeds, with potentially fewer spray days to control them. Soils would also dry out more rapidly in spring.

Early cultivations may also be difficult, with a shorter period of suitable conditions.

Fields could also become wetter sooner in the autumn, leaving fewer opportunities for late season herbicide spraying.

Understanding how climate change will affect the type and timing of farming operations could be just as important as any impacts on crop type, yield and weed pressure, the researchers suggest. &#42

Could climate change make weeds harder to control? Probably, particularly where windows for control start narrowing, warn scientists.

CLIMATE CHANGE

Typical changes by 2050

&#8226 40% longer growing season.

&#8226 9-13% more autumn/winter rain.

&#8226 0-20% more summer rainfall.

&#8226 70% fewer frost days.

&#8226 Three times more days over 25C.

&#8226 CO2 levels up 66%.

&#8226 Short-wave radiation up 3-8% summer, 4% autumn.

&#8226 Summer evapotranspiration up 6-17%.

Weed implications

&#8226 Control timings trickier.

&#8226 Weed growth effects limited.

Based on UKCIP98 Medium High climate change scenario.

Weed-flush forecasting might help in fight

Computerised forecasting of germination flushes could help growers combat weeds more effectively, particularly in root and vegetable crops.

Scientists at Horticulture Research International have shown that some weeds follow characteristic patterns of emergence each year.

That information could help growers target cultivations, mechanical weed control and herbicide sprays more effectively. Indeed WeedCast forecasting software is already in use overseas to fight important weeds.

But better weather forecasting, a quick, reliable and economic way of assessing how many weed seeds are present in the soil and more information on weed seed dormancy is needed before robust advice can be offered in the UK, says the HRIs Andrea Grundy.

In the meantime generalised advice based on pooled research data and farmer experiences could be made available to support decision-making, while more sophisticated models are constructed, she concludes.