Is it worth paying a little extra for a fungicide with growth regulatory activity, or will a standard conazole control phoma stem canker just as well?
That is one of the questions ADAS plant pathologist Peter Gladders hopes to answer during a three-year project comparing the performance of commonly used and new fungicides for control of oilseed rape diseases.
“We need to measure responses to each product at different rates on disease control and yield, but also benefits from physiological factors such as lodging and rooting ability.
Some fungicides green up the crop, but does this improve disease control or translate into extra crop vigour and yield, in other words, extra profit?”
Optimising rates is paramount to cost-effectiveness, too.
For phoma, a sequence of two half doses is considered appropriate using most products, but Dr Gladders is comparing quarter, half, three-quarter and full recommended rates.
The trials will show how products perform under high disease pressure.
Each product is used once the threshold of 20% of plants with phoma leaf spotting has been reached, and again six to eight weeks later.
He acknowledges some treatments were running out of steam after four weeks last autumn, but considers it fair to stretch them to their limits.
So far, all seven treatments have controlled leaf spotting, even at a quarter rate, but he fears that amount may be insufficient to maintain good canker control and yield.
Light leaf spot control is proving difficult to achieve in the Aberdeen area, where one of the experiments is located.
These trials should pick up any shift in the sensitivity of the various oilseed rape pathogens in time to avoid a situation like the one complicating product choice for septoria control in wheat.