Reglone application before flailing could improve tuber quality by reducing the risk of vascular browning and stem end rot caused by flail operations in vigorously growing potato crops. Syngenta is evaluating the use of a pre-flail treatment to trigger crops into senescence to minimise damage this season, reports Syngenta Technical Manager, Jon Ogborn.
Research at Cambridge University Farms has shown rapid haulm removal by flailing can cause problems, particularly if the crop is suffering soil moisture stress. CUF researcher, Dr Mark Stalham, advises the greatest risk is for crops that are being stopped early when haulm growth is still vigorous, to meet specific tuber size requirements such as early bakers or salads.
"Once senescence is advanced, symptoms are minimal, even in very dry conditions," according to Dr Stalham; if crops reach 50% ground cover he considers they should be relatively safe.
The symptom of most concern is stem end rot. "The problem lies when the stolon dies quickly and detaches from the tuber, so the tuber skin doesn't get time to develop a scar of suberized tissue, rather than the natural senescence process where the stolon dies back slowly." The result of rapid stolon detachment could leave a wound that can allow soil bacteria to enter and encourage rotting.
Jon Ogborn reports Reglone application at 0.5 to 1.5 l/ha will trigger early senescence prior to flailing. ""The initial low dose appears insufficient to shock the crop or cause tuber damage. It is, however, adequate to trick the plant into commencing early senescence and skin set. Even vigorous crops will reach 50% ground cover within a few days of Reglone application."
Furthermore, with predominantly just the stems left to chop following a pre-treatment, flailing will be faster and far more effective. "In crops, such as salads, tuber size is critical. It has also been suggested that an early Reglone may help growers time the main flail defoliation more accurately by slowing crop bulking."
"Removal of the majority of green material will reduce the risk of blight infection following flailing, but growers should include Shirlan in the tank mix to protect from tuber blight," adds Mr Ogborn.
"The trials have confirmed growers' field observations that symptoms of vascular browning or stem end rot can be found in crops defoliated by all rapid defoliation techniques. The causes of vascular browning are not fully understood, although it appears to be linked with stem end rot."
On sandy soils Dr Stalham reports two to three days of hot, drying weather can be sufficient to cause problems. "Our work in 2004 showed that flailing crops at a soil moisture deficit (SMD) of 51mm can increase symptoms compared with defoliating at 9 mm, but it had also been very hot and drying in the 10 days prior to defoliation," he added. "Growers must take care with irrigation scheduling in the run up to desiccation."
Although the development of stem end rot in the trial crops defoliated in dry conditions was not severe, it would have reduced potential marketability. The effects would become clearly visible in any crop destined for storage.
