Keeping late blight out of potato crops is a season long battle for growers and one that seems to be getting tougher as the years go by, with seven day spray intervals now standard practice in most parts of the UK where potatoes are grown.
With resistance to fluazinam now established in the blight populations and a continuing shift towards more aggressive P. infestans populations such as 36_A2 and 37_A2, a robust resistance management strategy is essential to safeguard crops.
Blight sprays can be further compromised by the conditions when they’re applied – something that’s become even more important as blight sprays have to be applied at a seven-day interval, which increases the pressure on spray windows. Syngenta application trials have shown that even on a perfect spray day, with an average wind speed of 1.2m/s (2.7mph), the actual wind speed can vary from 0.1-4.3m/s (0.22-9.6mph).
“Gusts of wind have the potential to leave patches of the crop under-dosed with blight fungicide, which can expose them to a risk of infection,” says Stuart Sutherland, Interagro’s technical manager. Even the strongest fungicides can have weak spots due to poor coverage,” he says.
SRUC specialist in blight epidemiology Dr. Ruairidh Bain, believes that spray coverage is one of the key factors of the blight control programme that needs to be improved to protect potato crops.
In comes Crusade, a specialist drift retardant designed specifically to maximise the performance of blight fungicides by removing the physical limitations on them to work at their best.
“Crusade helps maximise fungicide dose and deposition on the potato crop and provides full canopy protection by modifying droplet size and distribution,” says Stuart Sutherland. “This makes Crusade a vital addition to ensure fungicide sprays are both timely and targeted for maximum protection.”
By reducing the number of fines (smaller than 100 microns) in the droplet spectrum, Crusade reduces the susceptibility to drift. This effect also increases the spray angle uniformity at the nozzle which helps ensure the correct dose is applied to the leaves, says Stuart.
“Crusade also optimises droplet size in the upper end of the spectrum so that the blight spray is better able to penetrate the canopy and be retained there, which helps improve coverage of the lower leaves and stems and thereby limit the risk of scattered blight infections occurring in the crop.”
Because Crusade modifies droplets at both ends of the spectrum (large and small), it has a beneficial effect with all nozzle types – from flat fans to low drift nozzles.
Crusade has been rigorously tested and proven in SRUC and Eurofins blight trials over the last 7 years with a range of fungicides, where it has been shown to improve blight control and blight free yield.
“A key feature of Crusade is the maximisation of blight control with a wide range of different fungicide active ingredients,” says Dr. Ruairidh Bain.
Cover photo: Dr. Ruairidh Bain inspecting a potato field
Stuart Sutherland, Technical Manager