Virtual forecasts are only guides to risk of blight

2 June 2000

Virtual forecasts are only guides to risk of blight

Blight forecasts, black dot

and off-label uses were

among topics for discussion

at Roots 2000 at Newark,

Notts last week.

Andrew Blake reports

POTATO blight forecasts obtained over the internet are useful indicators of the likely risk of the disease.

But they are no substitute for crop monitoring and local knowledge, explained several specialists.

The British Potato Council has three "virtual" crops in the East, the Midlands and the West, using Dacoms Plant-Plus modelling and local weather data to provide blight forecasts updated several times a day.

Now Cyanamid is offering a similar service for crops in the East, the Midlands and the North-West on its Agricentre web-site*.

The Plant-Plus model combines local weather forecasts, information from in-field monitoring stations and details of crop canopy growth to produce spray recommendations.

Unlike other models which only account for spray chemical wash-off it allows for degradation of applied fungicides, explained DMA Crop Consultants Howard Hines.

This season illustrates one of its potential benefits, he said. "It showed that the risk of blight has been higher in the east than in the west. Normally it is the other way round." Plant-Plus, used commercially by 18 growers on 1400ha (3460 acres) last season, showed a need for more early season sprays. But it also pinpointed longer intervals towards the end of the season when crops could safely be left, cutting overall applications by about 20%, he said.

The latest web-site information is not field specific but should give growers a better guide to timely treatments, he added. "Anything that focuses growers minds on the crucial points is helpful."

Another advantage of using the system is that it allows fungicide use to be justified, an increasingly important crop assurance point, said Cyanamids Mike Barrett.

But Abbey Growers director Simon Bowen warned against over-reliance on "virtual" crop advice. The information is derived from real crops, but it could be misleading if applied too rigidly, he suggested.

"You cannot rely on average situations. It could be very dangerous, particularly this year when the range of crop development is considerable."

"There is no substitute for walking your crops," agreed the BPCs Ewen Brierley. "You have to look at local level."

"Its important to know the levels of inoculum in your own locality," said NIABs Pete Saunders. "The level of humidity under your own canopy is a key point."



&#8226 Virtual crops good guide.

&#8226 BPC & Cyanamid sites.

&#8226 Local inputs essential.

&#8226 Assurance implications.

Spray intervals

Blight fungicide Invader (dimethomorph + mancozeb) may now be applied every seven days up to harvest, says Cyanamid. Previous minimum spray interval was 10 days.

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