Blight risk remains low despite warm temperatures - farmers weekly

BLIGHT RISK REMAINS LOW ACROSS MOST OF THE COUNTRY, DESPITE RECENT RAINS ACROSS WEST AND CENTRAL ENGLAND. Denis Buckley of Highfield Lodge Agronomy reports that there has only been one half

Smith period this month, which occurred on 8 May, keeping the risk relative to other years at a low level. “Although half Smith periods have triggered blight before, it’s only where they’ve

been preceded by a half period before that,” he says. The very cold winter, which dealt with volunteers, together with a dry April, has helped to keep the risk contained, he says. “And

although some areas have had rain, the temperatures have dropped since then and it’s been cooler.” Warm, wet conditions are needed for blight development, continues Mr Buckley. “So pay

attention to forecasts and make use of the internet tools available. It has to be hot and humid for blight to take off.” An important lesson learned from 2007, when things went badly wrong,

is that Smith periods are a very good indicator of risk. “The information is available, so ignore it at your peril,” he stresses. However, even in low risk situations, fungicide protection

should be applied to advanced crops, advises Mr Buckley. “But it does mean that cheaper products can be used at the start of spray programmes.” In East Anglia, Darryl Shailes of Hutchinsons

says the lack of rain for two months has reduced blight risk considerably, as well as having an effect on crop development. “We need rain before anything changes. The forecasting system we

use is telling us the risk is almost zero.” That may not be the same in areas west of Northampton, he warns. “Where there has been rain, the risk will have increased.” Independent agronomist

John Purslow in north Norfolk reports a similar picture to that of Mr Shailes. “In non-irrigated crops there hasn’t been the humidity required and the risk is very low.” But he adds that

local issues must be taken into consideration. “Irrigation can make a difference and there’s no room for complacency with blight. Remember that the new strains can come in earlier and are

more aggressive.” His intention is to maintain normal spray programmes until there’s any change in the weather. In Scotland, SAC’s Ruairidh Bain confirms there have been no outbreaks of

blight yet. “Temperatures are high enough, but all the criteria haven’t been met yet. Not surprisingly, the risk isn’t high and, looking at the weather forecast, there’s no reason to see

that changing immediately.” In the west of England, the situation is more variable, reports Faye Ritchie of ADAS. “We’ve now had enough rain and are starting to see the conditions that

favour blight. If temperature and humidity remains high, growers will need to get on with sprays quickly. We are seeing Smith period criteria starting to be met in a few areas.” And Stephen

Williams of Syngenta points out that where rain has fallen, potato crops are racing ahead to make up for lost growth. “The soft growth of rapidly expanding leaves is especially vulnerable to

blight infection. As soon as crops are touching between the rows, blight sprays should go on.”