Growers warned to protect against apple scab earlier

Warm temperatures and an early spring could lead to apple scab problems if spraying not correctly undertaken.

Apple and pear growers are being warned they should start spraying against scab earlier than usual, ADAS top fruit consultant Chris Nicholson has advised. After exceptionally warm temperatures for much of the autumn and winter, he said an early spring was on the cards. As many growers learned to their cost last year, once scab gets established on the easily infected pristine leaf it is very difficult to eliminate. If the fruit is infected, as happened in some Weald of Kent Bramley orchards last year, it becomes fit only for juice production, resulting in a significant reduction in its value. Nicholson said: “The most effective sprays are the first ones. Get [scab control] right from bud burst to petal fall and it’s more likely to remain right for the rest of the season. Spray at [or just before] bud burst of the earliest variety in the orchard — not necessarily the main one — and not a few days later.” If the spring is early, growers must ensure that their orchards are clear of prunings to allow ease of access by sprayers, he urged. There was a dry spell towards the end of January and into early February when the pulverising of prunings without rutting alleyways was possible but then frequent rain made tractor operations very difficult. “If there’s no chance all your pruning will be finished in time, ensure that orchards that are most at risk are pruned and the prunings pulverised or cleared before spraying begins,” advised Nicholson. “At the very least make sure every other alleyway is clear for the tractor.” There is likely to be plenty of inoculum to launch a scab epidemic this spring. This is because warm, wet weather last August and October reactivated leaf scab so further infection occurred in orchards not receiving late fungicide sprays. Then conditions and the absence of hard frosts until well into autumn delayed leaf fall, which means infected leaves have had less time to rot and thus reduce the amount of inoculum. This overwinters in the form of ascospore-producing pseudothecia. Some growers sprayed orchards pre-leaf fall with five per cent urea to accelerate leaf rotting. That has proved successful, particularly because there has been much more winter rainfall than last year. A few growers went further to eliminate leaf inoculum by sweeping leaves into the alleys with rubber paddle machines and then pulverising them. Another method, adopted by a number of Continental growers, was to use forage harvesters to suck up the leaves and blow them into trailers and then cart them away to be composted. But spraying with urea is the easiest option and, according to tests carried out at East Malling Research, it has the added advantage of destroying some superficial infection and preventing pseudothecia formation. It also favours the multiplication of microbes antagonistic to scab development and the bacteria causing leaf decomposition, and appears to make leaves more attractive to worms so they are pulled underground quickly.

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