A few weeks ago the UK meteorological service issued its long range forecast for the coming summer as one that will be hotter and drier than usual. Needless to say, since then it has been raining in Ireland (although the prospects are for better weather quite soon).
This wet weather is following a wet spring, which means that soils have been saturated for some time, and apple scab pressure has been very strong. At the moment I am two days overdue on a 7 day apple scab program which so far this season has incorporated dithianon (an old-fashioned protectant with similar activity to Captan), Scala (pyrimethanil), Mancozeb, Captan and Bellis (a pyraclostrobin and boscalid mixture), as well as bupirimate for powdery mildew. Despite this rigorous program, I have still spotted some apple scab lesions in one block, and plan to use a difenoconazole mancozeb mixture as soon as weather permits. I attribute the presence of scab to the late growth of some shoots into early winter, and the subsequent persistence of little leaves on a few un-pruned shoot tips over the winter; these over-wintering leaves carrying lesions capable of infecting new green tissue as soon as it emerged in the spring. Of course, if the weather had not been so wet, spray covers would have been more reliable, and infections less likely to occur, but that is not how it turned out. It will be interesting to see the effect of the difenoconazole when I do get to use it. As long ago as 1993/94 we experienced DMI resistance (to myclobutanil). Since then we have used DMI's very irregularly, but laboratory tests on lesions as late as 2001 showed that myclobutanil resistance was still widespread within our orchard. However, difenoconazole appears to be much more active than myclobutanil, so I am hopeful that it will work. If I can still collect samples in a few weeks time, I plan to test them for DMI resistance again. Apart from that, I do have the option of using dodine. This is a chemical that we never used routinely in our spray programs, and I do not believe that our scab is resistant to it yet. I am reluctant to use it for fear of russet, but it may present the lesser of two evils, the other being scab infections on the apple. Alternatively, I may have to continue with a low-rate protectant program during the season to keep fruit and emerging leaves scab-free. Time will tell, but the unfolding weather will play a big part. Which brings me back to the long-range UK met service forecast. I hope they are right. Con Traas The Apple Farm Cahir, Ireland.
