The post infection use of Lime sulphur to control apple scab. Experiences in the Netherlands 1999-2002

Summary

Until yet the fongicides in organic fruit growing (sulphur, lime sulphur, copper, claypowders) are used as protectants applied before the rain, or as stop-spray or during infection development. Post infection use of lime sulphur could reduce the number of spray rounds, allowing for the use of less pesticides, and reducing the adverse effect on beneficial insects and mites. In the 30's of the last century, post-infection effects of lime sulphur were found in lab and field trials. Effective control was achieved by applications 30 to even 72 hours after the start of rain. Field trials in the Netherlands in 1999, 2000 and 2001 confirmed that post-infection applications of lime sulphur are effective under field conditions till at least 20 hours after the start of the infection.
Evaluation of the practical experiences with the use of lime sulphur as post-infection spray in 2000 and 2001 however showed that a dose of at least 0,15 % should be used, and the product should be applied with a high water volume, or on wet leaves to allow for an effective contact between the pentasulphides and the fungus.
In 2000 one application of lime sulphur two weeks after blossom lead to severe russeting of the fruit skin on the variety Jonagold.