I am very puzzled by the unsightly and obviously troubling leaf streaking and spotting which afflicts some cultivars. Last year, towards the end of the season, ‘Charlotte’ was a mess, but this year, two cultivars, ‘Baerbel’ and ‘Zwanenburg Blue’ have begun their season with the problem which is obviously affecting their health and holding back growth. In this picture, ‘Purewell Giant’ on the left is unaffected and growing strongly, whereas ‘Zwanenburg Blue’ on the right is struggling by comparison.
However, healthier growth is now appearing and I am hopeful that this is a temporary setback and that the plant will recover in the coming days and weeks.
‘Baerbel’ is even worse and is way behind its neighbours as this picture amply demonstrates. It literally came out of the ground as a sick patient.
However, there is new growth and also seedlings appearing (which will have to be removed!), so I am hopeful of a recovery
To some extent, this negates the advice from the RHS that ‘environmental factors’ are to blame for the streaking and poor health. In both cases, the plants began re-growth with the problem alongside the strong, healthy re-growth of neighbouring plants without similar problems. If it was caused by ‘environmental factors’ it would surely affect neighbouring plants in the same way?
Currently, there are no other plants suffering from leaf streaking or spotting although I am expecting to see it in some of what seem to be the more ‘susceptible’ cultivars later in the season. Currently, all plants are being fed and watered at regular intervals but I am about to begin trials of bicarbonate of soda sprays to see if this makes any difference, as some suggest it might.