Powdery Mildew Fungi
Flower beds and borders are often looking a little unkempt at this stage in the year, but that ‘Could do Better’ look is often made a lot worse by the appearance of powdery mildew fungi. If you’ve seen a white or off-white dust like growth appearing on the foliage of plants such as Acanthus (bears’ breeches) , Michaelmas daisies , Echinacea, roses and phlox, then this is likely to be to blame. There is a powdery mildew fungus for just about every plant in your garden and once they have infected the plant (usually the leaves succumb first) there is yellowing and dieback.
So what can you do? Well, with some plants, like courgettes, unless they are still flowering well, I’d not be too worried right now as their season will soon be at an end but if you can, pick or cut off affected parts of the plant promptly, as this may help to reduce spread of the infection. Bin or burn the offending leaves or incorporate them in to your compost heap if you’re a good, thorough composter. It is also really important to try to reduce the risk of the problem occurring in the first place and there are two easy ways to achieve this: Plants which are either dry around the roots (so those in post are particularly prone!) or too moist around the top-growth are far more likely to succumb to powdery mildew, and often badly too. So, even if you don’t feel it is worth doing much about infected eaves now, you should still do what you can to reduce the problem next year by keeping plants well watered and mulched and by avoiding wetting stems and leaves when you water. On some plants, like roses and other woody plants, a bit of careful pruning won’t go amiss either, as well-spaced, ‘open’ top-growth means better air circulation and so less moisture.