Comments on: Powdery mildew

By: Annie Ludford

Annie Ludford — Tue, 29 Jun 2010 03:53:32 +0000

How do I tell the difference between powdery and downy mildews? My zuccinis are pretty bad at the moment.
Annie, downy mildews are furry, and powdery mildews look as though the leaves have been roughly dusted with a fine white powder. Downy mildews usually only affect stressed zucchini in very wet weather, and powdery mildews are more common on zucchini in warm, dry conditions. As you have not said where you live, it is difficult to make a judgment on which one would be affecting your plants.
Downy mildews respond to a 10% milk solution, which makes the leaf surface more alkaline and the fungus can’t survive. The chemical treatment for powdery mildew is sulphur (which is acidifying) and the milk treatment is not likely to be effective for this fungus group. Plants affected by either disease will benefit from the application of fertiliser that includes potassium. – Lyn

By: Chris

Chris — Wed, 06 Jan 2010 11:00:32 +0000

When making the chamomile tea spray, why does it need to be diluted? Will it burn the foliage if used undiluted?

Chris, undiluted chamomile tea has a silky feel (which is why it is an excellent hair rinse, too). I don’t know about it burning leaves but perhaps what gives it the silky feel could clog pores on leaves. I know it needs to be diluted for seedlings but if you want to treat zucchini or larger plants, you could try it undiluted on a couple of leaves – observe the results – and share your findings with the rest of us. That’s how most good gardening tips come into common practice. – Lyn

By: greg

greg — Sat, 05 Dec 2009 11:55:34 +0000

What about milk spray? Recommended often, and a study by a university in Adelaide found it not only effective, but determined the mechanism at work. Something to do with free radicals and the reproductive structures of the fungus. Spray in full sun!
Greg, that is a very interesting explanation for how milk spray works. I understood that it (and baking soda spray) worked by changing the pH of the leaf so that the fungus can’t survive. However, I’ve found a 10 percent milk spray more effective for downy mildew and black spot.
Powdery mildew is produced by a different group of fungi and its cause is insufficient potassium – either through inadequate fertiliser or inadequate watering when the plants can’t absorb the potassium from dry soil. Organic seaweed extract contains potassium and a range of trace elements that plants need to resist disease. Chamomile tea is an organic fungicide that works on a range of fungi.
Milk spray makes leaf surfaces more alkaline, whereas wettable sulphur (a common treatment for powdery mildew) has an acidifying effect.
Sulphur can’t be used in hot weather or when plants are short of water. – Lyn

By: adele Taylor

adele Taylor — Fri, 06 Nov 2009 09:10:47 +0000

My snow peas got affected with mildew … What I’m not sure about is whether to chuck them out in the rubbish bin or is it OK to put in compost bin?

Adele, as the fungi that causes this problem is spread by air currents, you can chop them up, wet them down, and put them in the compost bin if it is a moderate infection. Then put a layer of manure over them, and the good bacteria will break them down fairly quickly. If the plants are badly affected, and you don’t have an active compost heap, then bag and bin them. – Lyn

By: Nancy @PlantAvenue

Nancy @PlantAvenue — Wed, 28 Oct 2009 12:57:56 +0000

Great post. I’ve read lots of other posts about how to spray to get rid of powdery mildew, but have never read about the temperature or the link to insufficient fertilizer. Thanks!