Hi Lena,

Black Jack Zucchinis developed a major case of Downey mildew and it spread
to neighbouring Lebanese Cucumbers.. causing early demise of all the plants
effected. We have pulled them out and safely disposed of the diseased
plants but now I wonder if I should treat the surrounding soil or just
replant with something else as though nothing has happened.

I would be grateful for any advise on what to do for the best.
--
OK, so you've learnt about watering the hard way. All cucurbits are very
prone to powdery mildew, zucchini especially. In the end that's what
will do them in, no matter how healthy they are.

There's no need to treat the soil before planting anything else, as the
fungal spores responsible for powdery mildew tend to be in all soils.
Instead you should concentrate on avoiding splashing the spores onto
your plants, by low watering for example. If yo do begin to notice
powdery mildew on your plants, try spraying them weekly with a 1:10
dilution of powdered milk, or chamomile tea at the same ratio (let the
teabag soak in the cup for 1/2 an hour before diluting). They're the
best organic anti-fungal agents but they still won't help a bad case of
powdery mildew. You should also try to plant the next zucchini plants in
a different spot to avoid a buildup of any pathigens (crop rotation)

If anyone starts noticing black and yellow "ladybugs" on their plants,
they're an indication that you'll have powdery mildew within a week or
two. The bugs like to feed on the exudations of the mildew spores.

I have also heard from a very good source recently that sprinkling
coarse yellow cornmeal (polenta) on both leaves and soil can result in a
stronger anti-fungal effect than both milk and chamomile. I haven't yet
had the chance to try it for myself. If anyone does try it could they
let me know what the results are?

Tara