“Wettable sulfur, sprayed on tomatoes every two weeks at a rate of 2 tablespoons per gallon will absolutely prevent mildew. And….it is cheap.
One tablespoon of wettable sulfur to one gallon of water sprayed on squash leaves AFTER you have removed all infected leaves will control mildew on your squash.
Preventive spraying is the best way to control mildew.
Only spray in the evening when the leaves of your plants have had a chance to cool down. Spraying on hot leaves will burn them. Ditto with the tomatoes.
Cucumbers are a problem and they do not like the sulfur. Skim milk seems to do well on cucumbers.
Keeping all leaves that do not look perfect removed daily from your plants, tomatoes, cucumbers, and squash, goes a long way in preventing the spread of the mildew. Mildew, after all, is a fungus and spreads via spores that blow in the wind.
Just to make it clear regarding the micronized sulfur dilution for spraying for preventing mildew: That is 2 tablespoons of sulfur to one gallon of water. Of course, if your brand of sulfur calls for a different amount of sulfur, use what your manufacturer says to use.
If you only want to use “Organic” solutions, you can buy a gallon of skim milk (non-fat) and just spray it from the bottle. No dilution is necessary. Or, you can buy non-fat dry milk and mix it as follows – one part dry non-fat milk nine parts water.
A good schedule is every two weeks or oftener if you see a problem sooner than the two week period.
It is really important to spray in the cool of the day, I do it in the evening after leaves have cooled down.
It is also really important to keep all bad looking leaves trimmed off of plants so that spores don’t continue to infect healthy leaves.
Remove all leaves that touch the ground; remove leaves that overlap; remove all leaves with mildew showing.
Always water at ground level, do not wet the leaves. Always water in the morning in case the leaves do get wet, so they have a chance to dry before nightfall.
Hot days and cool moist nights are perfect conditions for powdery mildew. That is exactly what we are dealing with here in Long Beach, California. Our plants are simply dripping with dew each and every morning.
Joanne – Contributing Member of MittleiderMethodGardening group