Can you tell me why my squash and cucumber leaves are suddenly turning white?
This is one of the rare cases where I was sent photos and those photos show an impressive outbreak of powdery mildew. While many plants are susceptible to this fungus - including grapes, roses, phloxes and maples - members of the squash family show it off to dazzling effect.
Often the problem is noticed when white patches first appear on otherwise healthy leaves. As the disease progresses, those leaves turn yellow then brown and soon the shoots, fruit, and blossoms are affected. It can speed the decline of flowers, slow overall plant growth and reduce yields. However, it's rarely fatal.
The best way to control powdery mildew is to cut off affected plant parts and dispose of them off-site (not in your compost pile) and/or spray both sides of affected leaves with a sturdy stream of water once every week or so.
However, these tactics are only really effective in the initial phases. Once the problem has spread beyond that, there isn't a whole lot you can do except plan for next year when you can buy resistant cultivars, space them far apart so that they get proper air circulation, give them lots of sun and make sure they are growing in nutrient rich soil.
Even then, there are no guarantees.
If you have any questions or comments, please send them to me at vanessa@gardenmuse.ca.
