Ellen writes, “Help! I have powdery mildew on my tomato plant!”
Powdery mildew is definite reality to face when growing tomatoes anywhere on the west coast of North American from Canada to Mexico. Cool maritime conditions create the perfect environment for powdery mildew to thrive. So what is powdery mildew?
You can see my previous blog What is Powdery Mildew? Here are the basics:
Powdery mildew is a fungal disease that is common to many vegetable crops (e.g. tomato, beans, peas, cucumbers, squash, kale) and ornamental plants (e.g. Columbines, Delphinium, Nandina). Overhead water spreads the diseases once it is present. However a plant that is lacking consistent water is way more likely to contract the disease in the first place. An inconsistently watered tomato plant or a tomato planted in poor soil is far more likely to get powdery mildew.
That being said, you could do everything right and still get powdery mildew on your tomatoes, especially in community gardens. Why? Because the powdery mildew spores are everywhere, especially in community gardens.
Neem Oil is an excellent organic control for sucking insects and certain diseases. Neem Oil works great for controlling powdery mildew on tomatoes. It doesn’t seem to work as well controlling powdery mildew on other types of plants (e.g. roses) or other plant diseases (e.g. rust). I use Bonide brand Neem Oil for all my clients that grow tomatoes.
There are a few cultural practices we can do to reduce the likelihood of powdery mildew:
Remove any leaves or branches touching or within 12″ of soil.
Remove any yellowing leaves on the plant.
Remove any tomato leaves on the ground.
Space plants at a minimum of 3 feet apart; if they are any closer, air flow is reduced and mildew thrives.
Avoid overhead watering; water the ground, not the plant.
Avoid watering in the evening. We do not want water sitting on our tomato leaves overnight.