Powdery Mildew

Since I'm a first year gardener, I'm a bit of a hypochondriac when it comes to pests and diseases in the garden. I was worried about some potato leaves that kind of looked like they had blight, but that didn't seem to spread, so it probably wasn't. There was attack of flea beetles on my Pak Choi, but that seemed to pass. Two of my Broccoli plants seemed to just wither and die, which made me worried about club root. The rest of the Broccoli plants seem OK and when I pulled up the dead plants they didn't have messed up roots, so it probably wasn't that. The newest thing to worry about.....Powdery Mildew (heartofore called PM).

After noticing white spots on a few of my Spaghetti Squash leaves, I started doing research. PM is arguably the most common garden ailment. Its a fungus that attaches to the leaves and can spread rapidly. It drains nutrients and eventually kills individual leaves. It can kill whole plants in bad cases that are allowed to run rampant. It can affect most types of garden veggies, but each vegetable type has a specific species of PM that can infect it, so PM on squash won't infect potatoes. Some species are more suceptible to PM, though. That list of most suceptible plants includes Cucurbits. Turns out that is the actual name for the group of plants that I have been calling "viney plants". This includes squash, melons, cucumbers, gourds, etc. Most of the pictures I have seen online range from white blotches to a general white dust on the whole leaf. My white spots are very well-defined, but I did see a couple pictures that looked like that. The picture below is one of my Spaghetti Squash leaves. Its possible that this is something else, or its nothing at all, but I'd rather be safe than sorry.

There are some pretty nasty sounding fungicides that I could spray that should be effective in controlling PM, but I'd rather not go that route if I don't have to. There is quite a bit of talk on the internet about a baking soda solution being effective. This appears to be backed up by studies at Cornell and other places. It is believed that the high pH affects the fungus a lot more than the plant leaves. So I mixed up a batch of 3-4 tsp baking soda, 2-3 tsp vegetable oil, and 1-2 tsp liquid soap with one gallon of water. The oil is to help the solution stick to the leaves, and the soap is a surfactant that helps to disperse the oil evenly throughout the solution. (As an interesting aside, the dispersants talked about so much in relation to the gulf oil spill work the same way and are very similar to dish detergent. They just cause the oil to break into fine droplets and diffuse throughout the water column rather than just floating on the surface.) I sprayed the solution on all of my Cucurbits (Spaghetti Squash, Cucumber, Melon, and Zucchini) yesterday. I sprayed the tops of all of the leaves, and the bottoms of the leaves that had white spots (25% of the Spaghetti Squash leaves and one Zucchini leaf). I really hope that protects them since those plants are doing very well at the moment. Perhaps its not even Powdery Mildew, and I'm just being a hypochondriac.

One thing I certainly am not imagining is bugs on my Broccoli and Kohlrabi. There are a few little green worms and a whole lotta aphids. I saw a few aphids and was just going to knock them off, but after I looked closer I saw big clumps of them on all the baby leaves. Some of the leaves were so infested that they are curled and crumpled. So much for the idea that a natural, healthy, diverse garden will have a balanced ecosystem with predatory bugs to keep parasites in check. Time for some chemical warfare. I pulled out a spray-bottle full of pyrethrins and went to town. Pyrethrins are derived from Chrysanthemums and are certified organic, but very effective against many types of bugs. I think thats actually what is used in most flea sprays.