It’s been years since I’ve grown Fava beans and I didn’t recall them being so attractive to black aphids. A quick Google search, however, proved just how strong that attraction was. I saw advice on dealing with them from pinching the growing tips because the aphids like the new growth, to spraying with all sorts of chemicals I would never use. But my aphids looked a bit different. Not all were black, some were tan and a bit… well… fat. Why did I have these fatty aphids? Did they eat too much Fava?
Actually I had seen aphids like this once before and already knew their days were numbered if not already up. In fact, most of what you see are pretty much dead already These are parasitized aphids which is good news for me, bad news for the aphids. A tiny black wasp has laid a single egg inside each of those tan aphids. The offspring of the wasp will then grow inside the aphid, using it as a food source, until it bursts out. (You can see a diagram of their life-cycle here.) Definitely a creepy way to go if you are an aphid, but this should be a welcome sight for most gardeners. The best thing you can do for your garden right now is to hold back on spraying anything, even an organic pesticide. If you spray now, you risk killing off the beneficial wasp babies and you want those. Each beneficial wasp that hatches will then go on to parasitize more aphids. After the wasps hatch, you can easily rinse off the remaining aphids with a sharp stream of water. You will know the wasps have hatched when you see a small hole in the aphid and it looks like nothing more than a hollow shell of its former self.
Sometimes you just have to give nature a hand for the amazing things it does. For me growing organically isn’t just about eschewing chemicals, it’s also about finding balance with nature. Sometimes finding that balance means doing nothing and that can be hard. Plants coated with yucky aphids just scream “kill it with fire” to me. But I’m not anywhere near harvesting any beans, the plants are still growing vigorously and the aphids really are on their way out. As a matter of fact, here is a photo of the same plant, taken just one week later. Not too shabby nature!