Thursday, July 15, 2010

Broccoli Leaves and Aphid Poop


Creatures are feasting on the leaves of my romanesco broccoli. The good news is: they left the gorgeous purple broccoli head untouched, and I'm probably going to eat it soon anyway, so no worries. This is the last of my romanescoes this year. I started with six plants, and the other five all matured much earlier this spring. They are delicious - very delicate flavor when steamed and served with butter and salt and pepper. For some reason, this one lonely broccoli took much longer to mature than the other 5. None of my broccoli plants showed any pest damage until now.

I peeked under the leaves and found some aphids (see below). But the aphid population isn't all that large. The picture shows one of the largest clusters that I found. Are the aphids causing the main damage, or is it something else? I would like to know for future reference and also to assess whether the problem might spread to my other veggies nearby, which include swiss chard, leeks, carrots, tomatoes, green beens, and squashes.


So, the good news is that the aphids aren't really a problem. I mean, get them off of there before the population explodes. If you have a few warm days, that little colony could overtake the garden. Seriously. Females can reproduce asexually. Each adult female can produce up to 80 offspring in one week. Each of those 80 offspring then produce 80 of their own, who produce 80 more. That brings us from 1 female up to 512,000 aphids in less than three weeks. Anyway, wipe them off. I assume you already have, but it bears repeating. Do this even though you're about to harvest the broccoli, cause they'll just create some winged forms, pop out a few males, and fly over to your tomatoes to start all over again.

Aphids don't take bites. They have piercing sucking mouthparts. It's like a straw. They insert this straw into the leaf and look for a vein full of phloem. This is the sugar/sap and basic life-blood of the plant. They drink a lot of this. Actually, they drink enough to poop out some stuff that is basically sugar. We call this honeydew. There's a lot of evidence suggesting that the manna the Israelites ate was Honeydew from a particular kind of insect. It's pretty sweet, and not at all poopy tasting. (and I probably shouldn't admit that I know that, but, whatever). Ants will eat it. Ants will actually farm honeydew producing insects, protecting them from natural enemies. So, while ants are not pests, they're a pretty good indication of a problem if you find them all over a plant. Anyway, you can see how the leaf has turned yellowish underneath the aphids. That's typical aphid damage.

About the bites. Are you sure that's not slug damage? I'm less familiar with slug damage. I always look for slimy trails, because I can never remember the size of their bites. Those don't look like smooth margins. You have a lot more experience with slugs than me, so I'll defer. I'm curious about your slug program, though. Have you ever used beer traps? Copper barriers? I've heard inverted melons work really well too.

If it isn't a slug, then it's probably some type of caterpillar. These things are voracious. Since you'll be harvesting soon, let's focus on preventative measures. Look for caterpillars in the early evening or late morning. A little Bt wouldn't hurt, just as a preventative for your nearby plants. I'd suggest that you at least remove all of the leaves right after harvesting. It might be a good idea to remove the plant and turn the soil.


  1. Speaking of aphids, I've noticed that the aphids that show up on my tomatoes are red, whereas those on the brassicas (infesting the brassicas, I should say) are gray-green. Are these different types of aphids, or do aphids have chameleon-like properties? And while the ladybugs showed up and have apparently demolished the aphids on the tomatoes, those little gray-green beasties are absolutely encrusted on the undersides of the cabbage/broccoli/cauliflower leaves. Squishing aphids has become a morning ritual (lovely, no?). So, why haven't the ladybugs found the cabbage-patch aphids? In this regard, I'm speculating that the clover I sowed for a living mulch under the tomatoes is attracting beneficial insects, whereas no such mulch exists in the brassica bed. So next spring I'm thinking to sow clover there as well to see if that helps. Any thoughts?

    Ladies, this blog is way, way cool!


  2. Monette,

    Aaak, I can't believe I missed this comment way back when. If you're still around and checking...

    It's amazing how choppy insect populations can be, isn't it? I think there might be something to your theory. Beneficial insects really don't like dust, because it can scratch their wax layer and make them lose water. Mulch helps, but a living ground cover is even better. Lady beetles also love yellow flowers, like tansy. Actually, tansy is great for lacewings and hover flies as well, because the adults are nectar feeders. And one hover fly larva can eat 400 aphids. Tansy might even attract parasitic wasps too, which are great for all manner of pests. Fennel, parsley, and cilantro flowers work really well too. It's best to let them fower at the end of the year to encourage beneficials the next season. Leaving them in the garden through the winter gives the beneficials a place to live and some food when the garden isn't going. Anway, if you have some tansy in a pot, you can move it close to whichever plant needs some predators to encourage the population. Doesn't always work, but it doesn't hurt either.

    Another thing you can do to attract beneficial insects (bees too) is provide good sources of water. Ground cover plants hold small pools of water better than mulch, so that's another way they help. You can make an insect watering hole pretty easily with a small dish filled with rocks or pebbles. Just fill it up so that water pools between the pebbles. That way the insects have something to stand on without drowning, and it isn't deep enough to grow mosquitoes.

    If you still see localized populations of lady beetles, you can always collect a few of the immatures and move them to the aphid population. Unlike the adults, they can't really move too far.

    I'd love to hear how the clover works out for you this year. And I'm so sorry I took so long to respond!