Monday, July 5, 2010

Purple Coneflower

Rachel's Question

Something is wrong with my purple coneflower. All the sepals around the bud are curling and looking mangy. Upon a closer examination, I noticed that there was a very small centipede-looking creature - see the far left-hand side of the second photo. Additionally, there are a lot of very, very tiny white dots. You can barely see them in this photo. Are these two separate pests or are they related somehow?

Amy's Answer

The "centipede" thing is good. It's an immature lacewing, and it's eating the bad things. Lacewings are seriously bad-ass. They're also very pretty. So don't disrupt anything that looks similar to these pics.

The dots are pest eggs. Wipe them off with a damp cloth. I see some immature leaf hoppers on the plant. I've circled them in the picture. This is kinda bad, actually.

Leaf Hoppers are piercing/sucking feeders that feed on the phloem of the plant (much like aphids, but not as easily removed as slow, clunky aphids). They're hard to treat with a surface deterrent, because they eat the sugary syrup inside the plant. Unlike aphids, they also produce more winged adults, so they can just come back after you clean them off. Do it anyway, though. Look for the rounded little green things and GET THEM OFF. Also the dots.

So, here's the really bad news. Leaf Hoppers transmit Yellows disease to Purple Cone Flowers. Yellows disease is caused by a phytoplasma that reproduces in living plant tissue. It causes, well, yellow leaves, stunted growth, and sometimes a reddish tinge to the leaves. The flowers produced will be sterile, and organs and shoots will be deformed. I don't know if your plant has it, and the only way to tell would be to look for characteristic structures in living plant cells under an electron microscope. I'm assuming you don't have one of those sitting around the house. Also, I wouldn't even be able to tell you what to look for. This wouldn't be such a big deal except that those filthy little (even though they're cute) leaf hoppers will spread the disease to anything else they taste in your garden. Things that are affected by Yellows Disease - in addition to echinacea - include: monarda, caraway, marigold, snapdragon, aster, mum, daisy, carnation, strawflower, carrot, broccoli, tomato, radish, squash, ragweed, thistle, plantain, and dandelion. So you really don't want it in your garden.

There is no cure for Yellows Disease, other than removing the plant. Now, we don't know for sure that you have it. All of this damage could be caused by the leaf hoppers. They like to eat flowers first. If you're really worried, you could sacrifice the plant right away. First, though, I'd like to see if the plant gets better if we treat the leaf hoppers. Try removing as many as you can. Go crazy on the dandelions in your yard, just in case. Check your other plants for leaf hoppers, as well. And watch any new growth on the plant. If you can't see anymore leaf hoppers, and the new growth is still wonky, then you'll need remove the plant.

There are some systemic pesticides out there that minimize harm to other insects - you pour it into the ground and it only affects insects that feed on the phloem. But they aren't organic. Some are nicotine-based and pretty selective in damage due to the type of receptor they attack. The FDA assures us that they aren't harmful to humans. They're probably correct in that, but there is some data indicating that they might be harmful to bees. I only mention this in case it becomes clear you have Yellows Disease and you need to save the garden by killing all of the infected leaf hoppers. This is worst case scenario, and pretty unlikely. Just an FYI.

Meanwhile, I'm going to look for some IPM methods to deal with leaf hoppers. We'll see how the plant does and move on from there."


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