Last year these things(tree hoppers) did major damage to my Zinnias first. I planted the Zinnias from seed, and they were the tall type, which reached almost 6 feet due to a slight lack of sunlight, but before they grew that tall, I came out one day to see the top 8" of the stems of 2 Zinnia plants laying on the ground. The plants were about 15" tall then, and when I looked closer, there were actually 3 pieces of stems on the ground, and it looked like someone had taken pruning shears and just cut the top half of the stems off, then cut one of the fallen stems again into half.

Then I noticed these green and sometimes brown insects standing on the stems right near each leaf junction. Then I watched them eating a perfect circle around the stems, and eating about 1-2mm deep, so that the stems would quickly break off and fall to the ground. So I started spraying them.

Then I grew new Zinnias from seed, and didnt notice the Tree Hoppers there anymore. But then I started noticing ants climbing up my dahlias and going under the leaves. There I once again saw the same Tree Hoppers, but this time they were eating on the veins underneath each leaf, and where they were eating, there were these swelled areas on the veins where damage had been done.

So I began spraying, and I also noticed Spider Mites on other plants at the same time too. The Tree Hoppers are funny looking, and come in green and brown. When you pick them up, they will fling themselves off your hand far away. Even though they are small, you can feel the power of their little legs when they jump off your hand or arm! Its like they make a clicking sound when they jump, and you can feel it too.

But I called the local cooperative extension and talked to the "experts" there, and these "geniuses" told me that Tree Hoppers dont damage Zinnias or Dahlias, which was complete nonsense of course! I watched them damaging BOTH plants. PLus there were ants following them to get the honeydew or whatever they leave behind while eating.

I've seen a few on my dahlias this year now too.