Insect Issue

fawnee0214(9)February 28, 2012

I have small Eastern Redbud seedlings I have started indoors. While watering one I noticed the edges of the bottom most leaf (also the first true leaf after the pair of baby leaves) were turning a tan-ish brown and dying. There was( and still is) no yellow surrounding the brown dying area. Little teeny black dots are within the dead brown edges. I looked the plant over and didn't find a trace of insects. However, after bringing other plants home from the fair, I noticed the brown on the leaf had gotten larger and worked its way in. When I turned the leaf over, it had 6 or 7 long, thin, white/plae green, small (smaller than one 16th of an inch long) insects on it. It was only on that one leaf. The soil had been dry for quite a while. I did see some small, about 1/4 inch, gnat-like insects hiding under the rim of the pot. They were brown, had wings, and 6 legs. Possibly the adult form of the white insects? Again, only the one leaf was affected. So, worried it would spread to the other, more vigorous seedling, I put them both in a peanut butter jar turned upside down with the lid screwed on the bottom to isolate them both. I'm glad I did. I only did that this Saturday and when I checked back today, I saw many more of the gnats in the jar of the infected seedling. The browning had spread to the other leaves. Whatever it is seems to prefer the older leaves, since the still turgid leaf at the top is untouched. The ones closest to the first linfected leaf are now beginning to turn brown and each has 1 of the small white/pale green worm-looking insect on the underside of the leaf that the first leaf had. It only has about 4 leaves and is less than 6 inches tall, while the (hopefully) unaffected seedling grown under the same conditions has more, larger, leaves and is taller. I took the affected one outside.

Does anyone have an idea of what these insects are? Are the three(brown-edged leaves, gnats, and white bugs on the underside of the leaves) symptons seperate? What can I for the affected seedling? Will this affect my Lucky Bamboo, Draceana marginata, and AVs grown in the same windowsill?

By the way, I am asking this in the Houseplant Forum because I doubt that this only would affect eastern redbud trees. Sorry, but I cannot post pictures. My camera just broke a few weeks ago. Any help is greatly appreciated!

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rhizo_1 (North AL) zone 7

The gnat-like insects are almost certainly fungus gnats, the larvae of which live in the potting medium. Fungus gnats thrive when the soil is kept too moist for too long, possibly due to chronic over watering and/or the result of a potting mix that is simply too mucky, peaty, and fine-textured. Those mediums simply don't drain very rapidly.

I can't help but think that the brown edged leaves and the fungus gnats are associated (poorly drained potting mix/over watering), but I'm not willing to try to ID the critter on the underside of the leaves.

The sooner you can get this plant outside, the better. Introduce it to sunlight very slowly. These plants are not meant to be grown inside, even for a short period of time.

    Bookmark   February 28, 2012 at 10:28PM
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tapla (mid-MI z5b-6a)

To add to what Dori said, there would be no harm in thoroughly spraying the plant with an insecticidal soap solution in the hope that it will keep populations of the insect with sucking/rasping mouth parts that might be attacking the plant in check. Getting the plant outdoors will not only increase the plants metabolic rate, which increases its resistance to insects and disease, but it will also expose pests to natural predators.

The best cure for fungus gnats is usually a restrained hand on the watering can. They're attracted to soggy soils that are wet on the surface for extended periods and soil materials that break down quickly. Don't water unless your plant is almost dry.

Changing to a soil that drains freely and remains well-aerated will probably not only solve your gnat problem, but would ease the effects of over-watering as well. As Dori said, it's a good possibility your foliage issues are in large part due to watering habits.

Al

    Bookmark   February 29, 2012 at 7:39AM
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