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I have a planter with several lettuce plants and other plants growing on my balcony. Recently, all of "normal" leafy lettuces were rapidly overcome by a bug. A sawtooth, more mizuna-like lettuce was spared, as were sage, parsley, onions, and basil.

When I first saw this bug, I thought it was a fungus, because the bugs come so thickly clustered, and have this bulbous appearance to them like they are all outgrowths of the same fungus. Looking closer, I was able to see that some of them indeed have legs and move around, although some still look very much like unmoving lumps. In the picture I took for this post, they look entirely grey, but in person they definitely seem a little bluish.

When I first noticed them, they had spread so quickly to coat these inner surfaces of the leaves, that I went with the scorched earth strategy. I cut each lettuce back to a stump, and now they are slowly starting to sprout small leaves again. To my dismay, the bugs have already returned to one lettuce. I'm looking for a more permanent solution now. Any ideas?

UPDATE:

  1. I tried @kevinsky's solution. Lacking a hose, I used a spray bottle and toothbrush, using the toothbrush to knock bugs off the leaves
  2. So far, two days after implementing, I've only seen a few bugs reoccur. I've tried to be extremely proactive about disrupting returning bugs. I found that an easy way to find bugs is to shine a very bright LED behind the leaves at night (using my phone's flashlight)
  3. Rinsing off the soap with a spray water bottle was less effective than I'd hoped, although not catastrophically so. It looks like some leaves sustained minor damage. Plants that weren't part of the treatment have some mottled yellow spots where (apparently) splashing from the soapwater spray hit them. For anybody at home trying this solution who also lacks a hose, I'd use a more dilute soap solution, or make sure to rinse the leaves with the spray bottle VERY enthusiastically.

Pending further updates, I'll make @kevinsky's answer correct.

Click for full size

Bluish-grey bugs

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Mealybug is my guess but they are usually warm season bugs and it's a bit early for them. They are sucking on the plant juices by clustering on the veins of the lettuce leaf.

Or they could be aphids that are whitish. Aphids come in a lot of colours.

Frankly it doesn't matter what they are, you need to control them. A good hose down followed by a spray of 1 tablespoon dish soap to one liter of water does the job. Given that lettuce is fairly delicate I would follow up on a spray with another hosedown after a few minutes to remove the soap. The fatty acids in soap can burn delicate leaf tissue if applied too strongly or left on too long.

  • I tried this - given that I don't have a hose up here (balcony garden), I just sprayed the heck out of it with a spray bottle, while using a toothbrush to dislodge any bugs I could find. Then I sprayed on a soap solution, and sprayed at back off after a few minutes with some more water. We'll see how it turns out! – Jonathan Apr 15 '12 at 21:18
  • I'm in Southern CA by the way, so it's pretty warm over here already. – Jonathan Apr 15 '12 at 21:21
  • I could tell that the bugs like to hide among the youngest leaves that cluster very tightly together, creating a closed environment. That's probably why they seemed to appear so fast in the first place, they multiply invisibly and then are suddenly visible when the leaves open up. – Jonathan Apr 15 '12 at 21:23
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My best guess is whitefly (larvae), but it doesn't look quite right. If you see tiny bright-white flies around, that's it.

Is your balcony enclosed? If so, can you open it? Whiteflies don't like cool weather, wind, rain, etc.

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    I don't think these are white flies - these seem to be big slow bugs that latch on and suck juice from the plant, they don't fly around. I had white flies on my parsley earlier, and these are very different. – Jonathan Apr 15 '12 at 18:41
  • I don't think these are white flies either. However, the lack of colour and pale appearance also suggests that they've either just hatched or molted and will take a while to get to their true colours. Of course, this could just be their true colour too, but from an evolutionary standpoint, it looks unlikely. – Lorem Ipsum Apr 15 '12 at 18:49

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