What are these small black things appearing on my cucumber leaves, and are they harmful?

Question

There are these little black things on my cucumber plants that have started appearing recently. They are more concentrated towards the 'top' of the plant.
They don't seem to be eating away the leaves or anything like that at the moment but they don't look benign.

I have tomatoes, zinnias, lettuce and eggplants nearby and the only other plant I see them on are the eggplants.

I tried Neem spray (I used Bayer Advanced - Natria Neem ready to use spray) but it had no effect whatsoever:

Any suggestions on what they are and how to treat them?

Answer 1

I believe those are flea beetles, from the family Chrysomelidae.

They can be a bad pest, but I have successfully ridded them from my property, and haven't seen one here for some time. I've successfully used neem oil, but I use 2% mix, which is twice as strong as what you used. Maybe that explains why it worked so well for me.

Here are some of the ideas I've tried that worked for me. I apologize for the length of this list.

• Stressed plants are the most attractive to flea beetles. Improving conditions has been shown to drastically lower attack.

• Organic fertilizers usually contain micro-nutrients and makes the plants more pest resistant as compared with conventional fertilizer.

• Chinese southern giant mustard is very attractive to flea beetles, and is often planted near affected plants to draw them off.

• Sticky traps (white or yellow) trap quite a few, but should be used along with another control method.

• Adult beetles overwinter in the litter/plant growth on the soil, under the host plants. ploughing and rototilling has been used successfully, to work up the soil.

• Microcotonus vittage is a braconid wasp that controls adult beetles.

• Neem oil is what I personally use.

• Rotenone is another natural control.

• Pyrethrin is a common and effective natural insecticide that I've used in the past.

• Kaolin clay controls beetles, but may stick on the fruit.

• Diatomaceous earth can be effective.

• Herbicidal soaps are effective, but also kill all the beneficials.

• Garlic oil is a good deterrent.

Also see:

• How can I deal with the beetles eating my grapevine?
• Pumpkin sprout and pepper plants have holes in leaves

Answer 2

I agree they're most likely flea beetles - close examination of the pics shows very small holes appearing in leaves. You can try this to control them: 2 parts rubbing alcohol, 5 parts water and 1 tablespoon of liquid soap, mixed in a sprayer, spray all leaves, including the backs, till run off. This 'recipe' is from the Old Farmers Almanac - the only thing that troubles me about it is, it doesn't specify what kind of liquid soap, but I'm guessing an eco dishwashing liquid might be fine, or horticultural soap solution.

Flea beetles will be present in the ground over winter - dig over the soil in autumn/fall to unearth them a bit, then again in spring. Try to delay planting your crops for a couple of weeks after the time you'd normally put them out - this will deprive the beetles of a food source for longer, and delay their laying of eggs, which they do at the base of food plants. Remove your existing crops as soon as they're over, don't leave them in the soil over winter - flea beetle larvae feed at the roots. This is a good time to dig over the area too.

Flea beetles aren't much of a threat in terms of devouring leaves on mature plants, but they can spread bacterial diseases from plant to plant, and are much more of a threat to young plants or seedlings. Treat any crops as soon as you notice anything next year.

Answer 3

For anyone browsing this question more recently: those are not flea beetles. They're aphids. Aphids can multiply quickly, so it's a good idea to get on them. They're not to be treated like flea beetles, which are hard to control.

Aphids can be controlled without insecticides by simply washing/brushing most of them off the plant and letting beneficial predators do the rest. Or, if you don't have a lot of beneficial predators in the yard, then a smothering treatment that works mechanically, such as insecticidal soap or horticultural oil, will work fine on them without toxicity to pollinators or other non-target organisms.