May 4th, Via Facebook.
A. HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA. Sorry. Um.
We have flea beetles like crazy at the farm right now. There's not much you can do about them. Any spray that kills them also kills a ton of beneficial insects and throws your whole ecosystem out of whack. Rotating crops doesn't help because they're quite mobile, unlike a lot of pests who stick to the same area year to year and won't eat what's there if they don't like it. There are some things you can do to prevent them next year (or at least confuse them enough that they don't snack on your lettuce), but for this year you're 99% screwed (and that last 1% is just the margin of error).
The tactics you can employ for next year include: 1. planting a trap crop around the perimeter of the area so that it matures a week or two before you put out your susceptible crops, 2. starting a low-growing cover crop and then planting the lettuce through it (flea beetles arise from ground level, and if they can't find their target crop they shrug their evil little shoulders and wander off), and 3. making sure that the area you'll be growing stuff in next year is COMPLETELY devoid of vegetation over the winter (this is about a 50/50 proposition, as the jury is out on whether the little bastards winter over in the soil itself or in clumps of weeds). You can also delay planting your lettuce out until the first batch of overwintering adult beetles has emerged and figured out where they're going to do most of their feeding, but this a) only helps for a while, and b) puts you kind of late in the season for lettuce.
As for the trap cropping . . . it will help to know whether you have crucifer flea beetles or pale-striped flea beetles. If they're on your lettuce, they're probably the pale-striped. Capture a few, check them out, and let me know. See pictures above for comparison; the first is the pale-striped, the second is the crucifer. The third is just a neat graphic of their life cycle. I already know that the ideal trap crops for crucifer flea beetles are a) mustard and b) nappa cabbage. For striped, I'm not sure, but I'm working on finding out.
At the farm, we seem to have exclusively crucifer flea beetles. Unfortunately, we also have mustard and nappa cabbage . . . .
One last thing. If it makes you feel any better, the unusually warm weather we had very early this year seems to have prompted a bumper crop of the nasty little things. Here's hoping next spring is long and cold! (I can't believe I just said that)