New Garden Pest: Beet Leafminers

This spring has brought us a few new insect problems. In addition to the usual cutworm issues in beds where things were wintered over and very minor winter moth problems, we’ve got some new bugs as well. The potato beetles have pretty well ruined one potato bed and ignored another — in the latter, the ladybugs seem to be prevailing. 

Our other insect infestation this spring is affecting our beets:

This is one example of a scorched-looking leaf. We’ve seen these in our beets, spinach, and Swiss chard this spring, and at first we assumed that the sun had burned them out on our first hot day a few weeks ago, since the issues seemed to coincide. But there were also other leafy greens in the same bed that were unaffected, and once we realized that the problem was only with plants in the same family, we figured it was either a disease or an insect issue.

A closer look makes it fairly obvious that bugs are the problem:  

I’m not sure what gardeners did before Google, because it makes diagnosing and dealing with problems so much easier. A quick search revealed that these dead leaves are caused by beet leafminers, which are small flies that lays eggs on the leaves. The larvae burrow into the leaf to feed, which is what makes those trails and eventually kills the whole leaf.  

Apparently, we need to be removing all the leaves with signs of infestation, because if they fall to the ground, the leaf miners will burrow into the soil to complete their life cycle. We can also spray with neem oil to kill the eggs before they hatch, which should help break the cycle. 

For next year, it looks like we’ll need to invest in more row cover to keep the flies from finding the beets in the first place. We’ll also have to be diligent about crop rotation with these leafy greens. We might be a little bit screwed for this year (though the chard looks fine now that the crappy leaves have been removed), but at least we know for next year how to do some preventive maintenance at planting time.