Of all the greens I like to grow in summer, Swiss chard is usually the one that is most trouble-free. It doesn’t get bitter or tough in the summer heat. It produces leaves for months on end, without sending up a flower stalk that triggers an end to leaf-production. The crop also, usually, attracts very few pests. However, this summer, something started eating my Swiss chard.
Damage in the Swiss chard patch
When I first noticed the damage to the Swiss chard, I figured it was caterpillars because of the kind of damage I saw on the leaves. There were big holes in the leafy parts, but the thick middle stem, or midrib, was undamaged for every leaf.
However, when I examined my patch of Swiss chard, I did not find any caterpillars, even though I found plenty of frass (caterpillar poo). I looked under the leaves, down the stems, and around the bases of the plants in my search.
University of Minnesota Extension offers several possibilities for which pests might be eating my Swiss chard, but I did not find any of the named pests. The list includes cabbage loopers, slugs (which also make holes in leaves as they eat), diamond back moths, flea beetles (which make smaller holes), and cabbage worms.
Some caterpillars are harder to find than others, so I sprayed all the chard plants with Bt for caterpillars (Thuricide, organic-approved) and figured that would stop the problem.
It didn’t. When I rechecked the patch a couple of days later, some leaves had been stripped completely down to the midribs. Caterpillars were still feasting on my plants. Since I didn’t find any caterpillars in the daytime, I changed the plan.
That night, before heading to bed, I went out to my chard patch with a flashlight and a tub that contained soapy water, prepared for a hunt.
I found caterpillars.
Caterpillars at night
That night, I found seven caterpillars on the Swiss chard, and I dropped them all into the soapy water. The caterpillars were on the Swiss chard variety ‘Perpetual spinach’, which is my favorite. The variety ‘Verde de taglio’, which has less tender leaves, also had some damage, but I did not find caterpillars on that variety.
The two groups of caterpillars most often identified as night-feeders are armyworms and cutworms.
I think of cutworms as those little lumberjacks that cut down garden seedlings in the night. It didn’t occur to me that cutworms might eat bigger leaves until I saw an article about the winter cutworm, Noctua pronuba, at AskExtension.
The winter cutworm is found all across the U.S. The AskExtension article notes that the winter cutworm can be controlled with Bt for caterpillars, which is what I use on caterpillar pests, but only when the caterpillars are small. The caterpillars I found were large enough that, if they had been winter cutworms, they would have been unaffected by the Bt/Thuricide.
However, my caterpillars do not look like winter cutworms.
A couple of nights after the big hunt, I went back out with the flashlight to hunt again, because leaves of my Swiss chard were still being eaten.
I found a couple more caterpillars, this time on both varieties of Swiss chard. To get a better look, I brought one of the little pests inside before drowning it in soapy water. I am pretty sure the caterpillar is an armyworm, possibly a yellow striped armyworm.
When the armyworms are as big as this — longer than an inch — handpicking and drowning the caterpillars may be the best organic option for stopping the damage in a small garden. As with the cutworms, larger caterpillars are not killed by the organic-approved Bt.
Worse, it sounds like (from reading multiple articles), a particular form of Bt is needed to get rid of the armyworms. My Thuricide won’t work on these pests. The special variation is in a product called XenTari BT. This is still an organic-approved Bt, but the strain of bacteria used to produce it is slightly different.
When I checked the product page for XenTari on amazon.com, it says the product is currently unavailable. I am guessing that is because armyworms are causing problems in more gardens than just mine, here in September.
Luckily, the batteries in my flashlight are still good. If the damage continues, I will just keep on hunting through the Swiss chard at night, until I’ve removed all of the pests.