By this evening, the plants were looking so bedraggled that I started to fear we'd lose the whole crop (and with Zucchini-Sneaking Day still nearly a month away!). So I Googled the problem and found a page from the University of Minnesota Extension that listed several potential causes, including squash bugs and squash vine borers. The bugs aren't so bad—you can pick them off by hand and they're only really dangerous to young seedlings—but the borers are particularly nasty. As the name would suggest, the adults lay their eggs on the squash vine, and the larva burrows in and starts feeding on the stem, keeping it from getting water and eventually killing it. And while you can't spot the larvae themselves from the outside, a key sign of their presence is "holes near the base of the plant filled with moist greenish or orange sawdust-like material." Yup—we got that.
The UMN article wasn't very encouraging on the subject of dealing with an infestation, saying, "Most management options are limited to control the hatching larvae before they enter the plant." But it was obviously too late for that, and I wasn't prepared to give up all hope of salvaging the plants. So I dug a little further and found this three-year-old blog entry in which a gardener explains how she saved her own zucchini plant with a little timely surgery:
I made about a six inch slit with a sharp knife. I couldn’t see a bug so I scraped out that entire section of the stem and trimmed off the dead leaves. I buried the cut section of stem under a mound of compost.This initially "sent the plant into shock and it stopped producing flowers," but after a week it perked up, and a week after that it started producing both flowers and fruits again. So I figured it was worth at least attempting the procedure with ours.
Gloved and armed with a paring knife, I went out and started cutting into the stems where the orange dust was showing. On the smaller plant, I couldn't actually find the borer, so I just dug out as much of the goop as I could, covered up the stems with dirt (having no compost ready to hand), and hoped for the best. On the other plant, I dug in with my knife and eventually extracted first one, then two fat white larvae like this. And despite my gentle, nature-loving disposition, I took considerable satisfaction in squishing their little guts out. Then I covered up the stems and crossed my fingers. I know it's likely the plants still won't survive; the blogger said "This is the first time I’ve ever been able to save a plant," and she attributed her success to the fact that she performed her surgery at the first sign of wilting, before the stem itself was affected. So it's entirely possible that I was too late with my surgery, and the plants won't make it, but since there was really no chance they'd survive otherwise, I guess I had nothing to lose. Now we watch and wait.
And if it works, you can call me Doctor Zuke.