A the Plant-a-Row-for-the-Hungry garden, we noticed, a few weeks back, something odd about our summer squash plants. The stems had split. In the lower right part of this first picture, the split shows as a wide place:
Here, in this close-up, the split is easier to see:
If this were caused by squash vine borers, the split areas would look a lot more "chewed" and frass (caterpillar poop) would be all over the place. The Squash Vine Borer Damage page from the University of Nebraska's entomology department shows the damage from squash vine borer activity very clearly (sorry I don't have a photo of my own to post. Maybe later this summer...).
Also, when we first noticed the damage, it was VERY early in the season for squash vine borers. In another week or two, I won't be surprised to hear that evidence of the borers has been seen (except that we are spraying the plants with Bt this year, to head that off some), but early May is just too soon.
When I went online to sort out the problem, I didn't find any university or research related sites that discussed the split stems in any context other than as damage from squash vine borers, but I found some discussion sites, populated by gardeners and farmers, that did.
Several mentioned that split stems can be a result of mechanical damage, and is common when young plants with long stems twist and turn in the wind. Others mentioned that such damage is often seen when the plants experience temperature extremes.
The squash at the PAR garden were set out as transplants with fairly elongated stems, so the first category of damage is a possibility. However, this spring and early summer, the daily high temperatures have been all up and down the thermometer, so the second category is another possibility.
Since my zucchini plants at home all experienced the same temperature extremes without also having split stems, I am thinking that the wind-action on spindly stems was a larger factor.
The good news is that the plants seem to be producing well in spite of the weirdness. The plants are blooming abundantly and don't seem to be at all stressed by the heat. Yesterday when we met for our usual workday, the first harvest from those plants totaled 38 pounds!