This week I have received a phone call, an email and a text question on the same subject: squash plants that are not setting fruit. On a case-by-case basis, here are the three mysteries and their solutions.
Squash Flowering but not Fruiting
Debby has grown squash many times before, but never in containers. This year her crop consists of four zucchini plants in two big, half-barrel planters, and the plants are blooming heavily but not setting fruit. I had her take a close look at the blossoms to see if they were male, female, or a mix of the two. Male blossoms are borne on a straight green stem, while female blossoms sit atop a tiny squash. Only female blossoms set fruit.
As it turned out, Debby’s plants were doing what many older, open-pollinated squash and cucumber varieties do, which is to attract pollinators with an early flush of male blossoms, followed by a mixture of male and female blossoms. With only four plants, there is also a risk that insects alone won’t do a good job pollinating the plants, especially if the blooms open in cool or rainy weather. Debby decided to watch for bees during the morning hours, and got ready to use a small artist's paintbrush to dab pollen from the inside of male flowers on open females if few pollinators showed up for work.
Poor Squash Pollination
Marietta’s yellow crookneck squash, which she described as the kind “everyone can grow,” were setting plenty of tiny fruits, but they were shrivelling and rotting off on the ends instead of growing into little squash. She checked to make sure there were some male flowers among the females, because some hybrid varieties produce almost all female flowers. She had to dodge buzzing bees in the process, so we ruled out lack of pollinators.
Instead, it looked like two other things were going wrong. Inside a female squash flower, a large, moist corolla that produces nectar (but no pollen) sits atop a soft-fleshed ovary (the baby squash). Under very warm or damp conditions, the entire set up can fail because of the premature death of pollen grains or slow growth of pollen tubes. The situation is further aggravated by moisture-loving bacteria and fungi eager to chow down on the failing flower and shrivelling fruit.
Marietta had been doing the right thing by clipping off the sad little squash and composting them, and because her soil is sandy, she topdressed the plants with compost to take care of any micronutrient deficiencies. We are hoping for better weather and a happy ending.
Controlling Cucumber Beetles Organically
I heard from Mark twice – first to ask what to do about the yellow-and-black striped cucumber beetles that were taking over his squash, and a few days later to ask where they had gone. In the US, both striped and spotted cucumber beetles are obnoxious little pests of cucurbit crops that weaken plants and transmit diseases, and by midsummer they are active on squash, cucumbers and melons.
I am a big believer in early intervention of pest problems, so I directed Mark to make a “sticky wand” by mounting a piece of cardboard or plastic on a stick, coating it with thin glue and using it to collect at least some of his cucumber beetles, which he did. Because squash are hairy plants, you can touch small insects on the leaves with a sticky wand to pick them up, but the wand won’t stick to the leaves.
Meanwhile, Mark found more of the beetles on his cucumbers, and planned to go after them the next morning. But when he went out to wage battle, the enemy was gone. Except for a few beetles that appeared to have spent the night inside closed blossoms, they seemed to have disappeared.
Insects that are happily feeding and reproducing rarely leave their preferred host plant, but cucumber beetles are so terrified of wolf spiders that they will fly away and hide. But no place is really safe, because they are also on the menu for harvestmen (daddy longlegs) lurking in foliage, or ground beetles that forage at night. The predator-prey cycle was humming in Mark’s garden, where mulches and lush towering tomatoes provided plenty of habitat for beneficial insects. He covered his smallest, most ravaged plants with row cover to protect them from further damage, but now he has a new worry – what to do if he gets too many squash.