3 Common Squash Problems (and How to Solve Them)

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Zucchini harvest

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.

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Male (top) and female (bottom) squash flowers

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 shriveling 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.

Squash flower corolla

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 shriveling 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.

Cucumber beetle damage

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.

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Comments

 
"You didn't address vine borers, which have kept me from even attempting zucchini this year. Any ideas? I tried covering them each afternoon but they still got in somehow. "
Bernice on Friday 15 July 2016
"What I've been told is there is not much you can do about the squash vine borers (svb). They are very difficult to control. So, plant rotation is really important, but also successive plantings of squash so that you will get some squash before the borers hit. I've also read that the svb have cycles, with periods of inactivity, and if you can learn to plant at the right time your vines will be either too small or too mature for the grubs to eat into. I'm trying succession planting this year, but because we were out of town for an extended time I just put in my first seeds. Where I live I can put in two more plantings two weeks apart. I'm hoping to get at least a few squash this year as we love them, but usually only get one or two off each plant before they die."
Sadaajit on Friday 15 July 2016
"LOADED with cucumber beetles and squash bugs. I'll try the sticky method...I assume duct tape rolled over my hand will work? I got some Organic spray, organic certified and everything says kills on contact. Ha. They swim in a pool of it as it relaxing then fly away. We also use a mix of Neem and Dr Broners Peppermint Soap as fungus is also a problem. If there is an issue, you will find it in our garden :) We live in Amesbury, Massachusetts. "
Carolyn on Friday 15 July 2016
"I have been able to prevent vine borers on summer squash in my garden by covering the squash hill with a dome of agricultural row cover fabric as soon as it is planted. Using the wire hoops you can purchase with the row cover ( brand names, Agribon and Remay) I shaped the dome and covered it with the fabric, tucking the edges into the soil to exclude the adult moth that lays eggs on the squash plant stem. I left the cover on as long as possible - until I saw female blossoms that would require pollinators. Doing this I apparently have been able to protect the young plants until after the egg-laying period. So far, so good."
Christie on Friday 19 August 2016
"I heard that if you have the squash bugs, the only way to get rid of them is to get rid of all the dirt and replace it. Is this correct?"
Alvera on Sunday 21 August 2016
"last year I grew yellow squash and zuccinni it first went well, had some fruit and then the leaves got spotty turned grey and the plants died what happened. I also had acorn squash which did weoll "
peter oudshoorn on Saturday 25 February 2017
"Why does my summer squash have green on the fruit? I will have nice yellow squash with green dots of spots. "
Kimberly on Wednesday 27 September 2017

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