Growing squash – problems and solutions

Squash plants love the hot summer sun, and Kansas has plenty of it! Any vegetable gardener in the state who has been growing for very long will likely have planted some variety of squash. There are a few issues that can pop up when growing squash, but overall, it is usually pretty easy to grow.

In the Demo garden, we are growing both summer squash and winter squash. Contrary to what the names imply, both types of squash are grown during the heat of summer; one main difference is that summer squash is grown for its young or immature fruit (think zucchini), while winter squash is grown for its fully mature fruit, so it takes longer to be ready (think butternut squash or pumpkins).

Summer squash grows in a bushy shape and is generally ready to harvest by mid-summer. When harvested at small sizes, they have a soft, thin skin and unsubstantial seeds and can be eaten raw. If left on the plant to grow very large, though, they become tough and too bitter to eat raw. The most popular types of summer squash are zucchini and yellow squash, but other types include pattypan and tromboncino.

We have two varieties of summer squash in the demo garden, and both are varieties of zucchini: ‘49er’ and ‘Astia,’ which both are beginning to yield a harvest.

‘49er’ is a yellow zucchini which has about 50 days to maturity (DTM), and ‘Astia’ is a dark green zucchini with 48 DTM. Both are best harvested at about 5-6 inches long. (Yellow squash and yellow varieties of zucchini are similar, but different; zucchini maintains a relatively consistent diameter, whereas yellow squash is broader at one end and tapers toward the other, and often has a slightly thicker skin than zucchini.)

’49er’ zucchini
‘Astia’ zucchini

Winter squash generally has a vining nature and needs either lots of space to sprawl out or a trellis to grow vertically when space is at a premium. Because it is harvested when fully mature, it has a tougher skin than summer squash that is not usually eaten. Winter squash is usually ready to harvest late summer or early fall. One of the benefits of growing winter squash is that it can store well, even through the winter months. The winter squash in the demo garden (‘Waltham’ butternut and ‘Autumn Frost’ acorn squash varieties) are setting fruit but won’t be ready to harvest for several more weeks. We’ll keep you posted!

Winter squash has reached the top of the trellis!
‘Waltham’ butternut setting fruit

A couple of the biggest challenges with growing squash are the squash vine borer and the squash bug.  Both of these insects can wreak significant havoc and are taking their toll now in the Demo garden.

The classic symptom of squash vine borer is a wilted plant when the plant has been watered well and shouldn’t be drooping. Upon closer inspection, you may be able to see that the stem has small holes or is chewed up close to the ground with larvae frass at the base. At this point, it is important to remove the larvae by either disposing of the plant completely, or, if you’re feeling surgical, slitting the vine with a sharp knife until you find the larvae and then removing it. The slit vine can be placed back in the soil and kept moist in the hopes that it will send off new roots, but some plants may have been damaged beyond repair and won’t recover from the “surgery.” If the larvae are not removed and are allowed to complete their life cycles in your garden (in which they eat their way out of the stem, burrow 1-2 inches into the soil, and wait in a cocoon until the next season), the problem will likely return next year. Once you have squash vine borers, there is not a whole lot you can do; to learn about treatment options and cultural controls, see this helpful publication.

Vine borer holes in plant stem
Vine borer larvae found in a plant stem

Another pest we are facing in the Demo garden is squash bugs. Adults look similar to stink bugs and can be found on many species of the cucurbit family, but squash is their favorite. Adults and nymphs (which are lighter grey with black legs) cause damage by sucking out juices from plant leaves, resulting in yellowing, wilting, and death of the plant when populations are large. Squash bug eggs can be found by scouting on the under sides of leaves – they are glossy brown and laid in groups in between leaf veins. These eggs can be scraped off and disposed of to help control, but here in the Demo garden, the problem has passed the egg stage, and we have begun chemical control to limit the damage. Squash bugs are best controlled at the nymph stage, since adults have a hard shell that protects them from pesticides. We have applied one round of spinosad by spraying it on the vine and branches where the nymphs are congregating. We won’t be able to harvest zucchini for at least three days after spraying, and depending on what the squash bug population looks like after the application, we may spray again in about a week. We use chemicals sparingly in the Demo garden, which are safe when used appropriately. As always… when using chemical pesticides, make sure read and follow the label! To learn more about squash bugs, click here.

Squash bug adult and eggs
Squash bug nymphs

One last issue we had with the zucchini earlier this year was small fruit (around 3 inches) that shriveled up or rotted from the blossom end of the fruit before coming to harvestable size. This symptom can be due to a couple of different culprits, but is ultimately related to an issue with pollination.

Sometimes high temperatures following a mild or cool spell can limit the number of pollinators that are active in the garden; sometimes over-fertilization (high nitrogen levels) in the soil can cause the plant to produce too many male flowers; and sometimes plants don’t produce enough male and female flowers at the same time to ensure enough pollination (this issue usually resolves itself as the season progresses.)

We stepped in to lend our zucchini plants a pollinating hand, and you can too if you see this issue in your garden – it is as simple as taking the pollen from the male flowers and transferring it to the female flowers. First, identify which flowers are female and which are male; female flowers often have a swelling behind the flower head where the fruit is barely beginning to form, whereas male flowers have a straight stem behind the flower head. Another, perhaps more reliable way to tell is to look inside the flower: the female has a stigma which is larger and slightly round or bulbous, and the male has a single, straight appendage – the anther – inside the flower.

Hand-pollinating can easily be done by using a small artist-sized paint brush to transfer pollen from the male to the female flowers; lightly touch the tip of the brush to the anther on a male flower and dab the pollen that the brush picked up onto the stigma of a female flower.

With a couple hand-pollinating sessions, a relative evening-out of temperature, and an uptick in pollinators in the garden, our zucchini are now producing harvestable fruit. Now it’s a matter of fending off the squash bugs so that we can keep harvesting this delicious summer garden staple!

Resources for further reading:

Squash bugs

Squash vine borers

Pollination problems

By: Maureen Wilbeck, Master Gardener

Posted on July 28, 2020, in Insects Abound!, Plant Problems & Diseases and tagged , , , , , , . Bookmark the permalink. 1 Comment.

  1. Excellent post, clear photos, and the referral article was very helpful. Thanks!

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