Yard and Garden: Solving Common Problems with Summer Squash


July 7, 2016, 10:59 am | Richard Jauron, Greg Wallace

AMES, Iowa – Summer squash is a popular garden crop in Iowa, but problems can pop up that limit its success and hinder its overall growth. ISU Extension and Outreach horticulturists can help solve these issues and create a bountiful harvest. To have additional questions answered, contact the ISU Hortline at 515-294-3108 or hortline@iastate.edu.

My squash plants are blooming heavily, but aren’t producing many fruit. Why? 

Squash and other vine crops are monoecious. Monoecious plants have separate male and female flowers on the same plant. Male and female flowers are similar in appearance. However, female flowers have small, immature fruits at their base. Pollen is transferred from the male to the female flowers by bees and other pollinators. When properly pollinated and fertilized, the female flowers develop into fruit.

The first flowers to appear on squash and other vine crops are predominately male. As a result, fruit production is poor when the plants begin to flower. The squash plants should begin producing a good crop within a few weeks as the number of female flowers increases.  

Unfavorable weather and the use of insecticides also can affect fruit set on vine crops. Cool, rainy weather during bloom reduces bee activity. Fewer bees visiting the garden results in poor pollination and poor fruit set. Apply insecticides in the garden only when necessary to avoid harming bees and other pollinators. 

Summer Squash

The fruit on my summer squash begin to grow, but quickly turn brown at the blossom end and rot. Why?

The rotting of the squash fruit is likely due to blossom-end rot. Blossom-end rot is a physiological disorder that occurs on tomatoes, peppers, eggplant and summer squash. On zucchini and other summer squash, the blossom end of the fruit begins to rot and within a short time the entire fruit has rotted.

Blossom-end rot is caused by a lack of calcium in the developing fruit. In most cases, there is no need to apply calcium to the soil. Try to maintain an even moisture supply by watering once a week during dry weather. Also, do not over-fertilize plants. Uneven moisture supplies and excessive nitrogen inhibit calcium uptake. 

Why are some of the fruit on my summer squash misshapen?

Misshapen fruit may develop if pollination is inadequate. When pollination is incomplete, the fruit develops unevenly because the ovary wall enlarges more adjacent to fertilized seeds. Inadequate pollination may be due to low pollinator numbers or unfavorable weather.  

Virus infected plants also may produce small, deformed fruit. Viral diseases cannot be controlled with pesticides. If disease symptoms appear on just a few plants, remove and destroy the virus infected plants to prevent the further spread of the disease.

When should I harvest my summer squash?

Harvest zucchini and other long-fruited summer squash cultivars when the fruit are 1½ to 2 inches in diameter and 6 to 8 inches long. Scalloped types are best when 3 to 5 inches in diameter. Fruit should have soft skins (rinds) that are easy to puncture with a fingernail. Seeds should be soft and edible. Harvest plants frequently for continuous production.  

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