We’ve received questions at the Extension Office about squash and cucumber plants that are blooming but not setting fruit. Sometimes there are “tiny fruit that don’t grow, but just shrivel up and die.” Have you noticed this in your garden?
The most likely cause of such fruit problems on squash, muskmelons (cantaloupe), cucumbers, watermelons and other cucurbit vegetables is a lack of pollination. These plants have separate male flowers (bloom attached by a small, thin stalk) and female flowers (small fruit at base of bloom). Pollen must be moved from the male blooms to the female blooms for pollination to occur. Without pollination the tiny fruit will abort.
I should add that on some species and varieties it is not uncommon for the plant to initially produce only male blooms before starting to produce female blooms too. This may be one reason you see blooms but no fruit. Assuming there are both male and female blooms on the plant, a lack of fruit may be due to a lack of bees working the flowers to transfer pollen. The problem can be due to a lack of bees or due to inclement weather conditions which prevent the honeybees from getting out and doing their work.
If you are using insecticides on the plants or on nearby flowering plants that kill bees this can contribute to the problem. Nearby neighbors spraying their flowers can also be causing a decline in the bee population around your neighborhood. Spinosad is highly toxic to bees if sprayed on them or if they encounter recently sprayed foliage or flowers. However, once it has dried completely the danger of toxicity has been shown to be negligible in research trials. It may also be that your plants are located where the bees have just not yet discovered them. In the absence of bees you can use a very small artist’s type paintbrush to gently brush the male blooms and then the female blooms to transfer pollen manually and do the work of the bees!
Finally, if fruit do set and then start to rot away, the cause is a fungal pathogen such as choanephora rot (this disease produces fungal strands that appear as “whiskers” on infected
fruit). Such diseases are common during wet rainy periods. While there are fungicide sprays to prevent these diseases, it is usually too late when you finally notice the problem. Remove affected fruit promptly and avoid overhead irrigation to minimize such disease problems.