July
2005
By
B. Rosie Lerner
Extension Consumer Horticulturist
Purdue University
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Squash Blossom Drop
A common complaint among vegetable gardeners is that their squash plants
have a lot of flowers, but many of them just fall off without producing
any fruit. This same observation can be made of cucumbers, melons, pumpkins
and gourds, all of which are collectively known as "vine" crops
to home gardeners. These plants are all members of the Cucurbitaceae family
and are also commonly referred to as "cucurbits."
All of these vine crops produce separate male and female flowers, but
usually there are both types on the same plant. In order for a fruit to
be produced, pollen must be successfully transferred from the male flower
to the female flower. In the garden, pollen transfer is conducted primarily
by bees. If pollen does not successfully unite with the egg cells within
the female flowers, then no fruit will be produced and the female flowers
will abort.
It is easy to tell the difference between female and male flowers in this
group of plants. Female flowers look as if they have a miniature fruit
(squash, cucumber, gourd, etc.) just below where the petals are attached.
Male flowers simply have a slender stalk below the petals.
If the male flowers are the ones falling off, this is normal! Often, the
very first flush of flowers early in the growing season will only be males,
and, of course, these male flowers are expected to fall off after pollen
is shed. The next flush of flowers should include both male and female
flowers.
However, if female flowers are the ones dropping, then it is safe to conclude
that some factor is preventing successful pollination. The most common
culprits include excessively hot or cold temperatures and lack of bee
activity due to weather, low population, etc. Some commonly used insecticides,
including carbaryl (Sevin), are highly toxic to bees; so if you must apply
such products, try to time your sprays for periods when the bees are not
active.
7-21-05
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