My Baby Butternut Squash Are Turning Yellow and Falling Off the Vine

Fruit Set

• Each morning, squash plants faithfully produce new, large, orange flowers that close by evening. Male and female flowers bloom on the same plant, with male flowers borne on long stalks held away from the plant and female flowers held close to the vine with what looks like a miniature version of a squash fruit, or a baby squash fruit, at their base. Each miniature squash swells after pollination, but at least one male flower and one female flower need to be open on the same day in order for pollination to occur. Squash plants commonly produce many male flowers before female flowers appear.

Fruit Drop

• The most common cause of baby squash fruits falling from the vine is pollination failure. If an insect does not carry pollen from a male flower to a female flower, then the attached baby squash fruit turns yellow and falls from the vine within several days. That process is normal, and it is no indication of an ailment as long as the rest of the plant is in good health. One tactic to improve fruit set in your butternut squash plants is to encourage more pollinators such as bees and hover flies to visit the garden by planting a variety of other blooming plants nearby and by avoiding the use of broad-spectrum pesticides.

Hand-Pollination

• If bees are a rarity in the garden and butternut squash plants just don’t seem to produce even when female flowers are present, then try pollinating the squash plants by hand. Use a small, soft paintbrush with a narrow tip to collect pollen from a male flower, and transfer that pollen to the interior of a female flower on the same plant, swishing the brush around the interior thoroughly but gently to coat the stamen with pollen completely. Hand-pollination must be done in early morning from newly opened flowers because the quality of the pollen degrades steadily throughout the day.

Other Problems

• Disease and stress can cause the fruits to fall from butternut squash plants even after pollination. A common squash disease is powdery mildew, which is caused by high humidity and consistent watering from an overhead sprinkler. Another common disease is blossom-end rot, which results from a calcium deficiency; it causes young fruits to blacken at the flower end and sometimes fall from the vine prematurely. If a soil test indicates a low calcium level, apply 1 to 2 pounds of gypsum per 100 square feet of soil, working it into the top 6 to 8 inches of soil at least three months before the next planting. Prevent moisture stress to butternut squash plants by watering their soil deeply during hot weather, providing 1 to 2 inches of water per week.