Poor Pollination
Plant disorder
Description
Poor pollination occurs when too little viable pollen reaches a flower’s receptive stigma, or when pollen fails to fertilize enough ovules. Flowers may fall without setting fruit; developing fruit may be small, misshapen, or shed early. In corn, incomplete pollination can leave gaps where kernels should have formed. The disorder is especially noticeable in crops that depend on insects, such as squash, apples, and many berries, but wind-pollinated crops can also be affected. Common causes include a shortage of pollinators, rainy or windy weather during bloom, temperatures that reduce pollen viability, and a lack of a compatible flowering variety. Poor pollination is not an infectious disease. Its effects vary by plant: a flower may produce no fruit at all, while another may form fruit with only part of its normal shape. Healthy-looking foliage can remain unchanged.
Symptoms
- Flowers or buds dropping
- Distorted new growth
How to Identify
Look for flowers that wither without setting fruit, or for fruit that begins growing but stays small or develops an uneven shape. On squash, an unfertilized young fruit may yellow and shrivel soon after the flower closes; on corn, ears may have scattered missing kernels. Check whether male and female flowers were open at the same time, whether a required pollinating variety is nearby, and whether bees visited during bloom. If fruit has soft, decaying tissue, investigate rot instead. If flowers and young fruit drop during extreme heat or drought, those stresses may be responsible even when pollen is available.
Prevention
Grow plants in suitable light and keep soil moisture reasonably consistent so they can support flowers and fruit. Where a crop requires cross-pollination, plant compatible varieties that bloom together and within pollinating distance. Grow enough plants of crops with separate male and female flowers, such as squash, to improve the chance that both are open together. Provide flowering plants and nesting habitat for pollinators throughout the season. Avoid spraying insecticides during bloom; if a treatment is essential, follow the label and choose a time when pollinators are not foraging. Protect blossoms from frost where practical. In a greenhouse, provide access for pollinators or plan to pollinate by hand. Weather cannot be controlled, but repeated plantings may avoid a brief spell of unfavorable conditions.
Treatment
First, check for open, receptive flowers and give visiting pollinators access; uncover plants during bloom if it is safe to do so. Hand-pollinate when natural visits are scarce. For squash, transfer fresh pollen from a newly opened male flower to the stigma of a newly opened female flower, preferably in the morning. For tomatoes grown under cover, gently tap flower clusters or use a small vibrating tool to release pollen. Use pollen from a compatible plant where cross-pollination is required. Keep plants adequately watered during flowering, and wait for more favorable weather if heat, cold, or rain is interfering. Avoid insecticide sprays that could harm pollinators. A flower or fruit that has already aborted cannot be restored; remove decaying fruit if necessary and focus on the next flowers. If poor fruit set continues, check variety compatibility and whether flowers are blooming at the same time.
Plants Affected
Acorn Squash, Bottle Gourd, Butternut Squash, Chinese Chestnut, Corn, European Chestnut, Kabocha Squash, Pattypan Squash, Pecan, Scarlet Runner Bean, Spaghetti Squash, Zucchini
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