Heat stress (blossom drop)
Not an infection: hot days and warm nights damage pollen and flowers, so flowers drop before setting fruit
| Type | Not an infection |
|---|---|
| Cause | Not an infection: hot days and warm nights damage pollen and flowers, so flowers drop before setting fruit |
| When | Midsummer heat waves. |
About
In a heat wave, tomatoes, peppers and beans keep flowering but the flowers fall off without making fruit. Plants usually start setting fruit again once the weather cools.
Also called heat stress, heat damage, heat injury, blossom drop, flower drop, poor fruit set
How to recognize it
Symptoms
Flowers fall off without setting fruit, and small young fruit may drop too. Bean flowers turn brown and pods stay small or empty. Leaves may curl or cup, edges dry, plants wilt in the afternoon, and many crops take a midsummer break from fruiting, then pick up again in late summer and fall.
Often confused with
Cool nights, drought, too much nitrogen and pests can also cause blossom drop. Poor pollination in squash and cucumbers (see Poor pollination) is a different problem: there, small fruit forms and then shrivels.
Worse when
For tomatoes, days above about 85°F with nights above about 72°F (nights alone above 72°F can do it); for peppers, nights above 75°F or days above 95°F; for beans, temperatures above 85°F. Drought, hot dry wind and heavy nitrogen make it worse.
How it spreads
It does not spread.
When
Midsummer heat waves.
What to do, gentlest first
This is not an infection, so sprays for diseases won't help. Fix the cause below.
Choose heat-set varieties Prevent
Alabama Extension names heat-set tomatoes such as 'Solar Fire', 'Bella Rosa', 'Phoenix', 'Red Bounty' and 'Tribute'. Plant heat-sensitive heirlooms soon after the last spring frost so they set fruit before summer heat.
Heirloom tomatoes are more sensitive to heat than most hybrids.
Steady water, mulch, easy on nitrogen Prevent
Give tomatoes about 1 to 1.5 inches of water a week, mulch to keep the soil cool, and fertilize by a soil test.
Too much nitrogen or fertilizer salt can cause blossom drop on its own.
Wait it out By hand
Keep plants watered and healthy and keep picking ripe fruit; flowering and fruit set usually come back when temperatures ease.
Afternoon shade Barrier
Plant peppers and tomatoes where they get some late-afternoon shade, or put up shade cloth during heat waves.
Plants still need at least 6 hours of sun a day.
Plants it affects
Sources
Planting dates and advice are general guidance; check with your local Cooperative Extension office for your area.