UTK Question of the Week: What causes blossom drop in tomatoes?
It’s heating up out there! Last week we had an article on heat-related illnesses. Be sure to stay safe out there! We’re happy to bring you the question of the week, produce safety fact of the week, news, updates and upcoming webinars and workshops that may be useful. As always, we’re here to help, so if you have questions, don’t hesitate to ask and if you can’t find a resource that you need, please let us know. Please share this newsletter with others who may be interested, and if they’d like to receive it directly, they can subscribe to the UTK Newsletter.
Annette Wszelaki, Dave Lockwood, Margarita Velandia, and Brooke Emery
What causes blossom drop in tomatoes?
By Monica Ozores-Hampton and Gene McAvoy, UFL
Blossom drop is the loss of flowers. This is usually preceded by the yellowing of the pedicel. A tomato flower has both male (stamens) and female (pistil) parts within the same flower. The yellow stamens wrap around the greenish pistil in the center of the flower. Under proper conditions, pollen from the stamens transfers to the sticky stigma or tip of the pistil. This transfer requires a jarring wind or a flick of the finger or insects such as bumble bees and other native bees.
Tomato blossoms are self fertile, and a certain amount of self pollination of tomato flowers does occur. But pollen does not move well by itself from anther to stigma, as evidenced by the really poor pollination seen in greenhouses when no pollination aid is given. But shaking by wind or mechanical means can cause the release of the pollen, which drops down (the blossoms normally hanging downward) through the stamen tube to the stigma.
The best possible motion to release this pollen is from a bee that "sonicates" Sonication is the vibration of the wing muscles without flight, causing the whole flower to vibrate, and a cloud of pollen to be released onto the bee's body and at the same time, onto the stigma.
Without pollination, which stimulates fruit set, the flower withers and dies.
Blossom drop is a condition suffered by tomatoes, peppers, snap beans, and some other fruiting vegetables where the plant blooms but fails to set fruit, the blooms die and fall off. Tomato plants lose their blossoms for several different reasons usually related to some kind of stress. The stress may be either nutritional, environmental or some combination of the two. Anything which interferes with the pollination fertilization process may result in abortion of flowers.
Potential Causes
Blossom drop can be attributed to several causes, most often related to either temperature and/or stress.
Environmental causes:
1. Temperature: In extreme temperatures, such as high daytime temperatures (above 85 °F/29 °C), high nighttime temperatures (above 70 °F/21 °C), or low nighttime temperatures (Below 55 °F/13 °C) tomato plants will drop their flowers. Tomatoes grow best if daytime temperatures range between 70 °F /21 °C and 85 °F /29°C. While tomato plants can tolerate more extreme temperatures for short periods, several days or nights with temps outside the ideal range will cause the plant to abort fruit set and focus on survival (Mills, 1988). Temperatures over 104̊ °F /40 °C for only four hours can cause the flowers to abort. If the night temps fall below 55 °F or rise above 75 °F or if the day temps are above 85 °F, the pollen becomes tacky and nonviable. Pollination cannot occur. If the bloom isn't pollinated, the bloom dies and falls off. Chemical growth regulators can sometimes help overcome low temperature effects, but the resulting fruit is usually seedless and of poor quality.
2. Humidity: The ideal humidity range is between 40-70%. If humidity is either too high or too low, it interferes with the release of pollen and with pollen’s ability to stick to the stigma, so pollination will not occur. If humidity is too low, hose the foliage during the day. This will both cool the plant and raise the humidity. This is not recommended in areas with high humidity or when fungus diseases are present.
Read more about other potential causes of blossom drop.
Do you have a fruit or vegetable question? Send it to annettew@utk.edu.