Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu
The high temperatures we had last week, with daytime highs 95°F and above and nighttime lows only getting down to 80°F in most of the mid-Atlantic for several days in a row may cause blossom drop and fruit abortion in tomatoes. Normally in tomato fields pollination is achieved just by the action of the wind. Pollen is released from the tomato flower and falls downward onto the stigma. Without pollination flowers die and drop. This condition can affect tomatoes, peppers, snap beans, and other fruiting vegetables, but is especially prominent in tomatoes. In tomatoes, blossom drop is usually preceded by the yellowing of the pedicle (Fig. 1). Tomato flowers must be pollinated within 50 hours or they will abort and drop off. This is about the time it takes for the pollen to germinate and move up the style to fertilize the ovary. Tomato plants can tolerate extreme temperatures for short periods, but several days or nights with temperatures above 90°F (daytime) or 72°F (nighttime) will cause the plant to abort flowers and fruit (Fig. 2). At these temperatures the pollen can become sticky and nonviable, preventing pollination from occurring and causing the blossom to dry and drop. The relative humidity also plays a role in pollination, high levels (>80% RH) (which we had last week) during pollen shed will cause the pollen not to be released properly resulting in poor or incomplete pollination.
Figure 1. Several tomato pedicels are turning yellow (arrows)
Figure 2. Aborted flowers and fruit (arrows) on tomato plant caused by high temperatures