Emmalea Ernest, Extension Fruit & Vegetable Specialist; emmalea@udel.edu
Bell pepper fruit must reach adequate size, have a symmetrical shape, and have an acceptable height to diameter ratio in order to be marketable. Bell pepper fruit characteristics are influenced by variety, but also by environmental factors that occur during flower formation and early fruit development. Horticultural researchers have attempted to identify specific environmental factors that affect pepper size and shape, but some mysteries remain.
High and low nighttime temperatures are known to impact pepper fruit set, size, and shape. Both high and low nighttime temperatures result in poor pollination which can cause small and lopsided pepper fruit (Figure 1). Night temperatures that are below 64 °F reduce pollination and increase the incidence of parthenocarpic (seedless) fruit. Parthenocarpic fruit tend to be smaller and are likely to be unmarketable. Low night temperatures also cause ovary enlargement during flower development that results in short fruit that do not elongate properly (Figure 2). These short, flattened peppers are also likely to be unmarketable. Longer pepper fruit develop from flowers that form during warm nighttime (68-75°F) conditions. Excessively high nighttime temperatures (90°F) applied to peppers in experimental situations cause fruit set to cease because of damage to pollen; high temperatures do not induce parthenocarpic fruit. The nighttime high temperature threshold for damage to pepper pollen has not been established but is probably higher than the typical night temperatures experienced in Delaware.
Figure 1. Small and misshapen peppers (left) have inadequate or uneven pollination compared to marketable fruit (right).
Figure 2. Conditions during flower development affect pepper size and length. Low night temperatures can cause short, unmarketable pepper fruit.
Pepper fruit size is also influenced by photosynthate availability during fruit development. The photosynthate availability will depend on plant size and leaf area and fruit load. Plants that do not reach adequate size before flowering begins will not produce marketable size fruit (Figure 3). Plants that set many peppers at the same time will also tend to produce small fruit because of competition between fruit. To avoid small fruit size, provide adequate nutrients and irrigation early in the season to promote leaf and stem growth in pepper plants. Use of shade cloth in peppers can help to promote early season vegetative growth. Later in the season, damaged, undersize, and misshapen fruit should be removed from the plant as early as possible so that they do not compete for resources with fruit that have potential to be marketable (Figure 4). Bell pepper plants tend not to abort fruit that has survived 14 days post pollination, even after significant damage. Pepper fruit that have a short, flattened appearance early in development will not develop a marketable shape later and should be removed. Pepper fruit that have begun to ripen will not grow larger so undersize peppers that begin to change color should also be removed.
Figure 3. Small pepper plants tend to make small pepper fruit.
Figure 4. Small fruit with sunscald or other types of damage should be removed to reduce competition with potentially marketable fruit. Pepper plants will not naturally abort such fruit.