It seems the season has shifted abruptly from wet to dry. Over the past week, we’ve begun to hear reports typically associated with hot and dry conditions. At the Southwest Purdue Agricultural Center, we conduct side-by-side comparisons of different fruiting vegetables under varying irrigation treatments. This article summarizes our observations on how different fruiting vegetable crops respond to drought stress.
Tomato
Tomato plants are about 3 feet tall and are setting fruit. The harvest has not started yet. A few days ago, we noticed blossom end rot (BER) on the plants that received the least irrigation. As the stress conditions persist, more green fruits are developing this symptom. It’s likely that we won’t be able to harvest many if any, marketable fruits from the least irrigated treatment. In contrast, we have not observed any BER in the tomatoes that received irrigation three times a day.
Additionally, we noticed more foliage and slightly taller plants in the treatment, which was irrigated the most. Interestingly, during a blind evaluation, I heard comments that the least irrigated plants had more blooms. While we did not count the blooms, it’s possible that the fewer leaves on the least irrigated plants exposed them more, creating the impression of more blooms. It is also possible that the stress condition prompted the plants to produce more flowers instead of growing leaves.
Many wonder if the curling of tomato leaves is a sign of drought stress, as often seen in corn. Our observations suggest this is not the case for tomatoes. Regardless of the irrigation treatments, the tomato leaves, especially the older ones, are heavily curled. This may be a plant response to high temperatures, pruning, or other factors, and the extent of curling likely varies by cultivar. More discussion about tomato leaf curling can be found in this article.
Figure 1. The different stages of BER on green tomatoes. The symptom is likely caused by drought stress resulted calcium deficiency (Photo by Wenjing Guan).
Figure 2. The curling of tomato leaves was observed on tomatoes grown on the frequently irrigated bed (Photo by Wenjing Guan).
Pepper
Peppers are also at the fruit-setting stage. The plants that received the most irrigation (right row in Figure 3) are taller and have more leaves compared to those that received the least water (left row in Figure 3). Damaged fruit has been observed in all treatments (Figure 4), although it is more severe in the least irrigated treatment. This suggests that the damage is caused not only by a lack of water but possibly also by heat and sun exposure. It is not always possible to distinguish between blossom end rot (BER) and sunscald symptoms on peppers. To address this, we added shade cloth to the pepper plants, hoping to reduce the number of unmarketable fruits in the adequately irrigated treatments.
Figure 3. The left row of peppers received the least irrigation, and the right row of peppers received the most irrigation (Photo by Wenjing Guan).
Figure 4. Unmarketable pepper fruit from plants that received ample water supply (left) and deficient water supply (right) (Photo by Wenjing Guan).
Cucumber
In this comparison, we selected a Belt-Alpha type cucumber and trained the plant using a single-leader trellising system. Harvesting began on June 3. The cumulative yields for the three irrigation treatments are shown in Figure 5. Initially, yield was higher on the least irrigated treatment. As the drought stress persisted, plant growth and yield declined in the least irrigated treatment (Figure 6). After around mid-June, the total yields of adequately irrigated plants have surpassed those of the least irrigated plants. All harvested cucumbers were marketable, with no unmarketable fruit observed due to drought stress.
Figure 5. Cumulative yields of cucumber plants receiving different amounts of irrigation.
Figure 6. Cucumber plants received different irrigation treatments (Photo by Wenjing Guan).
It is interesting to note that we have not observed strong wilting symptoms in cucumbers that received the least irrigation. In our previous experience, cucumbers would wilt within one or two days without watering during the middle of the season. In the current case, the least irrigated treatment has gone without irrigation for a few weeks. This greater drought tolerance is likely associated with the plants’ root structures. Since they were subjected to a deficient water supply from the beginning of the season, they likely developed stronger roots to access stored water in the soil. Conversely, plants that receive ample water supply early in the season may be more vulnerable to water stress.