Under waterlogging conditions, oxygen depletion in the soil injures roots, limiting their ability to uptake nutrients and water. In response, plants close their stomata to prevent water loss, leading to a subsequent reduction in photosynthesis. Common symptoms include wilting, stunted growth, and yellowing leaves. If the stress persists for an extended period, plants may eventually die. The severity of damage varies depending on plant types, growth stages, root structures, soil characteristics, water amount, and duration of the stress condition.
When flooding occurs in a field, the top priority is to minimize the duration plants are exposed to stress by removing excess water as quickly as possible. After the water is removed or dried out, the recovery of the injured root system can take days or even weeks.
The loss of chlorophyll content, resulting in yellowing leaves, is attributed to nitrogen deficiency due to reduced root activity and photosynthesis. Additionally, flooding significantly decreases nitrogen levels in the soil. Applying nitrogen fertilizers as a foliar spray can aid plant recovery after flooding. Once the root system is reestablished, additional nitrogen application to the soil may be needed, depending on the plant growth stages. Given the potential damage to the root system during flooding, additional attention must be paid to watering. Until the root system recovers, irrigation should be frequent but in small amounts to avoid the recurrence of waterlogging.
In tomato plants with setting fruit, excessive water may cause fruit splitting, rendering the fruit unmarketable. Timely removal of unmarketable fruit from the plants can reduce plant burden and aid in recovery.
Injured root systems are susceptible to many soil pathogens, such as Pythium and some Fusarium species. Plants may recover from these pathogens if the damage is moderate and new roots start to grow quickly upon improved environmental conditions. Yellowing leaves are also more susceptible to foliar pathogens, increasing the risk of foliar diseases. When possible, timely removal of senescent leaves can reduce disease pressure to some extent.
The most severe disease challenge associated with excessive water is disease caused by Phytophthora capsici, which causes significant economic losses in pepper and cucurbit crops. Water assists the pathogen in completing its life cycle and spreading over large areas. When Phytophthora capsici are present, fungicide application is essential in suppressing the disease after heavy rains. For more information about the pathogen and fungicide options, please refer to “Phytophthora Blight of Cucurbits” and the “Midwest Vegetable Guide“