Our thoughts are with the growers and communities affected by the recent flooding events caused by significant rainfall across Northern Niagara. These severe weather events have resulted in flooding of orchards, vineyards, nurseries, farm buildings, homes, and roads, creating substantial challenges for the agriculture sector. Waterlogged soils occur when the soil remains fully saturated for an extended period, reducing the availability of oxygen to plants. As oxygen levels decline, root function is decreased, reducing the plant’s ability to take up water and nutrients and increasing the risk of stress, disease and overall decline.

Click read more below to learn about:

• Factors affecting the impact of flooding on crops
• How does intense rainfall and prolonged waterlogging affect plants, soil, and agricultural operations?
• What are symptoms of flood injury to plants?
• What should I do if my farm is flooded?
• Conclusions

Factors affecting the impact of flooding on crops

The full impact of waterlogged soil is often not immediately apparent. Symptoms may develop days, weeks or even months after the flooding event. Ongoing monitoring is essential to assess crop health and identify issues.

The impact of flooding or waterlogging (saturated soils) is influenced by several factors:

• Duration of Waterlogging

The length of time soils remain saturated is one of the most important factors affecting crop survival. When soils remain waterlogged for extended periods (greater than 48 hours), oxygen levels decline rapidly and roots can begin to die from oxygen deprivation. Severe root injury can result in reduced vigour, increased susceptibility to disease, and in extreme cases, root and potentially plant death. The recent series of extreme rainfall events in Northern Niagara has resulted in repeated flooding and prolonged periods of saturated soils at some locations, increasing the potential for root injury.

Soil type influences drainage. Sandy soils typically drain more rapidly, while heavier clay soils may remain saturated for longer periods, increasing the risk of plant stress.

• Crop Sensitivity

Different plants will vary in their tolerance to saturated soils. Some trees, including species in the genus Acer, Carya, Platanus, Quercus and Salix, are more tolerant to wet soils than others. While listed as ‘more tolerant’ of wet soils, standing water for longer than 48 hours can still be detrimental for any tree.

• Age of the plant

Young trees are generally more vulnerable to flooding injury than mature plants because they have smaller, less developed root systems.

• Timing of when the event occurred

Flooding that occurs when the trees are dormant has less impact than during the growing season, as respiration rates are lower in the roots and less oxygen is required.

How does intense rainfall and prolonged waterlogging affect plants, soil, and agricultural operations?

Flooding and saturated soils can have immediate and long-term effects on plant health, soil health and farming operations.

Flooding Impacts on Plants

• Excess soil moisture excludes oxygen from the soil, reducing soil respiration, water uptake, and photosynthesis.  
• Roots are greatly affected by these conditions. Woody roots are more tolerant than non-woody roots to flooding, whereas important non-woody feeder roots are particularly sensitive and require more oxygen. These smaller roots are frequently the first ones damaged by water-logging and can stop growing, become damaged and eventually begin to die, impacting the entire plant.
• The plant’s ability to uptake nutrients (nitrogen, phosphorous and calcium, potassium, magnesium and calcium) is inhibited, impacting plant growth.
• Extended flooding can result in the accumulation of toxic compounds within plant tissues, leading to root death, premature leaf senescence, and reduced vigour  
• Heavy rainfall can leach nitrogen out of the root zone, making it unavailable to the plants.
• Prolonged periods of high humidity and leaf wetness may favour fungal diseases and make it difficult to effectively time fungicide applications.
• With moisture comes increased risk of soil-borne diseases such as Phytophthora root rot.
• Increased risk of insect damage. Some tree species can be more prone to insect attack after stressful events, especially by wood-boring beetle pests. Monitor for wood-boring pests such as: Pine bark beetles (Ips spp.), Twolined chestnut borers (Agrilus bilineatus) on oak, Bronze birch borer (Agrilus anxious), and Hickory bark beetle (Scolytus quadrispinosus) that often attack stressed trees.

Effects on Soil

• Excessive rainfall can cause soil erosion, particularly on sloped sites. This moves the nutrient-rich topsoil to downslope positions, affecting crop productivity and negatively impacting soil health.  
• Waterlogged soils are structurally unstable and unfit for tractors; compaction will occur if equipment is driven on waterlogged soils. Prematurely taking equipment onto farms with saturated soils increases the risk of poor traction and getting equipment stuck, creating an inconvenience with farm activities that involve equipment. 
• Intense rainfall and subsequent ponding can break apart soil aggregates into fine particles which create a crust layer on the top of the soil that “seals” and prevents oxygen and water from penetrating.
• Waterlogged soils lack oxygen needed for beneficial soil organisms like microbes and earthworms. Waterlogged soils have reduced number and diversity of microorganisms that normally live in the soil. Waterlogging also results in a shift to anaerobic microbes that can cause nitrogen losses through greenhouse gases emissions (nitrous oxide).

What are symptoms of flood injury to plants?

Symptoms of excess water depend upon the plant and are highly variable. Although some symptoms of waterlogging appear relatively quickly, symptoms of root damage may occur weeks or months after the actual flooding.  Symptoms of waterlogging stress to plants include:

• Changes to leaves, which include epinasty or downward rolling of leaves, chlorosis/yellowing of the foliage, edema or premature leaf drop.
• Reduced or stunted growth (this season and possibly next) and twig dieback due to lack of nutrient uptake
• Root death, and in extreme cases, whole plant death.
• Increased mortality from drought stress. When feeder roots are missing or damaged, they are unable to provide water to the top of the plant and a water deficit develops. Symptoms of water-logging may not develop in a woody ornamental until water demands on the root system increase, typically during the hot summer months and can appear as a sudden collapse of the tree.
• Symptoms of root rot may also show as dark and mushy areas or cankers near the soil line, reduced tree growth, and dropping foliage.
• Increased susceptibility to cold injury or other stresses. Plants may slowly decline over one or more years.

What should I do if my farm is flooded?

Short Term

Contact your crop insurance adjuster to make them aware of the flooding. Document the areas that have been affected by the flooding and take photos to document symptoms.

Drain or pump water from the field within 48 hours, if possible. Over time the water will be removed by transpiration by plants and evaporation.

Avoid driving in areas that are wet! Should be common knowledge, but sometimes we need reminders. Poor drainage is exacerbated by wheel ruts created by tractors and equipment. Consider options to deal with compaction where it is an issue.

Due to the potential risk of nutrient leaching due to flooding. It will be essential to conduct soil and petiole/leaf analysis in flooded areas this season and next to tailor fertiliser applications to the plant’s needs. If you observe soil crusting on the surface, a short-term relief measure would be a single pass of light, shallow tillage (e.g. rotary hoe) only once the soil is no longer wet and is fit for tractors and equipment. Till cautiously to avoid further degrading soil structure.

Monitor for the presence of diseases, cankers, or other pest issues and apply a disease management program accordingly.

Monitor plants closely for signs of drought stress during periods of elevated temperatures and dry soil conditions, as root damage can reduce water uptake and increase susceptibility to drought stress in the future.

Identify areas that remain waterlogged for long periods and determine remedial action in the future (i.e. connect drains and drains to carry drainage water away from the area and on a suitable grade).

Long term

Monitor long-term impact on the crops and be aware of increased risk of cold injury or other abiotic stresses on damaged crops. Conduct soil and tissue sampling next year to determine crop needs.

Examine areas that had issues with flooding and consider whether upgrading drainage infrastructure would assist with reducing the impact of future events.

Consider implementing soil Best Management Practices (BMPs) that increase organic matter and rebuild soil structure.  Cover crops and organic amendments (e.g. compost) can assist in replacing organic matter that may have been lost through soil erosion as well as improve soil aggregation, water infiltration, and aeration.

Conclusions

Several factors impact the extent of injury caused by a flood event, including the duration of the flooding event, soil type, organic matter in soil, age of plant, and plant type. When a flood occurs, remove the water from fields as quickly as possible by pumping it off. Avoid driving on wet soils to prevent compaction. Monitor crops to assess the long-term impact of flooding.

Some Additional Resources

How to manage flood damage to trees | UMN Extension

WEATHER-ASSOCIATED PROBLEMS OF ORNAMENTAL TREES AND SHRUBS

This article was originally written by Kathryn Carter, Stephanie Vickers and Wendy McFadden-Smith, (OMAFA) and adapted for nurseries by Cassie Russell