The Effects of Severe Weather on Horticulture Crops

  Hort Snacks - July 2018
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 Flooding / Excess Water | Impact of Flooding on Potatoes | Impact of Flooding on Carrots | Response / Solutions to Excess Water | Hail | Impact of Hail on Potatoes | Impact of Hail on Various Crops | Response / Solutions to Hail Damage | Heavy Rain | Response / Solutions to Heavy Rain

Flooding / Excess Water

Flooding or excess water damage can be caused by short to medium term, intense introductions of water, as a result of poor soil drainage causing soil saturation and pooling, from over-application of water through irrigation or through heavy rains or runoff from water bodies.

Impact on Soil
Excess water impacts both the plants and the soil. During and after excess water situations, soil quality and structure will be reduced, with an increase in compaction, clinging soil and the number of clods. Nutrients will be leached out of the soil profile, potentially resulting in nutrient deficiencies. Soils (and plants growing within them) may become contaminated with pathogens (human or otherwise), while produce may become contaminated with silt or other debris.

General Plant Damage / Impact
Plants that have been flooded or that grow in saturated soil situations will often exhibit reduced growth and/or stunting. Foliage (leaves and stems) may look yellowed and chlorotic and, if conditions persist, may become necrotic (dead). Seeds may rot and root death may occur. Plants may wilt and decline (depending on the duration of the saturated soil conditions). There will be an increase in the incidence of diseases (bacterial, fungal) due to weakening to the plants and due to improved conditions for disease development (increased humidity, prolonged leaf wetness periods, etc.).
Plants that are exposed to excess water will have altered plant hormone levels, which will result in abnormal growth, including twisting, epinasty, distortion, enlarged lenticels, and aerial or adventitious root formation.

The main impact that comes from excess water is due to a reduction in the amount of oxygen that is in the roots, which affects respiration and metabolic transport systems. Reduced oxygen also damages roots, which reduces uptake of nutrients (such as calcium) and can result in increased uptake of toxins and attack from pathogens.

Different crops respond to flooding in different ways, depending on the previously outlined factors. The following tables outline the specific impact of flooding on different crops.

Impact of Flooding on Potatoes

Timing / DurationPlant ResponseOther Damage
Anytime Leaching of nutrients from soil
8 -12 hoursRoot death
Irreversible wilting and plant death
After PlantingDelayed emergence
Increased seed piece decay
Planting to EmergenceSeed piece decayIncreased clod formation
Vegetative Growth StageMore prone to development of Verticillium wiltIncreased compaction & clod formation
Tuber InitiationDevelopment of tuber disorders - brown centre; stem and hollow heart
Tuber BulkingLush canopyNitrate leaching
Increase in Early blight, Late blight, Aerial stem rot, sclerotinia stalk rot, bud end hollow heart
Tuber MaturityEnlarged lenticelsIncreased bacterial soft rot
Delayed senescence and skin setIncreased Pythium leak, pink rot, late blight tuber rot
HarvestIncreased susceptibility to shatter bruise and thumb nail crackingMore soil cling
Increased tuber rot

Impact of Flooding on Carrots

Timing / DurationPlant Response
Anytime (at higher temperatures)More permanent affect
Plant wilting
Persistent floodingChlorotic / necrotic tissues
Increased chance of attack by pathogens / secondary pathogens
Increased bacterial soft rot
Forking of tap root (due to death or restriction of growing tip)
Reduced carrot quality
      · Decreased root length and colour
      · Increased lateral root development (e.g. hairy roots)
      · Stimulate cellular growth at later root emergence sites
      · Blemishes

Response / Solutions to Excess Water

The most important thing when dealing with excess water is to remove it as quickly as possible. When at all possible, improve drainage of the soil to prevent future issues. Removing water will improve access of the roots to oxygen, which immediately will improve nutrient uptake. Root growth will resume to replace lost roots.

Tillage, once soil is dry, may remove soil crusts and hard layers and improve aeration. You might consider replacing lost nutrients, if you feel it is necessary and appropriate. Consider waiting for a short time to allow plants to recover somewhat, otherwise applications may be less effective wasted. Foliar applications can supply necessary nutrients quickly to plants, which might be more effective than a soil-based application.

During recovery, it is important to monitor plants (especially young ones) closely. Increase monitoring for diseases. The application of fungicides may be appropriate to protect recovering plants from disease, but carefully consider the cost/benefit of applications. In some cases, tilling under unsalvageable crops to reduce spread and development of disease will be necessary. You may replant shorter maturing crops to try and recover lost revenue.

Harvest mature crops as quickly as possible after flooding damage, however only harvest if product is safe. Increase culling to remove any reduced quality product and avoid use of harvested product where flooding may have introduced human pathogens. Wash/disinfect all harvested product carefully.


Hail (and similar severe weather) can be devastating, both in the physical/tangible sense, and psychologically, as it can be pretty random and pretty much impossible to predict or prevent. Hail can cause partial to complete defoliation of leaves and stems, tearing or shredding leaves and breaking stems and branches. The plant will often focus on recovery of lost tissues, which results in the diversion of resources away from storage areas (such as fruits, tubers, storage roots, etc.). As a result of the loss of the foliage/foliar area, the plants have reduced photosynthetic capacity and reduced sugar (metabolite) production and increased sunburn to exposed fruit.

If hail occurs at a generative stage of plant growth, flowers or fruit may be physically knocked off (e.g. strawberries, tomatoes, etc.), reducing yields, while fruit, bulbs, root shoulders, etc. may be bruised and tissue browning may be observed. Injured tissues also represent an entry point for pathogens. Product may not be marketable or may be reduced in quality (e.g. storage organs such as tubers). Some delay in maturation of produce may be evident, as the plant regrows or recovers.
As with all severe weather damage, the severity of the damage and associated losses depend on a number of factors, including how much damage actually occurs, what stage of growth the plant is at, specific cultivars, as well as cultural practices and the subsequent weather that follow the injury. In the case of crops like potato, if slight to moderate damage is combined with good subsequent weather/growing conditions should result in a rapid recovery.

The specific impact of different types and levels of damage at different growth stages of potatoes and other crops are outlined below.

Impact of Hail on Potatoes

Level of Injury / Plant Stage Plant Response
Slight leaf damage (any stage of growth)Minimal impact on yield
Partial defoliation to complete mutilation of leaves and skinsReduction of yield and tuber quality
Delayed maturity
25% Foliage loss
(especially if before mid-season)
Reduced total and marketable tuber yield
Increased DamageReduced marketable tuber yield
More small and malformed tubers
Lower specific gravity
Severe stem damage
Shortly before/during or just after bloomReduced yield
2-4 weeks after bloomHighest losses
Percent DefoliationReduced tuber starch content in proportion to % foliage removal
Delayed maturity
Secondary growth

Impact of Hail on Various Crops

Level of Injury / Plant Stage Plant Response
During flowering or fruitingReduced yield /Highest losses
Bruising on mature fruit / brown scars on immature fruit
Cotyledon/seedling stageDeath if cut off below cotyledons or cotyledons are severely damaged
Flowering stageReduced yield and split sets (uneven maturity)
Other stagesSimilar response to damage to other crops
Vegetative stage or silkingReduced marketable ears and reduced yields
At harvestMinimal impact

Response / Solutions to Hail Damage

After heart rates have settled, take some time to assess the level of damage that has occurred. This isn’t necessarily a one-time process. As plants recover to some degree, it will become easier to see permanent versus temporary damage. In some cases, wait up 7-10 days to make the final assessment. This allows clear distinction between dead and living tissues. Assessment will help you to determine the reduction in both yield and quality.

Once a reasonable assessment has been made, some actions may help plants to recover. The application of fungicide treatments may help in recovery and can help to protect damaged tissues from attack by pathogens. Additional nitrogen can encourage new vegetative growth, however, ensure that plants have recovered sufficiently to be able to take up nitrogen and use it. Pruning or removal of damaged tissues (e.g. trimming carrot tops in field) can be undertaken with moderation.

Heavy Rain

Rain is rarely considered to be negative weather, however if it arrives in excessive amounts in a short time, resulting in localized flooding of soil and associated excess moisture damage. Sudden, heavy rains can also produce damage that is very similar to hail damage, causing varying degress of defoliation, bruising of plants (particularly soft fruit), specifically in the shoulder regions. Some cracking of the shoulder regions can also occur. Disease development may increase due to soil splash, damaged tissues and increased humidity.

Response / Solutions to Heavy Rain

Dealing with heavy rain is similar to dealing with excess water / flooding or hail, depending on the situation. Producers should ensure that there is good drainage (or actively work to drain soils) and may apply protective fungicides may help protect damaged tissues from infection. Replacement of lost nutrients may also be necessary.
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For more information about the content of this document, contact Robert Spencer.
This information published to the web on June 26, 2018.