Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
There is still considerable acreage of watermelons, sweet corn, pumpkins, beans, cabbage, potatoes, and other fresh market vegetable crops in the field on Delmarva. On the processing side, the majority of lima beans have yet to be harvested and there are significant acres of pickles, snap beans, and other processing crops in the field. Many of these crops will be at risk in the coming days due to hurricane Irene.
A late summer hurricane or tropical storm with both wind damage and excess rain can cause major issues in vegetable crops, most notably:
● Damage due to flooded soils in all vegetable crops
● Increased disease incidence in all vegetable crops
● Lodging damage in crops like sweet corn
Other articles will address diseases in with excess rainfall. I will focus on flooding effects on the physiology of vegetable plants.
Flooded and Waterlogged Soils
In flooded soils, the oxygen concentration drops to near zero within 24 hours because water replaces most of air in the soil pore space. Oxygen diffuses much more slowly in water filled pores than in open pores. Roots need oxygen to respire and have normal cell activity. When any remaining oxygen is used up by the roots in flooded or waterlogged soils, they will cease to function normally. Therefore, mineral nutrient uptake and water uptake are reduced or stopped in flooded conditions (plants will often wilt in flooded conditions because roots have shut down). There is also a buildup of ethylene in flooded soils, the plant hormone that in excess amounts can cause leaf drop and premature senescence.
In general, if flooding or waterlogging lasts for less than 48 hours, most vegetable crops can recover. Longer periods will lead to high amounts of root death and lower chances of recovery.
While there has not been much research on flooding effects on vegetables, the following are some physiological effects that have been documented:
● Oxygen starvation in root crops such as potatoes will lead to cell death in tubers and storage roots. This will appear as dark or discolored areas in the tubers or roots. In carrots and other crops where the tap root is harvested, the tap root will often die leading to the formation of unmarketable fibrous roots.
● Lack of root function and movement of water and calcium in the plant will lead to calcium related disorders in plants; most notably you will have a higher incidence of blossom end rot in tomatoes, peppers, watermelons, and several other susceptible crops.
● Leaching and denitrification losses of nitrogen and limited nitrogen uptake in flooded soils will lead to nitrogen deficiencies across most vegetable crops.
● In bean crops, flooding or waterlogging has shown to decrease flower production and increase flower and young fruit abscission or abortion.
● Ethylene buildup in saturated soil conditions can cause leaf drop, flower drop, fruit drop, or early plant decline in many vegetable crops.
Recovering from Flooding or Waterlogging
The most important thing that you can do to aid in vegetable crop recovery after floods or waterlogging is to open up the soil by cultivating (in crops that still small enough to be cultivated) as soon as you can get back into the field. This allows for oxygen to enter the soil more rapidly. Nutritionally, sidedress with 50 lbs of N where possible.
In fields that are still wet, consider foliar applications of nutrients. According to Steve Rieners at Cornell “Use a low salt liquid fertilizer to supply 4 to 5 lb nitrogen, 1 lb phosphate (P2O5) and 1 lb potash (K2O) per acre. Since nitrogen is the key nutrient to supply, spraying with urea ammonium nitrate (28 % N solution) alone can be helpful. These can be sprayed by aerial or ground application. Use 5 to 20 gallons of water per acre. The higher gallons per acre generally provide better coverage”. As with all foliar applications, keep total salt concentrations to less than 3% solutions to avoid foliage burn.