Sep 19, 2011

Dealing with flooded berry fields

Record-breaking rains in the East have left many berry growers with unmarketable crops. What had been shaping up to be a decent season for fall raspberries and day-neutral strawberries has quickly turned into a bad situation.

Floods and Food Safety

There are two types of flooding. The first is more typical and occurs after a heavy downpour when fields become saturated and water pools on the soil surface. This type of flooding can reduce yields and even kill plants but usually will not result in contamination of produce with human pathogens.

The second type of flooding is more severe and occurred with the recent storm. This occurs due to runoff from stream/river overflows and will more likely be contaminated with human pathogens as well as chemicals.

Unless you are absolutely sure that flooding is not from streams and surface water, do not use berries that were covered with floodwater.

Plant Survival under Water

Berry crops can tolerate a great deal of flooding when they are dormant, but when actively growing in summer, flooding for any length of time can be detrimental. This time of year is particularly bad because plants are preparing to make flower buds for next year, and stress can compromise this process. If plant roots were under water for more than 48 hours, expect next year’s crop to be compromised as well.

Plants previously flooded may develop an off-green or yellowish color. These plants are suffering from a complex of nutrient deficiencies, nitrogen, phosphorus, potassium and perhaps others, even though the soil contains adequate amounts. But the main deficient element is oxygen. Plant roots need oxygen to take up nutrients and water to utilize the photosynthate from the tops and to grow.

With the heavy rains we have had, soils are saturated; that is, nearly all of the pore space is filled with water, leaving little room for air. Ideally, for good root growth 50 percent of the pore space should be filled with air. As soils drain, air is drawn into the soil, but when it rains, the water forces the air out of the pores. What is needed now is several rain-free days so the soils can drain and draw in air to stimulate root growth and help disperse toxic compounds that accumulate when plants lack oxygen. Once the plant roots get adequate oxygen they will begin to grow and take up the nutrients present in the soil. Anything that can be done to remove surface water will be helpful.

Many plant diseases will be much worse following flooding rains (e.g. Phytophthora and Botrytis), so closely monitor crops and manage these diseases. Phytophthora spores are spread under flooded conditions, so chemical treatment may be warranted in susceptible crops such as red raspberries and strawberries.

By Steve Reiners and Marvin Pritts, Cornell University