Hurricane Matthew’s lingering effects can threaten turfgrasses and trees
CLEMSON, South Carolina – Hurricane Matthew’s pounding rainfall and heavy winds generated widespread flooding, knocked down trees, took out power lines and forced more than one million people to evacuate the state’s coastal regions.
To rub salt in the wound, the storm’s Oct. 8 assault on South Carolina will continue to have negative effects that could linger for months to come. Besides wind damage and debris, hurricanes can impact the recovery and management of turfgrasses and trees. Irrigation ponds can be compromised by saltwater, weeds will be more likely to thrive, some insect pests might multiply, diseases can increase and tree health might be precarious.
“Tidal storm surges can result in saltwater intrusion into irrigation ponds, and if the pond is also fed by stormwater runoff, then any tidal storm surge from elsewhere might also enter the pond,” said Dara Park, a Clemson University associate professor in the plant and environmental sciences department who specializes in soil and water quality dynamics. “The good news is that the excessive rainfall also ends up in the pond, which helps dilute the saltwater and stormwater pollutants.”
In addition to irrigation issues, higher-than-normal levels of sodium in the soil can be toxic to turfgrass, ornamental plants and trees. Flushing sandy soils with fresh water is the most cost-effective method of removing the salts. Soils with heavier texture might require additional measures to correct pH levels.
“Either way, you should test your soil to help identify the best management strategies, and then test again after your management strategies have been applied to determine if they were effective,” said Park, who added that Clemson’s Agricultural Service Laboratory tests water for minimal fees. Information on how to submit a sample can be found online at the university’s Irrigation Water section.
When it comes to soil fertility, root systems will be the most susceptible to damage, with the level of harm determined by how long the turfgrass was under water.
“You should hope that most areas were not submerged for more than 48 hours,” said Haibo Liu, a Clemson professor in the plant and environmental sciences department who specializes in turfgrass and soil sciences. “Mechanical aeration and top-dressing will assist in the recovery of both cool-season and warm-season turfgrass roots. If possible, you should have a soil test done immediately to gauge how much salt is in the soil profile.”
Probably the biggest long-term agronomic effect from flooding and tidal surge is the lack of weed control, which is mainly caused by the leaching and dilution of previously applied herbicides.
“This is why you often experience more weed outbreaks like crabgrass during wet conditions,” said Bert McCarty, a Clemson professor in the plant and environmental sciences department who specializes in turfgrass science and management. “Some herbicides can be leached out of the upper inch of soil, which is where almost all of the small-seeded grasses germinate. The inundation of weeds will also weaken the permanent grass.”
Though a hurricane’s impact on the management needs for insect pests might be relatively minimal, certain insects often thrive in saturated conditions.
“With high soil moisture and a rising water table, more tunneling by mole crickets might be observed,” said Juang Horng Chong, a Clemson assistant professor in the plant and environmental sciences department who specializes in pest management of turfgrass and ornamentals. “Typically, as temperatures drop in the fall, mole crickets move deeper into the soil and tunnels become less numerous and obvious. With the passing of the storm, the soil dries and the mole crickets return to deeper areas. If tunneling activity abates over time, no management will be necessary. But if it continues or reaches damaging levels, insecticides should be applied.”
Saturated soils are susceptible to disease outbreaks because heavy rains can leach fungicides and stimulate pathogens.
“We saw very high disease pressure and outbreaks this last fall, winter and spring that were likely the result of prolonged cloudy, wet weather and flooding from the now legendary October rains that drenched most of the state,” said Bruce Martin, Clemson’s research and Extension turfgrass pathologist for South Carolina. “The Carolinas once again bore the brunt of Hurricane Matthew, and effects of that storm are still being keenly felt. Pythium blights and root rots are the most likely diseases, but other diseases such as leaf spot, Microdochium patch and even dollar spot can also increase.”
Just because a tree wasn’t knocked down doesn’t mean it’s not going to suffer or die. Trees that have lost large limbs can be susceptible to insects and diseases, and those in standing water are at greater risk than trees in soils that are saturated but not submerged.
“Hurricane Matthew hit at a time when trees on the coast were starting their dormancy process, which will make it more difficult to determine if deciduous tress are losing their leaves because of the time of year or because of declining health,” said Bob Polomski, a Clemson adjunct assistant professor who is an award-winning horticulturist and author. “Also, deciduous trees still might lose roots over the fall and winter and not be able to overcome the stress when spring arrives and prompts new growth. And if evergreens such as pine trees are excessively shedding needles, it’s important to evaluate them to determine if they’re in decline.”
For a more in-depth look at Turfgrass and Tree Management after Hurricanes, click HERE.