Heavy rains can pose landscape problems

Heavy rainfalls during recent weeks have caused many homeowners to worry about disease in their landscape plants.

While it is true that most plant pathogens prefer lots of water and high temperatures —that doesn’t mean your plants automatically will become diseased in our recent scenario.

And, just because conditions are right for disease, it doesn’t mean that you automatically should spray chemicals.

Spraying chemicals into the environment without confirming that disease is present is potentially harmful, not to mention that it’s a waste of time and money. It’s also important to know that it will not “cure” or make waterlogged plants stronger.

Positive confirmation of disease requires visual signs of the pathogen, such as fungus on the leaves, and symptoms of the disease like spots, wilting or dieback. Only then should a fungicide be considered.

But remember: Applying fungicides cannot cure diseased plant parts, such as roots and leaves. Fungicides simply will help reduce spread to other plants in the landscape.

If you determine that your plants are infected with a disease that can be treated with chemicals, be sure to follow the label directions.

The UF/IFAS Pasco Extension Office can help you determine if your plants are diseased and can recommend your best method of control.

While disease is a threat in wet conditions, unless plants are naturally adapted to watery environments like the bald cypress, standing water will more quickly become a problem by taking a toll on the roots.

Plants need oxygen. Waterlogged soils can deprive them of that oxygen. Even the bald cypress found in aquatic environments needs oxygen; hence the stump-like “knees” which help move oxygen into the plant roots.

It’s not always evident that plant roots are suffering from oxygen deprivation, since saturated soils don’t always have standing water.

Saturated soils are simply those that are so wet that plant roots cannot obtain oxygen. In other words, standing water is not required to waterlog a plant. Plant roots in waterlogged soils appear stunted and withered, with the root tips decomposing and rotting away.

Waterlogged plants quickly show signs of stress by yellowing and wilting. However, if the soil drains relatively quickly, plant roots will start to get oxygen they need once again, and the plant has a good chance of recovery.

However, plants left in waterlogged soils for extended periods of time will die.

Unfortunately, there is no established period of time that roots are in waterlogged soils that tells us whether or not a plant will survive.

The length of time a root can be deprived of oxygen and be able to recover varies greatly, based on plant species and environmental conditions.

So, what are we to do with our plants when extended rains put our landscapes at risk?

Here are some practical steps you can take to reduce damage and disease in your landscape if waterlogging doesn’t claim your plants.

Keep in mind that many of these steps are proactive and need to be considered prior to and not during or after the rains begin.

• Don’t fertilize your plants during periods of high rainfall. Our sugar-sand soils quickly leach nutrients wasting your money and polluting our waterways with fertilizers that plants don’t have a chance to uptake before its whisked away into the drinking water reserves below ground. Wait for more favorable conditions to fertilize plants, when rainfall is not so heavy and soils are well drained. This is especially true for stressed plants, which may actually be harmed by fertilizer applications.
• Prune areas of diseased or dying tissue. Leaving diseased tissue behind can further spread disease, so remove the debris. Do not compost diseased tissue because it can harbor disease-causing organisms.
• Turn off the sprinklers. When plants are getting more than sufficient rainfall, there is no need for supplemental irrigation. This will only encourage disease, saturate the soil further and waste precious water resources. Established plants, with a few exceptions including some turf grasses, do not usually require supplemental irrigation even during periods of dry weather.
• Properly mulch plants. Mulch is effective at holding in moisture during drought, and the same holds true during periods of high rainfall. Mulch plants with no more than 2 inches to 3 inches of mulch such as pine bark or melaleuca. Leave a couple of inches between the bark and, mulch to keep moisture away from the bark, which causes rot. When plants are waterlogged, pull the mulch layer back to expose roots to as much oxygen as possible. Once the soil has dried out, replace the mulch.
• Reduce soil compaction, which limits drainage, by limiting foot traffic in wet areas.
• When mowing, remove clumps of grass, which can harbor pathogens and limit exposure of underlying turf to sunlight.
• Put the right plant in the right place. Obviously, this comes way before the rains, but it’s often overlooked and is the simplest way of protecting your plants during high rainfall. Areas of your landscape that are depressed and frequently hold water should not be planted with species that cannot tolerate standing water. Instead, use plants adapted to wet conditions or consider installing a rain garden as a centerpiece for a beautiful addition.

For help identifying disease, or with general questions about irrigation and plant management in your turf or landscape, call the UF/IFAS Pasco Extension Office at (352) 518-0156.

Whitney C. Elmore is the Pasco County Extension director and Urban Horticulture agent III.

Published September 2, 2015