Abrupt Weather Change Results in “Soggy Stress Syndrome”

By MUNews

05-27-2010

For trees and shrubs, a sudden change from cool and rainy weather to hot and dry conditions is particularly stressful.

After a rainy spring and return to normal temperatures, homeowners may see leaf scorch, dieback or leaf drop on their landscape plants.

“When soil is saturated and air temperature is cool, plants develop an imbalance between their roots and leaves,” said Chris Starbuck, University of Missouri Extension horticulturist.

In “soggy stress syndrome,” deep roots suffocate while new roots proliferate near the surface, where more oxygen is available. The soggy soil temporarily impairs water uptake by the surviving deep roots. Leaves that develop during cool, cloudy conditions are often large and succulent and lack a well-developed protective cuticle.

Such leaves are less efficient at preventing moisture loss. When the sun comes out and air temperature suddenly spikes into the 90s, these leaves lose water faster than the impaired roots can supply it.

Some plants, like birch, respond by simply dropping some of their leaves. Other symptoms include browning or blackening of leaf tips or edges and dieback of stem tips. Once the soil dries out and air temperature stabilizes, plants usually are able to gradually regain a balance between shoots and roots, Starbuck said.

Foliar diseases can also develop during cool wet conditions, leading to leaf drop.

When dealing with soggy stress syndrome, the goal is to help the plant develop a root system that can take up enough water for normal plant growth. Because waterlogged plants have shallower-than-normal root systems, at first they may need frequent light irrigations-perhaps a third of an inch, three times a week-to keep the surface moist.

Use a rain gauge to avoid overwatering. “Keep in mind that saturated soil and high temperature are a deadly combination,” he said.

A mulch layer two to three inches deep will help maintain surface moisture without contributing to waterlogging. As the soil dries out and roots grow deeper, you can apply more water at less frequent intervals.

It’s particularly important to irrigate plants with soggy stress syndrome regularly during drought periods following a very wet spring. The inch-per-week rule is a good goal to shoot for by midsummer, Starbuck said. However, resist the temptation to water plants that are wilted now due to saturated soil. This will do more harm than good.