Fungi Attack Azaleas
“We’ve had a number of samples come into the lab,” said Jean Williams-Woodward, aplant pathologist with the University of Georgia Extension Service. “So far, we’re findingtwo main causes of the branch dieback.” In Georgia landscapes, azaleas practically sing spring. So do rhododendrons in much ofthe state. But this year, many people are finding dead branches in both of these prizedornamentals. The less serious of the causes, she said, are fungal diseases that got into the branchesthrough some kind of wound. “These fungi get in and cause a canker — a sunken, dark brown, grayish area,”Williams-Woodward said. “Sometimes they can girdle the stem. And when that happens,the branch dies.” Once these fungal cankers have girdled a branch, she said, you can’t save it. But you canspare the rest of the shrub. Just prune out the dead branch and keep the plant properlymulched and watered to reduce stress. “We had a warm fall last year,” she said. “Many shrubs weren’t properly hardened off yetwhen we had a sudden cold snap in December. That caused some bark splitting in sometender branches.” “Then change the drainage,” Williams-Woodward said. “Raise the bed, or amend the soil.You have to make the site drain better, or the next plant won’t fare any better.” A long, mild spring then complicated the problem, allowing fungi to infect the wounds thecold snap left. The main culprits, she said, are Phomopsis in azaleas and Botryosphaeria inrhododendrons. Sometimes, though, the problem isn’t contained with the branch. Sometimes a single fungal canker won’t girdle a stem, she said. But two or more on thesame stem can produce the same result. You can tell the difference, she said, by cutting along the branch. If the dead, cankeroustissue isn’t contained within the stem but goes to the base of the plant, the problem is rootrot. “The more serious problems we’ve seen are root rots,” Williams-Woodward said. “Theseare caused by fungi, too. But they’re the result of poorly drained or compacted soils.” And the remedy isn’t so simple. The first step is to remove the plant — it isn’t going tosurvive.