Are yellow leaves on your oak trees a sign of trouble?

Green is undeniably the color of spring, but owners of oaks around Starved Rock Country may be seeing slightly more autumnal hues on their trees this May.

Numerous oak trees around the extended area are sporting leaves tinted more yellow than the customary green.

While yellow leaves on oaks — especially the locally prevalent but non-native pin oaks — could be a sign of a potentially serious problem known as iron chlorosis, area tree experts say other factors could be contributing to or exacerbating the fall-like colors in the spring.

"What they might be seeing is, we've had two late frosts already, and that can manifest itself in light-colored leaves," said Morgan Wilson, a horticulturist/plantsman with Wilson Landscaping Co. in La Salle. "Oaks are just now leafing out. It's probably too early to tell if it's iron chlorosis.

"Let the leaves grow out ... and (if it is iron chlorosis), the veins will be dark green and the areas in between will be paler."

Arlette Salata, owner of Danchris Nursery in Streator, agrees that, while iron chlorosis can be a serious issue, it might be a bit premature to attribute the yellow-leaf symptom to a disease.

"A brand new leaf that grows is naturally going to be lighter-colored than an older, more mature leaf," she said. "Some of the (yellow leaves people are seeing) could just be new growth. ...

"The best way to determine is to give it a little time to mature, look at the leaves, and if you think it's better to seek a professional, you can take pictures, bring leaves in to us or other professionals, extension centers or arborists."

If early-season yellow leaves return or persist, Salata and Wilson said iron chlorosis — an inability of the tree to gather enough iron from the surrounding soil — is the likely culprit.

"There might not be enough iron there to support the tree," Salata said. "Or some of it could have been leeched out of the soil because of the wet weather we've had the past couple years. There are lots of possibilities, and older oaks require more iron than younger trees."

Wilson said the chlorosis issue is especially prevalent in pin oaks, because they are common but not native to north-central Illinois.

"They don't like the pH," Wilson said. "They are native to southern Illinois, but they just don't like our soil."

Wilson said when pin oaks reach about 20 years old, they may start to show signs of iron chlorosis.

"That's what makes it a shorter-life species than some of the others native to the Illinois Valley, such as white, shingle and red oaks."

If iron chlorosis is affecting your oaks, there are treatments.

"You can add iron in lots of different ways," Salata said. "There is liquid iron, granular, and if it's really bad, you can add a plug."

"We have treated many pin oaks over the years," Wilson said. "If you have a pin oak and you like it and it's past 10 years of age, it's a good idea to treat it every other year with iron chelate, a wettable powder. We sell quite a bit. People can do it themselves if they want to; otherwise, they can hire a guy like me."

Wilson added a good alternative to the pin oak is the scarlet oak.

"It has the fall color of the pin," he said, "but the soil tolerance of the red."