2005 Year in Review

Why is "Iron" Chlorosis More Severe in a Drought?

Chlorosis is a common problem in Illinois on several tree species, including pin oak, sweetgum, maple, and birch. In most cases the soil has plenty of macro- and micronutrients for tree growth, but high pH soils bind up the iron or manganese, making it unavailable to the roots. No pathogen is involved in this noninfectious problem, although secondary leaf-spotting fungi often invade the weakened tissues. Soil conditions are the cause of the chlorosis.

So why are we seeing more chlorosis than usual? Most of Henry and Stark Counties are currently in moderate to severe drought status, adding to root injury and limiting absorption of nutrients. Soils with high clay content or poor drainage aggravate the problem. Some growers have been watering trees, especially shallow-rooted trees such as birch. This is helpful, but the pH of the water is also an issue. City water often has a very high pH level and can influence the soil pH where supplemental watering is frequent. Any and all of these factors may explain the increased appearance of this noninfectious problem in 2005.

What can be done to remedy the situation? For older trees there may be nothing we can do to help. Prune out dead wood to avoid secondary wood rots. Try to improve drainage from the site to areas away from the tree. Consider treating the tree for chlorosis and possibly using an acid fertilizer in spring or fall.

Several types of treatment can be used for chlorosis are discussed in University of Illinois Extension fact sheets like RPD No. 603, Iron Chlorosis of Woody Plants: Cause and Control, which addresses both manganese and iron deficiency. The treatment method you choose will depend on the intensity of the problem, the age of the tree, the pH of the soil, and site restrictions. The RPD can be found in Illinois Extension offices and online (http://web.aces.uiuc.edu/vista/pdf_pubs/603.pdf). If you are not online, please contact Henry-Stark Extension at 853-1533 for a hard copy fact sheet.

by  Editor, theCity1.com
August 2, 2005