March 17

1 - Symptoms of iron chlorosis in sycamore trees such symptoms are common in trees and shrubs from regions with more acidic soils.

Yard and Garden March 17, 2012

Q.

I am attaching a couple of photos of one of my sycamores ('Bloodgood' sycamore, actually London planetrees, Platanus x acerifolia) which I took last year, in early summer. I have two of these trees that I planted as balled and burlapped saplings in late 2007.

Every single year since I planted them, the leaves on these trees start turning yellow in late spring/early summer, and quite a few die and fall off. The remaining leaves continue to turn yellow and brown. By the end of the season, the trees look quite ragged.

I have treated them with soil-drench insecticide for scale insects the last two seasons, so I do not think that is the problem.

Due to last year's very late and cold spring, they were affected by anthracnose fungus, which killed the leaves at the tips of the branches, but that problem ended when the weather got hot, and that is not what these pictures are showing.

They get plenty of water, I am quite certain of this. I watered them a bit less last summer than their first three years, but still twice a week during summer. I have not used any fertilizer on them.

Any advice would be welcome.

Dave McB.

Albuquerque

A. Thank you for the excellent pictures. They provided the necessary information. As I looked at the pictures of your sycamore trees (London planetrees) I saw that they exhibited symptoms of iron chlorosis. The whole tree exhibited a yellowish appearance and the close-up pictures of the leaves indicated yellowing of leaf tissue between the veins. Such symptoms are common in trees and shrubs from regions with more acidic soils when they are grown in the Southwest. This is a result of the calcareous nature of our soils (high calcium and high pH). The high pH causes the iron in the soil to be unavailable to the trees' roots. You can treat for this by treating with sulfur (or other acidifiers), or you can treat with iron chelate products. Trees treated with iron chelates often exhibit a better response. The products containing EDDHA as the chelating agent are the most effective products for use in our soils.

Chelating agents are organic (Carbon, hydrogen, and oxygen based) chemicals that protect iron in the product from being too rapidly inactivated by our soils. EDDHA based iron chelate products have proven best in New Mexico's soils. EDDHA is ethylenediamine-N,N'-bis(2-hydroxyphenylacetic acid). Look for this chemical listed among the ingredients on the label.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

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