Horticulture

Common Landscape Issues

Iron Chlorosis

Image of trees turning colors
Image of Iron Chlorosis
Image of Iron Chlorosis in tree leaves

This past summer, many homeowners in Taos County noticed that the leaves on some of their landscape trees were turning yellow. On closer inspection, it was noted that the veins remained green. In more severe conditions, the leaves were actually bleaching out, and some had brown necrotic spots on them. This condition is called chlorosis.

According to Dr. Robert Flynn, NMSU Extension Service Agronomist, the cause of chlorosis can be related to iron, zinc or other micronutrient deficiencies. The most common deficiency is iron caused by high pH soils (alkaline) and/or the presence of lime. Soil testing may reveal sufficient iron, but plants that are sensitive to alkaline soils or excess lime are not able to extract the iron for use in the plant. The solution to this problem is to supply iron to the plants in a readily available form. This may be done as foliar sprays or soil application of iron chelates or iron sulfate. Chelates (pronounced "key-lates") are organic (carbon-based) compounds that hold the iron, releasing them to the plant roots but preventing them from becoming bound to the soil and unavailable to plants.

Dr. Flynn points out that all iron chelate products do not work equally well in New Mexico soils. He recommends iron chelates based on ethylenediamine di(o-hydroxyphenylacetic) acid (EDDHA), which are best at providing iron to plants in our high pH soils. The most common chelate, EDTA, is really meant for soils with a pH of less than 7 that are common in the eastern part of the U. S. Dr. Flynn recommends soil testing to determine the soil pH and help determine which chelate will be most effective for soil application in a specific garden or landscape. He says that most chelates should work well as foliar applications as long as label directions are followed. Iron sulfate can also be effective in New Mexico soils when applied at the right time. Foliar feeding needs to occur in the development phase of leaf tissue (spring). Time of day can also impact the efficiency of foliar feeding. Dr. Flynn noted that plants sensitive to chlorosis often need more than one feeding of iron each year. He suggests multiple applications during the growing season in order to keep these plants healthy..

Cytospora Canker

The drought this summer posed significant challenges to Taos County agricultural producers, and the challenges weren't limited to crops and cattle. Landscape trees and plants were also stressed because of the weather, and as a result, landowners reported problems related to adverse environmental conditions. Cytospora canker is unsightly and disturbing for many people, and they want to know how to best handle it. It is caused by an opportunistic fungus that otherwise does not cause problems to healthy trees. It attacks trees under stress and is most commonly seen in aspens, willows, and cottonwoods. There isn't a "cure" for this problem, rather it can be managed by keeping trees healthy. Prune out diseased wood and make sure to clean your tools with a 10% bleach solution (1 part bleach to 9 parts water). Destroy all diseased materials. Maintain an adequate water and fertilization schedule, and prevent any damage to the tree from lawnmowers or weedeaters.