Problems With a Locust Tree Turning Yellow in the Northeast

Locust trees are classified in either the Gleditsia or the Robinia genus. Popularly grown species include the black locust (Robinia pseudoacacia), native to the southeastern United States and honey locust (Gleditsia tricanthos), which is native to the eastern region of the U.S. Locusts are deciduous trees, some with edible pods. The trees naturally turn yellow in the northeast in fall. Discoloring, during other parts of the year, is a symptom of a problem.

Insects

Locusts trees grown in the northeast are prone to a number of pests. Most of them, such as eriophyid and locust spider mites, turn the foliage bronze. Others cause yellow spotting. When your honey locust is completely yellow, suspect a honey locust plant bug infestation. This pest, fairly common in the northeast, feeds on foliage. As it does, it injects toxic saliva that turns the leaves yellow before completely killing them. Spray the tree with insecticidal soap in early spring to rid the tree of this pest. Leafhoppers and spider mites are common northeast tree pests

Disease

Root collar rot is a common disease of locusts that grow in the northeast. This is a deadly disease that may kill the tree, and yellowing is a sign of advanced rot. Let the soil at the base of the locust tree dry out before watering it then water it less frequently. Remove any vegetation around the base of the tree and pull back 2 to 3 inches of soil. Replace it with gravel. Canker is another common disease in the northeast, and yellow foliage is one of the main symptoms. Look for brown, sunken areas on the trunk and twigs. Control the disease by pruning back infected branches until you see healthy wood then cut at least 1 inch of the healthy wood as well. Prevent canker by avoiding wounding the tree with lawn equipment.

Environmental Stresses

Locust trees have shallow root systems and are sensitive to fluctuations in soil moisture. Drought stress may bring on discoloration. Give the tree extra water during abnormally dry periods. Pest infestations stress the tree as well so take care of them at the first sign. Soil compaction around the roots, caused by heavy foot traffic, is another stress factor for a locust tree.

Nutrient Deficiencies

Yellow foliage is a symptom of a disorder known as chlorosis. The leaves do not produce enough chlorophyll -- the substance that makes them green -- causing problems with photosynthesis. This may lead to the tree's inability to produce carbohydrates, leading to its death. Chlorosis is generally caused by a lack of minerals, such as iron or magnesium in the soil, but may be caused by insufficient sunlight as well. The best way to cure deficiencies is to know first what is lacking in the soil. This requires a soil analysis, which you can obtain at your local county cooperative extension office.

References

• Penn State: "Honeylocust Plant Bug"; Greg Hoover, et al.; April 2007
• Colorado State University Extension: "Insect and Mite Pests of Honeylocust"; W.S. Cranshaw; June 2000
• Arboriculture and Urban Forestry: "Identification and Control of Cankers Caused by Nectria Cinnabarina of Honey Locust"; P.J. Bedker, et al.; February 1984
• University of Nebraska: U.S. Drought Monitor
• "Landscape Management: Planting and Maintenance of Trees, Shrubs and Turfgrass"; James R. Feucht, et al.; 1988