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Saturday - June 07, 2014

From: Austin, TX
Region: Southwest
Topic: Diseases and Disorders, Soils, Herbs/Forbs
Title: Stress on Goldenball leadtrees from Austin
Answered by: Barbara Medford

QUESTION:

I know of two separate instances where young Goldenball Lead Trees (leucena retusa) have shown symptoms of defoliation and a bleeding of white sap from sores that have developed on the bark. The first died aggressively. The second is under stress now. What are they susceptible to? Too much water or inadequate drainage might have weakened them for a pathogen or critter to get started?

ANSWER:

According to this USDA Plant Profile Map, Leucaena retusa (Goldenball leadtree) grows in Travis and Blanco County, but the other counties where it has been reported are all in the Big Bend area of southwest Texas, so there might be a cultural problem of which we are not aware. If you will follow the plant link above to our webpage on this plant, you can compare the growing conditions, soils, etc. for this plant to those of the plants you have observed as being stressed.

Not having found an answer on our own website, we went hunting on the Internet, and the only clues we got were similar to our supposition that maybe it didn't really belong in Travis County, but was reported to the USDA because people were growing it here. We learned that it does not do particularly well in clay soils which we have, because it needs really good drainage. We also learned it likes sandy soils, which we don't have.

One reference mentioned it could be susceptible to root rot in poorly drained soils. From the Missouri Botanical Gardens, we found this article on Phytophthora Root Rot of Trees and Shrubs. Especiially note this paragraph:

"Life Cycle

Root rot-causing Phytophthora species can survive in the soil for years, as long as moist conditions persist. It can spread through splashing rain, irrigation water, and runoff water. Disease fungi can spread through contaminated soil and garden equipment as well. Rot is more likely to spread in early spring and late fall during cool, rainy weather. But symptoms are more likely during stress periods of low rainfall. Flooded and saturated soil conditions for 6–8 hours are especially conducive to the spread of root rots. Wounds are not required for infection."

If you are noting these symptoms in the Goldenball Leadtree, it could very well be because they are getting too much love from the gardener. If other plants nearby need more water, like non-native grasses, that may precipitate the problem. We would suggest either remediating the conditions in which the plant is being grown, or not try to grow it out of its natural region.

From the Image Gallery

Goldenball leadtree
Leucaena retusa