Question
Hi!  I have a two Purple Robe Locust trees (probaly about 4 years old) that we transplanted to a different area in our yard last fall. This spring and early summer the trees seemed to be doing great and then all of a sudden the leaves started to yellow and get brown spots on them. We watered our trees about three times a week, 30 mintues each time on a slow drip system.  We live in New Mexico so we thought that maybe they weren't getting enough water so decided to up the watering schedule to five times a week.  Doesn't seem to be helping the problem.  I was told by a local nursery that is may be an iron deficiency so we started an iron supplement and this is not helping either.  Alot of the leaves have fallen and the tree is almost bare.  We really love these trees and would hate to lose them since they are know about 20 feet tall and look and smell wonderful in late spring.  Please help!  What can I do?

Answer
My first thought was a response to the move--this is a fairly good size tree to move and the root system would that was dug would have needed to be large--For deciduous trees and shrubs the soil ball should be:

Width = 9-12 in. in diameter/every 1 in. of tree diameter
Depth = 6 in./every 1 in. of tree diameter

For example: A tree trunk 2 inches wide would need a soil ball of 18-24 inches wide and 12 inches deep.

OR there is an insect that will infest the leaves and make them look brown. Leaf miner. It is common on locust trees. Identifying the Injury - Adults skeletonize and eat holes in the leaves, whereas larvae mine the leaves (the latter damage is more destructive). Under outbreak conditions, whole hillsides turn gray or brown, often suggesting fall color change.

The primary and most conspicuous damage is caused by the leafmining activities of the larvae. Larvae feed inside the leaves on the inner layers. In the beginning the mine is small, but it is gradually enlarged until most or all of the leaf is affected. A single leafminer may attack several leaves. The mine or blister is at first clear, but later turns brown as the leaf dries out. Leaves damaged by the locust leafminer may turn entirely brown and cling to the tree for some time, giving the tree a blighted look. This damage is most noticeable in the late summer along major interstate highways where it will seem that miles of trees have brown leaves.

If the leaves are as above i would treat next spring with an insecticide called Bayer Advanced Tree %26 Shrub Insect Control. This is applied to the soil around the tree and the roots transport it to the leaves and when the insects feeds they are killed.

Check to see if the tree branches are still alive--start near the end of an upper branch and scrape a small bit of bark off and if the color under the bark is green the branch is still alive at the point on the branch. IF the color is brown the branch is dead at the point on the branch--if brown continue down the branch scrapping at intervals until you find green or reach the trunk. If it is green, which is what I would expect, the tree is still alive and will leaf out next spring.

I would fertilize with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and water3ed in good, Do this now and again in the spring.