Answer: It's difficult to diagnose a plant problem without seeing it, so I'll be cautious in answering. Could be simply heat stress, or it could indicate your soil is binding up important nutrients. One possibility could be iron deficiency. Iron deficiency can cause the chlorosis (yellowing) symptoms you have described. If the chlorosis is not too severe, the yellow leaves will have green veins. In more severe cases, the leaves will be quite yellow and will begin to turn brown and die. Try spraying a solution of iron sulfate on the leaves to see if you get a development of green in the leaves. If you see green spots where the iron sulfate solution collected on the leaf, this is a good indication that iron deficiency is the problem. If this is the case, use an iron chelate or iron sulfate application to the soil. Such treatments are most effective before mid-summer. If iron treatment doesn't help, you might try applying a micronutrient fertilizer to the soil at the dripline of the tree. There are other mineral deficiencies that can cause yellowing and browning. Another possibility is salt accumulation in the root zone. These salts may have occurred naturally in the soil or may have resulted from irrigation with salty water. Some salts can interfere with mineral uptake causing the symptoms you described. A soil test can help determine if salt is the problem.
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