Yellow guava leaves should be evaluated by pattern, age of affected foliage and overall plant vigor.
Check irrigation and roots
Confirm whether the root zone is staying excessively wet or drying too far between irrigations. Poor root conditions can reduce nutrient uptake even when nutrients are present.
Inspect for sap-feeding pests
Check leaf undersides and stems for mealybugs, scale and other insects. See our mealybugs on guava guide.