Often time these insects are brought to the trees by ants. So, if you see a trail of ants going up your citrus, there are probably aphids or scales in your tree as well. Another indication of these insects is a sticky residue on the leaves. Most of the insects will be found on the back side of the leaves. Scales may be found along the branches as well and will look like bumps along the limbs.
Scale can be white, black, or brown.
These insects are seen most often in the Spring and Fall, but can be a problem at any time of the year. Yellowing Leaves Yellow leaves can be a result of several things. It could be a result of lack of fertilizer and minerals, a watering problem, or insect damage. When diagnosing a problem, take into account how often you water, when and how often you fertilize, and when the last time you inspected your tree for insects. If the older leaves are turning yellow and the other leaves are a pale green, then you may need to add nitrogen.