Palm Aphids

• Palm aphids become sedentary scales on windmill palms that appear as a black ring surrounded by a white wax. Ladybeetles feed on these aphids, but if they are not present, you should use an insecticide on the scales.
  
  

Scales

• Scales, knotty brown growths, sometimes show up on palm leaves. In most cases a chemical solution is needed to take care of them.
  
  

Root Rot

• In especially moist regions, the roots of the windmill palm have the tendency to rot. If there is too much water present in the soil, it becomes impossible for the tree to get the proper air needed for survival.
  
  

Lethal Yellowing

• This disease can occur in southern states where leaves turn yellow and drop off. It is caused by an organism called a phytoplasma, and antibiotics are needed to treat it.
  
  

Leaf Spots

• Some fungal and bacterial infections cause a condition called leaf spot disease in which brown or black spots appear on leaves. Chemicals are used to care for the condition, which can stem from overcrowding.