Melampsora Leaf Rust

• Melampsora leaf rust is a two-part infection requiring a second host, generally a nearby coniferous tree, to complete its lifecycle. This infection causes bright-orange pustules on the leaves' undersides. The top surface fades and turns yellow in spots corresponding to the pustules below them. The entire top leaf surface may yellow if the pustules are abundant. Mature trees usually recover on their own. Plant Carolina poplars away from larch, fir and other coniferous trees, as spores travel back and forth on the wind between the two types of trees. Clear away and destroy all plant debris and weeds near the poplar. Apply a fungicide if the tree is young. Follow manufacturer's directions and ensure the product works on melamspora leaf rust.
  
  

Leaf Spots

• Infections caused by marssonina and septoria leaf spots are indistinguishable without laboratory analysis. The fungi overwinter on infected leaves. The spores travel in the spring via wind or in moisture splashed on the tree by heavy rains or overhead irrigation. Both diseases cause the poplar's leaves to yellow and develop spots initially resembling tiny, black specks. Infections begin in the lower branches and progress upward. Leaves often drop from the tree, so clean up and destroy all plant debris and weeds that may harbor the fungus. If a septoria infection is severe, the tree's branches may develop cankers or lesions. Pruning infected areas and destroying the cuttings avoids spreading spores. Keeping the tree properly watered and fertilized helps it recover.
  
  

Aphids

• Aphids are small, soft-bodied insects that feed on the sap of the Carolina poplar's leaves and stems. Heavy feeding by the insects and their larvae interferes with the tree's ability to circulate nourishment and moisture to the foliage. This causes the leaves to yellow and become stunted or disfigured. The leaves may drop early and twigs suffer dieback. A strong stream of water from the garden hose knocks the insects off the foliage. Aphids and their larvae are a favorite meal for a variety of insect predators, including parasitic wasps, stinkbugs, spiders and ladybugs. Aphids are unlikely to cause permanent damage or kill the Carolina poplar. Use insecticidal soap or horticultural oil for heavy infestations. Dormant oil, used after the leaves fall in winter, suffocates the eggs.
  
  

Chlorosis

• When a tree is unable to take in the nutrients available in the soil, or if the soil lacks nutrients, the leaves often fade or turn yellow. This is chlorosis, and iron deficiency is often the culprit. However, other nutrient deficiencies may be to blame. Test the soil for nutrients. If the tree is unable to make use of existing nutrients, re-evaluate gardening practices, so that the Carolina poplar gets enough sunlight, air circulation, fertilizer and water for good health.