Tulip trees are a favorite among landscapers due to their beautiful flowers and big, shade-providing branches. When grown in optimal conditions with proper care, they are typically hardy and resist pests and disease. Like any other plant, however, they are not invincible. When faced with stressful environmental factors, they will develop problems. If left untreated, these problems can sometimes prove fatal.
All trees are susceptible to pests in one form or another. Aphids are the tulip tree’s biggest enemy in the insect kingdom. Aphids are small insects which suck the cell juices out of stems and leaves, especially new growth. When this occurs, the leaves begin to pucker and will feel sticky. Controlling insects usually appear in spring to combat aphids. If you have a serious infestation, use insecticides on both sides of the leaves.
Fungus often occurs after the appearance of aphids on tulip trees. This is because aphids leave behind a sticky "honeydew" that doesn’t easily dry and makes for perfect fungus growing conditions. Many different types of fungi also attack tulip trees in places where they’ve been cut open or otherwise injured. Fungal infestations cause leaves to turn brown, wilt and fall from the tree. Prune out infected leaves and apply a fungicide to stop the spread.
Fungus can sometimes cause mildew to grow on the leaves of the tulip tree. You will most often see the large, grayish spots on the leaves well into spring. While unsightly, mildew does no real damage to the tree. The only reason to treat mildew are for cosmetic reasons. Individual leaves can be removed, or light pruning can take out larger affected areas. Just be careful not to prune too much away. You don’t want to damage the health of the tree in the pursuit to make it somewhat more attractive.