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fusiform rust

Q: What is the orange colored powder on some of the trunks or stems of nearby trees?

Q: My home backs up to a large natural area and I have seen a few of the small pine trees with large areas of an orange colored powder on some of the trunks or stems.  It is such a bright orange color that it reminds me of cheddar cheese.  What is it?

A:  More than likely, this is a disease called Fusiform rust, caused by the fungus Cronartium quercuum.  This fungus is native to the southern United States so the disease if very common in our area. Many rusts require an alternative host to complete the life cycle and this one is no exception.  Part of its life cycle is spent on oak trees which is a requirement for survival.  It causes little or no noticeable damage to the oak tree but the second part of its life cycle does cause damage to pines.  The fungal spores are spread by wind from the pine to the oak and back again. Usually during the spring (March or early April) galls will form on pine trees. These galls will produce the bright orange colored spores you spotted which are carried by the wind onto newly forming oak leaves.  These spores will form pointed structures on the underside of the oak leaves where they are transferred by the wind onto pines. There are some management strategies for pine farms but for the average homeowner, it is not practical to remove oak tree stands from around your property.  One option would be to remove the small pine trees if this natural area is part of your private property. Since this gall is part of the trunk of the tree, it is unlikely the tree will survive anyway.