Diagnosing Common Garden Threats

Aug 28, 2015

If you see lumps or weird shapes on the leaves of your oak tree, don't panic, says Laura Jesse, director of the Plant and Insect Diagnostic Clinic at Iowa State University. She says it's likely a gall, which is harmless to the plant.

"They're the most interesting shapes," says Jesse, who calls them "beautiful." Jesse also says if you break them open you can usually find a wasp larvae that began feeding on the tree and prompted it to grow a gall around the insect.

Plant pathologists are also seeing a lot of yellowing of tree and shrub leaves, along with scorching. That could be a wilt disease, but it could also be a nutrient deficiency according to Lina Rodreguez-Salamanca. She says diagnosing the problem is helpful, so that you can plant a resistant variety of the plant in that location instead. Rodreguez-Salamanca says it's been a difficult year, disease-wise, for trees.

The two clinicians talked with host Charity Nebbe on this edition of Horticulture Day on Talk of Iowa. Other common garden threats that seem more prevalent this year include Japanese Beetles and, of course, the Emerald Ash Borer.