Hello,

Forsythia are susceptible to several diseases including crown gall, leaf spot and twig blight. Other pests that infest it include four-lined plant bug, Japanese weevil. Dieback of twigs can be caused by white mold, a fungal disease caused by Sclerotinia sclerotiorum and occurs when there is cool wet weather. Early symptoms include stem cankers followed by wilting. Read more here: https://extension.psu.edu/forsythia-diseases

The disease can be managed pruning out and removing affected stems and branches. Prune to improve air circulation within the shrub. Forsythia benefits from renewal pruning after flowering. Prune out one-third of the shrub (the old stems) each year.

For a more definitive analysis, you can submit a sample and photo of the forsythia to the Plant and Pests Diagnostic Lab at MSU Extension. To learn how to make a submission, go to: https://www.canr.msu.edu/pestid/

You can also contact a certified arborist at www.treesaregood.org, the website of the International Society of Arboriculture to find an arborist in your area.

Thank you for contacting Ask Extension.