Take steps to prevent quince rust

You are probably familiar with cedar-apple rust caused by Gymnosporangium juniperivirginianae.

However, you may not be familiar with another very common cedar rust called quince rust. The causal agent of quince rust is Gymnosporangium clavipes. You can find this rust sporulating on eastern red cedar and some upright junipers twigs and branches during spring months. Later during the summer you may see this rust sporulating on galled twigs and fruit of hawthorn. (Figure 1)

I have also observed this rust on the fruit of crabapple and serviceberry. This rust can be quite damaging to ‘Washington’ hawthorn twigs and fruit.

Disease Cycle: Gymnosporangium clavipes overwinters and is perennial on junipers, including eastern red cedar. With the advent of warm, moist spring weather, telia erupt and produce teliospores. Teliospores germinate and produce basidiospores which infect rosaceous hosts including hawthorn. Infection may take place in as little as two hours if conditions are optimal. After 30-60 days aecia-spores which are produced on hawthorn stem galls and fruit will infect juniper twigs and needles from late summer to fall. You will see no sign of infection until the next spring.

Management: Growing hawthorn in close proximity to cedar usually leads to trouble, but can be difficult to avoid in Tennessee. Cultivar resistance is an option; do some research before choosing a cultivar to grow. Also, fungicides can be used to protect young hawthorn fruit and green shoots.

Fungicides to protect hawthorne should be applied as the new growth appears and 3-4 times at 7- to 10-day intervals. Applications are especially important before rainy periods. Suggested fungicides include Banner, Bayleton 25WP, Daconil 2787 WDG, Dithane T/O 75 WP, Dithane WF, Fore 80WP, Fore Flowable, Rubigan AS, Strike 25WP, and Zyban 75WP.

No doubt some infection has taken place already this spring; however, spraying might be useful to prevent infection that would take place between now and the end of May.

(Information and image provided by Dr. Alan Windham, UT Extension)