On October 29, 2004, the Animal and Plant Health Inspection Service (APHIS), National Identification Service confirmed the identification of Puccinia veronicae-longifoliae Savile, an exotic “rust” fungus. A commercial nursery operator in Michigan observed foliar disease symptoms on field-grown Veronica plants. Samples were collected by the Michigan Department of Agriculture (MDA) for preliminary identification at their laboratory.
The source of the infection is unknown at this time. The nursery uses both in-house stock and cuttings obtained from a facility in Costa Rica. Trace backs determined that the Costa Rican facility received its nuclear or “mother” stock from both the United States (California, Colorado, Pennsylvania, and Washington) and Europe. More than 1.2 million un-rooted Veronica cuttings were shipped last year from the Costa Rican facility to growers in 30 U.S. states and four provinces in Canada. To date, there have been no other reports of P. veronicae-longifoliae from any other Michigan nursery or from nurseries in any other U.S. state, or in Canada, Costa Rica or the facility in Costa Rica. As soon as rust in the Michigan nursery was positively identified, all suspect plants were restricted by MDA. However, prior to confirmation, plants had been shipped to 41 establishments in 19 U.S. states. Reportedly, actions will be voluntarily taken to disinfest the Veronica field site to prevent spread of the pathogen.
Puccinia veronicae-longifoliae is an obligate plant parasitic fungus that requires one host species to complete its life cycle. Veronica spicatum, V. longifolia and V. montana are reported hosts. The known distribution of the pathogen is China, Denmark, Germany, Japan, Sweden, Taiwan and the United Kingdom. Typically, rust-infected plants develop pustules on leaf surfaces that rupture the epidermis and eventually release colored spores-hence the name rust. When infections are not controlled, rust pustules reduce the aesthetic value of plants. Pustules can coalesce to form necrotic areas and severe infections can cause premature leaf drop and reduced vigor and flower production.
The New Pest Advisory Group (NPAG) held a teleconference November 5, 2004 to discuss the Veronica rust situation. Subsequently, the risk and hazard of this pathogen were assessed by NPAG through literature research, PPQ database queries, and discussions with subject-matter experts. Based on NPAG’s assessment, APHIS will not classify P. veronicae-longifoliae as a quarantine significant pest and no Federal regulatory action will be taken. The rationale for this action is:
· P. veronicae-longifoliae is a host-specific, fungal pathogen, only known to affect the foliage of three species of Veronica, none of which are listed as Threatened and Endangered in the United States.
· Veronica is an herbaceous perennial landscape plant of minor economic, environmental and social importance.
· State Integrated Pest Management programs are likely to provide efficacious control of Veronica rust.