INDUSTRY RESEARCH
Why NCDA&CS Plant Industry Division Prohibits Currant and Gooseberry Plants in North Carolina Fungal structure erupting from stem of young tree. Photo: Bruce Watt, University of Maine, Bugwood.org
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he risk of an invasive fungal pathogen destroying North Carolina’s white pine trees (Pinus strobus) may be an increasing threat due to mail order shipments of gooseberries and currants (Ribes spp.). The North Carolina Department of Agriculture & Consumer Services (NCDA&CS) Plant Industry Division hopes to spread the word about why planting these popular edible fruits could have detrimental agricultural impacts on wild and cultivated white pines. Regulation through education is often the most successful way to garner public understanding and participation. Targeting wellmeaning homeowners with foundational knowledge regarding the potential risks associated with their thriving backyard garden may be the key to protecting white pines across our state. In the early 1900s, a rust fungus known as Cronartium ribicola, the causal agent of white pine blister rust, destroyed the white pine forests of the northeastern United States. This rust fungus arrived on white pine seedlings imported from Germany, used to replant the lands stripped by timber companies. The widespread devastation caused by this fungus alerted U.S. legislators to the importance of custom and border protection and led to the passage of the Plant
Quarantine Act in 1912. However, the law itself could not stop the pathogens that had already arrived in the U.S. and become widely dispersed. Early attempts to control white pine blister rust focused on destruction of infected white pine; unfortunately, this effort proved to be ineffective as researchers learned more about vectors and spread of the disease. Modern day efforts to control white pine blister rust focus on the known, required alternate hosts plants in the Ribes genus which contains about 150 known species. The Ribes species grown by homeowners and niche farming operations for their edible fruit (currants and gooseberries) play a critical role in the spread of white pine blister rust. Like many other rust fungi, white pine blister rust requires an alternate host to complete its life cycle. The devastating disease starts when the orange rust spores (basidiospores) produced on the leaf of Ribes species infect the white pine — up to 1,000 feet away when spread by wind — through the needles. White pine blister rust infections occur when the weather is cool and moist. Spread of the disease occurs when the white pine blisters (which contain numerous spores called aeciospores) erupt through the bark of the white
By Hsien Tzer (HT) Tseng, Ph.D. Plant Pathologist, North Carolina Department of Agriculture & Consumer Services, Plant Division
Join HT Tseng for a session on disease regulations and newly-reported diseases at Green & Growin’ 21 Virtual Education.
FALL 2020 | NURSERY & LANDSCAPE NOTES | 35
