Sweet Viburnum (Viburnum odoratissimum) is thought of as being an ironclad landscape shrub, generally a rapid, healthy grower free of insects and disease. However, this spring, many Sweet Viburnum specimens across the Panhandle have experienced varying degrees of dieback, from individual shoots to entire sections of shrubs, caused by the fungal pathogen Botryosphaeria – commonly known as Bot Rot.
Typical symptom of Bot Rot on Sweet Viburnum. Photo courtesy of Daniel Leonard.
Bot Rot almost always appears after some kind of major stress event that impacts susceptible plants – drought, pruning wounds, nutritional deficiencies, or another environmental stress. We haven’t been afflicted lately with any serious drought conditions and the disease occurrences are too widespread to have been a result of isolated pruning or poor plant nutrition. However, the Panhandle did experience a major environmental event around Christmas 2022 that was plenty stressful for landscape plants, a weeklong Arctic blast of extreme cold. This abrupt hard freeze event in an otherwise mild winter is my best guess for what brought about the increased incidence of Botryosphaeria we have experienced this spring.
The Botryosphaeria fungus enters plants via wounds – in this case one probably caused by cold – and begins destroying the plant’s vascular system in the area. As the pathogen progresses, it eventually causes sunken cankers to appear, girdles the affected branch, and cuts off “circulation” in that stem. The first symptom of Bot Rot that gardeners notice is shoots rapidly wilting and exhibiting a blighted appearance, with brown, dead leaves holding onto affected limbs. Unfortunately, dieback isn’t always limited to individual shoots and can spread back into plants to eventually encompass whole branches. Entire plants dying from Bot Rot infection is not uncommon.
While there aren’t any fungicides that are effective in controlling or preventing Bot Rot, gardeners can arrest its spread by pruning out infected branches. To completely rid the plant of the fungus, make sure to prune 4” or so below the last infected plant tissue (symptomatic tissue will appear dark and discolored; healthy tissue will appear light and greenish). After pruning each affected plant, it is important to sanitize pruning equipment with either a 10% bleach solution or 70%+ isopropyl alcohol to prevent spreading pathogens to other healthy plants! Plants that have been irreparably disfigured by Bot Rot or outright killed may be pulled and discarded offsite.
While this year’s Bot Rot infestation has been extremely frustrating and similar future freeze events can’t be ruled out, gardeners should not give up on Sweet Viburnum, an excellent specimen or screening shrub. Keeping plants healthy with proper pruning, good fertility, and adequate irrigation is the best defense to ward off future infection when we experience harsh environmental conditions! For more information on Bot Rot, Sweet Viburnum, or any other horticultural topic, contact your local UF/IFAS County Extension Office! Happy Gardening.
I’m hard pressed to tell you my favorite song, movie, or place to eat, but when we start talking plants I can come up with whole categories of favorites. I won’t commit to just one species, but when it comes to woody shrubs I am a huge fan of viburnums. We have small ones, tall ones, evergreen, deciduous, smooth leaves, textured leaves, berry producers and sterile types. There are so many different types there must be one for every gardener.
Buds and flowers of Viburnum luzonicum. Photo: J_McConnell, UF/IFAS
I thought I knew a lot of viburnums after spending ten years in the nursery industry, but had not seen Luzon Viburnum, Viburnum luzonicum, until Dr. Gary Knox gave one to me in the fall of 2014. The plant was little more than a couple of stems and light green leaves, but he assured me it would get large and would perform well in the Florida panhandle.
That scrap of a plant went into a large, non-irrigated, full-sun bed in my yard and was hand-watered through the first summer, but after that has been left to fend for itself. My Luzon viburnum is currently over 6 feet tall by 4 feet wide and covered in flowers. It gets no TLC in my landscape, but has yet to be plagued by any pests. The foliage emerges with a slightly pink tone then settles into a light green usually starting in February or March. By late March clusters of small white flowers cover the shrub. It is reported to have the potential to produce berries that transition from red to black, but I have not yet observed that in my garden.
This is not a plant you are likely to stumble across in most garden centers, but is worth keeping a lookout for in case you see it. It is on display with many other wonderful plants in the Gardens of the Big Bend at the UF/IFAS North Florida Research and Education Center (NFREC) in Quincy and in the past has been available at Gardening Friends of the Big Bend plant sales.
A new IPM guide is making it easier to grow five common southeastern shrubs. Growing five southeastern shrubs is now easier thanks to a free, new IPM resource from the Southern Nursery IPM Working Group.
IPM for Shrubs in Southeastern U.S. Nursery Production is a compilation of Integrated Pest Management (IPM) information for five major shrubs in nursery crop production in the southeast. This 175 page book covers sustainable management for insects, mites, diseases, and weeds for these shrubs, as well as nursery production information. This IPM resource was developed for nursery growers although professional landscape managers and collectors of these plants also will find the information valuable.
Individual chapters cover abelia (Abelia spp.), camellia (Camellia spp.), shrub rose (Rosa spp.), blueberry (Vaccinium spp.) and viburnum (Viburnum spp.). Each chapter provides comprehensive information on the species, primary cultivars and their nursery production. Major pests, diseases, weeds and abiotic disorders are presented for each genus along with sustainable management methods and tables listing labeled pesticides and fungicides by mode of action and site. An additional chapter discusses weed management in shrub production. Future volumes covering additional shrubs are anticipated.
Edited by Clemson University’s Sarah A. White and University of Tennessee’s William E. Klingeman, this free guide was developed by the Southern Nursery IPM Working Group, including University of Florida NFREC’s Gary Knox and Mathews Paret. The award-winning, multi-disciplinary group is composed of experts from universities across the southeast. This group formed in 2008 to develop and deliver educational programming to the southern U.S. nursery industry and Extension personnel. The team recently won the 2014 Bright Idea Award from the Friends of Southern IPM and Southern IPM Center.
This resource joins the tree IPM book previously released by this group, IPM for Select Deciduous Trees in Southeastern US Nursery Production. The tree IPM book is similar to the new resource in that it contains IPM information for insects, mites, diseases, and weeds of nine major tree crops as well as production information. Individual chapters cover birch (Betula spp.), cherry (Prunus spp.), crapemyrtle (Lagerstroemia spp.), dogwood (Cornus spp.), chinese elm (Ulmus parvifolia), magnolia (Magnolia spp.), maple (Acer spp.), oak (Quercus spp.) and redbud (Cercis spp.).
Both books can be downloaded free through iTunes (http://www.apple.com/itunes/) or each chapter is available as a free pdf through the Southern Nursery IPM Working Group website, http://wiki.bugwood.org/SNIPM. A limited number of hardcopy books were printed and distributed to authors. Thanks to the Southern Region IPM Center for their generous support to make this resource possible!
