Roots are the foundation of a plant, vital organs that anchor it in the soil, absorbing water and nutrients. Unfortunately, because roots are rarely seen in full, the problems that affect them are often misdiagnosed or go unnoticed until it’s too late to act.
Root rot occurs most often in wet, poorly drained soil. In cooler, wetter periods, infections may stay hidden, allowing plants to appear deceptively healthy. As spring and summer rains give way to hotter, drier conditions, the underlying damage reveals itself when plants wilt or collapse.
Diagnosis is needed to develop a management plan
It is easy to examine the roots of an infected annual or perennial. Simply dig it up, rinse off the roots, and check them for signs of rot. Look for poor growth, water-soaked areas, brown or black discoloration (below), or roots that lack fine root hairs. Make sure you know what normal roots look like—some roots are naturally brown, whereas others may be quite colorful (see Swiss chard roots below). Examining the roots of established woody plants, especially trees and shrubs, may require the skills of a tree care professional.
A few fungal root rots produce mushrooms and conks, which makes diagnosis easier for both home gardeners and professionals. However, laboratory diagnosis is usually needed to identify the microscopic signs of root rot caused by other pathogens like Thielaviopsis basicola, Fusarium spp., Phytophthora spp., Armillaria spp., or Pythium spp. A conclusive laboratory diagnosis is essential to develop the appropriate management plan, which may include the application of fungicides or cultural controls and identifying susceptible nearby plants that could succumb should the disease spread. These services are available at your state’s plant and pest diagnostic laboratory.
Prevention and treatments can save some plants
As root rot progresses, insects such as borers and opportunistic fungal canker pathogens like Botryosphaeria or Phomopsis often attack plants, and may be blamed as the cause of the plant’s poor health. Death results when the plant’s roots are not able to take up sufficient water or nutrients to support branch, leaf, flower, or fruit development. For annuals this may occur in a few days, but large trees will slowly decline and symptoms may not be obvious for several years. By the time you recognize a problem exists, it may be too late to save the plant.
Prevention is the best approach to managing root rot. Before buying plants, unpot them and inspect their roots. You are buying the entire plant—why only look at half of it before deciding on a purchase?
When buying plants prone to certain root rots (e.g., azalea, beech, andromeda, and rhododendron for Phytophthora; pansies, hollies, and elder for Thielaviopsis), avoid setting the plant up for failure. Don’t place Phytophthora-susceptible plants in heavy clay or poorly drained soil, near downspouts, or in low spots that collect water. Consider berming plants to raise their roots out of flooded conditions. Phytophthora can be prevented, or its damage minimized, if the problem is caught early. Fungicides labeled for Phytophthora management contain the active ingredient phosphorous acid (e.g., Monterey Garden Phos, AgriFos, and many others); these may be used as a preventative treatment or as a curative treatment after a positive diagnosis.
After removing a tree or shrub infected with Armillaria, grind any stumps completely. If possible, wait until the root system has fully decomposed before planting in the vicinity of the previous tree or shrub. Avoid planting highly susceptible trees in previously infected areas, particularly oaks (Quercus spp. and cvs., Zones 3–11). Some tree species that are reportedly resistant to Armillaria include American sycamore (Platanus occidentalis, Zones 4–9), bald cypress (Taxodium distichum, Zones 4–10), black cherry (Prunus serotina Zones 3–10), dawn redwood (Metasequoia glyptostroboides, Zones 4–8), ginkgo (Ginkgo biloba, Zones 3–9), holly (Ilex spp. and cvs., Zones 5–9), and sweet gum (Liquidambar styraciflua, Zones 5–9).
With successful fungicide treatment or changing weather, an infected plant may compartmentalize and outgrow root damage. Factors that impact successful treatment include the type of host plant, its susceptibility to the pathogen, and its vigor and overall health, as well as the site and the type of pathogen. Remember that damage occurred over several seasons, and recovery may take just as long, even under the best of circumstances.
In some instances, saving a tree or shrub simply isn’t possible or cost-effective, and cutting losses involves a chain saw. Most plants can be replaced, sometimes with the same species or cultivar, but be sure to correct any underlying cultural problems that may have contributed to the failure. Avoid future problems by choosing plants that are noted for root rot resistance. Disease-resistant plants improve landscape sustainability and reduce the need for pesticides. As always, source plants from reputable places—local nurseries are excellent resources to identify the best plants for your area.
Janna Beckerman, PhD, is a professor emerita at Purdue University and the ornamentals technical manager for Envu Environmental Science.
Fine Gardening Recommended Products
Fiskars 28" Power-Lever Garden Bypass Lopper and Tree Trimmer
Fine Gardening receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.
Felco Pruning Shears (F 9) - High Performance Swiss Made One-Hand Left-Handed Garden Pruners
Fine Gardening receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.
BLACK+DECKER 40V MAX Hedge Trimmer, Cordless, 24-Inch Blade, Battery and Charger Included (LHT2436)
Fine Gardening receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.
Comments
Root rot can sneak up on plants, often going unnoticed until it's too late. Catching it early and ensuring proper drainage can help save your plants. If you're dealing with trees, experts like Penrith Tree Removal can help manage and assess any issues.
Log in or create an account to post a comment.
Sign up Log in