Tis the Season for Plant Dieback – Here’s How to React

by | May 9, 2024 | Best Management Practices, Florida Friendly Landscaping

In the last couple of weeks, I’ve had multiple questions regarding trees and shrubs that aren’t looking too hot.  These types of calls are common this time of year – it has gotten hot and dry, and plants have fully emerged from winter, causing issues that have been hiding under the surface during the dormant season to manifest as crown or branch dieback.  While there are a wide variety of things that can cause dieback, in most cases a little detective work can help pinpoint the issue.  Let’s look at a few of the most common causes of dieback and some corrective measures that may help restore the plants to health.

The first thing to do when you notice a plant in decline is nothing.  Don’t try and oversaturate it with water.  Don’t run out and dump a bunch of fertilizer around it.  Many times, these panic measures exacerbate the stress the plant is already under.  Instead, I encourage you to give us a call at your local  UF/IFAS County Extension Office.  We can likely help identify the cause of the problem through a site visit to your property or by you sending us diagnostic photos of the plant with a description of what’s been going on with it – the more information you can provide about the plant and the management practices it has experienced, the better (you can email diagnostic images/information to d.leonard@ufl.edu).

The most common cause of tree/shrub dieback that I see arises from improper planting practices.  Most landscape plants should be planted at or just above the surrounding soil level, preferably where the topmost root arises from the trunk.  To accomplish this, planting holes should be dug slightly shallower than the rootball’s height and about twice as wide.  Planting any deeper than that is probably too deep and can cause problems like trunk and root decay, which lead to crown dieback.  Unfortunately, once a plant is planted too deep, it cannot be corrected other than digging up and replanting at the proper depth, which may or may not be possible depending on the size of the tree.  Another common issue that can arise after planting is girdling roots.  This occurs when plants are grown in plastic containers and develop a root system that circles the inner wall of the pot.  If not trimmed, the plant’s root system will continue to grow in this manner, eventually encircling the plant’s trunk, cutting off water and nutrient flow, and leading to crown dieback.  Fortunately, this condition can be prevented by cutting, removing, or redirecting these roots at planting.

The next most common cause of plant dieback occurs due to soil disturbance by people.  It’s easy to forget but the root zone of trees and shrubs can reach out several times farther than the plant is tall and is easily damaged.  Disturbances to the root zone from digging or trenching near trees or compaction from prolonged vehicle travel over the area cause damage that might be slow to appear but can lead to plant decline. If you are doing construction or building near a shrub or tree, try to keep digging machinery as far out of the root zone as possible and avoid repeatedly parking or driving vehicles over the root zone area.  Like below ground root damage, trunk damage that occurs from injury by string trimmers, mowers, or animal feeding activity can all disrupt the flow of water and nutrients in plants and prove deadly.  There is no cure for this type of damage, so employing physical barriers to prevent damage is key.

  • A Shumard Oak exhibiting crown dieback as a result of being planted in a poorly drained site. Photo courtesy of Daniel Leonard.

  • A healthy Shumard Oak in a well-drained site. Photo courtesy of Daniel Leonard.

The last major stress is environmental in nature and is caused by a water imbalance – either too much or not enough.  Dry soil conditions during the planting and establishment phases (first several years after planting) should obviously be avoided if possible – keeping the developing rootzone moist and allowing plant roots to establish in their native soil is critical.  Too much water can also cause problems for trees planted in poorly drained soil.  Excessive moisture leads to root diseases, which ultimately presents as dieback in the canopy.  If planting in an area that tends to stay wet, select a species of plant adapted for that sort of site – some species are more tolerant of “wet feet” than others.  While many people expect disease and insect damage to be the cause of an unhealthy plant, they’re often not the biggest culprit and, if they occur at all, are generally secondary to one of the above issues.

For more information about crown dieback or declining landscape plants, contact your local UF/IFAS County Extension office.  Happy gardening!

Daniel J. Leonard
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