How Do I Treat Chlorosis in My Denver Trees?

Protecting your trees and shrubs from pests like the EAB is on on your radar; but what about diseases that quietly deplete your plants’ resources and cause irreversible damage? Chlorosis is one of these lesser-known diseases that is actually quite prevalent in the Denver region. Follow our guide to learn how to treat Chlorosis in your trees and get them back to full health.

What Is Chlorosis and What Causes It?

For starters, you are likely wondering, “What is chlorosis exactly?” Let’s take a trip down memory lane, back to middle school science class! You probably remember that leaves obtain their vibrant green color through the process of photosynthesis, but the details of that process may have been forgotten. Here’s the gist:

  • Plants convert light energy into chemical energy and produce oxygen in the process
  • Chlorophyll is the green pigment in leaves that promotes photosynthesis. 
  • Plants make their own chlorophyll, but to do so they need to draw upon key nutrients from the soil- nitrogen, magnesium, and iron. 

Chlorosis simply means lack of chlorophyll. It is caused by a deficiency of one or more of the key nutrients: nitrogen, magnesium, or iron. In Colorado, the alkaline soil is characterized by very high pH levels, and most of the iron is not in an insoluble form not usable by plants.

For this reason, trees in the front range suffer specifically from iron chlorosis due to the deficiency in iron that hinders them from properly creating chlorophyll. Lack of iron in a tree may be due to a high iron need, less effective iron uptake, or insufficient usable iron in the soil.

How Does Chlorosis Affect Trees?

According to the Colorado State University Extension, iron chlorosis can affect trees in a variety of ways. First, it typically makes a leaf become yellow while the veins of the leaf remain green. The newest leaves on the ends of branches seem to be the most affected by this condition. As the tree advances into a more severe state, all the plant’s leaves are affected. In dire cases, iron chlorosis will cause plant tissue to die. This results in brown and scorched-looking areas on the leaves.

Can a tree die from iron chlorosis? In short, yes. However, this worst-case scenario would only happen in the event that absolutely no action was taken to save the tree. Iron chlorosis would affect the tree in the following progression:

  • Individual leaves will appear white, the turn brown
  • Whole branches will suffer from dieback
  • The entire tree will die after several years

To recap, chlorosis in Denver trees is caused by a lack of iron nutrients needed to produce adequate amounts of chlorophyll. The disease causes the tree leaves to lose their green pigmentation, turn white and then become brown and scorched-looking. If left completely unattended for years, trees in advanced stages of iron chlorosis can die.

A more common fate that befalls trees infected with chlorosis is winter injury. Because chlorosis weakens the trees over vigor and immune system, it is more prone to winter damage and injury from freezing, road salt, and storm winds.

Now that you know how serious the effects of chlorosis can be, it’s important to learn more about how to identify it and treat it. We’ll also cover which front-range tree species are most likely to be affected by chlorosis.

How To Identify Chlorosis

Iron chlorosis is quite common in Denver trees, but luckily very treatable. Sadly, many trees suffer simply because homeowners aren’t aware of the warning signs. Learn the visible symptoms of chlorosis and keep a vigilant eye on the trees and plants on your property. Catching chlorosis in the early stages will help keep your trees healthy and strong!

Hallmark symptoms of iron chlorosis, as identified by the Master Gardeners at CSU:

  • iron chlorosis shows first and more severely on the newer growth at branch tips
  • newest leaves towards ends of branches are generally yellowed
  • veins of affected leaves remain green but leaves may be smaller than normal
  • on fruit-bearing trees, fruits may be small with a bitter flavor
  • in advanced cases, leaf edges become scorched and leaf interiors show dead brown areas as cells die
  • leaves may eventually curl, dry up, and fall
  • plants become unsightly and grow poorly
  • symptoms may only show on a single branch or on one side of a tree

It is important to note that chlorosis affects tree species differently, depending on their susceptibility to iron deficiency. More on that in our next section!

The list above is a great guide for keeping chlorosis on your radar, but sometimes these symptoms can be similar to those caused by other tree issues. The experts at CSU caution Denver homeowners that chlorosis is often confused with the following:

  • Zinc and manganese deficiencies result in similar leaf symptoms. Iron chlorosis appears first on the younger or terminal leaves. Under severe conditions, it may progress into older and lower leaves. By comparison, zinc and manganese deficiencies typically appear first on older, interior leaves.
  • Nitrogen deficiency shows a uniform yellowing of the entire leaf (including the veins). Nitrogen deficiency shows first in the older leaves, while iron chlorosis shows first in the newer growth.
  • Damage from soil sterilants (i.e., Pramitol, Atrazine, Simazine, Ureabor, and Diuron) used to prevent weeds result in similar symptoms. With these weed killers, the leaf tissue along the vein remains green. With iron chlorosis, just the vein itself remains green.
  • Natural aging of tissues may create similar symptoms in some plants. Root and trunk damage and some virus, phytoplasmas, and vascular wilt diseases may cause similar leaf symptoms.

How is a homeowner supposed to determine the root cause of the symptoms when they are so similar? No worries, just team up with our trained arborists to get a high-quality consultation. Our expert staff has the education and experience needed to accurately diagnose your trees and plants. From there, we can help create a custom care plan that fits your needs. 

Denver Trees Most Likely to Be Affected by Chlorosis

Some Denver trees are more susceptible to iron chlorosis than others. Just as you would be mindful of people with allergies or pre-existing conditions when they are in your care, you should know what kind of trees you are caring for and find out if they are at risk for developing chlorosis. Knowledge is the key to working on a successful preventative care plan.

Denver Maple Trees

The Silver, Red, and Amur maple species at notoriously at high risk for chlorosis. How can you tell if you’ve got a maple in your yard? All of these maple varieties have a distinguishing leaf shape, rough-toothed with 3-5 shallow lobes. The silver maple leaf, as its name would suggest, has a silver-colored underside. Red maples keep their red leaves all year long, while Amur maple has a glossy green leaf that turns fiery red in autumn. Silver and Red maple trees grow tall, to about 50-80 ft at full maturity, but the Amur maple stands just 15-20 ft fully grown.

Front Range Oak Trees

There are about 450 species of oaks, but in Colorado, the Red, White, and Swamp oak tree varieties are the most likely to develop iron chlorosis. There are a few factors that differentiate these oak species from one another. First, white oaks have gray-colored bark and leaves with rounded lobes without bristles. In contrast, red oaks have darker-colored bark and leaves with pointed lobes and bristles. Swamp oaks have dark, rough-textured bark and leathery dark green leaves that turn yellow and red in the fall. All three species can grow to 40-80 ft when fully mature.

Fruit Trees

In addition to maple and oak trees, fruit trees like crab apple, apple, and peach trees are also susceptible to chlorosis. These fruit trees do not get an adequate amount of iron uptake from the soil and have difficulty transporting iron nutrients throughout their cellular system.

Even with Google at your fingertips, identifying the trees on your property can be tough. During a quick consultation on your property, our trained arborists can identify your tree species and inspect for any symptoms of chlorosis!

The Best Way To Treat Chlorosis

Research by the Colorado State University Extension shows that there is no “one size fits all” best practice when it comes to treating chlorosis. Treatment programs instead should be customized, taking into consideration environmental factors like plant and soil conditions.

To begin, CSU staff recommends reducing springtime over-watering and soil compaction which are known to be contributing factors. Next, you can consider iron additives. There are four general approaches to iron treatments: 

1) Lowering the soil’s pH: Due to the high pH and lime content of many Colorado soils, this approach is seldom effective and therefore rarely utilized.

2) Soil iron treatments: this approach applies a mixture of equal amounts of iron sulfate and sulfur to the soil over a period of several months to a year. The mixture is inserted in holes around the drip line of the tree, where the sulfur reacts to lower soil pH. When effective, this treatment can last up to 3-4 years.

3) Foliar sprays: Foliar sprays of iron sulfate or iron chelates may provide a quick response, often in a matter of days. The downside is that the treatment is often inconsistent and only temporary, the effects will not carry over for multiple years. To be fully effective, complete coverage of all leaves is necessary, but full coverage on large trees may be near impossible.

4) tree injections: Professional arborists have trunk injection methods available for treating iron chlorosis on large trees. Trunk injections may last from one to five years and application methods vary depending on the specific product. This method is more effective for treating large trees than foliar spray. 

Determining and executing the most effective method for treating chlorosis is best left to the experts. Haphazard application of iron sulfate foliar spray products can stain and ruin your home exterior and sidewalks. 

Let our experienced team do the hard work so you don’t have to! We’ll help you determine the best course of action and execute the treatment plan with precision and care, getting your trees and plants back to good health.

Protect your Denver trees and plants from harmful chlorosis. Contact our expert arborists today for a free consultation!