I have a row of evergreen azaleas growing near my concrete driveway. The first couple seasons they looked very good, but now they look worse every year. The foliage is turning more and more yellow. Can these plants be saved?

The symptoms you describe appear to be iron chlorosis. This is a very common problem in acid-loving plants like azaleas. It is caused by a deficiency of iron in plant tissues. Although soil is seldom deficient in iron, the iron is often in a form that the plant cannot take up through its roots. This is especially true when the soil’s pH is 7 or higher. Plants located near concrete driveways, paths or walls are especially susceptible to chlorosis.

First, get your soil pH tested. There are several reliable products on the market that can correct the problem. Make sure the product label is followed correctly in accordance with the results of your soil test. Depending on the results, you can increase the soil acidity by adding the correct proportions of iron sulfate, ammonium sulfate, or sulfur. You can also mulch the soil with leaf mold or pine needles in combination with the application of an appropriate fertilizer for acid-loving plants. With some immediate treatment and moderate long-term maintenance, your azaleas should be looking as good as they did when you first planted them.

My hydrangeas are over seven years old and they have always been healthy and blooming until this year. One lacecap hydrangea was developing leaves, but they were small and curled. The stalks from this past year on the other hydrangeas were not developing any leaves even though they had buds on them when I checked a few weeks prior to this. It appears something is boring a hole into the center of the stalks and leaving “sawdust” on the new leaves. All the hydrangeas have this same problem. On the lacecap, I cut away more and more, until I reached the base of the plant and thus had to destroy the plant altogether. The bugs look like ants with wings. They are not termites, as their bodies have a shape to them. I know that the plants will not bloom this year and I don’t know if they will live. This appears to have happened in less than three weeks. Any ideas?

Although hydrangeas can be susceptible to leaf spots, blights, wilts and powdery mildew, it is rare that insects plague them. The hollow stems you are finding may be the natural growth of your hydrangeas. Some have hollow stems, while some have hollow stems filled with white to brown pith, depending on the age of the particular stem. The presence of pests may actually be a sign of another problem that is causing your plants stress. Insects that may trouble the hydrangea include aphids, leaf tiers, rose chafers, oystershell scale and four-lined plant bugs.

Aphids distort the new growth and coat the leaves with sticky honeydew. These insects can be dislodged with a high-pressure water spray from your garden hose.

A leaf tier is evidenced by webs on the leaves and over the tips of the branches. Pick these insects off by hand.

Rose chafers are light tan beetles with red, spindly legs. They occur in large numbers where the soils are sandy. Chemicals are ineffective because more rose chafers quickly move into the treated area to replace those killed by pesticides.

Oystershell scale infests the upper stems of the hydrangea and often goes unnoticed. Sprays of dormant oil should control the overwintering stages and are less harmful to beneficial predators that help to control scale. 

Four-lined plant bug causes round, brown, sunken spots on the leaves. The injury is often thought to be disease. Sprays are rarely needed for this.

Your local garden center will have pesticide sprays that you can use to control the crawlers. Ask their experts to help you choose the right product and, as always, read the labels carefully before using. Your keen observations and quick actions are the key to healthy plants.

I have an oak and a birch in my yard of many trees. Every late May or early June, the new leaves start to dry around the edges and some drop, looking somewhat fall-like. Both trees appear healthy until this happens almost overnight. What could this be?

Leaf scorch, sometimes called marginal leaf burn, describes the death of tissue along the edge of the leaf. This symptom develops when sufficient water does not reach the leaf margin cells. Causes include: 1) insufficient moisture in the soil; 2) water is lost too quickly from the leaves to be replaced adequately; 3) roots have been killed by plant pathogens, excavation, or compaction; 4) girdling; 5) injury; or 6) fungi or bacteria invade and plug the water-conducting vessels (xylem) in the plant. Here is a brief discussion of a few of these causes:

Make sure your trees get enough water. If your soil is very sandy (drains quickly), you might need to water more often. Or they might be in a very poorly draining site (heavy clay) and are waterlogged, of which the symptoms are the same as too little water.

Young leaves in the spring are often very tender and subject to damage from strong winds. Warm days following cool nights, when combined with frequent spring winds, can cause rapid desiccation of the leaves. The leaf margin is the most likely injured part of the leaf. This desiccation can occur even if the soil has adequate moisture, because the wind can draw water from the leaves faster than the tree can move it from the soil into the leaves. Very young trees may not exhibit symptoms because they are smaller, closer to the ground, and more protected from the wind, and also because they have less distance to move water through the plant to resupply the leaves. Newly transplanted trees, with limited root systems, and those which have just begun rapid growth after a couple of years of establishment following transplanting may be the most likely to show the symptoms. However, under the right conditions, this spring wind desiccation injury can occur in larger trees as well.

One of the most common and yet least recognized causes of tree problems is root disturbance, often associated with some sort of construction activity. Excavation, even at a distance of 10 feet from the trunk of a large tree, may destroy 30 percent of the root system. It does not take major soil disturbance to cause damage. Cutting a narrow ditch for laying utility cable effectively disconnects the entire root system on that side of the tree. Changes in grade will also damage tree root systems by upsetting the balance of air and water the roots need to survive. Soil compaction from heavy vehicles can kill roots. When tree roots are damaged by any of these causes, the tree begins to decline. The first symptoms may be leaf scorch.

Trees damaged by herbicides usually have leaves that are curled or cupped or have turned yellow or brown along the edges, depending on the kind of herbicide that caused the injury and the amount of exposure the trees received. Herbicides can drift through the air or move through the soil and injure trees some distance from where they were applied. Herbicide injury in trees is most often associated with the use of lawn weed killers. Herbicide exposure through the soil is longer lasting and usually more damaging than exposure through the air. Always make sure not to apply granular lawn weed killers too close to your trees.

A tree is girdled when something is tightly wrapped around the trunk or stem. Girdling chokes off the flow of water and nutrients between the roots and branches, as well as preventing food produced in the leaves from reaching the roots. Symptoms of stem girdling roots include leaf scorch, early fall color, and early leaf drop.

If you don’t recognize any of the above mentioned scenarios, it might also be an injury, or a bacterial or fungal disease. In any case, if your trees appear to be declining, it is best to let a specialist (an arborist) diagnose the situation before it is too late.