There are a variety of different insects and diseases that can infest your landscape plants and cause a considerable amount of damage. Many of the insects are so small they are are extremely difficult to see with the naked eye, unless you know what you are looking for. I’m going to give you a few helpful hints.
Scale insects are very common on Euonymus varieties and some varieties of Magnolias. Variegated Euonymus are extremely popular landscape plants among homeowners. There are many different varieties ranging in color from green, white, and yellow. The pattern of the variegation varies on the different varieties. All varieties are susceptible to attack from Euonymus scale insects.
Scale infestations are easy to spot because the insects build a very hard protective cover over top of themselves for protection. These protective covers look like little tiny white spots on the underside of the leaves and on the stems of the plants. These protective covers are like a garage for the insects to hide under. While hiding in this little garage the insects attach themselves to the plant and suck the nutrients from the plant. Thousands of these little insects feeding on a plant can cause severe damage.
The protective covers these insects build are very effective because even sprays will not penetrate this cover very well. That’s why one of the most effective ways to control scale insects is to spray with a dormant oil spray during the winter months. Dormant oil is heavy and seals up these little tiny garages and the insects suffocate. Dormant oil will harm the plant if sprayed during the growing season. Summer oil can be applied during the growing season, however, some professionals claim it has no effect at all.
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An insecticide labeled for scale insects can be applied during the spring, this is when the insects are active and come out from under their make shift bomb shelters. Visit a full service garden center and talk with somebody who is knowledgeable about the insecticides they sell.
Check your variegated Euonymus plants very carefully, inspecting both the stems and the underside of the leaves. Look for little tiny white specks that are firmly attached to the plant.
Euonymus scale can be controlled if caught in the early stages. Once the infestations become severe they are difficult to over come and the plant is usually damaged to the point that it must be disposed of.
Another insect that can quietly work away damaging your landscape plants without your knowledge are spider mites. Spider mites are very tiny and extremely difficult to see. Like the scale insects, spider mites are also sucking insects. They also reproduce by the millions. They are fairly easy to control, but because they do reproduce so rapidly if you miss a few it won’t be long before you have hundreds of thousands, if not millions.
Most professional nurseryman alternate with two different chemicals when they spray for spider mites. They’ll spray one chemical today, and ten days later spray a different one. That way they don’t have to worry about the few spider mites that survived the first spraying building up a resistance to the chemical, and then breeding thousands of babies that are also resistant.
At home you probably don’t need to worry about that because you probably only have a few plants that spider mites prefer. Spider mites can be found on many different landscape plants, but two of their favorite host plants are Dwarf Alberta Spruce and Burning Bush. To check your plants for spider mites do this simple test.
Take a plain white sheet of paper and hold it under a branch or two of the plant you would like to check. Using a pen, pencil or similar instrument quickly strike one of the branches above the paper. This should shake loose some debris from the plant. Most of this material will be dust like material. Hold the paper very still in the light and watch those dust particles very closely. If some of them appear to be moving around on the paper, you have spider mites. They are very, very, small. A magnifying glass will help you to see them better.
Your local garden center will have a spray to control them. If you prefer organic controls, soap sprays work fairly well. Some folks suggest washing the insects off the plant with a high pressure stream from your garden hose. Does this work? I honestly don’t know.
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Spider mites like a warm, dry environment which is why some shrubs planted close to the house in a landscape make good host plants. The heat reflected from the house makes the plant a nice, warm, cozy place to camp out, if you’re a bug! You can beat them at their own game by sprinkling the foliage of the plant on a regular basis. Mix in a little soap if you really want to ruin their party.
Just make sure you don’t make the soil around the roots too soggy, and don’t leave the foliage wet at night. You don’t want to trade your spider mites for a fungus.
Dogwood trees, Rhododendrons, Purple Sandcherry, White Birch, Mountain Ash, and many other ornamental trees and shrubs can become infected with insects that bore into the branches, stems, and the trunk of trees. Inspect your plants very carefully looking for tiny holes that appear to be drilled into the wood of the plant.
Controlling these types of pests is usually done best with systemic type of insecticides. A systemic is any pesticide that is absorbed by the plant. When the pests eat the plant tissue they also consume the insecticide, thus the plant is rid of the pest before the infestation becomes too severe, and little damage is done. Once again, visit your local garden store for the right product.
Your plants can also be attacked by a variety of insects that eat the foliage of your plants. Depending on the severity of the damage, this is not always a serious threat to deciduous plants because they completely replace their foliage each year. A deciduous plant is a plant that loses it's leaves during the winter. However, it is still a good idea to control all insects on your plants. When the leaves of a plant are damaged, the plant does not receive the nutrition it should. Your local garden center will have a general spray for insect control.
One of the most damaging foliage eating insects is the Japanese Beetle. Not only do Japanese Beetles eat the foliage of your landscape plants, they also lay eggs in your lawn. These eggs hatch into larva (grubs) that feed on the roots of your grass, doing considerable damage to your lawn. That's not even the worst of this situation. When your lawn is infested with grubs, skunks, moles, raccoons and even birds will dig in your lawn causing substantial damage. I've seen lawns that literally look like large sections have been roto-tilled, when in fact the damage was done by a skunk or raccoon digging for grubs.
For information on controlling Japanese Beetle grubs visit the page on "How to Keep Moles, Skunks, and other Critters from Digging up Your Lawn." Click here to go there now.
There are also fungi and diseases that can damage your plants. One that often goes unnoticed until it has done substantial damage is Fire Blight. Fire Blight attacks Cotoneaster, Pyracantha, and Crabapples as well as some other plants. The early symptom is a branch that has died in the middle of the plant, for what appears to be no apparent reason. The leaves of this dead branch do not fall off, instead they turn dark brown. This usually starts on one of the plants extremities, and works it's way toward the center of the plant.
There are no effect sprays that I am aware of. Effective control can be achieved by simply removing the affected branch. Cut it back as far as you reasonably can. Do not put this branch in your compost pile. Burn it if possible. If not cut it up and get it off your property. It is also a good idea to dip the blade of your pruning shears in rubbing alcohol after trimming branches that could be diseased.
If you catch Fire Blight early, you can keep it from spreading throughout the plant. Keep an eye on all of your plants, removing any branches that do not appear to be healthy.
The high humidity of the dog days of summer brings with it the potential for plant fungi. One of the most common is Powdery Mildew. This can occur on a variety of plants, but Dogwoods are highly suscepticle. The symptoms are a fine white powder like coating on the surface of the leaves. Although not extremely harmful, it gives the plant an unhealthy appearance. I have noticed on my Dogwoods that have developed this fungus during the summer that the plants don't seem to produce flower buds as well as they should. A plant must be healthy and happy in order to function as it should.
Powdery Mildew can be controlled with fungicides available at your local garden center. Be careful about watering in the evening. If you send your plants to bed with wet leaves, fungi can and will appear. When watering late in the day make sure you give you the leaves of your plants time to dry before the sun goes down.