Groundwork for July 14, 2013

BY Bob SOUVESTRE

Photo provided by the LSU AgCenter -- Natchez crape myrtle is among the popular varieties in Louisiana.
Photo provided by the LSU AgCenter -- Natchez crape myrtle is among the popular varieties in Louisiana.

The early spring months of March and April were not kind to spring growth on crape myrtles this year. But we are seeing very nice blooms on these great summer-flowering landscape trees as we reach their peak performance time of late June through July.

Keys to success with crape myrtles include correct sunlight, ideal soil pH and drainage, proper pruning, regular fertilization, proper mulching and insect control.

Crape myrtles need full sun in order to perform their best, grow their best and bloom their best. This means eight hours or more of direct sun daily. Less than eight hours of sunlight daily is not sufficient for ideal performance.

Many of us underestimate the amount of sun our landscape receives. To get a better handle on this, check sun patterns in the morning, during the middle of the day and again in late afternoon.

Proper soil pH is important for crape myrtles, but maybe not as important as it is for some of our other landscape plants. Crape myrtles like a soil pH of 6.0-6.5. This is considered slightly acid. Do not guess on soil pH — soil test. The pH level can be lowered with sulfur products and raised with lime products. But always do this based on the results of a soil test.

What about pruning? Although February is the time to prune crape myrtles, your particular trees may not need to be pruned. When it is needed, prune these trees to maintain a natural shape. Thin out branches. Do not top or just “hack off the top” of these trees. This is commonly referred to as “crape murder.” Major pruning is not recommended to reduce height.

Fertilization is important for crape myrtles. This is especially true if you don’t follow some of the other practices and care considerations.

To maximize spring growth and summer bloom, crape myrtles should be fertilized in early spring just prior to the start of new growth.

It is best to place fertilizer in drilled holes in the ground (about 8 inches deep) rather than just throw fertilizer on top of the soil. You can fertilize later in the spring and in the summer, but crape myrtles don’t benefit as much as when fertilizer is applied in late winter to early spring.

Mulching, unfortunately, is done incorrectly in many residential and commercial landscapes these days. Mulch “out” instead of “up.”

Many times you may see mulch piled around the base of a tree. Do not do this. Spread mulch outward toward the ends of the branches, and use pine straw, pine bark or wood chips to a depth of 2 to 3 inches. Refresh the layer of mulch as needed. Keep mulch off the stems and lower trunk.

One frequent problem on crape myrtles is insect damage. Actually, insects generally don’t do much damage to the trees, but aphids feeding on new shoots in spring can be a problem. White flies also may be occasional problems on crape myrtles.

Left unchecked, these insects will release their bodily fluids onto the foliage, and the resulting honeydew leads to sooty mold on the leaves. This is the black discoloration that occurs in early summer through fall. If you control the insects, no sooty mold will develop.

Popular crape myrtle varieties in Louisiana include Natchez, Muskogee, Tonto, Acoma and Sioux. Garden centers have the best availability now.

Companies have introduced many new groups and varieties of crape myrtles in the past few years. These include the dwarf Razzle Dazzle series, the black-foliaged Black Diamond varieties, the Barnyard Collection (Purple Cow, Pink Pig and Red Rooster), the Enduring Summer series, the burgundy-foliaged Delta Jazz, the Magic series and more.

Allen Owings with the LSU AgCenter is conducting adaptability studies for south Louisiana on all of these new crape myrtles at the Hammond Research Station.

Be mosquito vigilant

There have been no reported cases of West Nile virus this summer in the Baton Rouge area. But don’t let your guard down.

Summer rains will result in an increased mosquito population, and each homeowner has a role to play in both reducing mosquito numbers and the threat of disease.

It is impossible to eliminate all the mosquitoes around your home, but you can make your yard more enjoyable by getting rid of mosquito habitats around your property.

Mosquitoes love standing water and use anything that holds water as a breeding ground. Still or stagnant water less than an inch deep will support mosquito growth.

Look for and empty clogged gutters, leaf-filled drains, drain outlets from air conditioners, plastic wading pools, dog dishes, soft drink cans, plastic bags, old tires, birdbaths and potted plant saucers.

Even tire ruts, rotting stumps, old tree holes and puddles also need to be addressed. The goal is to eliminate as many sources of standing water as possible.

Bodies of water that cannot be permanently drained, such as birdbaths or other landscape water features, can be treated by using “Mosquito Dunks” to control the mosquito’s larval stage. Most of these larvicidal briquettes will last for several weeks and are safe to use around pets and animals.

Eliminating mosquito breeding habitats is only part of the battle. This will cut down on mosquito larvae becoming adults, but adult mosquitoes from other areas can fly in and cause pain.

Mosquitoes will hide in tall grass, shrubbery and other dark and shaded areas. Keep grass mowed and shrubbery trimmed.

In addition, use an insecticide labeled to kill mosquitoes on shrubbery and perimeter areas of your home.

Products containing the active ingredient bifenthrin, carbaryl, cyfluthrin, permethrin or malathion can be used to kill mosquitoes that land in these areas.

Wet surfaces uniformly, carefully treat vegetation, trying to coat bottom surfaces of shrubbery leaves. Read and follow pesticide label directions carefully. For a quick but temporary solution, aerosol foggers can be used as well as electric, propane, and gas-powered foggers.

Got a gardening question? Write to Bob Souvestre, horticulturist with the LSU AgCenter, at Burden Center, 4560 Essen Lane, Baton Rouge, LA 70809, or email to bsouvestre@agcenter.lsu.edu, or call Master Gardeners at (225) 763-3990.