Mealybug on pink althea hibiscus. Photo by Dan Gill, LSU AgCenter)

Scale on magnolia. (Photo by Dan Gill, LSU AgCenter)

Cottony cushion scale on Meyer lemon (Photo by Dan Gill, LSU AgCenter)

For Release On 09/04/15

By Dan Gill
LSU AgCenter Horticulturist

For gardeners tired of the heat and longing for cooler weather, September can provide welcome relief. Cool fronts often begin to make their way this far south in September. But days in the 90s are still not uncommon, and after a long, hot summer, these last scorching days are especially hard to bear for gardeners and their landscapes.

As summer ends, plants under heat stress are weakened, and we always see an increase in disease and insect problems. Keep your eye out for pests such as mealy bugs, aphids, leaf hoppers, scales and whiteflies. Another pest, spider mites, can also be very damaging to a wide variety of plants. A good low-toxicity pesticide for these pests is a light horticultural oil spray such as Year Round Spray Oil or All Seasons Oil. When daytime highs stay in the 90s, spray in the cooler morning hours before 9 a.m.

Diseases are particularly bad this year as most areas of the state have had lots of rain this summer. Root rots are common during periods of rainy, hot weather. Leaf spots also appear on many plants when the summer is rainy. But for deciduous plants – those that drop their leaves in fall – it’s really not worth treating in most cases this late in the growing season.

Continue to do most of your work in the cooler morning and evening hours – and don’t forget mosquito repellent.

Important chores include trimming back overgrown plants, especially bedding plants and tropicals such as lantanas, pentas, impatiens, periwinkles, hibiscuses and others. They will look better this fall if you do.

Remember, it’s too late to heavily prune spring-flowering trees and shrubs.

Also, continue weeding (mulch and you won’t have nearly so many weeds), watering (best done in the morning) and grooming plants by picking off faded flowers and trimming unattractive foliage.

If you have received garden catalogs offering spring bulbs, you should make your selections and order soon. We plant most spring-flowering bulbs in October and November. Also check local nurseries for what they have available.

It’s too late to plant warm-season plants and too early to plant cool-season bedding plants, so not much should be added to the flower garden now except in great necessity. You could still plant transplants of warm-season bedding plants, but we are getting toward the end of their season. Even a bare area would probably best be mulched and held until next month when cool-season annuals could be planted.

Lawns

A last fertilizer application to your lawn may be done in early September. If the lawn has an acceptable color and rate of growth, this fertilization is optional. You could use any commonly available lawn fertilizer, or use an all-purpose formulation following package directions carefully. Apply the fertilizer evenly with a spreader to a freshly mowed lawn, and water it in immediately.

You may see information this fall to “winterize” your lawn. This is meant to prepare the grass for the winter and increase its hardiness. Under most circumstances, winterizing is optional at best. If you choose to winterize, make sure the product you use has a very low first number (nitrogen) not greater than five. The third number in the analysis is the percentage of potassium, the nutrient important in winterizing the lawn, and it should be relatively high.

Chinch bugs will continue to damage lawns until cooler, moister weather arrives. Look for dead, tan, straw-like areas in sunny, dry locations, such as along concrete surfaces, between the sidewalk and the street, that get bigger each day. Treat promptly with cyfluthrin, bifenthrin or acephate following label directions carefully. Sod webworms have been a major issue in southeast Louisiana and can be controlled with the same products.

Prune roses now

Roses make vigorous growth during the spring and summer, and a late-August or early September pruning of everblooming roses is recommended. This pruning should not be as severe as the one done in late winter.

First, remove all diseased, dead or damaged canes as well as weak canes. Then, cut the more vigorous canes of hybrid tea and grandiflora roses back to about 2 to 3 feet above the ground. Other types of roses, such as antique and landscape roses, are pruned less severely – generally, cut them back about one-third their height or just enough to shape them the way you desire. Make your pruning cuts just above a leaf or dormant bud. Clean up all leaves and trimmings from the area, and give your roses a light application of fertilizer following label directions.

Insects and diseases stay active through the fall season, so continue to control rose pest problems with timely applications of the proper pesticides. Water well during dry periods, and you should have an excellent crop of flowers in October through November.