There are three problems homeowners have been seeing in their gardens lately:
If you have gardenias, be on the lookout for whiteflies. They came out on my gardenia about a week and a half ago. Whiteflies are tiny white insects that resemble small gnats. When you shake a heavily infested plant, the air is instantly filled with a cloud of these insects.
Whiteflies like to feed on certain plants. The most common, other than gardenias, are chinaberry trees and any plant in the privet family (includes ligustrum). They will flock to many other plants, but they are not causing them any harm.
Heavy infestations of whiteflies produce objectionable levels of honeydew and sooty mold, a parasitic fungus that grows on the leaves. Infestations might cause leaves to turn black or yellow and drop prematurely. All stages of whiteflies feed on the underside of the leaves.
The best treatment for whiteflies is with systemic insecticides such as imidacloprid (Merit) and disulfoton. Bayer Advanced sells both of these along with other brand names such as Di-Syston, Bonide Systemic Granules and Fertilome Systemic Rose Food. Both products are put on the ground for the plant to take up through its root system. Other contact insecticides that can be used are pyrethrins, insecticidal soaps and horticultural oils. Yellow sticky traps also can be used because whiteflies are attracted to yellow.
Keep in mind that there are only a few plants that the whiteflies will damage, but they blow in the wind and might wind up sitting on everything in the yard. Spraying everything in the landscape is unnecessary, expensive and environmentally unsound. The good news is that adult whiteflies are active for 2-3 weeks before they disappear until the second generation arrives during August. That's when you have to take action again.
Yellowing Leaves/Leaf Drop on Magnolias
Magnolia trees usually look pretty sick for a short time each spring. Many leaves turn yellow, get droopy and fall off.
All evergreen plants lose some older leaves. They just don't do it all at the same time like a deciduous plant. Evergreen leaves normally have a life span of one to four years. Leaf drop might occur every year or only every second or third year. When growing conditions have been favorable the previous season, leaf shedding usually occurs over several weeks and is less noticeable. If the tree has been exposed to unfavorable conditions during the previous season (for example a drought), leaf drop develops in a few days.
Don't worry if your tree looks sick. It will perk up and look normal when the older leaves fall off and the new leaves replace them.
Leaf gall is occurring on sasanqua camellias and azaleas. Leaf gall is a condition in which the new, expanding leaves become thicker and larger, and usually have a pinkish-green color on the upper leaf surface. The lower leaf surface will eventually turn white when the fungus is releasing the spores. Infected leaves dry and turn brown to black in late spring.
Remove and destroy diseased leaves before the lower leaf surface turns white. This will reduce the inoculum source for next year's infection. Don't leave the infected leaves on the ground after pruning because the spores can spread from the infected clippings.
Fungicide applications are seldom necessary and will provide only limited control. They also must be made as leaf buds swell in the spring, and we already have passed that time. Because this is not a major disease and not prevalent every year, I don't recommend spraying preventatively unless you have one or two prized plants in high-profile areas. The fungicides that work best contain mancozeb and triadimefon.
SID MULLIS IS THE DIRECTOR OF THE UNIVERSITY OF GEORGIA EXTENSION SERVICE OFFICE IN RICHMOND COUNTY. CALL 821-2349, OR SEND E-MAIL TO SMULLIS@UGA.EDU.