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Ornamentals and Turf |
A few years ago we introduced you to the new to North Carolina hackberry woolly aphid. This fluffy little creature can produce a lot of honey dew and subsequent sooty mold fungus. (I fortunately changed parking space on the North Carolina State University campus from under a hackberry tree.) Cabarrus County is reporting quite a population of Shivaphis celti this year. If you do not have much Celtis or hackberry in your landscape, you may not have noticed. Coincidentally, several other states seem to be reporting larger than average outbreaks of certain aphids. Since my Ouija Board only works when I already know the answers, I'm not going to speculate on the causes for this.
In keeping with the aphid theme, Guilford County is reporting probable woolly beech aphids, Grylloprociphilus imbricator. These woolly aphids are found on beech (Fagus grandifolia) twigs and leaves in large colonies. Control is the same for most aphids on trees, that is, it is usually too expensive to bother. Aoki and others site in the 2001 Florida Entomologist that these aphids are predatory on other soft bodied insects that happen to stumble into their colony.
This has been a particularly bad year across the Southeast for Cercospora needle blight on Leyland Cypress, caused by Cercosporidium (now called Passalora). This may be due in part to cooler night temperatures occurring earlier than normal. Dr. Jean Williams-Woodward has been studying this disease in Georgia for the past 3 to 4 years.
The symptoms of Cercospora needle blight show up first on the interior, lower branches of the tree and move upward and outward. The needles turn brown and small brown lesions can be seen on the twigs. Defoliation follows. Using a hand lens, you should be able to see masses of spores produced by the fungus. These appear as olive-green to grayish feathery tufts on the blighted needles or small twigs.
Jean has been doing spore trapping each year, and continues to find that the spores of this fungus are not active until about mid June, peaking in August and September, and remaining active until about the end of October. As such, early spring fungicide applications are not likely to be effective in managing this disease if spore production in North Carolina is similar to Georgia.
Based on her repeated fungicide trials, Jean's recommendation is to begin fungicide applications about July 1 and continue until the end of October. This is an expensive regime, but it has been effective in her trials.
Recommended rotation:
It is important to follow to retreat at the recommended intervals. Treating once per month, for instance, is not going to be as effective as you will be allowing new infections to start. If you haven't starting making any fungicide applications yet, it is not too late to combat this disease (it will just take longer to get the problem under control).
Fore, Daconil, and Kocide when applied at 7-day intervals have all worked very well in reducing disease in her trials (again, starting about July 1 and continuing until the end of October).
If you are growing Leyland Cypress as a Christmas tree, you also have the option of using Quadris, if available, on those trees. This Syngenta product has the same active ingredient, azoxystrobin, as Heritage. Quadris is not labeled for ornamentals, however.
*** It is critical that the needles in the inside of the tree are saturated with fungicide. Growers using air blast sprayers have not been getting good control as they do not seem to get enough fungicide into the center of the tree (which is where infection starts). It is better to still go down every row and wet the interior of the tree using a wand (however, this is not very practical in large scale production).
Jean has found that damaged trees generally do flush out again in about 2 months time if they are not too severely damaged. Therefore, BE PATIENT. Keep in mind that there is a lot of sporulation going on right now, but symptoms may not have developed yet. As such, even though you are spraying fungicides you will continue to see symptoms develop from the earlier infections. Again, BE PATIENT as you should eventually see a turnaround. She has never seen the disease kill a tree, but it can disfigure a tree enough to make it unmarketable if the disease is severe.
Jean has also observed that pruning greatly increases disease incidence and severity. Trees in nurseries as well as landscapes that have not been pruned do not tend to have the disease or as severe. There is something about opening up the interior of the tree that promotes disease development, which is different from most other foliar diseases in which opening up the canopy actually reduces disease severity.
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Last modified on October 7, 2004 by Stephen J. Toth, Jr.