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Issue link: https://read.dmtmag.com/i/105677
Shortly thereafter the young scale insects tuck in their legs and antennae and secrete their armor. An added insult caused by their feeding is the toxin in their saliva that results in twig and branch dieback. Oviposition and hatching-out occurs until mid-August. Because of the long crawler emergence period, expect to see crawlers, nymphs, and adults occurring at the same time during the growing season. We have seen heavily infested red maples whose bark and branches develop a grainy pebbled surface that often supports several layers of scale insects jammed cheek-by-jowl. The bark of unsprayed trees is often like a microscopic zoo with all sorts of predaceous mites, predaceous insects, parasitic insects, parasitic fungi, and other organisms, in addition to the scales. Although it's only anecdotal, many experts agree that a healthy tree should be able to tolerate a light level of gloomy scale infestations. Stressed trees are an exception. Their inability to compensate for nutrients lost to the scale insects impairs their ability to repair and maintain their tissues. As we've seen with many other tree species growing in urban settings, when their cultural requirements are not met, these trees fail to perform as expected, which compromises their ability to ward-off pests or to recover from injury. So, it is of paramount importance that urban foresters reduce stresses on red maples as much as possible. The first line of defense is to plant a healthy, quality tree with an adequate root system in an environment that's conducive for rapid establishment and growth. Avoid deep planting, which results in poor growth and increases a plant's susceptibility to pests. Also, remove any packing straps and non-biodegradable burlap. If the red maples are to be planted in parking lot islands, make sure that the islands contain enough soil volume to allow for good root establishment and growth. After establishment, fertilize according to soil test results and irrigate when necessary, especially during prolonged dry periods. Maintain a 2- to 3-inch (51 to 76 mm) layer of mulch to reduce soil moisture loss and suppress weed growth. Parasitic wasps, predaceous ladybeetles and mites, and diseases are very important natural controls to reduce gloomy scale numbers. A survey of gloomy scale populations by JC Chong along the Grand Strand area in South Carolina shows that 15 to 45% of the populations are killed by these natural enemies. Natural, biological controls may not be enough to reduce the population on a heavily infested tree, but they can certainly help keep the lightly infested and low-stressed trees healthy and beautiful. When the scale insect population is high and natural control does not seem to be enough, you may have to www.urban-forestry.com Practitioner Perspectives "We have very few maples … I tend to shy away from them with the heat that we have here. On the ones we do have, there are some infestations of gloomy scale. The critters cause pretty serious decline of branch structure. We may or may not try the horticultural oils in the spring. The trees are so recently planted that I may yank them and plant something else!" —Tom Rapp, Horticulturist, City of Aiken, Aiken, South Carolina "What can I say about gloomy scale? If you've got it, good luck. We have had some epidemic levels on the Hyatt block of our Main Street. They attack the red maples mostly. We spray them in the spring with horticulture oil and it usually keeps numbers down for a couple of years. It seems to be the most environmentally safe option. I have noticed gloomy scale this year on zelkova; we are going to spray those in the spring. The affected trees have constrained growing space. I think the best way to combat scale is to maximize the growing space and grow a healthier, more vigorous tree. This is not an easy idea to implement because of the many different colleagues that you need to persuade and get on board in the planning stage. I don't think it is always a case of 'right tree, right space'. I think it is planning the right space for a tree." —Drew Smith, Superintendent of Grounds, Parks and Recreation, City of Greenville, South Carolina consider using insecticides. The following insecticides are registered for scale insect control in the U.S.: acephate, azadirachtin (Ornazin 3% EC only), bifenthrin and imidacloprid, buprofezin, carbaryl, cyfluthrin, cyfluthrin + imidacloprid, dinotefuran, horticultural oil, hydrophobic extract of neem oil, insecticidal soap, lambdacyhalothrin (Demand CS, Scimitar CS, and Scimitar GC only), and pyriproxyfen. [Please see sidebar, "Before You Spray."] Spray these insecticides on the trunk or branches at the time of crawler emergence. Our studies have shown that the best approach to managing gloomy scale is to target the crawlers. Since gloomy scale crawlers emerge from late May to August during any typical year, make repeated applications every 2 to 4 weeks to reduce the number of settling crawlers during their long period of emergence. It is important that you thoroughly cover the trunk and branches with the insecticide solution. 33