Practical Armored Scale Management

Practical Armored Scale Management

By Richard S. Cowles, The Connecticut Agricultural Experiment Station, Valley Laboratory

rmored scales are small insects that they can become airborne; these are the on- feed by inserting their sucking mouth- ly dispersive stage. A parts into the needles of trees and Unlike other sucking insects like aphids withdrawing the contents of plant cells. They and adelgids, which excrete honeydew as a are named for the waxy “test” or armored waste product, armored scales inject their cover that protects the soft-bodied insect. waste and toxic saliva back into the plant, Armored scales are distinguished from soft which causes injury to the surrounding tis- scales by the characteristic that the test is not sue. Often, armored scale damage is charac- attached to the scale body. Therefore, we can terized by splotchy yellow, white or brown evaluate whether armored scales are alive or spots on foliage, poor growth and, sometimes, dead by flipping the scale cover over and ob- needle loss. Most species of Christmas Trees serving the condition of the scale insect un- are susceptible to economically significant derneath. injury from some species of armored scales. Armored scales typically have two gen- True firs and Douglas-fir are attacked by two erations per year, with a life cy- species – elongate hemlock scale and crypto- cle consisting of eggs, imma- meria scale – both of which are native to Asia. ture nymphs (two stages Spruces are damaged by hemlock scale, and for females, up to four certain species of pines are damaged by pine for males) and adult needle scales (two species), which are native males and fe- to North America. m a l e s . A du lt males have two Shortcomings of Conventional wings and only Management Methods function to fly For many years, there have been two basic to and mate approaches for managing armored scales in with the ses- Christmas Trees: full foliar sprays of insec- sile females ticides to intercept and kill crawlers as they t hat remain move on the surface of the plant; or under the test. use of systemic insecticides Mature scales or (products that are trans- scales with their ported in the sap of the eggs pass through tree) to kill the scales the winter. Eggs as they feed upon are protected under the plant. Sys- the mother scale’s cover. temic products  Hatchlings are oval, yellow- with which Fig. 1. Male and ish-white and mobile. Called growers may female elongate crawlers, they are ti- be familiar hemlock scales have ny enough that are disul- distinctively different foton (Di- appearances; this image shows the more numerous female scales. Males produce white wax “wool” that some may confuse with adelgids. This wool rubs off on neigh- boring foliage to leave a grayish film. This species is princi- pally a pest on true firs and Douglas-fir.

12 July 2011 • American Christmas Tree Journal Syston® granules), which were applied to the impossible and so the effective- soil and then picked up by the tree’s root sys- ness of these sprays suffers. tem, and dimethoate (Cygon® and other trade 2. Many species of Christmas names), which was applied through multiple Trees are injured by horticul- foliar sprays.1 Older materials that are used tural oil. For example, Douglas- to target the crawlers included chlorpyrifos fir becomes chlorotic, and true (Lorsban® and other names). All of these mate- firs have to be sprayed during rials are organophosphate insecticides, which dormancy to prevent yellowing of have been greatly restricted for use in Christ- the current season’s growth.2 mas Tree plantations because the U.S. EPA considers them to pose a significant risk to Based on their use in IPM programs applicators and wildlife. (They tend to be tox- in other crops, some insecticides would ap- ic to birds and fish). pear to have good prospects in Christmas Tree For several years I have been investigating scale management. Two examples are the in- alternatives to these insecticides with the fol- sect growth regulators buprofezin (Talus®) Fig. 3. The hemlock lowing objectives for finding superior prod- and pyriproxifen (Esteem®).3 In my trials, how- scale is injurious to all ucts: ever, Talus was ineffective. Esteem required spruces. These scales  lower toxicity to applicators two applications to provide significant ben- are easily recognized  selectively kill scales rather than their efit and was harsh on an important parasitic by the dark brown (al- predators and parasites wasp. A new systemic insecticide, spirotetra- most black) scale cover  acceptable cost mat (Movento®) was also ineffective. with a white dot in the  low toxicity to birds, fish and pollinators center. The bit of white that may be found in the row middles Successful New Options projecting from the side of the scale is an  good efficacy with as few applications as Two approaches that I have worked on appear insect pathogenic fun- possible to be practical for managing armored scales:  low potential to cause phytotoxicity. gus that can also kill 1. A basal bark spray with dinotefuran elongate hemlock and ® As a result of these tests, I have systemati- (Safari ) and cryptomeria scales. cally eliminated many potential options from 2. A full foliar spray with bifenthrin (Onyx- serious consideration for managing armored Pro®, Talstar® or a generic equivalent). scales. For example, horticultural oil, which is a standard treatment for managing armored These methods each have their own scales on many ornamental landscape plants, strengths and weaknesses so it is important is impractical in Christmas Tree plantations that growers recognize these limitations and because: use the most appropriate strategy. 1. The mode of action, suffocation, requires Basal Bark Spray with Safari nearly perfect spray coverage. Because scales Dinotefuran (Safari) is a neonicotinoid insec- develop on the undersides on needles, and ticide. Registration specifically for its use on often older needles on the lowest whorls of Christmas Trees is pending with the EPA; until the trees, obtaining perfect spray then certain states may al- coverage is prac- low its use based on tically nursery or or- namen-

Fig. 2. Cryptomeria scale are extremely damaging  because they build up to such high populations on foli- age, their feeding quickly causes spotting on foliage, and high populations will cause needle loss. These are espe- cially damaging on true firs. The translucent scale cov- er allows you to look through to see the yellow scale body underneath, giving it a “fried egg” appearance. The yellow dot in the center of the scale is also a good identifying characteristic.

American Christmas Tree Journal • July 2011 13 tals registrations. This class of sys- predict the amount of insecticide re- cryptomeria scale, this can lead to a temic products only moves upward quired to treat trees of various sizes. subtle mottled foliage discoloration. in plants. It is highly water soluble, Essentially, systemic insecticides are For trees that have not reached mar- which both presents some risk of po- diluted within the living tissues of the ketable size, this is acceptable, be- tential leaching in soil and also gives tree. The amount of living tissue (and, cause subsequent growth of foliage it rapid mobility within Christmas therefore, an effective dose) is approx- can be kept free of damage. Trees. In trials I conducted in 2008 imately proportional to the cube of the and 2009, I found that this insecticide tree height. The consequence of this Bifenthrin as an Effective Crawler Spray was efficiently absorbed through bark functional relationship is that small One of the problems with earlier prod- and transported in sap to the foliage trees (4 or 5 feet tall) should effective- ucts used to kill crawlers (dimetho- where it then killed armored scales. ly be treated with about 0.5 lb. of Safari ate and chlorpyrifos) is that they on- When targeting cryptomeria and 20SG per acre, 6-foot trees with about ly provided about two to three weeks elongate hemlock scales in Fraser firs, 0.75 lb., and trees taller than 7 feet will of protection to trees. For example, this product was most effective when require 1 lb. or more per acre. Because to effectively manage scales with di- applied as a basal bark spray during a this constitutes a steep increase in ex- methoate, growers sprayed three window of opportunity in Connecti- pense as trees increase in size, the Sa- times four weeks apart or four times cut that lasted from before bud break fari basal trunk spray is probably best three weeks apart. Bifenthrin, a py- (late April) to mid-June. Between mid- used in trees 6 feet or shorter. Howev- rethroid insecticide, can provide up June and mid-July, the effectiveness er, dinotefuran can effectively control to six months of residual insecticidal rapidly diminished.4 Experiments in scales on even the largest trees, if ad- activity. When growers need extend- eastern hemlock trees have shown equate product is used. ed periods of protection from insect it to be highly effective against ar- Most fields have varied sizes of damage, one application of bifenthrin mored scales when applied in basal Christmas Trees. The basal trunk can take the place of several sprays of bark sprays in September so autumn spray is readily adjusted to have the other products. Examples of applica- applications should be investigated for dose match the size of each tree. Ma- tions for this product include protec- Christmas Trees, too. ny growers are using a 3-gallon back- tion of roots from white grub dam- There are several advantages to pack sprayer and a wand fitted with age by doing a root dip at the time of applying this product as a basal bark a pressure-regulating controlled flow planting, a leader spray for white pine spray, rather than as a full foliar spray valve (14 or 21 psi). An appropriate weevil and a stump spray to kill pales (which can also be effective if there is mixture to use is 3.5 oz. of Safari 20 weevils, and a full foliar spray at bud thorough spray coverage). SG in 3 gallons of water. When fitted break to kill Douglas-fir needle midge with a vertically-oriented flat fan noz- adults.5, 6 Other pyrethroid products  The risk of leaching is mitigated zle (Spraying Systems 6503E or 6504E), have similar characteristics (such as due to minimal soil contact. the sprayer can be precisely calibrat- lambda-cyhalothrin, labeled in Cana-  Because it only moves upwards and ed so that 0.5 fl. oz. are delivered to da), but OnyxPro is a bifenthrin prod- outwards in the trees, a basal spray the base of the trunk of the tree from uct registered for Christmas Tree use can reach all the foliage. one side (this is calibrated for 6-foot- in the United States and has been the  There is no exposure of pollinators. tall trees). Addition of surfactants to focus of my research efforts. this spray mixture does not enhance Because bifenthrin has such broad  There is minimal exposure of the absorption into the trees. The opera- spectrum activity, growers need to worker to the residues while spraying. tor then walks slowly down one side of recognize that full foliar sprays using  Because residues on the plant sur- a row of trees, spraying only the base this insecticide will kill virtually ev- face are so limited, a basal trunk of the trunks, and then walks up the ery insect and mite – pests and ben- spray is compatible with beneficial other side of the same row to complete eficials alike. Furthermore, because predators and parasites. the spray so that the entire circumfer- they are such effective products, py- Safari is a relatively expensive in- ence of the tree trunks is treated. rethroids select very intensely for re- secticide and, therefore, it was im- The objective is to simply wet the sistant populations of insects and portant to determine the minimum base of the tree trunk from the ground mites. In other crop systems, when dosage resulting in acceptable scale level to about 10 inches in height. pyrethroid resistance has occurred, control. My dose-response experi- Less time is required to spray smaller pests are much more difficult to man- ments were conducted in a Choose & trees, so the dosage will automatical- age because there is no longer an ef- Cut field where the trees varied from ly be adjusted for trees 6 feet in height fective biological control “safety net.” 3 to 8 feet tall. When I collected data, or shorter. For trees taller than 6 feet, Therefore, whenever possible, I sug- I kept the samples from 4-, 5-, 6- and the operator needs to slow down gest that more selective products be 7-foot-tall trees separate and I was able and spray a wider band – perhaps a used rather than pyrethroids. How- to analyze the influence of tree height 15-inch band on 7-foot-tall trees and ever, when there is a large complex of on insecticide effectiveness. a 20-inch band on 8-foot trees. pests involved, or trees are of salable One equation described most of the Unfortunately, newly hatched size, I believe that use of a non-selec- variation in the experiment, and we scales have to feed to ingest a tox- tive insecticide is justified. Customers now have a model that can be used to ic dose of dinotefuran. Especially for dislike when beneficial predators (spi- 14 July 2011 • American Christmas Tree Journal ders and lacewings) exit trees indoors, scale infestations; larger trees prove es- and a “clean-up” spray in the year prior pecially difficult in which to achieve sat- to harvest is useful for avoiding the re- isfactory results. References 1. sulting complaints. Heller PR, Kline D. Multiple ap- plication management study Advantages of using the bifenthrin Other considerations to suppress elongate hemlock foliar spray are: Here are several other cultural practices scale with acephate and di- 1. It is relatively inexpensive. that may help to reduce the overall im- methoate on Fraser fir Christ- pact of scale insects. mas trees, 2003. Arthropod Mgmt. 2. An entire complex of pests pres- Tests. 2005; 30: G30. ent at bud break (spruce spider  Consider growing even-age stands 2. Varela LG, Cowles RS, Donald- mite, balsam twig aphid) and lat- of trees. This may mean clear-cut son DR. Spring insecticide treat- er (scale crawlers) can be managed harvesting infested blocks of trees ments control adelgids on Doug- with one spray. to make a clean start for the next las-fir. Calif. Agric. 1996; 50 (5): 3 4 -37. 3. Crawlers moving through bifen- crop cycle. This avoids planting clean thrin residues die before feeding nursery stock next to heavily infested 3. Grafton‑Cardwell EE, Lee JE, and causing needle discoloration. larger trees, which leads to rapid in- Stewart JR, et al. Role of two in- festation of the young trees. sect growth regulators in inte- The principal disadvantage with this grated pest management of cit- approach is that very thorough spray  Eliminate scale populations on small rus scales. J. Econ. Entomol. 2006; coverage is required. Adequate spray trees. It is relatively inexpensive and 99: 733‑44. easy to kill scales on small trees. If distribution generally requires some 4. Cowles RS. Optimizing a bas- sort of air-assisted spray technology, they are kept clean until they are 5 al bark spray of dinotefuran to such as either backpack or tractor-driv- feet tall, then it is unlikely that ex- manage armored scales (He- en mist blower sprayers. The swirl of traordinary efforts will be necessary miptera: Diaspididae) in Christ- to clean them up for market. mas Tree plantations. J. Econ. En- air allows small droplets to impact on tomol. 2010; 103: 1735-43. the undersides of foliage, where crawl-  If your fields have adjacent alternate 5. Cowles RS. Hard-to-control in- ers are active. If the spray just deposits hosts for scales (such as eastern hem- on the upper surfaces of needles, then sect pests in Christmas Trees: locks), then treat these trees with a white grubs and weevils. Shear- bifenthrin selectively kill predators basal bark spray of Safari to prevent ings (Newsletter of the Mass. and parasites rather than scales, which re-infestation. Christmas Tree Assoc.) April causes the scale outbreak to worsen. 2005. pp. 12-15.  Basal prune trees when they are A practical concern is optimum 6. about 4 feet tall. Maintain an herbi- Cowles RS. A report on the biol- spray timing when using bifenthrin for ogy and management of Doug- a crawler spray. Generally, one spray ap- cide strip within the tree rows. These las-fir needle gall midge. The plied at bud break will be adequate and efforts make conducting a basal Real Tree Line (Newsletter of the will control the various other pests, too. trunk spray much easier. Conn. Christmas Tree Growers’ Assoc.). 2007; 47 (2): 20-21. However, crawlers will occasionally set-  Use minimal applications of nitro- tle under the mother scale’s cover. These gen. Most Christmas Trees are na- Disclaimer: The use of trade are protected from contact by bifenthrin tive to and are adapted to growing in names does not constitute an and point out the advantages of using nitrogen-poor areas. Excess nitrogen endorsement for that product. systemic insecticides. For heavily infest- in foliage leads to better survival and Always read and follow label ed plantings, growers have found that faster population growth of spider directions. two years of effort are usually required mites, adelgids, aphids, and scales. with Safari and/or OnyxPro to clean up

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