COMPARISON OF FUNGICIDES FOR THE CONTROL OF POWDERY MILDEW ON DOGWOOD

Bulletin 659 November 2005 Alabama Agricultural Experiment Station Richard Guthrie, Director Auburn University Auburn, Alabama

CONTENTS

page Introduction ..................................................................................................................3 Materials and Methods.................................................................................................4 Plant culture ..........................................................................................................4 Fungicide evaluations ...........................................................................................5 Application rate and time comparisons for Compass™ 50W .............................5 Disease assessment ...............................................................................................5 Results and Discussion ................................................................................................6 Fungicide efﬁcacy .................................................................................................6 Compass™ 50W performance against powdery mildew.....................................6 Tree growth ...........................................................................................................8 Summary ....................................................................................................................10 Literature Cited ..........................................................................................................10

Web publication, November 2005

Auburn University is an equal opportunity educational institution/employee. Information contained herein is available to all persons without regard to race, color, sex, or national origin. http:www.auburn.edu http:www.ag.auburn.edu/aaes

Front cover, clockwise from top left: Heavy colonization of dogwood leaves by powdery mildew fungus. Severe powdery mildew outbreak on the ‘Pink Flame’ ﬂowering dogwood. Heavy leaf colonization of dogwood leaf surfaces by powdery mildew fungus. Note the slight stretching and dwarﬁng of heavily colonized juvenile leaves.

COMPARISON OF FUNGICIDES FOR THE CONTROL OF POWDERY MILDEW ON DOGWOOD
A. K. Hagan, J. W. Olive, J. Stephenson, and M. E. Rivas-Davila

INTRODUCTION lowering dogwood (Cornus ﬂorida L.) is one of the most widely cultivated small ﬂowering trees found in residential and commercial plantings in the southeastern United States. Showy bracts, attractive fall color, red fruit clusters, and widespread adaptation across this region account for the popularity of ﬂowering dogwood with consumers (4). Since 1994, powdery mildew, caused by the fungus Erysiphe pulchra, is the most common disease seen on ﬂowering dogwood in landscapes, as well as on ﬁeldand container-grown trees (2,3,6). Although disease-related damage on established ﬂowering dogwood appears to be largely cosmetic, slowed shoot elongation, reduced caliper diameter, and death of year-old seedlings have recently been attributed to severe outbreaks of powdery mildew (10). Cultivars and native ‘seedling’ ﬂowering dogwoods differ considerably in their susceptibility to powdery mildew. Several cultivars of ﬂowering dogwood, particularly Cherokee Brave™, Cherokee Chief™, ‘Bay Beauty’, and ‘Weavers White’, are resistant to powdery mildew and also to spot anthracnose caused by Elsinoe cornii (6). Recently, Mmbaga and Sauve (11) reported that ‘Fragrant Cloud’ and Cherokee Brave™ were moderately resistant to powdery mildew. However, the majority of trees in Alabama’s landscapes are native ‘seedling’ trees or cultivars that are susceptible to powdery mildew. Since powdery mildew recently emerged as a widespread and damaging disease, considerable information is available concerning the efﬁcacy of synthetic and biorational fungicides for control of this disease in production or landscape settings (5,14). In a recent Tennessee trial, Banner MAXX®, Spectro™ 90, Eagle® 20EW, and Terraguard® 50W, controlled powdery mildew on ﬁeld-grown ‘Rubra’ ﬂowering

F

Hagan is a professor and Rivas-Davila was a research associate in the Department of Entomology and Plant Pathology. Olive is superintendent and Stephenson is associate superintendent at the Alabama Agricultural Experiment Station’s Ornamental Horticulture Research Center.

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COMPARISON OF FUNGICIDES FOR CONTROL OF POWDERY MILDEW ON DOGWOOD

dogwood (15). Windham et al. (15) noted that the percentage of symptomatic leaves on trees treated with the above fungicides ranged from 10 to 25 percent compared to nearly 100 percent on the untreated controls. In contrast, bimonthly applications of First Step™ failed to protect ‘Rubra’ ﬂowering dogwood from powdery mildew (15). Mulrooney and Gregory (13) noted that Sunspray Ultraﬁne Oil™ and Eagle® were equally effective in controlling this disease. Over a three-year period, the soaps Ajax® and Equate®, as well as Armicarb® were nearly as effective in controlling powdery mildew and suppressing fruiting body (ascocarp) formation of the powdery mildew fungus as 3336™ 4.5F, Heritage® 50W, Phyton 27®, and Banner MAXX® on container- and ﬁeld-grown ﬂowering dogwood (9). Mmbaga and Sheng (9). also noted that more fruiting bodies (ascocarps) of the causal fungus developed when fungicide treatments were stopped in August than in October. Finally, stem caliper and tree height were signiﬁcantly increased by synthetic fungicides such as Banner MAXX® and several biorational fungicides (10). The fungicide triﬂoxystrobin, which is marketed for use on ornamentals and turf under the trade names Compass™ 50W and Compass O™, is classiﬁed as a strobilurin or QoI (Quinone outside inhibitor) fungicide. This fungicide is absorbed into the waxy leaf cuticle and has translaminar, or local, movement through the leaf but is not redistributed through the xylem like the systemic QoI fungicide Heritage™ 50W (1). Compass™ 50W is a broad spectrum fungicide that has activity against numerous diseases, including powdery mildew on a variety of annuals, perennials, and small ﬂowering trees. Previously, Windham et al. (15) obtained a high level of control of powdery mildew on ﬂowering dogwood with Compass™ 50W applied at the 2-ounce and 4-ounce- per-100-gallon rates on a two-week schedule. In a recent Delaware study (12), the 1-, 2-, and 4-ounce rates of Compass™ 50W when applied at two-, three-, and four-week intervals, respectively, restricted powdery mildew development to less than 2 percent of the leaves on ‘seedling’ ﬂowering dogwood. In this same study, all rates of Compass™ 50W also proved as effective in controlling this disease as the registered fungicides Heritage® 50W and Eagle® (12). Trials were initiated on container-grown ﬂower dogwood in 1997 and continued through 2003 to identify efﬁcacious fungicides for the control of powdery mildew. In addition, the efﬁcacy of the strobilurin fungicide Compass™ 50W was evaluated over a range of application rates and treatment intervals for the control of powdery mildew on ﬂowering dogwood. MATERIALS AND METHODS Plant culture. Bare-root ﬂowering dogwoods were potted in number 3 containers ﬁlled with in pine bark:peat moss (3:1 by volume)) or 100 percent pine bark amended with 14 pounds of 17-7-12 Osmocote, 6 pounds of dolomitic limestone, 2 pounds of gypsum, and 1.5 pounds of Micromax per cubic yard of potting mixture. They were maintained on a clam shell-covered bed under a 47 percent shade cloth and were watered daily with overhead impact sprinklers. While ‘seedling’ ﬂowering dogwoods were used in 1997, the cultivar ‘First Lady’ was used in 1999 and ‘Cloud 9’ in 2001, 2002, and 2003. A randomized complete block design with six or eight

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replications of one plant per treatment was used. Blocks of plants were re-randomized following each fungicide application. All studies were conducted at the Ornamental Horticulture Research Center in Mobile, Alabama. Fungicide evaluations. Fungicides were applied to run-off with a CO2-pressurized backpack sprayer at the intervals speciﬁed below. In 1997, 2001, 2002, and 2003, recommended rates of commercial fungicides were evaluated for the control of powdery mildew on ﬂowering dogwood. Fungicides evaluated in 1997 were Bayleton® WSP at 4 ounces per 100 gallons of spray volume, 3336™ 4.5F at 20 ﬂuid ounces per 100 gallons, Banner MAXX® at 5 ﬂuid ounces per 100 gallons, Phyton 27® at 40 ﬂuid ounces per 100 gallons, and Eagle® 40W at 6 ounces per 100 gallons. In 2001, Heritage 50W™ at 4 ounces per 100 gallons and Sunspray Ultraﬁne Oil® at the rate of 1 percent v/v were added. The non-ionic surfactant Sil-Spread™ at 0.06 percent v/v was added to Eagle® 40W, Heritage™ 50W, and Bayleton® WSP tank mixtures. Fungicides were applied at two-week intervals from March 30 until August 16, 2000; May 2 to July 24, 2001; May 24 to August 14, 2002; and May 7 to July 29, 2003. Canopy height and width were also recorded on August 14, 2001 to calculate a growth index (GI) according to common horticultural practice (7). Application rate and timing comparisons for Compass™ 50W. In 1999, the efﬁcacy of selected rates of Compass™ 50W was compared with Banner MAXX® at 5 ﬂuid ounces per 100 gallons of water, Eagle® 40W at 6 ounces per 100 gallons, and Heritage™ 50W at 4 ounces per 100 gallons of water for the control of powdery mildew on ‘First Lady’ ﬂowering dogwood. The 0.5 ounce rate of Compass™ 50W was applied on a one-week schedule and compared to a two-week schedule for the 1and 2-ounce-per-100-gallon rates of the same fungicide. While the application interval for Eagle® 40W and Heritage™ 50W was two weeks, Banner MAXX® was applied on a three-week schedule. Fungicides were applied from April 12 through October 6, 1999. In 2001, 2002, and 2003, the 1-, 2-, and 4-ounce rates of Compass™ 50W were applied at one-, two-, and four-week intervals, respectively, to ‘Cloud 9’ ﬂowering dogwood. Eagle® 40W, which was applied at the 6-ounce-per-100-gallon rate every two weeks, was included as a commercial standard. The non-ionic surfactant Sil-Spread™ at 0.06 percent v/v of spray volume was added to Compass™ 50W and Eagle® 40W. Fungicides were applied to run-off from May 2 to July 24, 2001; May 24 to August 13, 2002; and May 27 to July 29, 2003. Disease assessment. Fungicides were applied to run-off with a CO2-pressurized backpack sprayer at the previously speciﬁed intervals. Incidence of powdery mildew on the leaves was rated using the 1 to 12 Horsfall and Barratt rating scale where 1 = no disease, 2 = 0 to 3 percent, 3 = 3 to 6 percent, 4 = 6 to 12 percent, 5 = 12 to 25 percent, 6 = 25 to 50 percent, 7 = 50 to 75 percent, 8 = 75 to 87 percent, 9 = 87 to 94 percent, 10 = 94 to 97 percent, 11 = 97 to 100 percent, and 12 = 100 percent of the leaves colonized by the powdery mildew fungus. In the general screening trials, incidence of powdery mildew was recorded on October 1, 1997; July 10, 2001; September 9, 2002; and July 10, 2003. In the Compass™ 50W trials, powdery mildew ratings were logged on July 7, 1999; July 10, 2001; September 9, 2002; and August 6, 2003.

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COMPARISON OF FUNGICIDES FOR CONTROL OF POWDERY MILDEW ON DOGWOOD

Canopy height and width were also recorded on September 29, 1999 and August 14, 2001 to calculate a growth index (GI) according to common horticultural practice (7). RESULTS AND DISCUSSION Fungicide efﬁcacy. Although all treatments signiﬁcantly reduced the incidence of powdery mildew compared with the unsprayed control in 1997, signiﬁcant differences in the level of disease control among the fungicides were observed (Table 1). Eagle® 40W and Phyton 27® were equally effective in controlling powdery mildew. On the trees receiving applications of the above fungicides, disease development was limited to a few unobtrusive fungal colonies on 3 to 4 percent of the leaves. In comparison, 3336™ 4.5F and Bayleton WSP gave less control of powdery mildew than Eagle® 40W and Phyton 27®. The percentage of disease leaves on the 3336™ 4.5F- and Bayleton WSP-treated dogwoods, which exceeded 12 percent and 25 percent, respectively, was well below the 87 percent rate of leaf colonization seen on the untreated controls. In 2001, 2002, and 2003, Banner MAXX®, Eagle® 40W, and Heritage™ 50W consistently gave the best control of powdery mildew (Table 1). Only a few isolated colonies of the powdery mildew fungus were seen on a few, scattered leaves of the trees treated with Banner MAXX®, Eagle® 40W, or Heritage™ 50W. Incidence of fungal colonized leaves on the dogwood treated with SunSpray Ultraﬁne Oil® and Phyton 27® was in the range of 1 percent to less than 12 percent. Bayleton WSP® and 3336® 4.5F failed to protect dogwood from this disease, especially in 2001 and 2003 when powdery mildew pressure was high. Powdery mildew incidence on the untreated controls ranged from a low of approximately 35 percent of leaves colonized in 2002 to more than 80 percent in 2001 and 2003. In addition, extensive colonization of the entire surface of most leaves as well as noticeable leaf deformation was observed on the untreated controls in 2001 and 2003. Compass™ 50W performance against powdery mildew. In 1999, all rates of Compass™ 50W, as well as Banner MAXX®, Eagle® 40W, and Heritage™ 50W, greatly reduced the incidence of powdery mildew compared to the untreated control (Table 2). As indicated by a disease rating of 12.0, all of the leaves on the untreated TABLE 1. EFFICACY OF SELECTED FUNGICIDES APPLIED ON A TWO-WEEK SCHEDULE FOR THE CONTROL OF POWDERY MILDEW ON CONTAINER-GROWN FLOWERING DOGWOOD
Application ———Incidence of powdery mildew—— Fungicide rate (g ai/liter) 1997 2001 2002 2003 Bayleton WSP 4 ﬂ oz 5.3 4.2 2.5 5.6 3336 4.5F 20 ﬂ oz 4.1 3.8 2.2 6.3 Banner MAXX 5 ﬂ oz 2.5 2.0 1.0 2.6 Phyton 27 40 ﬂ oz 1.9 3.5 2.2 3.0 Eagle 40W 6 oz 1.6 3.2 1.2 2.2 Heritage 50W 4 oz —1 2.3 1.2 1.6 SunSpray Ultraﬁne Oil 1% v/v — 3.8 1.8 3.3 Untreated control — 9.0 7.8 5.5 7.6 1 — = Fungicides were not evaluated in 1997

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controls were colonized by the causal fungus. Although the percentage of leaves on all of the fungicide-treated trees was low, differences in the level of disease control were noted between fungicide treatments. Disease incidence was higher on the trees treated bimonthly with the 1- and 2-ounce-per-100-gallon rates of Compass™ 50W compared with weekly applications of the 0.5 ounce-per-100-gallon rate of the same fungicide. Also, fewer colonized leaves were observed on the ﬂowering dogwood treated with Eagle® 40W and Heritage™ 50W than on those trees with the two higher rates of Compass™ 50W at the same treatment interval. The highest rate of Compass™ 50W and Banner MAXX® gave the same level of control of powdery mildew. In 2001, Compass™ 50W greatly reduced the incidence of powdery mildew on ‘Cloud 9’ ﬂowering dogwood when applied over a range of labeled rates and treatment intervals, as compared with the untreated control (Table 3). Nearly 50 percent of the leaves of the untreated controls were heavily colonized by the powdery mildew fungus. At the 1- and 2-ounce-per-100-gallon rates, Compass™ 50W gave better disease control when applied on a one- and two-week schedule than when applied at TABLE 2. COMPARISON OF COMPASS 50W WITH SELECTED FUNGICIDES FOR THE CONTROL OF POWDERY MILDEW AND TREE DIMENSION OF CONTAINER-GROWN ‘FIRST LADY’ FLOWERING DOGWOOD, 1999
——Application—— Rate Interval g ai/liter wk. Compass 50W 0.5 1 Compass 50W 1.0 2 Compass 50W 2.0 2 Banner MAXX 5 ﬂ oz 3 Eagle 40W 6.0 oz 2 Heritage 50W 8.0 oz 2 Untreated control ------1 Growth index = (height + width1 + width 2)/3 Fungicide Powdery mildew incidence 1.8 4.3 3.0 2.1 1.6 1.4 12.0 Growth index1 141.1 157.9 162.0 149.0 156.0 153.0 133.1 Tree caliper (cm) 19.0 19.8 21.2 20.1 21.4 19.2 14.8

TABLE 3. INFLUENCE OF APPLICATION RATE AND INTERVAL ON THE EFFICACY OF COMPASS 50W FOR THE CONTROL OF POWDERY MILDEW AND THE GROWTH OF CONTAINER-GROWN ‘CLOUD 9’ FLOWERING DOGWOOD
Fungicide Compass 50W Compass 50W Compass 50W Compass 50W Compass 50W Compass 50W Compass 50W Compass 50W Compass 50W Eagle 40W Unsprayed control —Application— Rate Interval oz. wk 1.0 1 1.0 2 1.0 4 2.0 1 2.0 2 2.0 4 4.0 1 4.0 2 4.0 4 6.0 2 — — Powdery mildew ——incidence—— 2001 2002 2003 2.2 1.0 1.7 2.5 1.2 2.7 4.8 1.0 3.7 1.7 1.0 2.0 2.0 1.0 2.0 4.2 1.0 3.3 1.5 1.0 1.7 2.5 1.0 2.0 2.8 1.2 2.5 1.8 1.4 2.5 6.7 5.6 6.7 Growth index 2001 105 97 104 104 95 103 100 108 96 92 106

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COMPARISON OF FUNGICIDES FOR CONTROL OF POWDERY MILDEW ON DOGWOOD

monthly intervals. Disease incidence on the trees treated with the two lower rates of Compass™ 50W at one- and two-week intervals was similar. Incidence of powdery mildew on ﬂowering dogwood treated with the highest rate of Compass™ 50W at one, two-, and four-week intervals did not greatly differ. With the exception of the 1- and 2-ounce-per-100-gallon rates applied monthly, Compass™ 50W proved equally effective in controlling powdery mildew on ﬂowering dogwood as the fungicide standard Eagle® 40W. As indicated by a disease rating of 5.6 where 15 to 20 percent of the leaves on the unsprayed control were colonized, powdery pressure was relatively low in 2002 (Table 3). The level of powdery mildew colonization on all the Compass™ 50W-treated ﬂowering dogwood was similar. For most rates of Compass™ 50W at all three treatment intervals, very little if any leaf colonization by the causal fungus was seen. Also, all rates of Compass™ 50W were equally effective in controlling this disease. For 2003, the level of leaf colonization by the powdery mildew fungus was higher for the unsprayed control compared with for all of the Compass™ 50W treatments (Table 3). At all rates of Compass™ 50W application, powdery mildew incidence increased as the treatment interval was lengthened from one to four weeks. At each treatment interval, disease incidence on the trees treated with all three rates of Compass™ 50W was similar. When applied at one-, two-, and four-week intervals, no appreciable differences in powdery mildew control were noted between any rates of Compass™ 50W and the Eagle® 40W standard. The percentage of diseased leaves for any of the Compass™ 50W treatments was below 12 percent. Tree growth. The impact of powdery mildew on tree growth appeared to be related to disease severity in a particular year. In the 1999 trial, severe powdery mildew development on the unsprayed ‘First Lady’ ﬂowering dogwood had an adverse affect on tree growth. The growth index (GI) and trunk caliper logged for the untreated trees were considerably lower than those for nearly all of the fungicide-treated trees (Table 2). Although the lowest rate of Compass™ 50W gave excellent disease control, the GI for these trees did not differ signiﬁcantly from that recorded for the unsprayed controls. In contrast, the GI for ﬂowering dogwoods treated with the 1- and 2-ounceper-100-gallon rates of Compass™ 50W was higher than those for the lowest rate of this same fungicide, as well as the untreated control. Trunk caliper for the ﬂowering dogwood sprayed with the highest rate of Compass™ 50W was much larger than that for trees treated receiving the lowest rate of the same fungicide. Trees treated with the 1-ounce-per-100-gallon rate of Compass™ 50W had a similar trunk caliper as did the ﬂowering dogwood treated with the 0.5-ounce-per-100-gallon rate of the same fungicide. Generally, the GI and trunk caliper for trees treated with Banner MAXX®, Eagle® 40W, and Heritage™ 50W were similar to the results recorded for the two highest rates of Compass™ 50W. In 2001, the GI of untreated dogwoods was not appreciably different from those recorded for the ﬂowering dogwood treated with Banner MAXX®, Eagle® 40W, 3336® 4.5F, Phyton 27®, and SunSpray Ultraﬁne Oil®. Due to low disease pressure in 2001, application rate and treatment interval for Compass™ 50W had no impact on tree growth (Table 3). The height for the Eagle® 40W-treated trees was similar to that recorded for the dogwoods receiving all rates of Compass™ 50W.

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While Bayleton® WSP, 3336® 4.5F, Banner MAXX®, Phyton 27®, Eagle® 40W, Heritage™ 50W, and SunSpray Ultraﬁne Oil® are registered for the control of powdery mildew on a wide range of annual, perennial, and woody ornamentals, sizable differences in the level of powdery mildew control given by the above fungicides were noted in all four years. Banner MAXX®, Eagle® 40W, and Heritage™ 50W gave the most consistent and effective control of powdery mildew on ﬂowering dogwood. Typically, the few leaves colonized by the powdery mildew fungus on ﬂowering dogwood treated with the above fungicides had no detrimental impact on tree aesthetics. The superior activity of Banner MAXX® and Eagle® 40W for the control of powdery mildew on ﬂowering dogwood has been reported in previous studies in Tennessee (9,15). Mmbaga and Sheng (9) also noted a sizable reduction in fruiting body (ascocarp) formation on the Banner MAXX®-treated ﬂowering dogwood, which could also result early season suppression of this disease the following year. In at least one year, Phyton 27® and SunSpray Ultraﬁne Oil® were slightly less efﬁcacious in controlling powdery mildew than were Banner MAXX®, Heritage™ 50W, or Eagle® 40W. However, both of these fungicides, as well as Banner MAXX®, Eagle® 40W, and Heritage™ 50W were more effective against this disease than 3336 4.5F and Bayleton® WSP. While SunSpray Ultraﬁne Oil® appears as a biorational or organic alternative to the above synthetic fungicides, an objectionable mottling and marginal leaf burn was noted in 2003 and 2004 on ﬁeld-grown ‘Rubra’ ﬂowering dogwood in full sun that were treated at one- or two-week intervals in the spring and summer with this product (5). As previously noted by Windham et al. (15), Compass™ 50W demonstrated excellent activity against powdery mildew on ﬂowering dogwood. When applied monthly, the 2- and 4-ounce-per-100-gallon rates of Compass™ 50W often gave effective control of powdery mildew. The 1-ounce-per-100-gallon rate was more effective when applied at one- and two-week intervals than on a monthly schedule. Windham et al. (15) got excellent control of powdery mildew on ﬁeld grown ‘Rubra’ ﬂowering dogwood with the 4- and 8-ounce-per-100-gallon rates of Compass™ 50W applied on a two-week schedule but not with monthly treatments of the 8-ounce-per-100-gallon rate of the same fungicide. Under the heavy disease pressure seen in the 1999 study, treatment intervals may have to be reduced to two weeks or less in order to maintain effective disease control. While the application rate and treatment interval for Compass™ 50W evaluated here match the information on the product label, repeated applications of this or other strobilurin fungicides such as Heritage™ 50W over an extended period of time on vegetable, fruit, turf, and cereal crops can result in control failures due to the selection of strobilurin-resistant fungal plant pathogens, especially powdery mildew fungi (1). According to FRAC (Fungicide Resistance Action Committee, www.frac.info/) guidelines, the risk of control failures due to resistance can be greatly reduced by insuring that a strobilurin fungicide makes up no more than one-third of the total fungicide applications and that no more than two consecutive applications of a strobilurin fungicide are made. Either tank-mixing or alternating fungicides with different modes of action is also an effective strategy for reducing the risk of a control failure. When a

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COMPARISON OF FUNGICIDES FOR CONTROL OF POWDERY MILDEW ON DOGWOOD

strobilurin fungicide is applied alone or tank-mixed with another type of fungicide, no more than 50 percent of the total fungicide application made in that growing season should include any strobilurin fungicide.
Figure, top right: Difference in top growth on ‘Cloud 9’ ﬂowering dogwood obtained with Compass 50W at the 2-ounceper-100-gallon rate (left) compared with untreated control (right). Note differences in tree height, leaf size, and canopy density between the fungicide-treated and untreated trees. Figure, bottom right: Differences in top growth on ‘Cloud 9’ ﬂowering dogwood obtained with Heritage 50W at the 4ounce-per-100gallon rate (left) compared with the untreated control (right).

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SUMMARY Historically, the impact of powdery mildew diseases on woody plants has been considered largely cosmetic (4,8). Few published reports have noted a relationship between slowed shoot growth with severe outbreaks of powdery mildew. In the 1999 Compass™ 50W study, the GI of the untreated controls was well below the GI for all fungicide treatments except for the lowest rate of Compass™ 50W. Similar powdery mildew-related reductions in the growth of untreated ‘seedling’ and Cherokee Brave™ ﬂowering dogwood have recently been observed in Tennessee (10). Increased shoot growth and larger stem caliper on ﬂowering dogwood were obtained with Banner MAXX® alone or when alternated with Armicarb® as well as with Equate® soap and Heritage™ 50W (10). When powdery mildew pressure was relatively low, differences in tree dimensions or GI were not observed between the untreated and the fungicidetreated ﬂowering dogwood in this and an earlier Georgia study (2). In summary, Banner MAXX®, Heritage® 50W, and Eagle® 40W were shown to be highly effective in controlling powdery mildew on ﬂowering dogwood. Systemic Fungicide™ (ferti-lome®) contains the same active ingredient (propiconazole) as Banner Maxx® and is available at garden centers and other retail outlets as is Immunox™ (Spectracide®), which contains the same active ingredient as Eagle 40W. Phyton 27® also proved to be a possible control option. Due to the high risk of damage to the leaves of ﬂowering dogwood growing in full sun, Sunspray Ultraﬁne Oil® may not be an acceptable biorational or organic substitute for the other fungicides screened, particularly on ﬂowering dogwood not shaded by other trees. The new strobilurin fungicide Compass™ 50W, which gave effective control of powdery mildew over a range of rates and treatment intervals, is targeted for use by the commercial greenhouse and nursery industry. Bayleton® WSP and 3336™ 4.5F (Halt™ Systemic) gave inconsistent control and are not the fungicides of choice for managing powdery mildew on ﬂowering dogwood. LITERATURE CITED 1. Bartlett, D. W., J. M. Clough, J. R. Godwin, A. A. Hall, M. Hamer, and R. Parr-Dobzanski. 2002. The strobilurin fungicides. Pest Manag. Sci. 58:649-662. 2. Britton, K. O. 1994. Dogwood cultivar evaluations for disease resistance, 1993. Biological and Cultural Tests for the Control of Plant Diseases 9:159. 3. Daughtrey, M. L. and A. K. Hagan. 2001. Dogwood diseases. Pages 124-132, in Diseases of Woody Ornamentals and Trees in Nurseries. R. Jones and M. Benson, eds. APS Press. St. Paul, MN. 482 pp. 4. Dirr, M. A. 1998, Manual of Woody Landscape Plants. 5th Ed. Stipes Publishing Co. Champaign, IL 1187 pp.

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COMPARISON OF FUNGICIDES FOR CONTROL OF POWDERY MILDEW ON DOGWOOD

5. Hagan, A. K., J. R. Akridge, and M. E. Rivas-Davila. 2004. Control of powdery mildew, spot anthracnose, and Cercospora leaf spot on ﬁeld-grown ﬂowering dogwood trees. Proc. Southern Nursery Assoc. Res. Conf. 49:254-259. 6. Hagan, A. K., B. Hardin, C. H. Gilliam, G. J. Keever, J. D. Williams, and J. Eakes. 1998. Susceptibility of cultivars of several dogwood taxa to powdery mildew and spot anthracnose. J. Environ. Hort. 16:147-151. 7. Keever, G. J. 1993. Promotion of branching in nandina (Nandina domestica Thunb.) ‘Harbor Dwarf’ with ASC-66952. J. Environ. Hort. 11:141-143. 8. McRitchie, J. J. 1994. Powdery mildew of ﬂowering dogwood. Florida Dept. Agric. Cons. Ser. Plant Path. Cir. 368. 9. Mmbaga, M. T. and H. Sheng. 2002. Timing of fungicide applications in dogwood powdery mildew control. Proc. Southern Nursery Assoc. Res. Conf. 47:265-272. 10. Mmbaga, M. T. and R. J. Sauve. 2004. Management of powdery mildew in ﬂowering dogwood in the ﬁeld with biorational and synthetic fungicides. Can. J. Plant Sci. 84:837-844. 11. Mmbaga, M. T. and R. J. Sauve. 2004. Multiple resistance in dogwoods (Cornus spp.) to foliar pathogens. J. Arboriculture 30(2):101-107. 12. Mulrooney, R. P. 2001. Evaluation of fungicides for control of powdery mildew on ﬂowering dogwood, 2000. Fungicide and Nematicide Tests 56:OT9. 13. Mulrooney, R. P. and N. F. Gregory. 2003. Evaluation of biorational fungicides for control of powdery mildew on ﬂowering dogwood. Fungicide and Nematicide Tests 58:OT034. 14. Windham, M. T., A. S. Windham, M. A. Halcomb, D. E. Deyton, and C. E. Sams. 1999. Control of powdery mildew on ﬂowering dogwood using soybean oil. Proc. Southern Nursery Assoc. Res. Conf. 44:226-228. 15. Windham, M. T., A. S. Windham, and M. A. Halcomb. 2000. Control of powdery mildew in dogwood with fungicides. Proc. Southern Nursery Assoc. Res. Conf. 45:207-208.

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