ALABAMA A&M AND AUBURN UNIVERSITIES Common Diseases ANR-1047 of Crapemyrtle

rilliant fall color, exfoliating health and vigor of established as well as abortion of the flower Bbark, lush green leaves, and , both can detract from buds can be seen. On the most showy flowers make crapemyrtle their beauty in landscape - susceptible , leaves on ( indica) a favorite ings and from the market value tender, heavily colonized shoot in landscapes and gardens of container-grown crapemyrtles. tips can wither and die (Figure across Alabama. Introduced from 3). Also, heavily diseased trees in the mid-1700s, crape- Powdery Mildew may drop their leaves. Powdery myrtle selections range in size mildew can appear as early as from dwarf shrubs to sizable Powdery mildew, the most trees and are widely used in common and widely recognized screens, hedges, and mass plant- disease on crapemyrtles, is easily ings or individually as accent or identified by the cottony white specimen plants. to buff-colored patches or colonies of the causal fungus This highly versatile shrub or Erysiphe lagerstroemia on the tree, which blooms primarily in leaves, tender shoots, and scales June and July, adapts best in on the flower buds, particularly well-drained soils on sunny sites on selections of L. indica across Alabama. The flower (Figures 1 and 2). On heavily color of available crapemyrtle mildewed plants, twisting or dis- selections ranges from white to Figure 3. Leaves wither and die on tortion of the leaves and shoots the most susceptible cultivars pink, purple, and many shades of red. In the mid-1950s, the leaf-out in mid-April, but leaf crapemyrtle L. fauriei colonization usually does not was introduced from Japan and become noticeable before late later crossed with L. indica to May or early June. In favorable produce many highly attractive conditions, this disease will and powdery-mildew resistant intensify throughout the summer. selections of hybrid crapemyrtle The causal fungus over- x (L. indica fauriei). Within the winters as dormant mycelia in last decade, a number of leaf buds. Spores of this fungus improved cultivars of L. indica spread to healthy leaves and crapemyrtle have been released. tender shoots by air currents. See Extension publication ANR- Figure 1. Powdery mildew on crape- myrtle Warm days and cool nights as 1083, “Common Crapemyrtle,” well as extended periods of rela- for additional information on the tively dry weather favor the selection and care of crape- development and spread of myrtles. ARCHIVEpowdery mildew on crapemyr- In landscapes and nurseries tles. While nearby diseased across Alabama, crapemyrtles are crapemyrtles can be sources of relatively free of highly dam- powdery mildew, the powdery aging diseases. Powdery mildew mildew fungus is often intro- and leaf spot are the duced into landscape plantings most common diseases found on on infected plant material. crapemyrtles. While neither dis- ease is a significant threat to the Figure 2. Powdery mildew on crape- myrtle

www.aces.edu Cercospora Leaf Spot tips are lost (Figure 5). Although ceptible to powdery mildew and leaf spot symptoms can appear Cercospora leaf spot. In addi- Although Cercospora leaf as early as late June to early July, tion, most of the L. indica culti- spot, which is caused by the premature leaf drop usually does vars now in the nursery trade fungus Cercospora lythracearum, not begin until mid-August. By are susceptible to both diseases. is not a widely recognized dis- mid-September, 50 percent of ‘Catawba,’ ‘Cherokee,’ ‘Glendora ease, heavy defoliation in the the leaves on susceptible culti- White,’ and ‘Potomac’ are L. late summer and early fall vars can be lost. On leaf spot- indica crapemyrtles that have greatly detracts from the fall susceptible crapemyrtle cultivars, good powdery mildew and color of many crapemyrtle culti- severe leaf shed may not Cercospora leaf spot resistance. vars. Damaging outbreaks of this become noticeable until 1 to 2 Hybrid (L. indica x fauriei) disease occur on cultivars of L. years after plant establishment in crapemyrtles highly resistant to indica and L. indica x fauriei. the landscape. On disease both diseases include Symptoms of Cercospora leaf resistant cultivars, leaf spotting ‘Apalachee,’ ‘Basham’s Party spot first appear on leaves as cir- and defoliation are often con- Pink,’ ‘Caddo,’ ‘Tonto,’ cular to irregular brown spots 1 fined to the branches in the ‘Tuskegee,’ and ‘Tuscarora.’ about ⁄4 inch in diameter. lower canopy and have little Other desirable crapemyrtle cul- Diseased leaves may be twisted impact on aesthetics. tivars are the hybrids ‘Natchez’ or distorted. As the spots enlarge and ‘Sarah’s Favorite’ as well as and become more numerous, The causal fungus is associ- ‘Velma’s Royal Delight.’ The L. diseased leaves often turn ated with crapemyrtles in both fauriei ‘Fantasy’ also suf- yellow to bright red, depending the nursery and the landscape. fers little damage from powdery on the cultivar damaged, and Diseased cuttings are the most mildew or Cercospora leaf spot. then fall to the ground (Figure likely source of Cercospora leaf The L. indica cultivars ‘Carolina 4). spot in container-grown crape- myrtles. In landscape plantings, Beauty,’ ‘Wonderful White,’ Typically, spotting of the fallen diseased leaves from the ‘Raspberry Sundae,’ ‘Powhatan,’ leaves begins on the branches previous year are probably the ‘Peppermint Lace,’ ‘Majestic around the base of the plant and main sources of the Cercospora Beauty,’ and ‘Orbin Adkins,’ then gradually spreads upward leaf spot fungus. Spores are which are all highly sensitive to through the canopy until all but spread to the new foliage by powdery mildew and Cerco- the youngest leaves at the shoot wind. Later, disease develop- spora leaf spot, are poor choices ment accelerates, particularly in for a low-maintenance home or late summer, as spores are pro- commercial landscape. In a duced on leaves on the lower recent Alabama field trial, the limbs and dispersed to healthy powdery mildew resistant culti- leaves in the upper canopy. vars ‘Acoma,’ ‘Near East,’ ‘Yuma,’ Frequent showers or persistent ‘Souix,’ ‘Hopi,’ and ‘Comanche’ heavy dews facilitate spore for- suffered from heavy leaf spotting mation, their spread to healthy and defoliation due to Cerco- leaves, and disease develop- spora leaf spot. See Alabama ment. Agricultural Experiment Station (AAES) Bulletin 644 for more Figure 4. Diseased leaves turn yellow to bright red, then fall to the ground information on the susceptibility Control of crapemyrtle selections to The following procedures powdery mildew and Cerco- can help control powdery spora leaf spot. mildew and Cercospora leaf spot • Collecting and disposing ARCHIVEon crapemyrtles: of fallen, diseased leaves can • Planting a crapemyrtle cul- help slow the spread of both tivar that is resistant to powdery diseases. mildew and Cercospora leaf spot • Spacing out plants in new is the best and most effective plantings of crapemyrtles defense against both diseases. improves air circulation and pro- Antique L. indica selections that motes sunlight penetration into Figure 5. Spotting from Cercospora are commonly found around old the lower canopy. leaf spot spreads to all but the homesites are often highly sus- youngest leaves on the shoot tips

2 Alabama Cooperative Extension System • Making frequent applica- Table 1. Chemical Control of Powdery Mildew and Cercospora Leaf tions of low rates of nitrogen is Spot on Crapemyrtles better than making one applica- Application Rate tion of a high rate. Fungicide Per gal. Per 100 gal. Comments • Properly timing fungicide Powdery Mildew treatments protects powdery azoxystrobin mildew and Cercospora leaf Heritage 50W N/A 1 to 4 oz. Apply at 14- to 28-day intervals. spot-susceptible cultivars from Product for commercial use. copper hydroxide damage. 1 Blackspot and ⁄2 t. N/A Apply at 7- to 14-day intervals. Powdery mildew: Apply Powdery Product for home landscape use. the first fungicide spray shortly Mildew Control after leaf-out or as the character- myclobutanil istic white colonies first appear Immunox 2 T. N/A Apply at 7- to 14-day intervals on the leaves. Continue fungi- (1 fl. as needed to control disease. oz.) Product for home landscape use. cide applications at 1- to 2-week Eagle 40W N/A 6 oz. Apply at 7- to 14-day intervals intervals until midsummer. See Eagle 20EW N/A 6-12 fl. oz. as needed to control disease. Table 1 for fungicides recom- Product for commercial use. mended for the control of pow- propiconazole 1 1 dery mildew. Systemic Fungicide ⁄2 to 1 ⁄2 N/A Apply at first sign of disease and fl. oz. repeat at 14-day intervals. Cercospora leaf spot: Wait Product for home landscape use. until leaf spotting starts on the leaves on the lower limbs in Banner Maxx N/A 5 to 8 Apply at first sign of disease and early to mid-July to make the fl. oz. repeat at 14-day intervals. first fungicide application. Product for commercial use. thiophanate-methyl Repeat applications at 1- to 2- 1 Halt 50W 2 ⁄2 t. N/A Apply at first sign of disease and week intervals, depending on repeat at 7- to 10-day intervals. the fungicide selected, until early Product for home landscape use. 1 September. See Table 1 for 3336 50W 2 ⁄2 t. 12 to 16 Apply at first sign of disease and fungicides recommended for the oz. repeat at 7- to 14-day intervals. control of Cercospora leaf spot. 3336 4.5F N/A 10 to 20 Product for commercial use. When either powdery fl. oz. triforine mildew or Cercospora leaf spot Rose and Shrub is severe, apply a fungicide at Disease Control 1 T. N/A Apply at first sign of disease and the highest rate and shorten the repeat at 7- to 14-day intervals. treatment interval. Several fungi- Product for home landscape use. cides will effectively control Cercospora Leaf Spot both powdery mildew and azoxystrobin Cercospora leaf spot on crape- Heritage 50W N/A 1 to 4 oz. Apply at 14- to 28-day intervals. myrtles. Product for commercial use. copper hydroxide Blackspot and 1 References Powdery Mildew 1 ⁄2 t. N/A Apply at 7- to 14-day intervals as Control needed. Product for home Alfieri, S. A. 1969. Powdery landscape use. mildew of crapemyrtle. Fla. myclobutanil Dept. of Agric. Cons. Ser. Plant Immunox 2 T. N/A Apply at 7- to 14-day intervals as Path. Cir. 83. 2 pp. (1 fl. needed to control disease. Alfieri, S. A. 1976. oz.) Product for home landscape use. Cercospora leaf spot of crape- Eagle 40W N/A 6 oz. Apply at 7- to 14-day intervals ARCHIVEEagle 20EW N/A 6-12 fl. oz. as needed to control disease. myrtle, Lagerstroemia indica. Fla. Product for commercial use. Dept. of Agric. Cons. Ser. Plant Path. Cir. 171. 2 pp. thiophanate-methyl 1 3336 50W 2 ⁄2 t. 12 to 16 Apply at 7- to 14-day intervals as Dirr, M. A. 1998. Manual of oz. needed to control disease. woody landscape plants: Their 3336 4.5F N/A 10 to 20 Product for commercial use. identification, ornamental char- fl. oz. 1 acteristics, culture, propagation, Halt 50W 2 ⁄2 t. N/A Apply at first sign of disease and and uses. 5th Edition. Stipes repeat at 7- to 10-day intervals as needed. Product for homeowner use. Common Diseases of Crapemyrtle 3 Publishing Co., Champaign, Ill. 1187 pp. Hagan, A. K., G. J. Keever, C. H. Gilliam, J. D. Williams, and G. Creech. 2002. Resistance of selected crapemyrtle cultivars to powdery mildew and Cercospora leaf spot. Alabama Agricultural Experiment Station Bulletin 644. 14 pp. Williams, D., K. Tilt, and S. Valenti-Windsor. 1998. Common Crapemyrtle. Ala. Coop. Ext. Sys. Pub. ANR-1083. 6 pp.

A. K. Hagan, Extension Plant Pathologist, Professor, Entomology and Plant Pathology, Auburn University Use pesticides only according to the directions on the label. Follow all directions, precautions, and restrictions that are listed. Do not use pesticides on plants that are not listed on the label. The pesticide rates in this publication are recommended only if they are registered with the Environmental Protection Agency and the Alabama Department of Agriculture and Industries. If a reg- istration is changed or cancelled, the rate listed here is no longer recommended. Before you apply any pesticide, fungicide or herbicide, check with your county Extension agent for the latest information. Trade names are used only to give specific information. The Alabama Cooperative Extension System does not endorse or guarantee any product and does not recommend one product instead of another that might be similar. ARCHIVEFor more information, call your county Extension office. Look in your telephone directory under your county’s name to find the number. Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employment to all people without regard to ANR-1047 race, color, national origin, religion, sex, age, veteran status, or disability. 5M, Revised July 2004, ANR-1047

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