ALABAMA A&M AND AUBURN UNIVERSITIES Diseases of Pansies ANR-1214 and Their Control Leaf Spot Diseases here are two common fungal Tleaf spot diseases that may damage pansies, Viola x wittrock- iana, in the landscape or green- house. Anthracnose, caused by Colletotrichum gloeosporioides, Figure 2. Cercospora leaf spot on and Cercospora leaf spot, caused pansy Figure 5. Botrytis at 10X magnification by Cercospora violae, each causes severe damage to the overall appearance of pansy plantings and reduces the economic value of greenhouse crops. Both dis- eases require high relative humidity and moisture for their development and spread. Figure 6. Myrothecium crown rot Anthracnose can be a Figure 3. Small white spots of pow- with black fruiting bodies and white problem in landscape and green- dery mildew in early stages of develop- spore masses at 10X magnification house plantings throughout the ment on pansy leaves growing and production seasons, respectively. Symptoms first appear as pale white or cream- colored circular spots (one-eighth to one-fourth inch in diameter) on upper surfaces of leaves and occasionally on stems (Figure 1). Spots have thin dark brown or black borders. Often spotting is most severe on lower leaves Figure 7. Black roots typical of ARCHIVEFigure 4. Botrytis flower stem Thielaviopsis black root rot (Healthy blight with fungal growth plant on the right and diseased plant on the left) where humidity is highest. When conditions are humid or wet, tiny black specks may appear on the masses disperse the spores to surface of spots. These specks nearby healthy foliage. New spots develop into spore masses of the typically appear on the previously fungus. Splashing rain or irriga- healthy leaves and stems about 1 tion droplets falling onto spore Figure 1. Anthracnose leaf spots on week after infection. pansy www.aces.edu Table 1. Anthracnose and Leaf Spot Diseases Fungicides Rates Comments per gallon per 100 gallons azoxystrobin Heritage 50W —- 1 to 4 oz. Apply to foliage to runoff before symptoms are seen. Reapply chlorothalonil as needed every 7 to 14 days. Shorten interval and increase 3 Daconil Weather Stik —- 1 ⁄8 pt. rate when conditions favor disease development. Add a small 1 Daconil Ultrex —- 1.4 lb. amount of a spreader sticker or liquid detergent ( ⁄4 tsp. per Daconil 2787 4F 2 t. 2 pt. gallon) to improve coverage of foliage with wettable powder mancozeb (W) formulations. Fore 80W 1 T. 1.5 lb. thiophanate-methyl 3336 50W —- 12 to 16 oz. 3336 4.5F —- 10 to 20 fl. oz. Halt 50W 1 T. —- trifloxystrobin Compass 50W —- 2 to 4 oz. Cercospora leaf spot occurs debris. When preparing to plant reduce their vigor and ultimately most frequently in landscape in the spring, bedding plant loca- speed up plant decline. Pansy cul- plantings in early to midspring. tions should be rotated so that tivars differ considerably in their Outbreaks of this disease also the same type of plants are not susceptibility to powdery mildew. develop in early fall on green- installed into the same areas Small discrete, faint white house flat- and pot-grown pan- every year. Greenhouses should patches that consist of numerous sies. Spots are approximately one- be thoroughly cleaned between threadlike hyphae and spores of fourth inch in diameter, circular, crops. All pansy debris should the causal fungus Sphaerotheca and dark charcoal gray with a be removed from the house. macularis appear on the petioles slightly raised feathery texture Benches, pots, tools, and floors and leaves (Figure 3). These (Figure 2). Lower leaves are often should be thoroughly cleaned patches increase in size until the severely spotted and usually fall of debris. In landscapes, irrigation entire leaf surface is covered by from the plants. Spores of the should be scheduled for the the white threadlike growth of the fungus, which are produced when morning so that the foliage will causal fungus. conditions are humid, are easily dry quickly. Bedding plants Typically, outbreaks of pow- moved to nearby healthy foliage should be located in landscape dery mildew on pansy become by wind currents and splashing areas with well-drained soil. noticeable shortly before the water droplets. New leaf spots Greenhouses should follow similar plants are replaced with summer appear about 1 week after spore practices regarding irrigation and annuals. As a result, protective dispersal and infection begin. drainage. Where large numbers of fungicide treatments are rarely Control of these leaf spot plants are involved, application needed to protect plantings of diseases involves (1) removal of of protective fungicide sprays is pansy from powdery mildew. severely spotted plants or leaves; often recommended. Label direc- Plantings should be periodically (2) modification of watering prac- tions should be followed carefully. inspected for disease symptoms. tices so that foliage does not See Table 1 for specific fungicides If the characteristic white colonies remain wet for prolonged labeled for the control of these are seen and the plants are periods; and (3) fungicide appli- diseases. young, then begin fungicide cations, which are needed in applications. See Table 2 for a list some situations. In landscapes or Powdery Mildew of fungicides cleared for the con- greenhouses, removal of infected Powdery mildew may occur trol of powdery mildew on pansy. plants is recommended.ARCHIVE If diseased in March and April in landscape The fungicides used to control plants are not removed, they will plantings of pansy. Fluctuating Cercospora leaf spot (Table 1) serve as a reservoir of inoculum temperatures typical of spring and will also control powdery mildew. for future disease spread. If pos- fall and high humidity are condi- The severity of powdery sible, fallen leaves should be tions favorable for disease devel- mildew varies considerably removed from the area. In the opment and spread. Although among cultivars of pansy. In field late fall, the areas where disease powdery mildew will not directly trials in Alabama, ‘Bingo Clear is present should be thoroughly kill pansy, severe infections may Azure,’ ‘Imperial Silver Blue,’ cleaned by removal of all pansy 2 Alabama Cooperative Extension System Table 2. Powdery Mildew Fungicides Rates Comments per gallon per 100 gallons azoxystrobin Heritage 50W —- Apply to foliage at first sign of disease. Reapply every 7 to 14 thiophanate-methyl days as needed. Shorten interval and increase rate when 3336 50W —- 12-16 oz. conditions favor disease. Add a small amount of a spreader 1 3336 4.5F —- 10-20 fl. oz. sticker or liquid detergent ( ⁄4 tsp. per gallon) to improve Halt 50W 1 T. —- coverage of foliage with wettable powder (W) formulations. parafinnic oil Sun Spray Ultra Fine Oil 1% v/v 1 gal. trifloxystrobin Compass 50W —- 2-4 oz. ‘Crown Orange,’ and ‘Imperial foliage by wind currents or under conditions of low humidity. Beaconfield’ developed extensive splashing water. When disease does occur, how- powdery mildew of the foliage. Disease control involves (1) ever, it is wise to remove the dis- Little if any damage was seen removing diseased plants; (2) eased plants and, if possible, on most of the remaining pansy reducing humidity and moisture; increase plant spacing to improve cultivars evaluated. and (3) in certain cases, applying air circulation. Planting pansies in protective fungicide treatments. In low wet areas should be avoided. Botrytis Blight a greenhouse, diseased plants Watering should be done midday should be removed. Production so that foliage will dry quickly. Botrytis blight, caused by the Applications of a protective fungi- fungus Botrytis cinerea, may be benches, pots, and tools should be thoroughly cleaned. For details cide are recommended only a problem in the landscape and where large plantings are in greenhouse production. on this clean-up process, see Extension publication ANR-753, involved. See Table 3 for fungi- Temperatures in the low 50s cides labeled for Botrytis control, to upper 70s combined with “Identification and Control of Botrytis Blight on Floral Crops and always follow label recom- prolonged periods of high mendations. humidity and frequent rain or and Woody Ornamentals.” Irriga- overhead irrigation favor disease tion should be applied at midday development. Flowers and so that foliage does not remain Myrothecium Crown Rot flower stems are especially sus- wet during night hours. Plants The fungus Myrothecium ror- ceptible to attack by Botrytis. should be spaced and fans should idum causes a crown (lower be adjusted so that relative stem) rot and a petiole rot of Botrytis blight causes brown humidity is kept as low as pos- spots or blotches on flowers and pansy. This disease is typically a sible. Heating cool air to tempera- problem in greenhouses; how- flower stems (Figure 4). When the tures of 75 degrees F or higher disease is severe and conditions ever, Myrothecium crown rot has and venting warm moist air will been observed occasionally in are wet, leaves and major stems help prevent continued develop- may become spotted, cankered, landscape plantings. Infection and ment of the fungus, especially damage occur under conditions and blighted. In some situations, when these practices are applied individual spots on leaves may of moderate temperatures and during evening hours. Protective moderate soil moisture. have a slight zonate pattern. fungicides are recommended in Severely damaged plants may col- many greenhouse situations when Symptoms begin as a brown lapse and die. When humidity is Botrytis blight has been detected. soft rot of the crown and possibly high, the fungus will form a dark See Table 3 for fungicides labeled the nearby leaf petioles (Figure to light gray webby growthARCHIVE on 6). When crown rot is severe, a for Botrytis control on pansy, and the surfaces of blighted leaves follow all label directions. rapid wilt and collapse of the and flowers. If examined closely, plant follow. Tiny white and the fungal growth may display a Botrytis blight on pansy in the black bodies (spore masses), just branchlike network with scat- landscape is a problem only barely visible as specks, usually tered, small light gray knots or when the weather is cloudy, mild, develop on the infected crowns clusters (Figure 5).