Suppression of Cedar Apple Rust Pycnia on Apple Leaves Following Postinfection Applications of Fenarimol and Triforine

Transcription

1 Disease ontrol and Pest Management Suppression of edar pple Rust Pycnia on pple Leaves Following Postinfection pplications of Fenarimol and Triforine R.. Pearson, M. Szkolnik, and F. W. Meyer ssistant professor, professor, and research technician III, respectively, Department of Plant Pathology, New York State gricultural Experiment Station, Geneva, NY 446. The authors thank L. M. Henecke and J. R. Nevill for technical assistance. ccepted for publication 8 July 978. BSTRT PERSON, R.., M. SZKOLNIK, and F. W. MEYER Suppression of cedar apple rust pycnia on apple leaves following postinfection applications of fenarimol and triforine. Phytopathology 68: The experimental fungicides fenarimol and triforine were compared with mancozeb to determine control of cedar apple rust (caused by Gynmosporangium juniperi-virginianae) following postinfection applications to apple under both greenhouse and orchard conditions. Fenarimol and triforine inhibited normal development of pycnia and only small flecks developed. In the greenhouse, fenarimol at 0, 40, and 60 g!g/ml provided 98% control when applied days after inoculation; triforine at 0, 40, and 60 4g/ml provided 89-98% control day after inoculation with 9-94% and 68-8% control after and days, respectively. In the orchard, fenarimol at 0 and 40 4g/ml suppressed pycnial formation 96-99% and 97-00%, respectively, when applied or 7 days after commencement of infection periods. Triforine at 40 vg/ml suppressed pycnial formation by 80-8% with sprays within days after infection in the orchard, but control decreased to 7 and 79% at or days. Inadequate control was obtained with postinfection applications of mancozeb, a commonly used rust fungicide, in either greenhouse or orchard. dditional key words: Malus pumila. The efficacy of a fungicide usually is determined by examining its ability to prevent infection when the fungicide is present on the plant before or during onset of infection. Some fungicides, however, prevent disease development if they are applied after infection and are said to have "kickback," "eradicative," or "curative" properties (,). Fungicides used commercially to control cedar apple rust which is incited by Gymnosporangium juniperivirginianae Schw. have not provided control when applied after onset of infection and are classified solely as protectants. However, Szkolnik (8,0) demonstrated control of cedar apple rust following postinfection applications of N,N'-(,4-piperazinediylbis [,,trichloroethylidene])bis(formamide) (triforine) under greenhouse conditions. Pearson and Szkolnik () also reported briefly on postinfection control obtained with applications of triforine and a-(-chlorophenyl)-a-(4chlorophenyl)--pyrimidinemethanol (fenarimol) under greenhouse and orchard conditions. This paper elaborates on these preliminary reports. (70,000/ ml), (ii) trees were placed in a mist chamber (8 and 00% RH), (iii) dilute fungicides were applied at different intervals after inoculation, and (iv) trees were incubated in a greenhouse. Details of the technique have been published (0). Data were recorded as number of pycnial lesions per leaf. Lesions counts then were converted to a percent disease control rating. Values in each experiment were based on average ratings of three leaves on each of three trees per treatment. Experiments were repeated a minimum of five times. Field studies.--infection periods for cedar apple rust were identified by comparing the temperature and the duration of rain-initiated leaf wetness with required values determined previously in laboratory studies (R.. Pearson, unpublished). Golden Delicious apple trees were sprayed to runoff by handgun at 0 psi (8. kg/cm ). Treatments were applied to half-tree plots and the unsprayed half-tree was used as a buffer between treatments. Tags were tied on the youngest unfolded leaf after each fungicide application to identify sprayed leaves and date of application. Two types of data were recorded as Barratt-Horsfall ratings (6) of MTERILS ND METHODS leaf area covered by lesions: (i) total lesions including Greenhouse studies.--single-shooted Rome Beauty normal lesions with pycnia and chlorotic or necrotic apple (Malus pumila Mill.) trees were treated in the flecks without pycnia and (ii) normal lesions with pycnia. following sequence: (i) leaves were inoculated with a Barratt-Horsfall ratings were converted to percent leaf suspension of basidiospores of G. juniperi-virginianae area affected with Elanco conversion tables (6). Data were taken on all sprayed leaves on a minimum of 0 clusters or terminals per replicate. Treatments in all field X/78/0004$.00/00 opyright 978 The merican Phytopathological Society, 40 plots were replicated five times in a randomized complete Pilot Knob Road, St. Paul, MN. ll rights reserved, block design. 80

2 806 PHYTOPTHOLOGY [Vol. 68 RESULTS infection periods were recorded in relation to stage of flower development Greenhouse (): 4- studies.--fenarimol, pril (centimeter green), mancozeb, and - May (early tight cluster and three terminal leaves), triforine were applied,, or days after inoculation. 4- May, 6-7 May (tight cluster and three to five Fenarimol, at rates of 0-60 bg/ml, gave 98% control terminal leaves), - May (pink and seven to nine when applied as long as days after inoculation (Table ). terminal leaves), 6 May (bloom), - May, 0- Triforine gave more than 98% control when applied I day May, and 97. after inoculation at 40 and 60 jig/ ml but not at 0 In one trial, sprays were applied on 4 May ( days after l.g/ ml. Triforine used at 60 /g/ml still provided 94% start of rain) and on 9 June (4 days after the start of a rain) control when applied days after inoculation. Mancozeb (Table ). In another trial, sprays were applied only once showed no postinfection control, at,,, or days after the beginning of a wet period Field studies, 97--Fenarimol (Eli Lilly EL.- commencing 0 May (Table ). E) 40 Mg/ ml active ingredient (I), triforine (elamerck Lesions that developed on untreated leaves or those ME E) 40 g g/ml, and mancozeb (Rohm treated with mancozeb produced both pycnia and aecia & Haas Dithane M-4 80W) 9,90 /g/ml l were (normal lesions), whereas those treated with fenarimol or compared for postinfection control. Nine cedar apple rust triforine produced small chlorotic or necrotic flecks TBLE. ontrol of cedar apple rust (caused by Gymnosporangiumjuniperi-virginianae) on apple by postinfection application of fungicides in the greenhouse Dosage Disease control ratinga Treatment (active ingredient) dayb days days (l g/ml) Untreated check IOc 0 0 Mancozeb 80W, Fenarimol (EL ).E 0 tr tr i tr Triforine ( 700) 0E LSD (P < 0.0) "Minimum disease control for rating 0,,, etc. to 0 is 00, 98,94, 89, 8, 76, 68, 9, 47, 9, and 0%, respectively. tr = trace; more than 99.% control. 'Days refer to interval between inoculation and application of fungicide. 'Figures for,, and day intervals are based on the average of nine, eight, and five experiments, respectively. Values in each experiment were based on average ratings of three leaves on each of three trees per treatment. TBLE. Suppression of pycnia of cedar apple rust (caused by Gymnosporangiumjuniperi-virginianae) on apple by postinfection application of fungicides under orchard conditions in 97 luster leaves Leaf area infecteda after spraying: Terminal leaves Dosage 4 May (pink)b 4 May (pink)b 4 Mayb and 9 Junec Treatment (active ingredient) Totald Normale Total Normal Total Normal (ug/ ml) M% M% M% M% M% (%) Mancozeb 80W, B 6.9 B 6.9 B Fenarimol.E Triforine 0E B Untreated B.8 B.8 B. B. D "Percent leaf area infected determined by Barratt-Horsfall ratings of all leaves exposed to the fungicide treatment (0 clusters or terminals per replication). luster leaf data recorded and 9 June; terminal leaf data recorded 9- July 97. Values followed by same letter did not differ significantly (P < 0.0) according to Duncan's multiple range test on arcsin-transformed data. hfungicide applied days after start of rain on May. 'Fungicide applied 4 days after start of rain on June. dpercent leaf area covered with normal pycnial lesions and abnormal lesions (flecks without pycnia). 'Percent leaf area covered with normal pycnial lesions that subsequently gave rise to aecia.

3 December 978] 807 PERSON ET L: EDR PPLE RUST/HEMOTHERPY (-.0 mm) and aecia did not develop (abnormal lesions). Based on suppression of normal lesion development, fenarimol and triforine provided excellent postinfection control of cedar apple rust when applied within or 4 days after the beginning of a rain (Table ). When only one spray was applied during the season, mancozeb provided no control. However, terminal leaves sprayed with mancozeb 4 May and again 9 June significantly reduced both total lesions and normal lesions. Perhaps fungicide residue from the 4 May application was redistributed to unsprayed leaves that emerged after 4 May but before 9 June. Results of a second trial revealed significant and equal reduction of total lesion development of cedar apple rust following single applications of fenarimol and triforine - days after the start of a rainy period (Table ). Based on normal lesion development, however, fenarimol and triforine applied days after infection gave 9 and 7% control, respectively. Field studies, 976.-Fenarimol.E at 0 and 40 jg/ ml I was compared to mancozeb (DuPont Manzate 00 80W) at,400 Mg! ml l. Five infection periods were recorded: 4-6 pril (pink), - May (bloom), 7 May (petal fall), - May (-4 terminal leaves), and 6-7 May (-6 terminal leaves). Treatments were applied,, or 7 days after a long wet period between 4 and 6 pril. The mean temperature during this 48-hr rainy period was 6, which was too cold for basidiospore formation (4) and therefore precluded infection. These applications did provide protection for the infection periods of - and 7 May (Table 4). Even though all treatments were applied before the infection periods, subsequent normal lesion development was less than total lesion development in both rates of fenarimol. Normal lesion development in most fungicide treatments ranged from 0.4 to.9% leaf area infected, and only the 0 4g/ml rate of fenarimol applied on 7 pril resulted in significantly less (P < 0.0) protection. Nevertheless, the leaf area infected in this treatment was significantly smaller (P < 0.0) than the leaf area infected on untreated leaves. In another trial, treatments were applied 6 or 8 May, and 7 days, respectively, after the beginning of rain. dditionally, these treatments were day before or day after' the 7 May infection period. ll treatments except mancozeb provided 98-00% suppression of normal cedar apple rust lesions on cluster leaves (Table 4). Fenarimol at 0 and 40 M g!ml also provided 96% suppression of normal cedar apple rust lesions on terminal leaves. Mancozeb-treated terminal leaves contained significantly more (P < 0.0) normal lesions than fenarimol-treated leaves but bore significantly fewer (P < 0.0) lesions than nonsprayed terminal leaves. The infection periods of - May and 6-7 May that followed the above applications did not result in infection of previously sprayed leaves, indicating protection for at least 8-0 days. lthough no quantitative data are available, by midugust considerable defoliation by cedar apple rust was observed on the untreated trees and on the untreated half of fungicide-treated trees. DISUSSION Previous greenhouse studies have shown that fenarimol and triforine are capable of postinfection control of apple scab (Venturia inaequalis)(8,), cherry leaf spot (occomyces hiemalis) (8,), and peach brown rot (Moniiniafructicola) (). Spotts (7) showed that TBLE. Suppression of pycnia of cedar apple rust (caused by Gymnosporangiumjuniperi-virginianae)on apple after a single postinfection application of fungicide under orchard conditions in 97 pplication time after start of rain on: Treatment Mancozeb 80W Fenarimol.E Triforine 0E Untreated Dosage (active ingredient) (Mg! ml) Spray date,90 May June 40 May I June June 40 May June 0 May (days) (days) Leaf area infecteda Normal Total lesionsc lesionsb B (%) (%) B.6 B 4. B 6. B 4.4B B. 'Percent leaf area infected determined by Barratt-Horsfall ratings of all terminal leaves exposed to the fungicide treatment (0 terminals per replication). Data recorded Values followed by same letter did not differ significantly (P < 0.0) multiple range test on arcsin-transformed data. according to Duncan's 'Percent leaf area covered with normal pycnial lesions and abnormal lesions (flecks without pycnia). 'Percent leaf area covered with normal pycnial lesions that subsequently gave rise to aecia.

4 808 PHYTOPTHOLOGY [Vol. 68 fenarimol also has eradicative properties against grape same number of pycnial lesions developed after both black rot (Guignardia bidwelii). In the tests reported here treatments. pparently, the fungus is most affected by with cedar apple rust, fenarimol at 0 /g/ml provided fenarimol after infection develops but before lesions are 98% control when applied as long as days postinfection visible, hence the occurrence of flecks. The chance of total in the greenhouse and more than 9% control when prevention of symptom expression is better, however, if applied to 7 days postinfection in the orchard. Triforine sprays are applied soon after infection occurs. at 40 pg/ ml provided 98% control at day postinfection The occurrence of nonsporulating flecks in place of in the greenhouse and dropped to 76% control at and pycnial lesions is a form of control because the absence of days, whereas the same rate of triforine under orchard pycnia precludes the formation of aecia (), which cause conditions provided 79% control as long as days more leaf damage. Thus, the life cycle is broken by postinfection. More favorable conditions for infection in preventing infection of Juniperus virginiana, the alternate the greenhouse probably accounted for the weaker host. The occurrence of small flecks instead of pyncial postinfection control in greenhouse experiments, and aecial lesions and the reduction in defoliation may The flecks that developed when postinfection contribute to control by keeping leaves more functional treatments with fenarimol were applied before symptom than diseased leaves with full symptom expression. expression are equivalent to "presymptom" control Fungicides with postinfection control capabilities described for dodine and benomyl on apple scab () and should be valuable tools in controlling cedar apple rust. triforine on cedar apple rust (0) and cherry leaf spot (9). Previously, when weather conditions prevented adequate Symptoms that developed after preinfection applications coverage with protectant fungicides prior to an infection of fenarimol were similar to those that developed after period, disease was likely to develop. Less frequent postinfection applications (Table 4). More total lesions postinfection application of fungicides would reduce the developed on trees receiving preinfection applications of cost of disease control in an economically and fenarimol than on those treated with mancozeb, but the environmentally sound manner, TBLE 4. Suppression of pycnia of cedar apple rust (caused by Gymnosporangium juniperi-virginianae) on apple following preinfection or postinfection treatment with fungicides under orchard conditions in 976 pplication time Leaf area infected" in relation to start luster leaves Terminal leaves of rain period of: Dosage Spray Total Normal Total Normal Treatment (active ingredient) date - May 7 May lesionsb lesions' lesions lesions (g/ml) (days) (days) (%) (%) (%) (%) Preinfection treatments: Fenarimol.E 0 7 pril 4 before 0 before d 7. D 6. B 9 pril before 8 before.7 B. May 0 before 6 before 4.7 D.4 Fenarimol.E 40 7 pril 4 before 0 before.9 B.9 9 pril before 8 before.7b May 0 before 6 before. B 0.4 Mancozeb 80W,440 7 pril 4 before 0 before.4b.4 9 pril before 8 before.. May 0 before 6 before. 0.9 Untreated 4. E 4. IPostinfection treatments: Fenarimol.E 0 6 May after before May 7 after after Fenarimol.E 40 6 May after before B May 7 after after. 0.. B 0.9 Mancozeb 80W,440 6 May after before.8 B 6. B.8B.4 B 8 May 7 after I after 6.8 B 6.8 B 6.0 B 4.4 B Untreated 6. B 6. B 'Values based on Barratt-Horsfall ratings of leaves exposed to the fungicide treatment (0 terminals or clusters per replication). ll data recorded -6 July 976. Values followed by same letter did not differ significantly (P -< 0.0) according to Duncan's multiple range test on arcsin-transformed data. bpercent leaf area covered with normal pycnial lesions and abnormal lesions (flecks without pycnia). 'Percent leaf area covered with normal pycnial dno data lesions recorded that subsequently for cluster leaves gave in rise preinfection to aecia. treatments.

5 December 978] PERSON ET L: EDR PPLE RUST/HEMOTHERPY 809 LITERTURE ITED rot caused by Guignardia bidwellii. Plant Dis. Rep. 6:-8.. HPMN, P. J., and G.. TLIN Growth stage 8. SZKOLNIK, M. 97. Page in Fungicide and Nematicide in fruit trees-from dormant to fruit set. N.Y. Food and Tests: Results of 97. Vol. 8. m. Phytopathol. Soc., Life Sci. Bull p. St. Paul, MN. 9 p.. LEWIS, F. H., and K. D. HIKEY. 97. Fungicide usage 9. SZKOLNIK, M Unusual post-infection activity of a on deciduous fruit trees. nnu. Rev. Phytopathol. piperazine derivative fungicide for the control of cherry 0: leaf spot. Plant Dis. Rep. 8:6-9.. MILLER, P. R. 9. Pathogenicity of three red-cedar rusts 0. SZKOLNIK, M Unique post-infection control of that occur on apple. Phytopathology : cedar-apple rust on apple with triforine. Plant Dis. Rep. 4. PERSON, R.., H. S. LDWINKLE, and R.. 8: SEEM Teliospore germination and basidiospore I. SZKOLNIK, M Problems associated with the control formation in Gymnosporangium juniperi-virginianae: of deciduous tree fruit diseases. Pages in Proc. regression model of temperature and time effects. an. J. XIX It. Hortic. ong., Vol. (Warsaw, Poland). 48 p. Bot. : PERSON, R.., and M. SZKOLNIK Post-. SZKOLNIK, M fter-infection activity of fungicides infection control of cedar-apple rust on apple with applied after fruit tree inoculation. Page 49 in Fungicide triforine and EL. Proc. m. Phytopathol. Soc. :0 and Nematicide Tests: Results of 97. Vol.. m. (bstr.). Phytopathol. Soc., St. Paul, MN. 79 p. 6. REDMN,. E., E. P. KING, and I. F. BROWN, JR.. SZKOLNIK, M., and L. M. HENEKE fter Elanco onversion Tables for Barratt-Horsfall infection spray for control of brown rot blossom blight on Rating Numbers. Eli Lilly and o. Indianapolis, IN. 00 peach (976). Page 6 in Fungicide and Nematicide Tests: p. Results of 976. Vol.. m. Phytopathol. Soc., St. Paul, 7. SPOTTS, R hemical eradication of grape black MN. 86 p.