Sooty blotch causes heavy losses in Lake Constance organic apple production. In the last

five years research has been done at the research station for fruit growing

(Kompetenzzentrum Obstbau – Bodensee) on strategies to control Sooty blotch on organic

grown pome fruit. Different control strategies with lime sulphur, coconut soap and

potassium bicarbonate with different application rates, application times were tested in

several trials on the cultivar ‘Topaz’. Over the years the results show that lime sulphur has

significant effects in controlling Sooty blotch. In a first trial potassium bicarbonate showed

a promising efficacy against Sooty blotch. Concerning the right application times we need

further investigations. The problem is that Sooty blotch is a disease complex caused by

several fungi and it is likely that the fungi that are a part of the complex differ from area to

area

Mayr, U.

Späth, S.

English

Organic Eprints

82Sooty blotch of apple:  Efficacy of different application strategies U. Mayr1, S. Späth1AbstractSooty blotch causes heavy losses in Lake Constance organic apple production. In the last five  years  research  has  been  done  at  the  research  station  for  fruit  growing (Kompetenzzentrum Obstbau – Bodensee) on strategies to control Sooty blotch on organic grown  pome  fruit.  Different  control  strategies  with  lime  sulphur,  coconut  soap  and potassium  bicarbonate  with  different  application  rates,  application  times  were  tested  in several trials on the cultivar ‘Topaz’. Over the years the results show that lime sulphur has significant effects in controlling Sooty blotch. In a first trial potassium bicarbonate showed a promising efficacy against Sooty blotch. Concerning the right application times we need further investigations. The problem is that Sooty blotch is a disease complex caused by several fungi and it is likely that the fungi that are a part of the complex differ from area to area.Keywords: Sooty blotch, application strategies, lime sulphur, coconut soap IntroductionSooty blotch causes heavy losses in Lake Constance organic apple production, especially in orchards with apple scab-resistant cultivars that are managed with low fungicide input (Buchleither  &  Späth  2007).  This  fact  greatly  reduces  the  practical  benefits  of  scab-resistant cultivars, because the farmers have to treat these varieties against Sooty blotch as frequently as their standard varieties against apple scab. In comparison to apple scab, Sooty blotch is a disease complex caused by several fungi (Sutton & Williamson 2002). The  biology  of  these  fungi  is  not  known,  especially  what  time  of  summer  this  disease begins its fruit infections. Apart from experiments to determine when Sooty blotch occur by protecting  susceptible  fruits  with  bags  at  various  times,  winter  treatments  and  different control strategies with lime sulphur, coconut soap and potassium bicarbonate with different application rates, application times were tested in several trials with the aim to reduce fungicide treatments. Material and Methods All experiments were carried out in the years 2003 to 2007 on the apple cultivar “Topaz” with three or four replications. The orchard was planted in 2001. Treatments were carried out with a tunnel sprayer or a hand-gun sprayer.Incidence and severity were assessed using the following pattern: 0 = no symptoms, 1 = traces, 2 = until 10% of fruit surface, 3 = 10-25%, 4 = 25-50%, 5 = more than 50% of fruit surface.Disease severity (p) is expressed as: P = Σ (n*v)/(v-1)N*100                                                   1 Kompetenzzentrum Obstbau – Bodensee, Schuhmacherhof 6, 88213 Ravensburg, www.kob-bavendorf.de P: disease severity (%) N: total number of fruits v: evaluation number: 0,1,2,3, 4, 5 n: number of fruits of each evaluation number Archived at http://orgprints.org/13649/83Sooty blotch of apple:  Efficacy of different application strategies U. Mayr1, S. Späth1AbstractSooty blotch causes heavy losses in Lake Constance organic apple production. In the last five  years  research  has  been  done  at  the  research  station  for  fruit  growing (Kompetenzzentrum Obstbau – Bodensee) on strategies to control Sooty blotch on organic grown  pome  fruit.  Different  control  strategies  with  lime  sulphur,  coconut  soap  and potassium  bicarbonate  with  different  application  rates,  application  times  were  tested  in several trials on the cultivar ‘Topaz’. Over the years the results show that lime sulphur has significant effects in controlling Sooty blotch. In a first trial potassium bicarbonate showed a promising efficacy against Sooty blotch. Concerning the right application times we need further investigations. The problem is that Sooty blotch is a disease complex caused by several fungi and it is likely that the fungi that are a part of the complex differ from area to area.Keywords: Sooty blotch, application strategies, lime sulphur, coconut soap IntroductionSooty blotch causes heavy losses in Lake Constance organic apple production, especially in orchards with apple scab-resistant cultivars that are managed with low fungicide input (Buchleither  &  Späth  2007).  This  fact  greatly  reduces  the  practical  benefits  of  scab-resistant cultivars, because the farmers have to treat these varieties against Sooty blotch as frequently as their standard varieties against apple scab. In comparison to apple scab, Sooty blotch is a disease complex caused by several fungi (Sutton & Williamson 2002). The  biology  of  these  fungi  is  not  known,  especially  what  time  of  summer  this  disease begins its fruit infections. Apart from experiments to determine when Sooty blotch occur by protecting  susceptible  fruits  with  bags  at  various  times,  winter  treatments  and  different control strategies with lime sulphur, coconut soap and potassium bicarbonate with different application rates, application times were tested in several trials with the aim to reduce fungicide treatments. Material and Methods All experiments were carried out in the years 2003 to 2007 on the apple cultivar “Topaz” with three or four replications. The orchard was planted in 2001. Treatments were carried out with a tunnel sprayer or a hand-gun sprayer.Incidence and severity were assessed using the following pattern: 0 = no symptoms, 1 = traces, 2 = until 10% of fruit surface, 3 = 10-25%, 4 = 25-50%, 5 = more than 50% of fruit surface.Disease severity (p) is expressed as: P = Σ (n*v)/(v-1)N*100                                                   1 Kompetenzzentrum Obstbau – Bodensee, Schuhmacherhof 6, 88213 Ravensburg, www.kob-bavendorf.de P: disease severity (%) N: total number of fruits v: evaluation number: 0,1,2,3, 4, 5 n: number of fruits of each evaluation number Trials assessments were made directly after harvest. For each treatment, at least 150 fruits maximum 1700 fruits, were randomly chosen for the assessment. In 2003/2004 different management strategies were tested: a) starting with coconut soap treatments after a threshold value of wetness hours, b) application of coconut soap after a total number of wetness hours (Table 1). Another aim of the study was to verify whether the  primary  inoculum  of  Sooty  Blotch  can  be  reduced  by  winter  treatments  with  lime sulphur, copperoxychloride or quick lime.Table 1: Experimental setup 2003/2004 Treatments*  Application 2003 following   Number of treatmentsin 2003 Application 2004 following  Number  of treatments in 2004 A  Untreated    0    0 B  Coconut soap 8l/ha  Adviser recommondations  9  Adviser recommondations  9 C  Coconut soap 8l/ha  after 150 hours wetness  11  after 150 hours wetness  10 D  Coconut soap 8l/ha  after 200 hours wetness  10  after 250 hours wetness  8 E  Coconut soap 8l/ha  after 250 hours wetness  8  every 50 hours wetness  11 F  Coconut soap 8l/ha  every 50 hours wetness  8  every 100 hours wetness  6 G  Coconut soap 8l/ha  every 100 hours wetness  5  every 200 hours wetness  3 H  Lime sulphur 10l/ha  like B  9  like B  9 Winter treatments (end of February) with I  Lime sulphur 25 l/ha  combined with B  10  combined with B  10 K  Copperoxychloride 1kg/hacombined with B  10  combined with B  10 L  Quick lime 50kg/ha**  combined with B  10  combined with B  10 *all applications with 500 l/ha, exceptionally ** quick lime with 800 l/ha The value of the RIMpro Sooty blotch model as tool for timing fungicide sprays was tested in 2005 and 2006 (Table 2). The weather data to drive the model were collected from six weather stations located near the trial orchard. Fungicide treatments were made if the infection level was over 500 at least of three stations. Table 2: Experimental setup 2005/2006 Treatments  Number of treatments in 2005Number of treatments in 2006A  Untreated  0  0 B  Coconut soap 8I/ha, 500 l/ha  2  0 C  Coconut soap 8l/ha, 1000 l/ha  2  0 D  Lime sulphur 10l/ha, 500 l/ha  2  0 In 2007 the value of two models as tools for timing fungicide sprays to control Sooty blotch was tested: Mills and RIMpro (Table 3). Based on the experience in 2006 with RIMpro Sooty blotch model, the infection level for fungicide treatments was heavily reduced from 500 to 50.  Concerning the Mills model, applications were made if the infection level was over 3,5. Archived at http://orgprints.org/13649/84Table 3: Experimental setup 2007   Treatments*  Application following  Number of treatments A  Untreated    0 B  Potassium bicarbonate (Armicarb) 5 kg/ha  RIMpro Sooty blotch  1 C  Lime sulphur 15l/ha  RIMpro Sooty blotch  1 D  Lime  sulphur  15l/ha  combined  with  a pretreatment at BBCH 72 RIMpro Sooty blotch  2 E  Potassium bicarbonate (Armicarb) 5 kg/ha  Mills  5 F  Lime sulphur 15l/ha  Mills  5 *all applications with 500 l/haResults and discussion In the season 2003, Sooty blotch pressure was relatively low (disease severity in untreated control: p = 13,8 %) because of the very dry summer and the age of the orchard (planted in spring 2001). To increase infection pressure in 2004, branches of blackberry bushes were distributed two times (11.5 and 17.6) in the trial orchard. In contrast to 2003, Sooty blotch pressure 2004 was now relatively high in the untreated part of the orchard (p = 54,1 %). In the following years disease severity range from 60 to 90 % in untreated control. Table 4: Results of the experimental setup 2003/2004 Number of treatmentsin 2003 Number of fruits in 2003Diseaseseverity in 2003(%) Number of treatmentsin 2004 Numberof fruits in 2004 Diseaseseverity in 2004 (%) A  0  344  13,8  0  1410  54,1 B  9  355  8,7  9  1180  44,2 C  11  319  9,3  10  987  42,5 D  10  343  9,4  8  1347  63,5 E  8  282  10,3  11  1100  27,6 F  8  292  11,0  6  944  35,1 G  5  256  10,8  3  1268  46,8 H  9  333  1,4  9  939  20,2 Winter treatments (end of February) combined with B   I  10  403  9,37  10  1068  43,0 K  10  344  9,32  10  1051  44,5 L  10  421  14,9  10  1285  50,1 Both years show, that a winter treatment with lime sulphur, copperoxychloride, quicklime at high  rate  did  not  reduce  the  number  of  fruits  infected  by  Sooty  blotch.  This  results confirmed  earlier  work  from  Trapman  et  al.  (2004).  The  conclusion  will  be,  that  either Sooty blotch inoculum hibernating on the stem and branches of the apple trees is only of less importance for the primary infection or that even intense treatments with the most effective  fungicides  available  in  organic  farming  are  not  effective  enough  to  have  an measurable influence on disease severity at harvest (Table 4). However the rates of lime sulphur and copperoxychloride applied as a winter treatment in one single spray would be much  more effective by applying 3 to 8 well aimed applications during summer to control Sooty blotch. Archived at http://orgprints.org/13649/85The summer treatments with lime sulphur (H) reduced the disease incidence considerablyin  both  years.  The  alternative  program  with  coconut  soap  treatments  during  summer reduced the disease incidence slightly, but these effects are not significant (B). However in 2004 the efficacy of coconut soap treatments increased with the number of applications (B, E). A management strategy starting with coconut soap treatments after a threshold value of  wetness  hours  or  coconut  soap  treatments  which  have  been  applied  after  a  total number of wetness hours showed no strong effect. Table 5: Results of the experimental setup 2005 Number  of  treatments in 2005 Number of fruits in 2005  Disease severity in 2005 (%) A  0  1485  81,0 B  2  1540  71,6 C  2  1580  74,9 D  2  1550  70,7 In 2005 at harvest (October 10th) the disease incidence in the untreated plot was very high (81%, Table 5). First slightly visible symptoms were found on July 20th , the first “tear” was found  on  august  18  th.  This  infection  was  not  recognized  by  the  Sooty  blotch  RIMpro model. Only two treatments were applied  according to the infection model (24.8/12.9), but there was no significant reduction of Sooty blotch incidence. In 2006 the first visible symptoms were found two weeks later, but compared to 2005 the Sooty blotch RIMpro model never reached a infection level of 500, the threshold value for an application. In 2006 the disease severity was 70 % on average of all plots. Observations in 2005 suggest that the first infection was not as severe for the model as in reality. The favourable weather conditions in late summer and also the infection potential that has grown over secondary cycles during summer were responsible for the rapid build up of symptoms in the last weeks before harvest. According to the strong disease build-up, the two treatments were not enough to control Sooty blotch. Whatever the reasons were, that  the  Sooty  blotch  RIMpro  model  didn’t  recognize  any  infection  period  in  2006,  we concluded that the model, based on data of North America, is not simply transferable to Lake Constance weather conditions. Table 6: Results of experimental setup 2007   % of fruits of each evaluation number  Diseaseseverity (%) Numberof fruitsNumber  of treatments0  1  2  3  4  5       A  0,1  1,0  3,1  5,1  30,4  60,3  89,1  1641  0 B  0,9  4,3  10,6  14,1  38,5  31,7  76,0  1635  1 C  0,2  2,5  8,8  11,8  40,3  36,5  79,8  1692  1 D  0,3  2,7  8,8  13,1  42,0  33,1  78,6  1729  2 E  0,8  7,0  23,0  23,2  31,1  14,8  64,2  1667  5 F  0,7  4,9  17,0  21,0  41,0  15,4  68,6  1663  5 In 2007 we had the severest disease incidence in the untreated plot all over the years (89,1 %). The treatments B, C, D with one or two applications reduced the Sooty blotch incidence between 9 and 13 % compared to the untreated plot. Archived at http://orgprints.org/13649/86A pretreatment at T-stage of the fruits (BBCH 72) had no measurable effect on the disease level (Table 6). The treatments E, F with five applications reduced significantly the Sooty blotch  incidence,  21  to  25  %  compared  to  the  untreated  plot.  Especially  potassium bicarbonate (Armicarb) showed a promising efficacy against Sooty blotch. But also in plots E, F the Sooty blotch pressure was too high and leaded to unacceptable high yield losses. These results suggest that in seasons with a very high Sooty Blotch pressure, much more than five treatments with lime sulphur or bicarbonate are necessary to expect a good result in Sooty blotch control. The results of management practices on Sooty blotch published by Main & Gurtz (1988) and Rosenberger et al. (1996) confirmed this assumption. In the future spray treatments to control sooty blotch need to be exactly timed with disease biology.References Buchleither S. & Späth S. (2007), Regenflecken – nach wie vor ein ungelöstes Problem. Öko-Obstbau 3, 3-7Main C. E. and Gurtz S. K. (1988): Crop losses due to plant diseases and nematodes, N. C. State Univ. Dep.; Plant Pathol.; Spec. Publ. 8Rosenberger  D.  A.,  Engle  C.  A.,  Meyer  F.  W.  (1996): Effects  of  Management  Practices  and Fungicides on Sooty Blotch and Flyspeck Diseases and Productivity of Liberty Apples; Plant disease 80, 798-803 Sutton  T.B.  &  Williamson  S.  M.  (2002),  Sooty  blotch  of  apple:  Etiology  and  Management. Proceedings  of  the  10th  International  Conference  on  Cultivation  Techniques  and Phytopathological Problems in Organic Fruit Growing, 43-48 Trapman M., Tamm L., Fuchs J. G. Fuchs (2004), The effectiveness of winter treatments with cooper or lime sulphur to control Sooty Blotch on apple. Proceedings of the 11th International Conference  on  Cultivation  Techniques  and  Phytopathological  Problems  in  Organic  Fruit Growing, 67-72 Trapman M. (2004), A simulation program for the timing of fungicides to control Sooty Blotch in organic  apple  growing.  Proceedings  of  the  11th  International  Conference  on  Cultivation Techniques and Phytopathological Problems in Organic Fruit Growing, 56-66 Archived at http://orgprints.org/13649/

Sooty blotch of apple: Efficacy of different application strategies

Abstract

Similar works

Full text

Available Versions

Organic Eprints