AP130 ph modification on leaf and fruit surface as a control of apple scab. James Wong Tasmanian Department of Primary Industries & Fisheries

Transcription

1 AP130 ph modification on leaf and fruit surface as a control of apple scab James Wong Tasmanian Department of Primary Industries & Fisheries

2 AP130 This report is published by the Horticultural Research and Development Corporation to pass on information concerning horticultural research and development undertaken for the apple & pear industry. The research contained in this report was funded by the Horticultural Research and Development Corporation with the financial support of the Apple & Pear Growers Association. All expressions of opinion are not to be regarded as expressing the opinion of the Horticultural Research and Development Corporation or any authority of the Australian Government. The Corporation and the Australian Government accept no responsibility for any of the opinions or the accuracy of the information contained in this Report and readers should rely upon their own inquiries in making decisions concerning their own interests. Cover Price $20.00 HRDC ISBN Published and Distributed by: Horticultural Research and Development Corporation Level 6 7 Merriwa Street Gordon NSW 2072 Telephone: (02) Fax: (02) Copyright 1997

3 FINAL REPORT AP130 - ph modification on leaf and fruit surface as a control of apple scab, 1991/92 HORTICULTURAL RESEARCH & DEVELOPMENT CORPORATION The Research Arm of the Australian Horticultural Industries HRDCAND AUSTRALIANAPPLEAND PEAR GROWERS ASSOCIATION FUNDED PROJECT Department of Primary Industry and Fisheries tp^ T A S M A N I A Dr James Wong Department of Primary Industry & Fisheries New Town Research Laboratories NEWTOWN TAS 7008 May 1996

4 Horticultural Research & Development Corporation AP130 - ph modification on leaf and fruit surface as a control of apple scab (1 year pilot project, 1991/92) Organisation: Department of Primary Industry & Fisheries, Tasmania Postal Address: GPO Box 192B, Hobart, Tasmania, 7000 Administration Contact: Ms Wendy Dwyer-Kimber Ph (002) Manager, Research & Development Administration & Review Fax (002) Project Chief Investigator: Dr James A L Wong Ph (002) New Town Research Laboratories St John's Avenue, New Town Fax (002) Location of Research: New Town Research Laboratories, New Town and Grove Research Station, Grove Commencement Date: 1 July 1991 Completion Date: 30 June 1992

5 1. Summary a) Industry Summary The objective of the pilot project was to investigate whether modification of ph on leaf and fruit surface has the potential to control apple scab. The results to date indicate that the method is likely to be applicable for the control of apple scab. The one-year pilot project is of a preliminary nature and therefore the results are of no practical use for the industry at this stage. b) Technical Summary The new approach for controlling black spot (scab) on apples, based on increasing the ph on leaf and fruit surface was shown to be highly promising. A high ph of 9.0 and above were shown to inhibit apple scab spore germination and development of infection hyphae. Infection hypha formation was found to be particularly sensitive to high ph. Hydrated lime, a high ph material which is both enviromentally safe and inexpensive, was shown to be effective in controlling scab when applied as a spray at regular intervals. The results suggest that a comprehensive project is now warranted, both to confirm thefindingsto date and to investigate the non-target effects of hydrated lime. 2

6 2. Recommendations a) Extension/Adoption by Industry At this preliminary stage, the information obtained cannot be adopted by the industry. b) Direction for Future Research The pilot project has shown that the high ph method is applicable for apple scab control. The future direction would be to carry out a more detailed study and to develop the method for commercial adoption. c) Financial/Commercial Benefit Nofinancial/commercialbenefits have arisenfromthis preliminary pilot project. 3

7 3. Technical Report a) Introduction Community concern on pesticides in the environment and food is increasing, and a National Pesticide Charter has now been developed with the aims of reducing the use of pesticides by 50% in 5 years and by 75% in year The Australian Apple and Pear Industry has initialled this charter. For apples and pears, the most important disease is scab, (caused by the fungus Venturia inaequalis) as there is no market tolerance (especially the export markets) for any lesions on the fruit. Also, the single largest use of fungicides is for the control of scab. At present effective control of scab is based solely on fungicides applied at days intervals over the season (Penrose, 1968). The cost of fungicides and labour associated with spraying add significant costs to the production of the fruit. Possible approaches to reduce the use of fungicide for scab control include:- (1) integration of fungicide sprays with a scab predictor, which may save one spray per season (Penrose, 1989); (2) use of reduced amount of fungicides per application (Wicks); (3) use of older environmetally acceptable fungicides (eg sulphur and limesulphur), which may cause phytoxicity and is less reliable than the modern fungicides (Anon., 1990); (4) biological control with antagonistic micro-organisms, which would require long term research (10 to 15 years), with no certainty of commercial adoption, especially if only zero-scab tolerance is acceptable; another problem with use of antagonistic micro-organisms is that the control may not be consistent from season to season (Bourdreau and Andrews, 1987); and (5) orchard hygiene and other management practices eg use of urea to enhance leaf litter decomposition (Anon., 1990). A possible new approach to disease control could be based on raising and maintaining a very high ph on any surfaces which organisms need to germinate, grow or sporulate. The author developed this concept over a number of years based on his observation of cultural practices of traditional Chinese and Greek peasant farmers. Some peasant farmers use wood ash on soil surfaces in their vegetable gardens and other crops. It occurred to the author that these farmers, without realising or understanding the reasons, probably have a method of disease control generally applicable to a range of diseases, especially those which form spores or infection structures on or just below the soil surface. As wood-ash is highly alkaline, it can be expected to assist in inhibiting the growth and sporulation of fungi on the soil surface. 4

8 This hypothesis was tested for the control of Sclerotinia disease in lettuce, and very good disease control was achieved (Wong, unpublished data). This concept was tested for black spot control in apples in the 1991/92 season. The results of this research are present in this report. b) Materials and Methods (i) Field Studies Two trials were carried out at the Department's Grove Research Station, one on Red Delicious apples and the other on Golden Delicious. The two trials had similar treatments and were replicated six times as single trees, with sufficient number of buffer trees between treatment trees to prevent any overspraying. Treatment details are given in Table 1. The rates of the materials used are: Kocide (Copper hydroxide) 200g/100L Limil (hydrated lime) 4kg/100L at green tip and Benlate (benomyl, 50% WP) Rovral (iprodione, 50% WP) Tween 20 (wetter) Sprays were applied to run-off using a hand lance. 2kg/100L for subsequent sprays loog/lool loog/lool loomls/lool (added to Benlate + Rovral only) Table 1 Treatments for Apple Scab Control A B Untreated Limil at green tip (GT) to harvest #C Limil at 1st calyx to harvest Treatment* #D Limil at GT and 14 days later, then at 1st calyx to harvest #E Kocide at GT, then Limil at 14 days later, then Limil at 1st calyx to harvest F G Kocide at GT, then Limil at 14 days later, then Benlate plus Rovral at late pink and full bloom, then Limil at 14 days later to harvest Routine conventional Ziram fungicide sprays at GT to harvest * Green tip spray applied on 20/9/91; spray interval is 14 days except over pink and full bloom. # No Limil sprays applied at late pink and full bloom in these treatments with the intention of avoiding possible adverse effects on pollination. 5

9 ph readings of leaf cluster (green tip stage) were taken just prior and immediately after each spray for the first few sprays, and subsequently only just prior to the next spray (usually on the same day or the day before the spray). Five random leaves (or leaf clusters) per tree (replicate), were placed with 25mls of de-ionised water in a plastic bag and shaken 50 times. The leaves were then removed and the ph of the solution measured immediately. Disease on fruits were scored as incidence of fruit infected. ii) Laboratory Studies Scab infected leaves with one or two discrete single lesions were collected from four sites, spores from these leaves were then transferred onto the surfaces of buffered agar media in petri-dishes. Buffered agar ranging from ph7 to 10 were prepared from standard buffer systems based on ICH2PO4 (or H3PO4) plus NaOH (Clarke and Lube, 1916). The concentration of each of the standard buffer system prepared was further diluted eight folds to overcome germination inhibition effects that were apparently associated with solute concentrations. The calcium effects of hydrated lime was eliminated by checking germination against an increasing concentration of calcium ions using CaC03 and Ca (NC»3)2 solutions. Calcium ion levels in the agar equivalent to the calcium in 2kg hydrated lime/lool solutions did not inhibit germination at the relevant ph. The possibility of toxicity of higher levels of NaOH in high ph buffers was investigated also. High ph buffers were neutralised with hydrochloric acid. The neutralised buffers were found not to inhibit germination. Buffered agar was prepared by boiling the agar-buffer mixture. After pouring the agar mixture onto the plates. The ph of the cooled agar mix was determined again just prior to places scab spores onto it. Selected isolates of scab were studied on agar plates over a range of phs. Spores were placed directly onto the agar surfaces from the lesions on the leaves. A portion of the spores on the agar surface was overlayed by a glass cover-slip. This was to induce appressorium and infection hypha formation which require the germ tubes to come into contact with a solid surface. For some treatments, spores were placed on a cellophane membrane so that extra cellular enzyme secretions may be detected. The plates were examined after 24 hours for germination and infection hypha formation. For some plates, enzyme secretion was detected using indicator dyes. 6

10 RESULTS The results of the 1991/92 field trials are given in Table 2. Table 2 Scab infection on fruits of Red Delicious and Golden Delicious under high disease pressure TREATMENTS % FRUIT INFECTED* Red Delicious Golden Delicious A a a B 54.3 c 39.1c C 95.7 a 87.8 b D 99.4 a 77.2 b E 87.5 a b 80.2 b F 5.0 d 4.1 d G 74.2 b - * Results with a common letter do not differ significantly at P = 0.05 (DMR Test) The results showed that hydrated lime used alone and applied at 14 days intervals from green tip to harvest (Treatment B) was better in controlling scab than the routine conventional ziram fungicide sprays (Treatment G) in Red Delicious apples. When hydrated lime was integrated with two systemic synthetic fungicide sprays (Treatment F), scab infection was very significantly reduced. Fruit infection was only 5% for Red Delicious and 4% for Golden Delicious, compared to 100% infection for the untreated fruits for both varieties. Routine ziram fungicide sprays (Treatment G) for Red Delicious had 70% fruit infection. ph on the surface of leaves and fruit was maintained at above ph9 between sprays of hydrated lime. No apparent adverse (phytotoxic) effects due to hydrated lime were observed on the leaves or fruits (e.g. russet). Fruit colour and firmness also did not appear to be affected by hydrated lime. 7

11 Laboratory studies on the effects of high ph on scab spores showed that high ph has a marked inhibitory effect on spore germination and is especially effective in inhibiting infection hypha formation. A summary of the results is given in Table 3. Table 3 Effects of ph on scab spores germination characteristics ph Germ-tube formation Infection hyphae formation Extra-cellular acid mucilage (enzymes) % 100% Yes 8.0 some inhibition severe inhibition Not determined 8.5 severe inhibition complete inhibition Not determined 9.0 almost complete inhibition complete inhibition Not determined Isolates exhibited some variations in germination. Spore germination was inhibited moderately to severely at ph8 to ph8.5. At ph9, spore germination was almost completely inhibited. Infection hypha development in all the isolates examined was severely inhibited at ph8.0 and completely inhibited at ph8.5 and above. A reservation on the laboratory results was the degree of accuracy of ph measurements. (Subsequent studies have shown that the ph determined could have been underestimated by 0.5 ph units). This study is to be considered as preliminary only because of the lack of an accurate probe for measuring agar surface ph. No detailed data have been provided in light of the deficiency of the technique at this stage. Extracellular acid mucilage (and presumably extracellular enzyme) secretions was detected in the vicinity of the infection hyphae and appressoria when spores were germinated on cellophane membranes at ph7.0. 8

12 DISCUSSION The ph modification of surface of leaves andfruitto a highly alkaline level has now been demonstrated to control apple scab significantly. Under low to moderate disease pressure, an integrated use of slaked lime with some fungicide can be expected to replace the control method based on fungicide alone. If the integrated approval is shown to be reliable over a number of seasons, fungicide use in orchards could be reduced by at least 50%. The use of slaked lime for scab control, if proved reliable, would mainly replace the use of protectant fungicides such as ziram, thiram & mancozeb. The effectiveness of high ph in inhibiting germination and infection hyphae formation was demonstrated in laboratory studies. From these studies, it can be expected that maintenance of a ph level at ph 9.0 or above will effectively control scab. High ph affects three essential infection processes of the scab fungus (i.e. spore germination, infection hyphae formation and the action of enzymes). Inhibition of any of these processes will prevent successful infection of the leaves or fruits by the fungus. Having demonstrated that the ph modification method for scab control is valid, it is now important to capitalise on the discovery and to develop the method to commercial adoption. The use of slaked lime as the high ph material for scab control is both highly economic and ecologically sound. This approach addresses the industry's pesticide charter directly. Also, growers will be more easily be persuaded to adopt the method as the new approach is anticipated to be more economic than the current control measures. The high ph approach to disease control can also be expected to assist in controlling insects as well. Use of slaked lime, in particular, should improvefruitfirmnessdue to the uptake of calcium by the fruit. Also it should also reduce bitter pit and hence replace some of the current calcium sprays used for bitter pit control. Bitter pit is a calcium deficiency problem of apples. A comprehensive 4-year project to develop the ph modification method to commercial adoption has been prepared for HRDC funding for the 1992/93 season. 9

13 References: Anon. (1990). Pest management in apple orchards - an alternative approach. FarmnotesNo. 328 (8/1990) (Department of Agriculture, Tasmania): 3pp. Boudreau, M.A. & Andrews J.H. (1988). Factors influencing_antagonism of Clastomium globosum to Venturia inaequalis : A case study in failed biocontrol. Phytopathology 77: Clarke, W.M. & Lubs, H.A (1917). J Bacherology 2:1-11. Penrose, L.J. (1988). Apple and pear scab. Agfact H4.AB4 (NSW Department of Agriculture): 6pp Penrose, L.J. (1989). A national approach to apple scab control the role of disease warning systems and curative spraying. Plant Protection Quarterly 43 (3): Thwaite, W.G., Penrose, L.J., Wickson, R.J., & Withey, R.K. (1992). Orchard and Vineyard Plant Protection Guide. N.S. Department of Agriculture. 108 pp. ACKNOWLEDGMENTS: The project was supported by funds provided by HRDC and the Australian Apple and Pear Growers Association. 10