Control of Powdery
`Mildew on Leaves
`and Stems of
`Gooseberry
`
`Deric D. Picton1 and
`Kim E. Hummer2
`
`ADDITIONAL INDEX WORDS. Ribes uva-
`crispa, Ribes grossularia, Sphaerotheca
`mors-uvae, efficacy, mineral oil,
`biological control, Trichoderma
`
`SUMMARY. Powdery mildew
`(Sphaerotheca mors-uvae ) severely
`infects young leaves and stems of
`gooseberry (Ribes uva-crispa )
`throughout the world. Environmen-
`tally friendly control measures are
`being sought as alternatives to sulfur
`or demethylation inhibiting fungi-
`cides. This study examined the effect
`of a mineral oil spray, the biological
`control agent Trichoderma harzianum
`Rifai strain T-22 (Trichoderma), a
`combination mineral oil +
`Tricoderma, and the chemical fungi-
`cide thiophanate, on powdery mildew
`severity in ‘Industry,’ a susceptible
`gooseberry. Mineral oil at 8 mL·L–1
`(1.0 fl oz/gal), Tricoderma at 4 g·L–1
`(0.5 oz/gal) and thiophanate at 1.45
`mL·L–1 (0.186 fl oz/gal), and mineral
`oil + Tricoderma mix was applied to
`plants until runoff at 2-week intervals
`from February 2002 through April
`2002, on potted ‘Industry’ plants
`growing in a greenhouse in U. S.
`Department of Agriculture, Agricul-
`tural Research Service, National
`Clonal Germplasm Repository
`(NCGR), Corvallis, Ore. The percent
`of infected leaves per plant were
`calculated and the percent of infected
`stem surface areas were visually rated
`in mid-April. The fungicide, mineral
`oil, and mineral oil + Tricoderma
`treatment applications significantly
`reduced powdery mildew severity in
`
`The use of trade names does not imply endorsement of
`the products named nor criticism of similar ones not
`named. We acknowledge the Northwest Center for
`Small Fruits Research and CRIS 5358-21000-029-
`00D for providing funding support for this project.
`
`1Graduate research assistant, Department of Horticul-
`ture, Oregon State University, Corvallis, Oregon,
`97330. Present address: BARC-West, Floral and Nurs-
`ery Plants Research Unit, 10300 Baltimore, Ave. Bldg
`010A Beltsville, MD, 20705-2350.
`
`2Research leader, USDA ARS NCGR, 33447 Peoria
`Road, Corvallis, Oregon 97333-2521; to whom corre-
`spondence should be addressed; e-mail khummer@ars-
`grin.gov.
`
`365
`
`Fig. 4. Medium leachate analysis for pH and electrical conductivity (EC) in 1998.
`
`quirements. There was a sharp decrease
`in irrigation required from August to
`October with decreasing temperatures.
`Yeager (1998) reported that moni-
`toring both water use and discharge is
`essential in identifying water requirements
`and accumulation of soluble salts during
`times of inadequate rainfall. Effluent analysis
`during the month of August in this study
`determined nutrients (N, Phosphorus, Po-
`tassium, Calcium, Magnesium) were at
`acceptable levels and pH (7.8) at slightly
`higher than recommended (Fig. 3 and 4).
`Below normal rainfall high temperatures,
`and water evaporation may have been
`responsible for increased leachate electro
`conductivity (EC) and pH measurements
`(Fig. 4). Additional irrigation was required
`to leach accumulated salts.
`The closed capture system could be
`used as an objective nursery irrigation
`management tool providing data to
`make informed decisions. Yearly accu-
`mulated data could eventually be trans-
`formed into an irrigation model for each
`species, media, and climate. Previous
`research has shown that effluent based
`irrigation could reduce fertilizer and
`irrigation requirements (Davis, et al.,
`2001). Monthly monitoring reports
`could provide adequate data for manag-
`ing irrigation; as well as, monitoring
`nutrient availability and leaching.
`
`Literature cited
`Beeson, Jr., R.C. and G.W. Knox. 1991. Analysis
`of efficiency of overhead irrigation in container
`production. HortScience 26(7):848–850.
`
`Davis, M.K., E.W. Bush, and J.S. Kuehny. 2001.
`The effects of leaching fraction and fertilizer
`concentration on Euphorbia pulcherrima ‘Free-
`dom Red’. Proc. S. Nursery Assn. Res. Conf.
`46:140–143.
`
`Fain, D.C., Tilt, K.M., C.H. Gilliam, H.G. Pon-
`der, and J. L. Sibley. 1999. Cyclic irrigation
`improves irrigation application efficiency and
`growth of sawtooth oak. J. Arboricult. 25:200–
`204.
`
`Fare, D.C., C.H. Gilliam, G.J. Keever, and J.W.
`Olive. 1994. Irrigation reduces container leachate
`nitrate-nitrogen concentration. HortScience
`29(12):1514–1517.
`
`Mason, J. 1994. Nursery management. Kanga-
`roo Press, Kenthurst, Australia.
`
`Niemiera, A.X. and C.E. Leda. 1993. Nitrogen
`leaching from osmocote-fertilized pine bark at
`leaching fractions of 0 to 0.4. J. Environ. Hort.
`11:75–77.
`
`Yeager, T.H., C.H. Gilliam, T.E. Bilderback,
`D.C. Fare, A.X. Niemiera, and K.M. Tilt. 1997.
`Best management practices guide for producing
`container-grown plants. S. Nursery Assn.,
`Marietta, Ga.
`
`Yeager, T.H. 1998. Water sample collection pro-
`cedures for container nurseries. Proc. S. Nursery
`Assn. Res. Conf. 43:526–528.
`
`● April–June 2003 13(2)
`
`

`

`TECHNOLOGY & PRODUCT REPORTS
`
`both leaves and stems as compared
`with those of the unsprayed plants.
`The stem powdery mildew reduction
`levels of the mineral oil or a combina-
`tion of mineral oil + Trichoderma
`treatments, were not statistically
`different than that of thiophanate,
`which is reported as commercially
`acceptable. We recommend mineral oil
`spray, or mineral oil + Tricoderma, as
`alternatives to fungicide control of
`powdery mildew on leaves and stems
`of young gooseberry plants.
`
`P owdery mildew is a spring
`
`and summer disease of
`gooseberries in Asia, Europe,
`North America, Australia, and New
`Zealand (Diekmann et al., 1994). This
`disease can be severe in the rainy, mild
`climate of the Pacific northwestern
`United States. The fungus appears as a
`white powdery growth on the young
`leaf and stem surfaces and can cause
`stunting and a reduction in marketable
`fruit (Pscheit, 2002).
`Control recommendations for
`powdery mildew in fruit crops include
`inorganic sulfur in dust or wettable for-
`mulations, and demethylation-inhibi-
`tor fungicides (Dell et al., 1998; Pscheidt,
`2002). A biological control containing
`the fungal hyperparasite Ampelomyces
`quisqualis in a mineral-oil-based surfac-
`tant is a mildew preventative (Pscheidt,
`2002). Trichoderma harzianum isolates
`can control foliar and soilborne fungi
`including Botrytis cinerea, Pseudopero-
`nospora cubensis, Sclerotinia sclerotiorum
`and Sphaerotheca spp. (Elad, 2000;
`Scheuerell and Mahaffee, 2000). The
`organism has multiple modes of action
`that inhibit or kill the pathogen (Elad,
`2000). These organisms may not pro-
`vide commercially accepted control with
`present formulations.
`Mineral oil has proven effective in
`controlling powdery mildew on grapes
`(Vitis vinifera) (Dell et al., 1998), roses
`(Rosa spp.)(McWhorter, 1927) and
`hops (Humulus lupulus) (Pscheidt,
`2002). Oil is effective in low concentra-
`tions, has little or no toxicity to animals,
`and is relatively inexpensive (Dell et al.,
`1998). Mineral oil was effective in re-
`ducing mildew infection in black cur-
`rants (Ribes nigrum) (Hummer and
`Picton, 2001) and in reducing white
`pine blister rust (caused by Cronartium
`ribicola) on Ribes (Picton and Hum-
`mer, 2003). Calpouzos (1966) men-
`tions two disadvantages: that oil may
`not be effective against some of plant
`diseases, and that it may cause phyto-
`
`366
`
`toxicity. The object of this study was to
`determine if mineral oil, Tricoderma, or
`a combination of mineral oil +
`Tricoderma, could reduce powdery mil-
`dew on leaves and stems of susceptible
`gooseberries in contrast with control
`from the recommended commercial
`fungicide, thiophanate.
`
`Materials and methods
`‘Industry’ was chosen for this study
`based on preliminary observations of
`naturally occurring powdery mildew in
`the cultivated gooseberries at NCGR-
`Corvallis. ‘Industry’ is highly suscep-
`tible to powdery mildew (Brennan,
`1996). In January 2002, ‘Industry’
`plants were placed in the greenhouse in
`Corvallis, Ore., in a completely ran-
`domized design with four replicates of
`five treatments with a total of 20 plants.
`This study was conducted on 2-year-old
`plants that had not reached full fruiting
`capacity.
`The treatments were applied at 2-
`week intervals from February 2002
`through April 2002. They included an
`unsprayed control, mineral oil (JMS
`Stylet Oil; JMS Flowers Farms, Inc.,
`Vero Beach, Fla.), Tricoderma
`(Plantshield; Bioworks Inc., Geneva,
`N.Y.), thiophanate (Cleary 3336; W.A.
`
`Cleary Chem. Co., Summerset, N.J.),
`and a combination of mineral oil +
`Tricoderma. JMS Stylet-Oil, a highly
`refined paraffinic mineral oil with an
`unsulfonated residue of 99.1%, was
`sprayed on treated leaves until runoff at
`8 mL·L–1. PlantShield, a biologically
`active formulation of Trichoderma
`harzianum strain T-22 in a clay sub-
`strate, was applied at a rate of 4 g·L–1.
`Thiophanate, the recommended chemi-
`cal control of mildew on gooseberries
`(Pscheit, 2002), was applied at 1.45
`g·L–1. The mineral oil + Tricoderma
`treatment was applied mixed at the same
`rates as above. All sprays were applied
`using a handheld 1.51-L (0.4-gal)
`sprayer.
`In mid-April, the powdery mildew
`infection of leaves and stems on current
`year’s growth was visually assessed by
`observing the undersides of the leaves.
`Infected and total leaves of the plant
`were counted, and the percent of in-
`fected leaves per plant was calculated.
`Young, green stems were also rated for
`mildew damage and a percent infection
`rating was given per plant. The leaf and
`stem surface area covered by fungal
`infection was visually rated by estimat-
`ing the percent of the leaf surface show-
`ing mildew damage on a whole plant
`
`Fig. 1. Mean powdery mildew severity rating for leaves (percent infected leaves
`per plant) and stems (estimated percent area covered by infection), n = 4, for
`five treatments on ‘Industry’gooseberry: 1) no spray, 2) Trichoderma
`harzianum strain T-22 in a clay substrate (Tricoderma) (Plantshield; Bioworks
`Inc., Geneva, N.Y.) at 4 g·L–1 (0.5 oz/gal), 3) mineral oil (JMS Stylet Oil; JMS
`Flowers Farms, Inc., Vero Beach, Fla) at 8 mL·L–1 (1.0 fl oz/gal) + Tricoderma
`at 4 g·L–1, 4) mineral oil at 8 mL·L–1, and 5) thiophanate (Cleary 3336; W.A.
`Cleary Chem. Co., Summerset, N.J.) at 1.45 g·L–1 (0.186 fl oz/gal) applied at 2-
`week intervals from Feb. 2002 through Apr. 2002. Disease severity ratings were
`taken on 21 Apr. 2002. Standard deviation = 0 for the mean thiophanate rating.
`
`● April–June 2003 13(2)
`
`

`

`Literature cited
`Brennan, R.M. 1996. Currants and goose-
`berries, p. 191–295. In: J. Janick and J.N.
`Moore (eds.). Fruit breeding. vol. 2. Wiley,
`New York.
`
`Calpouzos, L. 1966. Action of oil in the
`control of plant disease. Ann. Rev.
`Phytopathol. 4:369–390.
`
`Dell, K.J., W.D. Gubler, R. Krueger, M.
`Sanger, and L.J. Bettiga. 1998. The effi-
`cacy of JMS stylet-oil on grape powdery
`mildew and Botrytis bunch rot and effects
`on fermentation. Amer. J. Enol. Vitic.
`49:11–16.
`
`Diekmann, M., E.A. Frison, and T. Putter
`(eds.). 1994. FAO/IPGRI Technical
`Guidelines for the safe movement of small
`fruit germplasm. Food Agr. Org. United
`Nations, Rome/Intl. Plant Genet. Resour.
`Inst., Rome.
`
`Elad Y. 2000. Biological control of foliar
`pathogens by means of Trichoderma
`harzianum and potential modes of action.
`Crop Protection 19:709–714.
`
`Hummer, K.E. and D. D. Picton. 2001.
`Oil application reduces powdery mildew
`severity in black and red currants.
`HortTechnology 11:445–446.
`
`McWhorter. 1927. Fungicidal value of oil
`sprays. Phytopathology 17:201–202.
`
`Picton, D.D. and K.E. Hummer. 2003.
`Oil application reduces white pine blister
`rust severity in black currants. Small Fruit
`Rev. 2(1):43–49.
`
`Pscheit, J.W. 2002. Gooseberry and cur-
`rant—Powdery mildew. In: Online guide
`to plant disease control. 25 June 2002.
`h t t p : / / p l a n t - d i s e a s e . o r s t . e d u /
`disease.cfm?RecordID=512.
`
`Scheuerell S.J. and W.F. Mahaffee. 2000.
`Assessing aerated and non-aerated watery
`fermented compost and Trichoderma
`harzianum T-22 for control of powdery
`mildew (Sphaerotheca pannosa var. rosae)
`of Rose in the Willamette Valley, Oregon.
`Phytopathology. 90(6 Supp.):S69.
`
`basis. Analyses of variance were ap-
`plied to the percentages and ratings to
`determine significance of the treat-
`ments. Tukey’s least square difference
`(LSD) test was applied to separate means.
`
`Results and discussion
`Analyses of variance for ratings on
`both leaves and stems were highly
`significant (P < 0.0001). All treat-
`ments were significantly better than
`the no-spray control for stem infection
`(Fig. 1). Thiophanate, mineral oil, or
`the mineral oil + Tricoderma treat-
`ments gave the best control (P = 0.05)
`for stem infection. For leaf infection,
`the thiophanate and the mineral oil
`treatments were significantly more ef-
`fective at reducing powdery mildew
`than was Tricoderma alone or the no
`spray control (Fig. 1). The combina-
`tion treatment was intermediate, pro-
`viding significantly less control than
`the fungicide treatment but not sig-
`nificantly less than the oil treatment
`(Fig. 1). These results agree with pre-
`vious studies for disease control using
`mineral oil (Hummer and Picton,
`2001; Scheuerell and Mahaffee, 2000).
`The lack of powdery mildew control
`on leaves for mineral oil + Tricoderma
`may be due to an interaction between
`a component of the biological control
`and the oil that reduced the coating
`capacity of the oil on the leaf.
`Tricoderma alone did not significantly
`reduce leaf infection (Fig. 1). Unfor-
`tunately, in this treatment we observed
`an increased level of leaf necrosis not
`caused by mildew. This damage was
`not observed in the other treatments.
`The damage appeared in the same
`vicinity as the mildew area. We do not
`recommend Tricoderma alone to con-
`trol powdery mildew on gooseberries.
`The powdery mildew reduction
`of the mineral oil or the combination
`of mineral oil + Tricoderma treatments
`were not statistically different than that
`of the thiophanate, which is reported
`as commercially acceptable. We rec-
`ommend the application of mineral oil
`or mineral oil + Tricoderma, as alterna-
`tives to fungicide in reducing powdery
`mildew in leaves and stems of young,
`greenhouse-grown gooseberry plants.
`Further study is needed to determine
`effective controls of gooseberry fruit
`mildew using environmentally friendly
`materials.
`
`● April–June 2003 13(2)
`
`367
`
`