A major limitation to organic apple [ Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] production is the available fungicide options for apple scab, a significant disease of apples in humid production regions. Apple scab can have
resistance to apple scab caused by the fungal pathogen Venturia inaequalis (Cke). In scab-susceptible crabapples, symptoms of infection include defoliation by early summer coupled with loss of winter hardiness and even death resulting from repeated
The potential impact of propane flamers on the development and release of ascosporic inoculum of Venturia inaequalis (Cke.) Wint. from infected dead apple (Malus domestica Borkh.) leaves that overwintered on the soil of an experimental orchard was assessed. Thermal reduction of scab primary inoculum was first conducted under controlled conditions using an indoor testing facility. At the time of ascospore maturation, heavily infected leaves were submitted to temperature rises ranging from 150 to 200 °C with open-flame burners, thus reducing the number of ascospores subsequently released by 76% and 87%, respectively. During Spring 1995, thermal treatments of overwintered dead leaves were performed directly on the ground of an apple orchard with an experimental propane flamer design to generate uniform heat at ground level. Four thermal treatment strategies, involving two dates of flaming and two heat intensities, were tested. Flaming orchard ground, when performed in early May, before significant development of ground cover, reduced the number of ascopores released from infected dead leaves by half. A significant residual effect of the treatments on ascospore ejection was still observed 2 and 4 weeks after the treatments, thus indicating that ascospore maturation inside the leaves may be reduced by heat treatment. These results indicate potential for propane flamers to reduce apple scab primary inoculum in orchards.
Vegetable oil emulsion (VOE) was applied to `Gala' and `Fuji' apple (Malus ×domestica) trees after harvest to hasten defoliation and reduce apple scab (Venturia inaequalis). Applied at 2%, 4%, or 6%, VOE applied to whole trees in the fall induced leaf drop, with the highest concentration causing the most defoliation. At the same concentration, VOE applied in early, mid, or late October had similar effects on leaf drop. VOE treatment reduced respiration and stimulated ethylene production in shoot tissue within 24 hours of application. None of the treatments affected tree hardiness during the winter, or shoot growth the following spring. Return bloom density was unaffected; however, VOE tended to delay anthesis by 2 to 5 days. Under controlled conditions, `Gala' and `Fuji' trees inoculated with scab spores developed 48% and 65% scab, respectively. VOE-induced defoliation reduced scab by 50% to 65%. VOE-induced defoliation plus manual leaf removal from the orchard floor, or VOE-induced defoliation in late fall (15 Oct.-15 Nov.) plus application of 5% lime sulfur in early spring, controlled scab to <5% on both leaves and fruit. Neither lime sulfur nor urea applied in late fall at 2% induced defoliation or controlled scab. VOE at 4% plus 2% lime sulfur and/or 2% urea applied in late fall, however, defoliated `Gala' trees effectively and controlled scab on fruit to <7% the following spring. In the `Fuji' planting, the combination of 4% VOE plus 2% lime sulfur and 2% urea reduced scab on fruit from 21% in controls to 0%.
Resistance to apple scab (Venturia inaequalis) in apple cultivar breeding has been derived mainly from the Vf gene from Malus floribunda 821, which introgresses horticulturally unfavorable characters. M. sieversii, now thought to be the primary progenitor of M. × domestica, grows wild in many diverse habitats in Central Asia and can have fruit quality comparable to commercial cultivars. Since 1989, four major collections of M. sieversii have been made in Central Asia, where scab is endemic. Some seed collections have been made from trees with superior fruit, that were not infected with scab. Over a 6-year period, 3000 seedlings from 220 wild M. sieversii trees representing 10 diverse ecosystems in Kazakstan, Uzbekistan, Kyrgyzstan, and Tajikistan have been inoculated with conidia of five races and two wild types of V. inaequalis. Suspensions (270,000 conidia/ml) were applied to 4- to 8-leaved seedlings, which were incubated for 48 h at 19°C with constant leaf wetness. Symptoms for three resistant reactions were assessed 2 to 4 weeks after inoculation: A = chlorosis with crinkling (Vf type reaction); B = stellate necrotic lesions (Vr type reaction), and N = large necrotic areas (uncharacterized resistant reaction). Results indicated that nearly 20% of the seedlings showed one or more of the resistant reactions. The range of resistance within seedling populations from each of the 220 single-tree sources ranged from 0% to 75%. Significant differences existed among seedlings from each of the ecosystems. Most resistance reactions appeared to be similar to those observed for Vr from “Russian seedling.” Resistant selections with superior horticultural traits may constitute a genepool for increased efficiency of breeding scab-resistant cvs. This genepool may also be useful to address the breakdown of resistance to V. inaequalis race 6.
Integrated peat management (IPM) strategies for control of apple scab and codling moth (Cydia pomonolla) were compared with a traditional protestant spray program in an Iowa apple orchard over a 3-year period. IPM tactics for scab included a postinfection spray program and an integrated, reduced-spray program based on the use of demethylation inhibitor fungicides. Codling moth spray timing was determined by pheromone-trap captures and degree-day models. The IPM tactics resulted in an average of three fewer fungicide sprays and two fewer insecticide sprays than the protestant program. Neither yield, incidence of fruit scab, nor incidence of codling moth injury on fruit was significantly different among the two IPM treatments and the protestant treatment. A no-fungicide treatment had significantly lower yield and greater scab incidence than the other treatments. A partial budget analysis indicated that the treatment using the postinfection strategy was more costly per acre than the protectant program for orchards <20 acres, about equivalent in cost for 20 acres, but leas costly for 40 acres. A treatment incorporating the integrated, reduced-spray strategy was less costly than either postinfection or protestant strategies at orchard sizes from 5 to 40 acres. Return (total revenue - cost for control of primary scab and codling moth) per acre for the IPM strategies was somewhat lower than for the protestant program.
Spray adjuvants alone and combined with benomyl in single and multiple applications were tested for their influence on net photosynthesis (Pn) and development of apple scab caused by Venturia inaequalis (Cke.) Wint. on trees of apple (Malus domestica Borkh.) grown in the greenhouse. Triton CS-7 increased and ×-100 and 70 second oil deceeased Pn. Nu Film 17, Triton B-1956, Regulaid and ×-77 when combined with benomyl had no influence on Pn. Addition of Biofilm, Nu Film 17 or 70 second oil to benomyl did not improve apple scab control. Three sprays of benomyl plus oil decreased Pn of fully expanded leaves, and 5 sprays decreased Pn of both expanded and newly expanding leaves with the latter showing the greatest reduction.
Spray treatment a single dormant application of high concentrations of anionic (Triton CS7) and nonionic (Triton N57 and Triton X100) surfactants caused up to 5 days delay in bud break in apple (Malus domestica Borkh.), but had less effect on grape (Vitis spp.) and peach (Prunus persica (L.) Batsch) and none on pear (Pyrus spp.). Surfactants tended to extend the bud break period but were frequently lethal to buds, particularly at concentrations of 3% and 5% active ingredient. In field studies, surfactants delayed the early stages of flower bud development but not bloom of apple or peach and did not control apple scab caused by Venturia inaequalis (Cke.) wint. or powdery mildew caused by Podosphaera leucotricha (Ell & Ev.) Salm.
‘Freedom’ is a productive, large, red apple, Malus domestica Borkh. that is very resistant to apple scab [Venturia inaequalis (Cke) Wint.], moderately resistant to apple powdery mildew [Podosphaera leucotricha (E. & E.) Salm], resistant to cedar apple rust (Gymnosporangium juniperi-virginianae Schw.), and to fire blight [Erwinia amylovora (Burrill) Winslow et al.]. It has been grown for 23 years without any disease-controlling sprays, and no losses have occurred in New York State. This apple was tested under the number NY 58553-1.
The polymorphism in nine enzyme systems in apple (Malus domestica Borkh.) was analyzed using horizontal starch gel electrophoresis. The systems studied included aspartate aminotransferase, diaphorase, glucosephosphate isomerase, isocitrate dehydrogenase, phosphoglucomutase, and triosephosphate isomerase. The products of at least 27 loci could be distinguished in these systems, 19 of which displayed polymorphism. Joint segregation analysis in populations derived from crosses between highly heterozygous cultivars revealed four multilocus linkage groups: Aat-c–Idh-1, Dia-2–Mdh-4, Gpi-c2-Aat–p, and (Dia-5, Pgm-p1)–(Mdh-2, Tpi-c2). Although several of the populations investigated had been prescreened for resistance to apple scab, cedar-apple rust, or fire blight, no correlation could be established between the inheritance of an allozyme and a resistant phenotype. The high frequency of duplicate loci encountered is in accordance with the postulated tetraploid nature of the genome.