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Although demand for organic produce continues to increase in the midAtlantic, few apple (Malus 3domestica Borkh.) growers in the region have adopted organic management practices due to the considerable disease, insect, and weed pressure, as well as the lack of effective crop loadmanagement tools. In this study, lime sulfur (LS) and Regalia (R) were applied in different sequences (i.e., LS/LS, LS/R, R/R, and R/LS), each in a mixture with JMS Stylet-Oil, to chemically thin apple flowers in an organically managed ‘Honeycrisp’/‘MM.111’ orchard. There was also a nontreated control, a ‘‘grower standard’’ control (LS at 11 mm fruitlet diameter), and a hand-thinned control. The treatments were evaluated for their ability to reduce crop load, as well as to control powdery mildew [Podosphaera leucotricha (Ellis & Everh.) E. S. Salmon], cedar apple rust (Gymnosporangium juniperi-virginiana Schwein.), and quince rust (Gymnosporangium clavipesCooke & Peck). All treatments reduced crop load compared with the nontreated control, and after the first application of LS or R, the number of fertilized king blooms was reduced and fertilization was prevented in all side blooms. All bloom thinning treatments had more fruit peel russet than the control and russet was more severe when LS was one of the applications. Bloom thinning applications of LS and R did not reduce powdery mildew leaf infection compared with the nontreated control. Cedar apple rust incidence was reduced by all bloom thinning treatments, though some lesions were detected in all treatments. There were minimal quince rust infections in any of the treatments, including the nontreated control. These results suggest that when LS and/or Regalia are mixed with JMS Stylet-Oil and applied as bloom thinners, they can reduce crop load, and, as a secondary benefit, they can also decrease cedar apple rust incidence from infections that occur during bloom. There is a need to conduct research specifically for organic apple (Malus ·domestica) production in the mid-Atlantic region (including the states of Delaware, Maryland, New Jersey, North Carolina, Pennsylvania, Virginia, and West Virginia), so that local growers can supply the increasing demand for organic products. In 2015, organic product sales exceeded $43 billion in the United States, of which produce accounted for 13% of the total sales (Organic Trade Association, 2016). However, under the current U.S. Department of Agriculture-National Organic Program (USDA-NOP) regulations, growing apples organically in the eastern United States can be challenging due to the lack of effective biological, cultural, or chemical controls for the immense insect, disease, and weed pressure experienced in this region (Cromwell et al., 2011; Peck et al., 2010; Williams et al., 2016). Additionally, crop load management options are limited in organic production because the USDA-NOP prohibits the use of the synthetically derived plant growth regulators that are used for this purpose in conventional systems (U.S. Department of Agriculture, 2016). Managing crop load in apple orchards is essential for improving fruit size and color, preventing broken limbs due to the excess weight of fruit, and ensuring adequate return bloom to minimize biennial bearing (Byers, 2003; Dennis, 2000). Thinning, or reducing the number of apples per tree and within each fruiting cluster, can also decrease disease pressure by allowing for more rapid drying conditions within fruit clusters and allowing for more complete spray coverage of the developing fruitlets. Thinning during bloommay increase these benefits and decrease the likelihood of biennial bearing cycles by eliminating excess fruit before flower bud initiation occurs (Batjer and Hoffman, 1951; Greene, 2002). In the experiment described in this paper, we evaluated bloom thinning materials applied according to output from a ‘Honeycrisp’-specific pollen tube growth model for their ability to reduce crop load and disease incidence. The pollen tube growth model uses hourly temperature data to predict the amount of time between pollination and fertilization (Peck et al., 2016; Yoder et al., 2013). This information is then used to allow a preset percentage of flowers to set fruit, while fertilization in later blooming flowers is prevented by treatment (most commonly liquid LS) with a chemical that kills the pollen tubes before they fertilize additional eggs. Liquid LS tank mixed with oil (either fish or a petroleum-based product) is a recommended chemical combination for apple bloom thinning under organic management in the eastern United States (Peck and Merwin, 2010). However, before OR-CAL, Inc. (Junction City, OR) changed the label on Rex Lime Sulfur Solution in 2015, LS was only legally approved for bloom thinning and for use with oil inWashington State (Lehnert, 2014). Additionally, LS is caustic and often causes fruit russeting, therefore reducing the value of the fruit (Peck et al., 2010). Other negative impacts of LS result from its phytotoxicity, which disrupts photosynthesis, and thus potentially yield, tree growth, and return bloom (Holb et al., 2003; McArtney et al., 2006). Additionally, LS can be a very potent bloom thinner and may over thin the crop in some years. For these reasons, additional bloom thinning product options are needed for use in the eastern United States. In prior tests, the biofungicide, Regalia (Marrone Bio Innovations, Inc., Davis, CA), made from the extracts of Giant Knotweed [Reynoutria sachalinensis (F. Schmidt) Nakai syn. Polygonum sachalinense (F. Schmidt)], was found to function as an apple bloom thinner (Peck et al., 2016; Yoder et al., 2013). Our interest in the product began after observing damaged petals in an apple disease control field experiment where Regalia was applied during bloom. We hypothesized that the Received for publication 3 Oct. 2016. Accepted for publication 11 Jan. 2017. Funding support was provided by a U.S. Department of Agriculture-Specialty Crop Block Grant administered by the Virginia Department of Agriculture and Consumer Services, Virginia Agricultural Experiment Station, and Virginia Tech’s Department of Horticulture. We thank Sierra Athey, Matt Borden, David Carbaugh, Allen Cochran II, Scott Kilmer, Abby Kowalski, Taylor Mackintosh, Jared Repass, William Royston, Jr., Ashley Thompson, and Jim Warren for their assistance with this experiment. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the authors and does not imply its approval to the exclusion of other products or vendors that also may be suitable. Corresponding author. E-mail: gmp32@cornell. edu. HORTSCIENCE VOL. 52(3) MARCH 2017 377 product was caustic and potentially damaging to other floral organs. The disease control efficacy of Regalia is reported to be from a unique mechanism of induced plant resistance that upregulates chalcone synthase and chalcone isomerase in the phenylpropanoid pathway and induces the production and accumulation of phytoalexins (Su et al., 2012). In a previous formulation, namedMilsana (Marrone Bio Innovations, Inc.), R. sachalinensis extracts were shown to decrease powdery mildew infection on cucumbers, tomatoes, begonias, and wheat (Daayf et al., 1995; Dik and van der Staay, 1995; Herger et al., 1988; Herger and Klingauf, 1990; KonstantinidouDoltsinis et al., 2006; Konstantinidou-Doltsinis and Schmitt, 1998). Regalia is currently labeled for use as a fungicide on many horticultural and agronomic crops, but its mode of action as a bloom thinner is unknown. Among the many fungal diseases that require grower intervention in the mid-Atlantic, cedar apple rust (G. juniperi-virginiana) and quince rust (G. clavipes) are formidable barriers to organic apple production because they are not effectively controlled by organically approved fungicides such as sulfur and copper (Yoder et al., 2006). An experimental formulation of R. sachalinensis (MOI-106020) that was tested before the commercial release of Regalia was found to provide cedar apple rust control (Halbrendt et al., 2010). Similarly, prior tests in Virginia indicated that control of rusts by a combination of Regalia and JMS Stylet-Oil (JMS Flower Farms, Inc., Vero Beach, FL) provides effective control of cedar apple rust and after-infection control of quince rust (Peck et al., 2016; Yoder et al., 2015). Thus, we saw an opportunity to target two of the key barriers for organic apple production in the mid-Atlantic, namely reliable crop load and disease management. The objective of this project was to test the disease control achieved while using different sequences of LS and/or Regalia , each in combination with JMS Stylet-Oil, for bloom thinning. We hypothesized that these bloom thinningmaterials would aid disease control in an organically managed apple orchard. Materials and Methods The study was conducted in an 8-year-old ‘Honeycrisp’/‘MM.111’ apple orchard located at Virginia Tech’s Alson H. Smith, Jr. Agricultural Research and Extension Center in Winchester, VA (39 06# N, 78 17#W). Trees were spaced 3 m between trees and 7 m between rows. In 2015, the year of this experiment, only USDA-NOP approved products were applied to the orchard (Table 1). Before 2015, all trees had been managed conventionally. A row of border trees on the west side of the block, as well as four trees on each end of each row with treatment trees were not sprayed for the entire season. The experiment was conducted on the remaining four rows. Treatments were applied at the dilute rate to the point of runoff with a single nozzle handgun at 1723 kPa. Maintenance sprays were applied with an airblast sprayer (Swanson Model DA-400; Durand-Wayland, LaGrange, GA) calibrated to deliver 935 L·ha. Weeds were managed by using Suppress Herbicide EC (Westbridge Agricultural Products, Vista, CA) at 28.3 L of product in 467.2 L of water/ha on 23May and 4 July. Full bloom occurred on 25 Ap

Managing Apple Crop Load and Diseases with Bloom Thinning Applications in an Organically Managed ‘Honeycrisp’/‘MM.111’ Orchard