2.1. Plot Layout
Insect, disease, and weed management programs were compared over three growing seasons in an organic apple research orchard at Cornell’s New York State Agricultural Experiment Station in Geneva, New York. The site, composed primarily of Collamer silt loam, had been a fallow field with no previous history of fruit production, and there was no documented presence of any fruit diseases or insect pests before orchard establishment. The orchard was planted in the spring of 2012 and consists of a 1-ha (2400 trees) organic apple orchard containing replicated plots of nine disease-resistant varieties on two disease-resistant Geneva
® rootstocks: Pristine, Williams Pride, NovaEasygro, Crimson Crisp, Juliet, Modi, Topaz, Goldrush, and CC1009; the rootstocks used are G.202 and G.935. The plot was planted in a modern high-density tall spindle orchard system at a spacing of 0.9 × 3.7 m, giving a planting density of 2990 trees/ha (
Figure 1). Trees have been trained as a slender fruiting wall. The plot has 3 replications with varieties in whole rows of 62 trees of each variety in each rep. No foliar nutrients or field-applied fertilizers were used during this study, and the site was not irrigated. Different arthropod and disease management regimens compared three treatment levels, set up in three replicates of 3-row plots (
Figure 1: Layout of organic apple orchard showing varieties, treatments, and replicated plots, New York State Agricultural Experiment Station, Geneva.):
Advanced Organic: use of the most efficacious options available, although recognizing that these tactics and materials are likely to be more expensive and possibly more labor-intensive.
Minimal Organic: use of tactics that technically meet most common certification standards, but with a greater reliance on options that are more commercially available, less expensive and easier to implement, but possibly also less efficacious.
Untreated Control.
The Minimal organic program reflected the typical selection of products employed by local growers who endeavor to grow apples organically, being characterized by a general reliance on the most economical options available, and the Advanced program represented our attempt to find what we felt to be the most efficacious options possible, without regard for cost or even necessarily the practicality of implementing them (e.g., in regards to labor requirements, time needed to realize their full effects, etc.).
2.2. Arthropod Management
A season-long spray program was maintained each year, with applications made using a standard airblast sprayer calibrated to deliver an industry standard rate of 950 L/ha (100 gal/A), starting at bloom (2014 and 2016) or tight cluster (2015), depending upon spring weather patterns, and proceeding through August. The products applied in the Advanced Organic plots (
Table 1: Organic Apple Spray Programs, 2014–2016) were: horticultural mineral oil (JMS Stylet-Oil, JMS Flower Farms, Vero Beach, FL, USA) for European red mite (ERM),
Panonychus ulmi (Koch);
Bacillus thuringiensis kurstaki (B.t.) (DiPel, Valent BioSciences, Libertyville, IL, USA) for obliquebanded leafroller (OBLR),
Choristoneura rosaceana (Harris); spinosad (Entrust, Dow AgroSciences, Indianapolis, IN, USA) for codling moth (CM),
Cydia pomonella (L.), OBLR, and apple maggot (AM),
Rhagoletis pomonella (Walsh); kaolin clay (Surround, Engelhard, Iselin, NJ, USA) for plum curculio (PC),
Conotrachelus nenuphar (Herbst); and 100% neem oil (Ahimsa Organics Neem Oil, The Ahimsa Alternative, Bloomington, MN, USA) for apple aphid,
Aphis pomi De Geer, spirea aphid,
A. spiraecola Patch, and potato leafhopper (PLH),
Empoasca fabae (Harris).
The products applied in the Minimal Organic plots were: horticultural mineral oil for ERM; B.t. for OBLR and CM; pyrethrin (Pyganic, MGK, Minneapolis, MN, USA) for PC and AM; and azadirachtin (Aza-Direct, Gowan, Yuma, AZ, USA) for aphids and PLH.
Additional tactics were used in the Advanced Organic plots. On 8 July 2013, infective juveniles (IJs) of persistent northern-NY strains of
Steinernema carpocapsae and
S. feltiae entomopathogenic nematodes (EPNs) were applied to the soil surface using an ATV-mounted modified spray boom with five fertilizer (0010) nozzles and traveling at 5.6 km/h. In laboratory and field bioassays, these nematodes have shown efficacy as biological control agents against last-instar plum curculio larvae, which burrow in the soil to pupate [
18]. Because these strains are native to New York State, they are adapted to persist and eventually spread to untreated soil under our typical climatic conditions. The application of a 50:50 combination of
S. carpocapsae and
S. feltiae IJs was made to the orchard rows and row middles of the three 3-row Advanced Organic plots, at a rate of approximately 11 billion total IJs/ha. Soil core samples taken from the treated rows annually since then and assessed for EPNs provided evidence of nematode establishment by the end of the 2015 season.
In addition, during the 2012 and 2013 growing seasons, predator mites (Typhlodromus pyri (Scheuten)) were collected from foliar terminals in a nearby research orchard and introduced over a period of several weeks on leaf discs (10 per disc) affixed to shoots in the Advanced Organic plots. The predator mites were introduced into trees of the middle rows in each target plot on six dates in July–August 2012 and on five dates in June–August 2013.
Pheromone traps were deployed to track flights of the major Lepidoptera pest species (oriental fruit moth, codling moth, obliquebanded leafroller), and fruit and foliar samples were taken at regular timings to evaluate insect pest presence and damage in the different treatments. For PLH and the green aphid complex (apple aphid and spirea aphid), three foliar terminals on each of 10 trees in the middle rows of each treatment plot were examined for the presence of infestations, and the results expressed as percent infested terminals.
Samples were taken to assess infestations of overwintered and summer broods of OBLR, as well as internal-feeding Lepidoptera such as codling moth, oriental fruit moth and lesser appleworm (LAW), Grapholita prunivora (Walsh). For the 2014 and 2015 overwintered OBLR samples, 10 trees per row were inspected for the presence of larvae during the late bloom-fruit set period, and the percentage of trees showing infestations was recorded. In 2016, because the trees were older and more established, 10 foliar terminals on each of 10 trees per row were examined to determine the mean percent damaged terminals in each treatment. In 2014 and 2015, we examined 10 fruits per tree on each of 10 trees per row, and the percentage of fruits with feeding damage caused by either OBLR or internal-feeding Lepidoptera was recorded.
Foliar samples were taken once each year during early August in 2015 and 2016 to assess populations of both predacious (T. pyri) and phytophagous mites (ERM and twospotted spider mite, Tetranychus urticae Koch). On each sample date, 25 intermediate-age leaves were picked at random from shoots on five trees (5 per tree) per row, and brushed in a mite-brushing machine to determine the numbers of phytophagous mite eggs and mite motile forms plus predacious mite motiles in each 25-leaf sample.
Insect damage at harvest was assessed each year by inspecting 100 fruits randomly picked from trees in each row of each plot (i.e., one row per treatment per variety) to determine mean percent fruit damage by treatment across varieties caused by each direct fruit pest. All varieties were sampled in 2014 and 2015, but, due to late spring frost damage and drought conditions during the 2016 growing season, only five varieties had sufficient fruit to include in the analysis that year.
2.3. Disease Management
Season-long trials were conducted to evaluate the effectiveness of organic fungicides and bactericides against the sooty blotch/flyspeck (2014, 2015, and 2016) late season summer diseases, cedar apple rust (2015 and 2016), a mid-season disease, and fire blight, a bacterial disease that causes infection during bloom (2015 and 2016) (
Table 1: Organic Apple Spray Programs, 2014–2016). Disease management programs began at tight cluster (2015 and 2016) or 2nd cover (2014), depending on spring weather, and continued through harvest in August. Applications of fungicides for flyspeck/sooty blotch and cedar apple rust were made using an airblast sprayer calibrated to deliver an industry standard rate of 950 L/ha (100 gal/A). Treatments for fire blight were applied using a gas-powered backpack sprayer (Solo 451, Solo Inc., Newport News, VA, USA). These sprayers were calibrated to deliver dilute (2850 L/ha [300 gal/A]) applications to runoff using the high droplet setting to facilitate the high-volume application. Fire blight applications were made at 80% bloom and full bloom to the Topaz, Modi, and Goldrush blocks. These cultivars were chosen for their susceptibility to fire blight and to minimize the extent of planting-wide impact. Trees were inoculated at full bloom with
Erwinia amylovora strain Ea 273 at 1 × 10
4 CFU mL
−1 using a hand pump backpack sprayer (Solo, Inc.) [
19,
20].
The products applied in the Advanced Organic plots (
Table 1) were: Copper Octanoate (Cueva 7 L/ha or 4.67 L/ha, Certis USA, LLC, Columbia, MD, USA),
Bacillus amyloliquefaciens d747 (Double Nickel LC 2.3 L/ha, Certis USA) and the products applied in the Minimal Organic plots were: copper hydroxide + copper oxychloride (Badge X2 5.6 kg/ha, Gowan Company, Yuma, AZ, USA), and sulfur (Microthiol Disperss 16.8 kg/ha, United Phosphorus, Inc., King of Prussia, PA, USA). All treatments were made to three replicate blocks containing a minimum of 15 trees per block. Please confirm if it is right.
The incidence of blossom blight was evaluated on 3 June in 2015 and 1 June in 2016. The incidence of blossom blight was expressed as the number of blighted blossom clusters out of 5 clusters, with 20 collections of clusters assessed for each treatment replicate. The incidence of sooty blotch/flyspeck symptoms on mature fruit was assessed at harvest. The incidence of cedar apple rust symptoms on terminal leaves was assessed on 19 August in 2015 and 23 August in 2016, and the incidence of cedar apple rust symptoms on mature fruit was assessed at harvest. The incidence of sooty blotch and cedar apple rust on mature fruit was calculated as the number of mature fruit with flyspeck or sooty blotch, out of five sampled fruits, with 10 such samples assessed for each treatment replicate. The incidence of cedar apple rust symptoms on terminal leaves was calculated from the number of terminal leaves with cedar apple rust lesions with pycnidia out of eight fully expanded leaves from the distal end of the shoots, with 10 shoots assessed for each treatment replicate [
21].
2.4. Weed Management
The weed management trial was designed as a separate experiment overlaid in a balanced design on each rep of the insect and disease treatments, with a strip split-plot design. Each row in each insect and disease treatment was subdivided into 7 subplots of 7 trees each with subplot weed control treatments laid out in strips across all 9 rows of the insect and disease rep. The weed control experiment was designed as a randomized complete block experiment with 3 replications of 9 rows each with plots of 7 trees in each row. Thus, the weed control experiment was balanced across each insect/disease plot and did not confound the results or analysis of the insect/disease treatments. Weed control treatments compared seven treatments applied to each of the nine scab-resistant varieties and were performed during 2014–2016. Weed control treatments were: (1) Flame weeding along each side of the tree using a propane flame machine; (2) Organic limonene (Avenger, Avenger Organics, Buford, GA, USA); (3) Mechanical cultivation on each side of the tree using a cultivator (Wonder Weeder®, Burbank, WA, USA); (4) Organic soap (Final-San-O, Columbia, MD, USA); (5) Organic acetic acid (Weed Pharm, Port Townsend, WA, USA) (2014 only); (6) Bark chip mulch 20-cm deep along the tree row; and (7) Caprylic acid (Suppress, Westbridge, Vista, CA, USA) (2015–2016 only). Each of the treatments was applied every 3 weeks during the season starting in late May (total of 5 applications). For the organic herbicides, the rate applied was as recommended on the label. Weed control was assessed by determining percent weed-free area in the 2-m-wide and 7-m-long weed control strip under the trees at two times during the season in 2014–2015 (11 August and 1 October), and once in 2016 (1 September). After the first weed control assessment in August (2014–2015), all the plots were hand-weeded, then a second round of treatments was applied in August and September and plots were re-assessed on 1 October.