In commercial fruit production in the midwestern United States, producers usually employ integrated pest management (IPM) to control a variety of insect and disease pests (Beckerman, 2018). IPM tactics include removing leaf litter and pruning out infected sections of plants, use of mating disruption of insects, application of pesticides and biological agents, and monitoring pests to optimize timing of management actions (Beckerman, 2018; UMass Extension, 2018). Among these pest control techniques, pesticide applications are essential to ensure yield and quality for the conventional nonorganic fruit industry (UMass Extension, 2018). According to the Midwest Fruit Pest Management Guide (Beckerman, 2018), apple and peach need to be sprayed ≈16 and 11 times in 1 year, respectively, and blueberry and black raspberry need to be sprayed approximately seven and five times, respectively.
For applying pesticides to control insect pests and diseases in fruit farms, the most commonly used spray equipment is radial air-assisted sprayers (Zhu et al., 2017). These conventional sprayers deliver pesticides at a constant rate and usually apply pesticides to the entire field regardless of plant absence or plant structure variation, resulting in underspraying or overspraying (Zhu et al., 2008). A large proportion of the spray drift is delivered to nonplant areas, such as ground and air (Zhu et al., 2006a), leading to pesticide loss and risk of environmental contamination, which increases the costs of production and exposure to pesticides for applicators, workers, and other people near the farms. A wide range of spray methods has been evaluated to improve the delivery of pesticides (Stover et al., 2003; Zhu et al., 2006a, 2006b, 2011a, 2011b).
To increase the efficiency of pesticide use on fruit farms, a laser-guided variable-rate intelligent sprayer was developed (Chen et al., 2012; Shen et al., 2017). The sprayer discharges appropriate variable amounts of pesticides in real time. Application rate is controlled by adjusting the spray output of each nozzle based on the presence, structure, and foliage density of plants, and sprayer travel speed. Chen et al. (2013a) reported the intelligent variable-rate sprayer reduced spray volume by 57% at the full-foliage stage and 73% at the leafing stage of apple while remaining comparable spray deposition on target areas compared with a conventional constant-rate sprayer. In an experiment with multiple-row nursery trees, ‘Sterling’ silver linden (Tilia tomentosa) and northern red oak (Quercus rubra), Zhu et al. (2017) found no difference in spray deposition and coverage on the trees between intelligent variable-rate and conventional constant-rate spray applications, despite the intelligent variable-rate application discharging significantly less spray volume ultimately resulting in substantial pesticide use reductions. However, there have been concerns on applying this technology to commercial fruit farms regarding whether insect and disease pests can be effectively controlled with such great reductions in pesticide use.
Codling moth is the most serious pest of apple in the United States (Beckerman, 2018). In nonorganic apple orchards, insecticide treatments are the most common method of controlling codling moth (Amarasekare and Shearer, 2017). For most insecticides, the initial applications should be timed to coincide with hatch of codling moth eggs (Brunner, 1993).
Oriental fruit moth is one of the most damaging pests of peach. It also attacks apple in eastern U.S. apple-growing districts (Brunner and Rice, 1993). Mating disruption and insecticide sprays are the two major strategies for controlling it in peach. Insecticide sprays should be applied before young larvae bore into shoots or fruit (Brunner and Rice, 1993).
Spotted wing drosophila has been a serious pest of black raspberry, blueberry, strawberry (Fragaria ×ananassa), sweet cherry (Prunus avium), and grape (Vitis sp.) in the United States over the past 10 years. Blueberry fruit is susceptible to spotted wing drosophila from the time it begins to color and becomes increasingly susceptible as the fruit ripen (Fulcher et al., 2015). Without insecticide treatments, yield of blueberry may be reduced by 30% to 100% (Fulcher et al., 2015). Spraying insecticides is the main method of controlling spotted wing drosophila in fruit crops worldwide (Haye et al., 2016). In Switzerland, ≈80% of sweet cherry growers in 2015 and 2016 used insecticides to control spotted wing drosophila (Mazzi et al., 2017).
Apple scab caused by the fungus Venturia inaequalis is a serious disease and occurs worldwide, leading to the greatest loss in apple yield among apple diseases (Ellis, 2008). Powdery mildew of apple caused by the fungus Podosphaera leucotricha also occurs worldwide in all apple-producing regions. The disease decreases flower bud production and fruit quality (Ellis, 2016a). Good fungicide spray programs (e.g., applying prebloom fungicide spray and shortening the spray interval) are major approaches of controlling these diseases.
Brown rot caused by fungus Monilinia fructicola is the most serious disease for stone fruit such as peach under warm and humid conditions (Hartman, 2007). Peach becomes increasingly susceptible to brown rot infection as the fruit ripens. Brown rot also increases in wounded peach. Application of fungicides is the primary method for controlling this disease. Peach powdery mildew, caused by Podosphaera pannosa, is another common disease when peach is grown near apple that is susceptible to powdery mildew (Blake et al., 2016).
Mummy berry caused by the fungus Monilinia vaccinii-corymbosi is one of the most serious diseases of blueberry. When mummy berry disease is established in blueberry plants, it can completely destroy the crop (Anco and Ellis, 2011). Thus, an effective fungicide spray program is critical for control of this disease. Phomopsis, caused by the fungus Phomopsis vaccinii, is the most common canker disease of blueberry (Fulcher et al., 2015). It can severely decrease yield because it kills stems and causes rotted fruit. Anthracnose, caused by the fungus Elsinoe veneta, is an extremely serious disease of black raspberry throughout the United States. This disease causes the death of canes, defoliation, and reduction of fruit size and quality (Ellis, 2016b). Spraying fungicides is required to effectively control these diseases.
The hypothesis of this research was that the use of intelligent variable-rate spray application would significantly reduce the volume of pesticide needed to control insect and disease pests under commercial fruit production conditions. The objective of this research was to evaluate effects of the intelligent variable-rate spray application on pesticide use and control of insect and disease pests in fruit plants in a commercial fruit farm and to compare with the results achieved using a constant-rate spray as the conventional standard spray practice.
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