Impact of Pesticides on Crop Injury, Yield, Market Quality, and Chemical Composition of Peanut (Arachis hypogaea L.)

Producing peanut with limited pest management options creates challenges in maintaining yield, market grade quality, acceptable flavor, and nutritional value of peanut (Arachis hypogaea L.) compared with conventional production systems where synthetic pesticides can be used. It is well known that limited or no inputs of synthetic pesticides leads to higher disease and arthropod incidence and weed interference. However, the impact of reduced or no-pesticides on nutritional composition of peanut has not been investigated. Field experiments were conducted in 2017 and 2018 in North Carolina to determine the impact of varying levels of pesticide inputs on crop injury associated with pests, pod yield, market grade characteristics, and nutritional composition of the high-oleic cultivar ‘Sullivan.’ Treatments included: 1) seed planted at 210 kg/ha without fungicide versus seed treated with commercial fungicide at a seeding rate of 140 kg/ha; 2) peanut treated with acephate within three weeks after peanut emergence and chlorpyrifos applied at pegging versus no insecticides; and 3) no fungicides applied for protection from leaf spot disease versus five sprays of copper salts of fatty acid rosins, and five sprays of diverse commercially-available fungicides. Lower plant population and pod yield were observed when seed was not treated with fungicides even though a higher seeding rate was used. Synthetic fungicides protected peanut from early and late leaf sport disease [caused by Passalora arachidicola (syn. Cercospora arachidicola) and Nothopassalora personata] more effectively than copper salts of fatty acid rosins. Insecticides used to suppress potato leafhopper (Empoasca fabae), tobacco thrips (Frankliniella fusca), and southern corn rootworm (Diabrotica undecimpuntata) did not affect peanut yield compared with non-treated peanut. No difference in the ratio of oleic acid content to linoelic acid content was observed regardless of pest management practices. Total oil content was lower while total tocopherol content was higher when insecticides were applied compared with non-treated peanut. Total oil content increased as yield increased based on fungicide program while total carbohydrate decreased as yield increased in presence of less peanut defoliation. While the interaction of fungicide seed treatment and seeding rate and insecticide treatment was significant for total oil content and total carbohydrate, differences among treatment combinations were minor and likely of limited biological significance. Total carbohydrate content was affected by the three-way interaction of pest management inputs. However, no clear trend of treatment effects was noted as related to pesticide treatments and associated yield. Results from this study indicate that lower peanut yield will occur when fungicide is not applied to seed even though higher seeding rates are used compared with fungicide-treated seed when lower seeding rates are used. While more effective fungicides for protection from leaf spot disease resulted in higher yields, acephate applied to suppress tobacco thrips and chlorpyrifos for southern corn rootworm did not affect yield compared with non-treated peanut, possibly due to relatively low insect populations. Though significant effect(s) of pest management on nutritional value were observed, the magnitude may have limited impact to consumers. Lack of difference in the ratio of oleic acid to linoleic acid suggests that differences in the pest management practices reported here will not affect expression of this trait in the high-oleic cultivar Sullivan.