Herbicidal management of stem hemiparasite Dendrophthoe spp. in mango orchards

Abstract

Dendrophthoe falcata (Loranthus), a stem hemiparasite of the Loranthaceae family, is a problematic weed in tree crops, including mango. Manual removal of this parasitic weed is the common practice, often involving cutting the infested tree branches. However, it is labour- intensive, often ineffective, and requires repeated intervention due to persistent sub-epidermal haustoria. Even herbicidal sprays for selective control are not available, and use of conventional spraying methods often results in toxicity to the host. Recent technologies such as air-assisted and electrostatic sprayers offer low-volume and target-specific applications with improved canopy penetration and more efficacy. Under this background a study entitled “Herbicidal management of stem hemi-parasite Dendrophthoe spp. in mango orchards” was carried out at the College of Agriculture, Vellanikkara, Thrissur, from October 2024 to September 2025 with the objectives, to assess the efficacy of various herbicides against Dendrophthoe spp. and to evaluate sprayers that can enhance the application efficiency of herbicides for effective management of loranthus. The experiment was carried out on 20-25-year-old mango trees in College Orchard that had been infested with Dendrophthoe falcata for 8-10 years. Treatments were 2,4-D Na salt 80% WP (5 g/L), 2,4-D amine 58% SL (10 mL/L), 2,4-D Na salt (5 g/L) + CuSO₄ (20 g/L), glufosinate ammonium 13.5% SL (10 mL/L), metribuzin 70% WP (5 g/L), ethrel 39% SL (25 mL/L), and metsulfuron methyl 20% WP (0.4 g/L) as targeted foliar sprays. Basal banding (padding) of 2,4-D Na salt (2%) and metribuzin (2%) was also included along with manual removal and unsprayed check. Phytotoxicity symptoms on the parasite and host were observed. In loranthus, changes in biochemical and physiological parameters, nutrient content of leaves, and regrowth up to one year after treatment were assessed. Four types of sprayers, i.e., battery-powered hydraulic, air-assisted, electrostatic, and air compression sprayers, were evaluated by comparing deposition efficiency, weed control efficacy, spray volume requirement, and cost of weed control in order to identify the most efficient technology for targeted herbicide delivery to loranthus clusters. Among the herbicides, though ethrel induced the fastest response through leaf abscission of parasitic weed by two days after spraying (DAS), total control was not obtained and regrowth started by 40 DAS. In metsulfuron methyl sprayed treatments regrowth started by 60 days, while metribuzin sprayed loranthus showed regrowth by 40 days. Foliar application of 2,4-D Na salt and 2,4-D amine provided the most effective and prolonged suppression without any regrowth even up to one year, which indicated complete drying of the parasite without any adverse effect on the host. Manual removal failed to suppress regrowth beyond 3 months. Herbicidal sprays markedly impaired leaf metabolism too. A drastic reduction in total soluble sugars (from 15.26 to 7.63 mg/g), protein (2.28 to 1.79 mg/g), relative leaf water content (50 to 11%), membrane stability (56 to 26%), and chlorophyll (1.64 to 0.92 mg/g) was observed. The NPK content in loranthus leaves also showed a sharp decline. These effects were linked to oxidative stress, disrupted carbohydrate translocation, and accelerated chlorophyll degradation. In contrast, padding with 2,4-D Na salt and metribuzin maintained higher physiological and biochemical values, indicating localized action with minimal systemic translocation and hence ineffectiveness. Significant variation was observed in droplet deposition efficiency among sprayer types, with electrostatic sprayers having the highest deposition (30.5 μL/cm²), followed by air- assisted (12.63 μL/cm²), battery-powered hydraulic (10.0 μL/cm²), and air-compression sprayers (7.23 μL/cm²). Advanced spraying technologies, particularly electrostatic and air- assisted sprayers, reduced spray volume requirement to nearly one-tenth of that used by conventional sprayers. Interestingly, a comparison between droplet deposition rate and weed control efficiency of battery-powered hydraulic and electrostatic sprayers revealed an inverse relationship, wherein higher deposition did not lead to enhanced herbicidal activity. This discrepancy is attributable to the parameters such as spray volume, droplet size, and lethal dose necessary for effective herbicide performance, ensuring adequate wetting, absorption, and translocation to facilitate metabolic action within the host-parasite system. It can be concluded that targeted foliar application of 2,4-D Na salt (80% WP) @5 g/L or 2,4-D amine (58% SL) @10 mL/L, using battery-powered hydraulic sprayer, is an effective method to manage Dendrophthoe infestation in mango orchards