Evaluation of Metarhizium brunneum- and Metarhizium-Derived VOCs as Dual-Active Biostimulants and Pest Repellents in a Wireworm-Infested Potato Field

Abstract

Wireworm, the larval stages of click beetles, are a serious pest of tubers, brassicas and other important commercial crops throughout the northern hemisphere. No effective control agent has been developed specifically for them, and many of the pesticides marketed as having secondary application against them have been withdrawn from EU and Asian markets. Metarhizium brunneum, an effective entomopathogenic fungus, and its derived volatile metabolites are known to be effective plant biostimulants and plant protectants, although field efficacy has yet to be validated. Field validation of a combined M. brunneum and derived VOC treatments was conducted in Wales, UK, to assess the effects of each as a wireworm control agent and biostimulant. Plots were treated with Tri-Soil (Trichoderma atroviridae), M. brunneum, 1-octen-3-ol or 3-octanone, or combinations thereof. Treatments were applied subsurface during potato seeding (n = 52), and potatoes were harvested at the end of the growing season. Each potato was weighed individually and scored for levels of wireworm damage. Applications of both the VOCs and the M. brunneum individually were found to significantly decrease wireworm burden (p < 0.001). Combinations of M. brunneum and 3-octanone were also found to significantly decrease wireworm damage (p < 0.001), while no effect on yield was reported, resulting in an increased saleable mass over controls (p < 0.001). Herein, we present a novel 'stimulate and deter' wireworm control strategy that can be used to significantly enhance saleable potato yields and control wireworm populations, even under high pest pressure densities.

Keywords: Metarhizium brunneum; potato; repellent; volatile organic compounds; wireworm.

Figure 1

Images of trial site taken after 0 and 28 days. Left-hand image shows potatoes being planted in furrows above M. brunneum and derived-VOC treatments in subplots. Right-hand panel shows potato plant (Solanum tuberosum) growth four weeks post-planting. Trials took place at field periphery in Pembrokeshire, Wales, UK.

Figure 2

Left-hand panel. Mean weight (g) per potato tuber. Middle panel. Total number of tubers per block (26 plants) during the course of the field trial. Right-hand panel. Total potato yield (kg) per block (26 plants). Values are marginal means and 95% confidence intervals from GLMMs. Letters above given value scores denote significance between treatments (p < 0.05) whereby letters (a–b) represent untreated control (a) and Trichoderma treatment (b).

Figure 3

Images showing severity of wireworm damage in harvested potatoes. Left-hand panel shows potato tuber taken from control plot at harvest with multiple wireworm attack holes present on surface of potato. Right-hand panel shows unaffected potato retrieved from M. brunneum and 3-octanone combination treatment plot.

Figure 4

Mean relative wireworm damage scores for potatoes treated with VOCs, Trichoderma, and M. brunneum conidia, or combinations thereof, during early plant growth phases. Scoring was relative to wireworm damage incidence in harvested potatoes (0 = no wireworm damage, 1 = 1 wireworm attack/hole, 2 = multiple wireworm attacks/holes). Left-hand panel. No damage [score 0] vs. damage (1,2). Right-hand panel. No damage or light damage (0,1) vs. severe damage (2). Values are marginal means and 95% confidence intervals from GLMMs. Letters above given values denote significance between treatments (p < 0.05), whereby letters (a–g) represent each treatment reading sequentially from left to right.