Pre-plant application of Metarhizium brunneum and black soldier fly (Hermetia illucens) digestate to reduce wireworm damage to agricultural crops

Wireworms are the larval stage of click beetles (Coleoptera: Elateridae) and can cause severe damage to a wide variety of field crops. Due to their long larval stage and subterranean lifestyle, they can be difficult to control. Synthetic chemical insecticides have traditionally been used to control wireworms but there are none registered for control in vegetable crops in Canada. Furthermore, there is growing interest in non-chemical, and particularly biological, approaches for pest management. Metarhizium brunneum, one of the best studied fungal entomopathogens for controlling insect pests has been studied for managing wireworms and can also be applied in an encapsulated form Attracap, which combines M. brunneum, calcium alginate and Baker's yeast (Saccharomyces cerevisiae). Digestate of black soldier fly (Hermetia illucens) larvae, sold as the fertilizer 'EnterraFrassTM', was previously observed in a fertility trial to protect the test crops from wireworm damage. The current study examined the pre-plant field application of these three bioproducts for their ability to reduce wireworm losses in lettuce (Lactuca sativa cv. 'Crispa', turnip (Brassica rapa subsp. rapa cv. 'Hakurei'), and carrot (Daucus carota subsp. sativus cv. 'Istanbul') at three locations over two years. The bioproducts were applied in a 10-cm wide band with 10 g rolled oats per 1 m of band length, which, through aerobic fermentation, generates carbon dioxide to attract wireworms. In Agassiz in 2019, the mean percent of marketable turnips were 39% ± 4% for M. brunneum conidiated rice granules (high rate, 1014 conidia/ha) and 37% ± 2% for Attracap (50kg/ha), both significantly greater than the marketable yield of EnterraFrass (8% ± 6%) and the untreated control (7% ± 2%). The loss of marketable yield in plots treated with EnterraFrass was from desiccation. In Agassiz in 2020, the mean percent of marketable turnips were 56% ± 3% for M. brunneum conidiated rice granules (high rate, 1014 conidia/ha), 59% ± 3% for M. brunneum conidiated rice granules (low rate, 5x1013 conidia/ha) and 54% ± 3% for EnterraFrass (1000 kg/ha), all significantly greater than the marketable yield of rolled oats-only control (17% ± 4%) and untreated control (22% ± 3%). No treatment effects were observed in the lettuce trial in Agassiz in 2019. In Courtenay in 2020, the mean percent of marketable turnips for M. brunneum conidiated rice granules (1014 conidia/ha) and EnterraFrass (1000 kg/ha) were 91% ± 2% and 88% ± 3%, respectively, significantly greater than the rolled oats-only control (52% ± 6%) and untreated control (44% ± 11%). No treatment effects were observed in the lettuce trial in Courtenay in 2020. In Prince Edward Island, M. brunneum conidiated rice granules (high rate,1014 conidia/ha and low rate, 1013 conidia/ha) and EnterraFrass (1000 kg/ha) yielded 227,265 ± 40,369, 178,888 ± 41,089, and 226,666 ± 50,821 marketable carrots/ha, respectively, with the high-rate granules and EnterraFrass being significantly greater than the untreated control that yielded 122,936 ± 34,406 marketable carrots. Mean carrot size (g/carrot) was not affected by the treatments. Together, the results suggest that pre-plant applications of both M. brunneum and EnterraFrass have utility as wireworm biocontrol products in turnip and carrot fields.