Abstract
The pigweed flea beetle, Disonycha glabrata, is the most damaging insect pest on Amaranthus spp. in the Piedmont zone of North Carolina (NC), United States. It is capable of causing severe yield loss on amaranth greens if uncontrolled. Field experiments were conducted over two growing seasons (Summer 2017 and 2018) in Greensboro, NC, to evaluate OMRI-approved biorational insecticides against D. glabrata in organic amaranth production. Insecticides evaluated included Azatin® O (azadiractin), Ecotec® (oils: rosemary, peppermint and geraniol), Entrust® (spinosad) and PyGanic® (pyrethrins) as stand-alone threshold-driven treatments applied at recommended label rates. Insecticide treatment action threshold (AT) was 2 (on a scale of 5) representing 20-40% leaf damage. The efficacy of the insecticides against D. glabrata population differed significantly within the amaranth varieties in comparison to their respective controls: treatments with Entrust® and PyGanic® on Green Callaloo and Red Leaf recorded 80% reduction in beetle population while Ecotec® gave only a 15% beetle reduction. The Azatin® O treatments recorded the highest D. glabrata population, sometimes greater than the control. Marketable fresh leaf yield from both Green Callaloo and Red Leaf amaranth was highest in the Entrust® and PyGanic® treatments. Hopi Red-Dye and Molten Fire amaranths showed some resistance to beetle damage; they are also intrinsically low yielding. These findings provide information that would make organic amaranth production possible with only limited and safe insecticide input using OMRI-approved insecticides in a threshold-driven manner, an important step towards the sustainable management of D. glabrata and amaranth production.
Highlights
Amaranthus spp. are underexploited and underutilized annuals or short-lived perennials with over sixty species and approximately six thousand varieties with only a few of them (Amaranthus hypochondriacus, A. caudatus, A. cruentus, A. retroflexus inter alia) cultivated for food world-wide (Brenner et al, 2000)
These findings provide information that would make organic amaranth production possible with only limited and safe insecticide input using organic material research institute (OMRI)-approved insecticides in a threshold-driven manner, an important step towards the sustainable management of D. glabrata and amaranth production
Efficacy of the four OMRI-approved insecticides, Azatin® O, PyGanic®, Entrust® and Ecotec® in reducing the D. glabrata population and the associated leaf damage for the two seasons are shown in Figures 1 and 2 (2017) and Figures 3 and 4 (2018)
Summary
Amaranthus spp. (commonly known as pigweed in the USA) are underexploited and underutilized annuals or short-lived perennials with over sixty species and approximately six thousand varieties with only a few of them (Amaranthus hypochondriacus, A. caudatus, A. cruentus, A. retroflexus inter alia) cultivated for food world-wide (Brenner et al, 2000). The plant is rich in minerals, vitamins, proteins, antioxidants and is gluten-free, making it a perfect choice in overcoming many health-related disorders in humans (Ezeh, Ogbedegbe, & Ogbedegbe, 2015). It has the potential as a biofuel feedstock (Viglasky, Huska, Langova, & Suchomel, 2008; Xaba, 2014). Specialty vegetables such as Amaranthus spp. and quinoa (Chenopodium quinoa), in the Amarathaceae family, have gained rapid acceptance among small growers in the state of North Carolina (NC) as demand for them increases, especially among immigrants and other individuals, especially those who are health conscious (Brenner et al, 2000; Vorsah et al, 2020).
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