Developing integrated pest management strategies for greenhouse gerbera daisies
Abraham, Cheri Muthirakalayil
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The serpentine leafminer, Liriomyza trifolii (Burgess) (Diptera: Agromyzidae) is a key pest in protected cultivation of ornamentals and vegetables. L. trifolii is the primary pest of greenhouse gerberas. Secondary pests including mites (Tetranychus urticae Koch), thrips (Frankliniella occidentalis (Pergande)), whiteflies (Trialeurodes vaporarioum (Westwood), and Bemisia tabaci (Gennadius)), aphids (Myzus persicae (Sulzer)), and powdery mildew-causing fungal pathogens (from the genera Podosphaera, Erysiphe, Leveillula, Golovinomyces, and Oidium) also require management. L. trifolii is resistant to many commercially available pesticides, while secondary pests are susceptible. Natural enemies can effectively control leafminer populations where pesticide use has been avoided. Pesticides when used often disrupt leafminer biocontrol resulting in over-use of pesticides yet ineffective control of pests. We investigated the compatibility of pesticides, commonly used against leafminers, mites, thrips, whiteflies, and fungal pathogens, with natural enemies of L. trifolii (Diglyphus isaea (Walker) (Hymenoptera: Eulophidae)) and T. urticae (Neoseiulus californicus (McGregor) (Arachnida: Acari: Phytoseiidae)). While commonly used pesticides, e.g., abamectin and spinosad were found to cause severe mortality in the natural enemies, a few others like bifenazate, pyriproxyfen, spiromesifen, and spirotetramat were found to be compatible with a biologically-based control program. Sixty cultivars of Gerbera jamesonii Bolus varied in leafminer preference and damage in a greenhouse choice test. Leaf toughness measured using a penetrometer varied among cultivars, but did not correlate with resistance. A biologically-based Integrated Pest Management (IPM) program was compared with a traditional chemical control regime in a grower greenhouse under realistic growing conditions. Not only was the biologically-based method possible, but also proved cost-effective. Traditional management using insecticides was more expensive and failed to control leafminers, resulting in low quality plants and flowers compared with the biologically-based IPM program. Implementation of a biologically-based IPM program can increase the competitiveness of our local cut flower industry by providing cost effective pest control for a sustainable production system.