Management of Whiteflies and Slugs on Greenhouse Poinsettia in Kenya

Abstract

Flower industry in Kenya, is today the country’s top industry after remittance, tourism, and tea. Key problems facing this sector are freight capacity, climate change and plant health regulations. Poinsettia, Euphobia pulcherima (Euphorbiaceae), is a flower plant vegetatively grown in Kenya for Europe, USA, Japan markets. Whitefly (Hemiptera: Aleyrodidae) particularly, Bemicia tabaci (Hemiptera: Aleyrodidae) is a serious challenge to Poinsettia production. Slugs (gastropoda) are another Poinsettia pest that can cause devastating effects on the crop during establishment if not controlled. Poinsettia and other flower growers depend mainly on insecticides for pest management. But their use is highly regulated especially on crops grown for European, USA and Japan Markets, due to their negative impacts on the environment and human health. Furthermore, pests quickly develop resistance to chemical pesticides. However, pest management with some chemicals is still desirable and practically unavoidable part of integrated pest management. This study evaluated the efficacy of Amblyseius swirskii (Acari: Phytoseiidae) on the management of whiteflies in greenhouse production of Poinsettia. This was compared to integrating the predatory mite with compatible synthetic chemical pesticides and a control where the pesticide was applied alone. The second objective, evaluated the effectiveness of physical barriers (type of growing benches and greenhouse floors) on the management of slugs in greenhouse production of Poinsettia. The study was carried out in Kenya, Muranga County where the growing of Poinsettias plants is done in greenhouses. A Completely Randomized Design (CRD) with two factors was applied. The first factor comprised of three pesticides treatments while the second one consisted of three different Poinsettia varieties. The three pesticides treatments were: Chemical pesticides, A. swirskii, and combination of A. swirskii with compatible synthetic pesticides (buprofezin and deltamethrin). The predatory mites were applied by broadcasting on the crop while chemical pesticides were sprayed. The experiments were conducted in two seasons in 2017 and 2018. For the slug experiments, two factors were also applied. The first factor comprised of physical barriers while the second one was the Poinsettia varieties. Treatments under physical barriers included benches with concrete legs on pumice floor, benches with steel legs on pumice floor and benches with steel legs on concrete floors. The results of the study showed that A. swirskii in combination with selected compatible chemical insecticides was as

effective as the application of pure chemical insecticides in reducing the population of the whitefly. The type of whitefly infesting Poensettia in the greenhouses was identified as Bemisia tabaci biotype while the slug was identified as Deroceras leave. Utilization of the predatory mite, A. swirkii, on its own to manage whitefly in the Poinsettia stock was not effective and had significantly (p<0.05) higher populations of whitefly compared to the combination of A. swirskii and the pesticides, buprofezin and deltamethrin, which in turn was not different from the average population of whiteflies recorded on pesticides alone. The tested varieties had no effect on the population of whitefly but Red with Horizontal Leaves (RHL) had slightly more whitefly populations compared to Red with Vertical Leaves (RVL) and White with horizontal leaves (WHL). Concrete pillars on pumice had significantly (p<0.05) higher populations of slugs compared with Steel pillars on concrete or on pumice. Steel pillars on pumice provided effective vertical physical barrier reducing the mobility of slugs hence the significant reduction of the slug population. The pumice floor provided slugs with conducive environment for laying eggs and hiding places and the pillars/legs that supported benches acted as vertical physical barriers. Poinsettia varieties had an effect on slug population in the greenhouses. The Red variety with horizontal leaves (RHL) was the most vulnerable and significantly (p<0.05) attracted more slugs on the benches compared to the remaining two varieties. Availability of good greenhouse structures such as concrete floor and benches supported on steel stands, may render the effect of variety as unimportant. Therefore, irrespective of variety type, Poinsettia will grow well in this kind of greenhouse conditions without the problems of slugs.