Disease Severity on Cabbage Protected from Arthropod Pests with Insecticide Treated Agronets in Kenya

Abstract

Cabbage (Brassica oleracea var. capitata L.) is one of the most important vegetables in Kenya, mainly grown by smallholder farmers for food and source of income. Its production is hampered by insect pests and diseases, leading to economic yield losses. Row cover insect proof nets have been used in the past to manage insect pests of cabbage and were recently introduced to Kenya. This study planned to document disease incidence and severity levels on cabbage grown under insecticide impregnated Agronets as a tool to manage insect pests and microclimate. The study was conducted at KALRO-Kabete and PTC (Practical Training Centre)-Thika, Kenya both at the nursery and in the field. Treatments included 1) use of insecticide (alpha cypermethrin) impregnated Agronets with (0.9 mm mesh), 2) untreated 0.4 mm mesh Agronet, 3) grass shading as a farmer practice (at nursery) and 4) control where there was no Agronet use. The treatments had five replications in a completely randomized block design. Plots measured 2 x 6 m, with a 1 m path between consecutive plots and 2 m between consecutive blocks. Three major diseases were recorded: damping off (Rhizoctonia solani), downy mildew (Peronospora parasitica) and black rot (Xanthomonas campestris pv. campestris). Treatments showed significant (P<0.05) differences on severity of damping off, which was lowest on seedlings covered with Agronets compared with the other treatments at nursery. Comparably, the downy mildew disease severity was higher on seedlings covered with Agronets than those with no cover or shading at the nursery. The findings show that frequent disease scouting is crucial when using Agronets for cabbage pests management. This would allow farmers to take action when diseases are noticed. Further supportive studies to understand threshold limits that can trigger growers to employ disease control application may be needed.