A guide to IPM in brassicas production in east and southern Africa

Abstract

Brassicas constitute the majority of cultivated Cruciferae In eastern and southern Africa. The main brassicas grown in the region include cabbage (Brassica o/eracea L. var. capitata), kale or choumolea (B. o/eracea L. var. acephala), Chinese cabbage (B. campestris L. var. chinensis/B. campestris L. var. pekinensis), cauliflower (B. oleracea L. var. botrytis) and rape (B. carfnata (indigenous) and B. napus (an exotic type). Other brassicas grown in the region are broccoli (B. o/eracea L. var. italica) , Brussels sprouts (B. oleracea L. var. gemmifera), kohlrabi (B. o/eracea L. var. gongylodes l.), savoy (B. oleracea L. var. sabauda), swede (B. napus L. var. napobrassica) and turnip (B. campestris L. var. rapa). Other cru cifers grown In the region include rad ish (Raphanus sativus L. var hortensis) and horseradish (Armoracia rusticana Gaertn.) These vegetables are grown mainly for the local market and for domestic use. They are valuable as sources of vitamins and minerals, as well as a source of cash for smallscale farmers in rural and peri-urban areas. However, production is often constrained by damage caused by a range of pests (insects, diseases, nematodes and weeds). The range of pests attacking the different brassicas is similar, but the relative importance of individual pest species varies between the different crops. The pest constraints of brassicas in the region were Identified during a planning workshop held in Malawi in May 1995 with participants from seven countries (Kenya, Malawi, Mozambique, South Africa, Uganda, Zambia and Zimbabwe), and revised in a second meeting held in Kenya in May 1998. The main pests were identified as insects: the diamondback moth (DBM), cabbage aphids, the headborer Hel/ula and Bagrada bugs. The most important diseases are blackrot and Turnip Mosaic Virus (Table 1 ). Farmers in Africa currently depend solely on the use of pesticides for pest contrc.l. The control of pests is becoming increasingly difficult and uneconomical. as well as environmentally harmful. Pesticides are often applied on a calendar basis. Important pests such as DBM have developed resistance to a wide range of the pesticides commonly used . Furthermore. the incidence ofTurnip Mosaic Virus. which is transmitted by aphids. has increased in the region in recent years. Consequently. many farmers have resorted to the application of insecticide cocktails, as well as increased spraying frequency. This has led to much higher levels of contamination of the farm environment, high pesticide residues in the produce, and increasing health risks to farm workers, as well as higher production costs. There is therefore urgent need for alternative control options in order to become less dependent upon synthetic pesticides. For instance, several countries in Asia have developed and implemented a biocontrol-based IPM approach for control of DBM. A similar attempt, coordinated by ICIPE. is underway for the eastern and southern Africa region. This manual provides descnptions and photos of the major pests and diseases of brassicas. and symptoms of damage , to aid In their identification. Available control options are summarised and wherever possible . IPM solutions suggested as a means of safer and more sustainable crop production