Effects of weeds on growth of bulb onion and some cost-efective control options at Thika, Kenya

Effects of weeds on growth of bulb onion and some cost-efective control options at Thika, Kenya

2009

E03639

The onion, Allium cepa L., is an important local market vegetable in Kenya. Production of the crop does not meet the demand due to several constraints including weeds. Hand-weeding, although strenuous and labour intensive, is the sole weed control method used by onion growers in Kenya. Two field trials were carried out at the Kenya Agricultural Research Institute, Thika to compare efficacy and profitability of weed management options in onion. The experiments were laid in randomized complete blocks with seven treatments replicated three times. The treatments included black polythene mulch during transplanting, grass mulch placed two weeks after transplanting, hand-weeding fortnightly, hand-weeding monthly, preemergent herbicide (Linuron) application, herbicide and hand-weeding after eight weeks and the control (un-weeded). Weeds significantly (P<0.05) reduced onion plant weight by 69.53% during the first trial and 86.74% in the second trial and final bulb yield by 89.45% and 95.13% in the first and second trials, respectively. The most common weeds were blue couch grass (Digitaria abyssinica), bristly foxtail (Setaria verticullata), goat weed(Ageratum conyzoides), black jack (Bidens pilosa) and the double thorn (Oxygonium sinuatum). Onion plants from the un-weeded plots grew thin and tall due to competition with weeds for nutrients and sunlight. Black polythene mulch resulted in the highest bulb yield (46,527 kg/ha) in the first season, while grass mulch resulted in the highest (65,700 kg/ha) in the second season. Black polythene mulch or grass mulch gave the best weed control, the highest plant weight and onion bulb yield, resulting in thehighest economic benefits in the first and second seasons. Mulching is therefore considered as a cost-effective weed control alternative to handweeding of onion. Further investigations are recommended to establish the other benefits of mulching besides weed control.

v.2:92-102, AFRICAN JOURNAL OF HORTICULTURAL SCIENCE

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