Effects of Insecticide Applications on Sunflower (Helianthus annuus L.) Pollination in Eastern Kenya
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Date
2007Author
Orornje, Mary-L.
Nyamasyo, Gideon
Kasina;, Muo
Nderitu, John
Type
ArticleLanguage
enMetadata
Show full item recordAbstract
Two insecticides (Dimethoate and Lambda cyhalothrin), commonly used in eastern Kenya to control
sunflower pests, were assessed to determine their use-effect on the crop pollination and its subsequent yield
Sunflower, cv Hybrid 8998, was planted in plots of 4x4 m in a Randomized Complete Block Design
experiment The insecticides were applied at two levels: at pre- flowering period and flowering period. Another
two levels of insecticide treatment involved timing of spray applications: in the morning and in the evening.
Unsprayed were maintained as control. The experiment was done in two consecutive growing seasons in 2004
and 2005. The results show that there was a significant difference in the productivity of sunflower across the
different treatments. Insecticide-treated plots had lower number of developed seeds per sunflower head than
the unsprayed plots. Likewise, the number of seeds per head from plots that were sprayed at pre-flowering stage
had significantly higher number of seeds than from plots sprayed while at flowering stage. The sunflower-head
size and the seed weight per head had similar trend as the number of seeds. The role of pollination was
confnmed in the number of observed bees on each plot Insecticide-treated plots had significantly lower number
of foraging honeybees (Apis mellifera L.) compared with unsprayed plots. Among the insecticides, Dimethoatesprayed
plots had the least number of bee foragers. The findings suggest that insecticide application on a
blooming sunflower reduces the efficiency of bees to pollinate, which results to lower yields. It is suggested
that farmers should manage sunflower pests at earlier growth stages and avoid pesticide use at flowering period
but instead they should use other control options that are friendly to bees.
Citation
Journal of Agricultural Sciences 3 (6): 731-734, 2007Publisher
IDOSI Publications, 'Department of Plant Science and Crop Protection, University of Nairobi Centre for Development Research (ZEF), University of Bonn. Postfasch: Walter-Flex-Str. 3,53113 Bonn Germany Department of Zoology, University of Nairobi