Study on the Effects of Manure Application and Host Plant Spacing on the Infestation Level and Damage of Thrips Tabaci Lindeman (Thysanoptera: Thripidae) on onion.
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Date
2006-07
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Addis Ababa University
Abstract
The study on the effect of manure application and other cultural practices
on the infestation level and damage of Thrips tabaci on onion was conducted
in Cheha Woreda, Luke Kebele of the Gurage Zone from December to April
2005. The field study was on the impact of manure application and plant
spacing on the infestation level, damage, size and number of leaf and bulb
yield were carried out on the demonstration site, and where as the effect of
organic manure application on onion thrips density was based on cage
experiments conducted using Complete Randomized Design (CRD) in five
replications. The field experiments was performed using a Randomized
Complete Block Design (RCBD) involving six treatments from a factorial
combination of organic manure application, plant spacing and untreated
controls.
The results on the effect of organic manure application on onion thrips
density indicated that, the lowest number of adult and larvae T. tabaci was
obtained from onions planted on soil with manure application before
transplanting. The highest density of onion thrips was recorded from the
untreated controls.
The investigation on the impact of manure application and plant spacing on
the infestation, damage levels, size and number of leaves of onion revealed
that starting from 45 days after transplanting treatments with before
transplanting manure application (BTMA) at 20x30cm and 20x25cm showed
lower mean count of thrips per plant, and highest leaf size followed by the
treatment at transplanting manure application with 20x30cm plant spacing.
The damage level was identified as mild at 15 and 30 days after
transplanting and at older stages intermediate damage was recorded on
most plants. On the other hand, the control treatments with 20x20cm and
20x25cm plant spacing had the highest infestation, with the smallest leaf sizes and characterized by intermediate damage at early stages and sever
attack as the crop matured.
The study on the effect of organic manure application in cage experiments,
demonstrated that the lowest mean number of larvae and adults were
obtained from manure application before transplanting followed by at
transplanting manure application and the highest being the control with no
manure application.
The survey on alternate host range of onion thrips in the study area showed
that five cultivated vegetables, a cereal crop and one wild plant were found
to harbor the insect pest on their leaves. The highest number of thrips per
plant and percent total infestation was recorded from onion followed by Kale
(Brassica oleracea L.var acephala) and wild Sorghum (Sorghum
arundinaccum). Finally, the survey on impact of the system on the
occurance of predatory beneficial insects showed that, three different
generalist insects and spiders were encountered in the field feeding on onion
thrips larvae and adult.
Finally, this study emphasized on a new strategy of managing onion thrips
in which host plant spacing and nutrient management were integrated to
suppress the pest population and improved the crop health and vigority to
withstand the damage to a certain limit.
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Biology