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Keywords: Applied Sciences
Agriculture & related technologies
Issue Date: 2016
Abstract: Canola, Brassica napus L. is a minor oilseed crop in Pakistan but for various reasons is increasing in importance as its oil being healthy and to share country oil production as currently 71% of the required edible oil in country is being imported. A complex of aphids is the main pest for low crop harvests sometimes reaching to complete crop failure. Prior work has found that plant resistance and natural biological control have minimal potential in managing aphids. Insecticides have been recommended in past research to reduce aphid damage but without any 11 guide lines regarding timing of applications or action thresholds. Altering planting time of crops is an important component of pest management for avoidance of pests. This component has not been previously exploited for developing pest management of aphids in canola production systems. Study described in this thesis involves the optimization of planting date and timing of insecticide applications. Canola variety (Shiralee) was planted on mid October, early November and mid November in crop seasons of years 2008-09 and 2009-10 at Multan and Bahawalpur districts of southern Punjab – Pakistan. The experiment design was a split plot with planting dates in main plots and insecticide applications in subplots. In each planting, insects pests including aphids and other hexapods were recorded. Acetamiprid and/ Imidacloprid against aphids were applied at flowering, pod formation, maturity (one spray), flowering and pod formation (two sprays), flowering, pod formation (three sprays) and maturity and pod and maturity (two sprays) stage of the crop. Untreated plots were also maintained as treatment. Aphids were recorded from top 10cm of central shoot of five randomly selected plants from each treatment while other hexapods from the whole five plants per plot. At crop harvest yield and yield contributing components and seed oil contents were recorded. Cabbage aphid, Brevicoryne brassicae Linnaeus (Hemiptera: Aphididae); turnip aphid, Lipaphis erysimi (Kaltenbach) (Hemiptera: Aphididae) were recorded as major/abundant among all other insect pests. Low and negligible populations of peach aphid, Myzus persicae Sulzer, (Hemiptera: Aphididae); whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae); and armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) were observed for short duration in early vegetative stages of seedling to rosette of the crop. However, B. brassicae, L. erysimi, and pod borer, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) appeared with the onset of flowering to pod stages, respectively. Crop sown in mid October got more aphid free days (105) than crops sown on early November (98 days) and mid November (72 days). At that time of aphid’s infestation, early November sown crop had 28% plants at flowering and 72% plants at bolting stages. While mid November sown crop was 25% at flowering and 75% at bolting stages. In contrast, early sown crop (mid October) had completed almost 94% flowering and 6% of pods setting before aphid invasion. Thus, mid October sown crop escaped the aphid damage at flowering to early pod setting stage. 12 Crop sown on mid October gave significantly higher yield compared to late sown crops. Timing of aphid infestation was noted as important as severity of infestation. Both flowering and pod stages were more vulnerable to damage (yield loss) by aphids pests. These stages proved to be critical for yield-aphid relationship and ultimately for applying insecticides to manage aphids as compared to maturity stage. Frequency of insecticide applications: flowering-pod-maturity stages (with 3 applications) and flowering-pod (with 2 applications) gave higher crop yields than untreated plots and were statistically at par with treatment of single application at flowering stage for three experiments of first two planting dates at both the locations. Insecticides applications at pod and maturity stages did not increase in yield if crop was not treated at flowering stage. Thus application of insecticides at flowering and pod formation stage is an action threshold based upon crop phenology. Insecticides applications (flowering-pod-maturity) for aphids increased around 44% grain yield than no insecticides. Reduction of aphids due to insecticides increased plant height, pods per plant, numbers of seeds per pod and 1000 seed weight (with substantially more for early plantings) but did not affect oil contents of seeds in all the experiments. Cost benefit ratio of these applications was 1:7.12, 1:3.37 and 1:1.90 for early, mid and late planting time, respectively. Integrating early planting at mid October and insecticide applications at flowering and pod stage, economic losses of the pest can be avoided with an increase in income for the growers. Moreover, manipulating early planting dates and timing of insecticide applications/action thresholds can result in more cost effective and environment friendly management program. Keywords: Canola; Brassica napus; sowing dates; Insect pests; growth stages; insecticides; aphid; yield; yield components; southern Punjab; Pakistan.
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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