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  • Author or Editor: Jiandong Wang x
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Purple blotch (Alternari a porri) and thrips (Thrips tabaci) can seriously reduce yields of short day onions in South Texas. The level of injury caused by these organisms is influenced by the concentration of nitrogen in leaf tissue. Lower levels of tissue nitrogen increase susceptibility to A. porri but decrease susceptibility to thrips. The purpose of this study was to evaluate the effect of tissue N levels on joint susceptibility of 4 onion cultivars to A. porri and thrips. Foliage was fertilized at 0, 4, 8, 12 or 16 lbs N/ac/wk for 6 weeks. Nitrogen concentrations in onion leaves varied over time and by leaf age, but showed very little effect due to foliar fertilization. Significant differences in thrips were noted among cultivars, but not among leaf N concentrations with cultivars. Purple blotch outbreak occurred late in the growing season and was not related to leaf N levels. Total N uptake failed to respond to foliar fertilization, therefore overall use efficiency of the foliar N applied averaged only about 10% relative to the amount taken up in the check plots.

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