Reducing Fertilization for Cut Roses: Effect on Crop Productivity and Twospotted Spider Mite Abundance, Distribution, and Management

Fertilization reduction could be a useful pest management tactic for floriculture crops if it reduced pest populations with little loss in crop yield and quality. We evaluated the response of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), to different fertilization levels for cut roses, Rosa hybrida L. 'Tropicana' and quantified fertilization effects on 1) management of T. urticae on roses, 2) abundance and distribution of T. urticae on roses, and 3) yield and quality of the cut rose crop. We tested two fertilization levels, 10% (15 ppm N) and 100% (150 ppm N) of the recommended level for commercial production, and three control methods: no control measure; a predatory mite, Phytoseiulus persimilis Athias-Henriot; and a miticide, bifenazate. Combinations of both bottom up (fertilization) and top down (biological or chemical control) tactics provided a greater degree of T. urticae control than either tactic alone. Rose productivity was reduced with fertilization at 10% of the recommended level; therefore, we conducted studies with T. urticae on roses fertilized with 33% (50 ppm N), 50% (75 ppm N), and 100% (150 ppm N) of the recommended level. Mean numbers of T. urticae and T. urticae eggs per flower shoot were twice as high on roses fertilized with 100 versus 33% or 50% of the recommended level. Number of rose leaves and total leaf area infested by T. urticae were similar at all fertilization levels. Cut rose yield and marketability were not compromised on plants fertilized with 50% of the recommended level.