Amanda Chau

Influences of fertilization on population abundance, distribution, and control of Frankliniella occidentalis on chrysanthemum

We examined the effects of fertilization on population abundance and within‐plant distribution of western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), on potted chrysanthemum, Dendranthema grandiflora (Tzvelev). We also investigated the effects of fertilization on the number of insecticide applications needed to control F. occidentalis on potted chrysanthemum. Under greenhouse conditions, rate of change in population abundance of F. occidentalis increased with fertilization levels from 0 to 100% of the standard fertilization level (375 ppm N) and was four times higher on plants fertilized with the standard level (rate of change = 0.14) than on plants fertilized with 0% during the first 4 weeks after thrips inoculation. Within‐plant distribution of F. occidentalis was influenced by the phenology of the plants rather than total nitrogen content of plant tissues. Prior to flower opening, more F. occidentalis were found in the middle region of the plants. When the flowers began to open, more thrips were found feeding inside the flowers than on the leaves. We further showed that production time, the time from transplantation to flower opening, shortened considerably with increased fertilization level. Production time was shortest, 12 weeks, for plants fertilized with 100% of the standard fertilization level. When the fertilization level was reduced to 20%, production time lengthened to 13 weeks. When fertilization level was reduced to 0%, production time lengthened to 14 weeks. Increased fertilization from 0 to 100% of the standard level did not result in higher numbers of insecticide applications. All three insecticides (acephate, bifenthrin, and spinosad) were effective in keeping the thrips infestation below a predetermined level, five thrips per plant, but bifenthrin required the most number of applications to do so. For chrysanthemum, a fast‐growing crop and heavy utilizer of fertilizer, fertilization influenced not only the population growth of pest insects but also plant production time. As a result, optimizing fertilization level to reduce pest population growth may be a useful tactic in an Integrated Pest Management program for managing F. occidentalis on potted chrysanthemum. However, the effect of fertilization on production time and plant quality should also be considered when implementing this tactic.

Influences of fertilization on Aphis gossypii and insecticide usage

Abstract:  Fertilization levels for ornamental crops may influence pest population dynamics, crop quality, and pest management strategy. We examined the effect of fertilization on population growth and within‐plant distribution of melon or cotton aphid, Aphis gossypii Glover, on potted chrysanthemum, Dendranthema grandiflora (Tzvelev). In terms of pest management implications, we also investigated the effect of fertilization on the number of insecticide applications needed to control A. gossypii on potted chrysanthemum. Population growth rate of A. gossypii increased with fertilization levels from 0 to 38 ppm N and reached a plateau from 38 to 488 ppm N. Increased fertilization beyond 38 ppm N, 10% of the commercial standard, did not result in higher aphid number. Aphids responded to nutrient availability of plants by distributing themselves in areas with higher level of nitrogen. More aphids were found in the apical and middle strata of the plants than the basal stratum, which had the lowest nitrogen content. Leaf nitrogen content increased with increased fertilization level and was consistently higher in the apical and middle strata than the basal stratum. Increased fertilization from 0 to 375 ppm N did not result in higher number of insecticide applications. All three insecticides (bifenthrin, kinoprene or pymetrozine) were effective in keeping the aphid infestation below a pre‐determined level, five aphids per plant, but pymetrozine required the least number of applications. For chrysanthemum, a fast‐growing crop and heavy utilizer of nitrogen, increased fertilization shortened the time to flowering, which would allow growers to harvest their crop sooner and reduce the time for aphid population growth. Reduction in time to harvest could result in significant reduction of insecticide usage by reducing the time for aphid population growth. As a result, high fertilization together with minimal runoff may be a useful tactic to an integrated pest management (IPM) programme for managing A. gossypii on potted chrysanthemums.

Manipulating fertilization : a management tactic against Frankliniella occidentalis on potted chrysanthemum

Fertilization during production of greenhouse chrysanthemum, Dendranthema grandiflora (Tzvelev), will influence Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) populations as well as plant productivity and postproduction longevity. It is essential to include fertilization effects in the development of crop management practices that reduce thrips populations and maintain plant marketability. In this study, we lowered fertilization to reduce thrips population abundance while maintaining plant productivity. We tested fertilization levels below and above the recommended level (375 p.p.m. N) for commercial production. We reduced mean rate of change in F. occidentalis abundance from 0.05 to 0.03 (day−1) and mean number of thrips per plant by 44% by fertilizing with either 188 p.p.m. N (50% of the recommended level) or 568 p.p.m. N (150%) and higher. Fertilization influenced not only the rate of change in thrips abundance but also the production time (from transplanting to flower opening). Lowering fertilization to 50% of the recommended level lengthened mean production time from 84 to 88 days. Plant height, flower size, and flower number were not adversely affected when fertilization was reduced to 50% of the recommended level. Mean postproduction longevity was shortened from 26 to 24 days when plants were fertilized with 50% of the recommended level. Two important advantages of lowering fertilization to 50% of the recommended level were (1) a 44% reduction in mean F. occidentalis abundance and (2) a significant reduction in fertilizer input for the production system. Manipulation of fertilization can be a useful management tactic against F. occidentalis.

Reducing fertilization for cut roses: effect on crop productivity and twospotted spider mite abundance, distribution, and management.

ABSTRACT 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.

Reducing fertilization: a management tactic against western flower thrips on roses

Fertilization reduction could be a useful pest management tactic for floriculture crops if it reduced pest populations with minimal impact on crop yield and quality. We evaluated the response of the western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), to different fertilization levels for cut roses, Rosa hybrida L. cv. ‘Tropicana’, and quantified fertilization effects on (i) abundance of F. occidentalis on cut roses, (ii) biological control of F. occidentalis on cut roses and (iii) nutritional quality of the cut flower crop. We tested a commercially available fertilizer (Peters Excel 15‐5‐15 Cal‐Mag; The Scotts Company, Marysville, OH) at 100% and 33% of the recommended nitrogen level (150 ppm N) for rose production using liquid‐feeding and two control measures: no thrips control measure; release of a predatory mite, Amblyseius swirskii (Athias‐Henriot). To maintain equivalent ratios of macro‐ and micronutrients for all our fertilizer treatments, we varied only the concentration of the fertilizer to the levels specified in our experiments. Lowering fertilization rate from 100% to 33% of the recommended level reduced mean F. occidentalis abundance on cut roses by 30%. Combinations of both bottom‐up (fertilization) and top‐down (biological control) tactics provided better F. occidentalis control than either tactic alone. Flower production was not compromised on plants fertilized with 33% of the recommended level. Nitrogen, phosphorous and potassium content of the leaf tissue decreased at 33% of the recommended fertilization level, but all values were within optimal ranges for cut roses. We propose that fertility management may be an effective means of reducing thrips numbers on cut roses.