Search Results

You are looking at 1 - 5 of 5 items for

  • Author or Editor: Amanda Chau x
Clear All Modify Search
Free access

Fred Davies*, Chuanjiu He, Amanda Chau, Kevin Heinz and Jay Spiers

This research details the influence of fertility on plant growth, photosynthesis and ethylene evolution of chrysanthemum (Dendranthema grandiflora Tzvelev var. Charm) inoculated with western flower thrips (Frankliniella occidentalis (Pergande). We tested the hypothesis that moderate levels of nitrogen would better control western flower thrips on chrysanthemum. While thrips are known to reduce plant quality, there have been few comprehensive studies on plant response to thrips population dynamics—analyzing changes in plant growth and development, plant gas exchange and ethylene evolution. Plants were exposed to four fertility levels that consisted of 0%, 10%, 20% and 100% (375 ppm N) of recommended nitrogen levels. Thrips abundance was greatest at high fertility. Thrips depressed plant vegetative and reproductive growth and altered carbohydrate partitioning. Thrips-inoculated (TI) plants also had reduced leaf area and lower leaf mass than thrips-free (NonTI) plants, but did not differ in specific leaf area [(SLA) leaf area (cm2)/leaf DM (g)]. However, high fertility plants had greater biomass and higher SLA, i.e., thinner leaves than low fertility treatments. Thrips reduced photosynthesis (Pn) and stomatal conductance (gs) in young, mature and older basal leaves, with gs showing greater sensitivity than Pn. Ethylene and chlorophyll levels in thrips damaged leaves did not differ from Non-TI plants.

Free access

James D. Spiers*, Fred T. Davies, Chuanjiu He, Amanda Chau, Kevin M. Heinz and Terri W. Starman

This research focused on the influence of insecticides on plant growth, gas exchange, rate of flowering, and chlorophyll content of chrysanthemum (Dendranthema grandiflora Tzvelev cv. Charm) grown according to recommended procedures for pot plant production. Five insecticides were applied at recommended concentrations at three different frequencies: weekly (7 days), bi-weekly (14 days), or monthly (28 days). A separate treatment was applied weekly at 4× the recommended concentration. Insecticides used were: acephate (Orthene®) Turf, Tree & Ornamental Spray 97), bifenthrin (Talstar®) Flowable), endosulfan (Thiodan®) 50 WP), imidacloprid (Marathon®) II), and spinosad (Conserve®) SC). Phytotoxicity occurred in the form of leaf burn on all acephate treatments, with the greatest damage occurring at the 4× concentration. Photosynthesis and stomatal conductance were influenced primarily by the degree of aphid and/or spider mite infestation—except for acephate and endosulfan treatments (weekly and 4×), which had reduced photosynthesis with minimal insect infestations. Plants receiving imadacloprid monthly had the greatest leaf dry mass (DM). Plants treated with acephate had lower leaf and stem DM with bi-weekly and 4× treatments. Spinosad treatments at recommended concentrations had reduced stem DM, in part due to aphid infestations. The flower DM was not significantly different among treatments. There were treatment differences in chlorophyll content as measured with a SPAD-502 portable chlorophyll meter.

Free access

Fred T. Davies Jr., Chunajiu He, Amanda Chau, Kevin M. Heinz and Andrew D. Cartmill

This research details the influence of fertility on plant growth, photosynthesis, ethylene evolution and herbivore abundance of chrysanthemum (Dendranthema grandiflora Tzvelev `Charm') inoculated with cotton aphids (Aphis gossypii Glover). We tested five fertility levels that consisted of 0%, 5%, 10%, 20%, and 100% (375 ppm N) of recommended nitrogen levels. Aphid abundance was greatest at high fertility. Fertility affected the vertical distribution of aphids. A higher population of aphids were observed in physiologically mature and older leaves at low fertility, whereas at high fertility young leaves had 33% more aphids than older, basal leaves. Aphids depressed plant vegetative and reproductive growth, and altered carbohydrate partitioning at high fertility. Aphid-inoculated (AI) plants at high fertility had increased specific leaf area [(SLA), i.e., thinner leaves] and greater leaf area than aphid-free (NonAI) plants. Aphids caused greater ethylene production in reproductive buds and young leaves of high fertility plants, but had no effect on ethylene evolution in physiologically mature or older, basal leaves. Plant growth, leaf nitrogen (N), phosphorus (P), iron (Fe) and manganese (Mn) increased at higher fertility, as did chlorophyll and photosynthetic rates. Leaf N was highest in young and physiologically mature leaves compared to basal leaves. Aphids decreased leaf N and P. Aphids reduced photosynthesis in young leaves of high fertility plants, whereas physiologically mature and older leaves were unaffected.

Free access

James D. Spiers, Fred T. Davies Jr., Chuanjiu He, Carlos E. Bográn, Kevin M. Heinz, Terri W. Starman and Amanda Chau

This study evaluated the influence of insecticides on gas exchange, chlorophyll content, vegetative and floral development, and plant quality of gerbera (Gerbera jamesonii Bolus `Festival Salmon'). Insecticides from five chemical classes were applied weekly at 1× or 4× their respective recommended concentration. The insecticides used were abamectin (Avid), acephate (Orthene), bifenthrin (Talstar), clarified hydrophobic extract of neem oil (Triact), and spinosad (Conserve). Photosynthesis and stomatal conductance were reduced in plants treated with neem oil. Plants treated with neem oil flowered later—and at 4× the recommended label concentration had reduced growth, based on lower vegetative dry mass (DM) and total aboveground DM, reduced leaf area, thicker leaves (lower specific leaf area), higher chlorophyll content (basal leaves), and reduced flower production. Plants treated with acephate at 4× the recommended label concentration were of the lowest quality due to extensive phytotoxicity (leaf chlorosis). Plants treated with 1× or 4× abamectin or spinosad were of the highest quality due to no phytotoxicity and no thrips damage (thrips naturally migrated into the greenhouse). The control plants and plants treated with 1× bifenthrin had reduced quality because of thrips feeding damage; however gas exchange was not negatively affected.

Free access

James D. Spiers, Fred T. Davies, Chuanjiu He, Carlos Bogran, Amanda Chau, Kevin M. Heinz and Terri W. Starman

This research focused on the influence of insecticides on gas exchange, chlorophyll content, vegetative and floral development, and overall plant quality of gerbera (Gerbera jamesonii var. `Festival Salmon'). Insecticides from five chemical classes were applied weekly at 1× and 4× the recommended concentrations. Insecticides used were: abamectin (Avid® 0.15 EC), acephate (Orthene® Turf, Tree & Ornamental Spray 97), bifenthrin (Talstar® Nursery Flowable), clarified hydrophobic extract of neem oil (Triact® 70), and spinosad (Conserve® SC). Phytotoxicity occurred in the form of leaf chlorosis on all acephate treatments, with the greatest damage occurring at the 4× concentration. Photosynthesis and stomatal conductance were significantly reduced in plants treated with neem oil extract. Plants treated with the neem oil extract (1× and 4×) flowered later and had reduced growth [lower shoot dry mass (DM) and total DM]. Plants that received 4× the recommended concentration of neem oil extract had reduced leaf area, thicker leaves (lower specific leaf area), higher leaf chlorophyll content, and reduced flower production, as determined by flower number and flower DM. Plants treated with acephate 4× concentration were the lowest quality plants due to extensive phytotoxicity (leaf burn), which also reduced photosynthesis. The highest quality plants were treated with spinosad and abamectin due to zero phytotoxicity and/or no thrips damage (thrips naturally migrated into the greenhouse). The control plants and plants treated with bifenthrin 1× were not marketable due to thrips damage; however, plant growth characteristics and gas exchange were not statistically different.