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- Author or Editor: Kevin M. Heinz x
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.
Twenty-one cultivars of vegetative annuals were treated with 0%, 50%, or 100% of the production fertilization rate of 300 mg·L−1 N starting 2 weeks before and continuing until harvest. At harvest, plant width, flower number, and quality rating were measured. The plants were then placed in a simulated interior environment where flower number was counted and quality rating was assigned to each plant weekly for 3 weeks. Overall, 14% of the cultivars maintained a marketable quality (i.e., quality rating of ≥3.0 of 5) for 3 weeks, 43% for 2 weeks, 38% for 1 week, and one cultivar did not maintain quality during the postharvest evaluation. Reduced end-of-production fertilization rate (EPFR) resulted in higher quality ratings for at least one additional week of simulated shelf life for three cultivars, including ‘Dreamtime Copper’ bracteantha (Bracteantha bracteata), ‘Vanilla Sachet’ nemesia (Nemesia ×hybrida), and ‘Bridal Showers’ sutera (Sutera hybrida). ‘Comet White’ and ‘Sunlight’ argyranthemum (Argyranthemum frutescens) retained flowers an additional 2 weeks and ‘Caritas Lavender’ angelonia (Angelonia angustifolia), ‘Dreamtime Copper’ bracteantha, ‘Liricashowers Deep Blue Imp.’ and ‘Starlette Trailing Purple’ calibrachoa (Calibrachoa hybrid), ‘Vanilla Sachet’ nemesia, ‘Cascadias Pink’ petunia (Petunia ×hybrida), and ‘Bridal Showers’ sutera retained flowers an additional 1 week when treated with 0% compared with 50% or 100% EPFR. Four cultivars had decreased plant width at harvest with 0% EPFR. These results indicate that reducing fertilization 2 weeks before harvest can prolong shelf life of some vegetative annuals. Differences in the length of shelf life and responses to reduced EPFR occurred among cultivars of all the affected species. Reduced EPFR did not increase the shelf life of two species, including diascia (Diascia ×hybrida) and lantana (Lantana camara).
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.
This research focused on the effects of nitrogen fertilization on jasmonic acid accumulation and total phenolic concentrations in gerbera. The phytohormone jasmonic acid is known to regulate many plant responses, including inducible defenses against insect herbivory. Phenolics are constitutive secondary metabolites that have been shown to negatively affect insect feeding. Gerbera jamesonii `Festival Salmon Rose' plants were grown in a growth chamber and subjected to either low fertilization (only supplied with initial fertilizer charge present in professional growing media) or high fertilization (recommended rate = 200 mg·L-1 N). Plants were fertilized with 200 mL of a 15N–7P–14K fertilizer at 0 or 200 mg·L-1 N at each watering (as needed). Treatments consisted of ±mechanical wounding with a hemostat to one physiologically mature leaf and the subsequent harvest of that leaf at specified time intervals for jasmonic acid quantification. Total phenolics were measured in physiologically mature and young leaves harvested 0 and 10 hours after ±mechanical wounding. Low-fertility plants had reduced aboveground dry mass, were deficient in nitrogen and phosphorus, and had about a 10× higher concentration of total phenolics when compared to high fertility plants. In low-fertility plants, young leaves had greater concentrations of phenolics compared to physiologically mature leaves. There were no differences in total phenolics due to wounding. The effect of nitrogen fertilization on jasmonic acid accumulation will also be discussed.
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.
Endophytic fungi are increasingly studied for their ability to enhance plant performance in field crops, yet there are few equivalent studies in floricultural crops. Given the economic importance of these crops and pressures faced by growers to produce plants of high aesthetic quality, we surveyed the natural occurrence of foliar fungal endophytes in Knock Out® roses to identify candidate beneficial isolates. We also tested the effects of entomopathogenic fungal inocula on marigold and zinnia plant growth using different application approaches. Our survey of Knock Out® rose foliage collected from five sites within central Texas revealed at least 24 different fungal genera and 30 probable species, including some isolates providing plant stress tolerance and pathogens or antagonists of insects and nematode pests. The effects of entomopathogen inocula on plant growth varied with host plant (marigold vs. zinnia) and inoculation method (soil drench vs. seed soak). Plant responses were complex, but inoculation with Isaria fumosorosea Wize tended to have a negative effect on plant performance characteristics whereas Beauveria bassiana (Bals.-Criv.) Vuill. tended to have positive effects. When applied to marigold as a seedcoating, I. fumosorosea reduced germination, seedling fresh weight, and produced seedlings with a less compact form. By contrast, seeds inoculated with B. bassiana required less time to germinate, had higher germination rates, and increased the plant compactness. These results show that the impact of fungal entomopathogens applied as endophytes depends on the specific fungi-plant combination being examined. The effect of plant inoculation with entomopathogenic fungi within a pest management context requires further evaluation.
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.
In this study, we surveyed the initial whitefly (Aleyrodidae) populations on rooted poinsettia (Euphorbia pulcherrima) cuttings at two commercial greenhouse facilities in both 2017 and 2018 to determine the initial whitefly population at the beginning of poinsettia production and surveyed finished poinsettias at multiple retailers in Tyler, TX, over 2 years to determine whitefly densities considered acceptable by retailers. The initial whitefly population (mean ± se) for all poinsettias was 0.02 ± 0.02 (2017) and 0.33 ± 0.13 (2018) nymphs per plant for grower facility A and 0.05 ± 0.05 (2017) and 0.02 ± 0.01 (2018) nymphs per plant for grower facility B. Of the total 2417 rooted poinsettia cuttings inspected at both locations over 2 years, 29 cuttings had whitefly nymphs (1.2%), 18 had pupae (0.7%), and 23 had exuviae (1.0%). On finished poinsettias sampled at retailers, 4.38 to 40.38 immatures (nymphs + pupae) per plant were found within 60 seconds for any given retailer over the 2 years. We found poinsettias with as many as 220 immatures and 32 adults on a single plant at retailers. This study is the first to quantify densities of whiteflies at retail stores over multiple years.