Western flower thrips (WFT) [Frankliniella occidentalis (Pergande)] is a pest of greenhouse-grown floriculture crops worldwide. To determine if plant resistance varied in three populations of impatiens (Impatiens wallerana Hook. f.) collected near San Vito, Costa Rica, 59 genotypes were evaluated for resistance to feeding by WFT. Individual insect-free plants of each genotype were inoculated with 20 laboratory-reared WFT. Thrips were allowed to feed on individual plants for a 4-week period followed by visual evaluations to estimate feeding damage. Feeding damage varied among genotypes. Thirty-seven genotypes had feeding damage levels similar to the susceptible control, while 22 entries were significantly more resistant than the susceptible control. Of the 22 genotypes with some level of resistance, six genotypes were commercially acceptable, having mean visual ratings below 4.0 on a 1 to 9 evaluation scale. Five of these six genotypes were seedlings from a single population and represented 13.9% of the seedlings in that population. The remaining seedling was from a second San Vito population. The plants in these populations identified as having acceptable levels of damage may be useful in a breeding program designed to enhance resistance to WFT feeding damage. Because WFT feeding damage varied among genotypes, the potential for improving impatiens resistance to WFT exists within available germplasm.
Daniel F. Warnock
Late season control of whitefly is problematic in many production ranges as systemic insecticides may not provide full season control. Most commercially available contact insecticides are not labeled for use on fully colored poinsettia, Euphorbia pulcherrima, plants due to potential phytotoxicity or residue on colored bracts. Recent formulation changes in TriStar make late season applications possible. This study assessed phytotoxicity and residue impacts of two formulations of TriStar on potted poinsettias. On 4 Aug. 2004, rooted cuttings of 47 poinsettia cultivars obtained from four commercial suppliers were transplanted into pots containing a soilless medium. A total of 235 cuttings were used to arrive at five pots per cultivar. Plants were grown using standard production techniques. On 11 Nov. 2004, all plants were fully colored and treated with TriStar 70 WSP or TriStar 30SG at maximum label rates. Phytotoxicity and residue levels were assessed 7 days later using a 1 to 9 visual scale. Overall the formulations had few negative impacts on poinsettias. Phytotociticy ratings were minimal for most cultivars; however, some cultivars, such as `Silverstar Red' expressed an elevated level of phytotoxicity. Dark colored cultivars showed more residue than light colored cultivars. The TirStar 30SG formulation had the least amount of residue. TriStar 30SG may be an acceptable insecticide for late season control of whitefly on poinsettia crops. Producers are cautioned to test cultivars for phytotoxicity before applying to an entire crop as some cultivars are sensitive to TriStar 30SG.
Daniel F. Warnock
Greenhouse production of rosemary (Rosemarinus officinalis) as small potted Christmas-tree topiaries for holiday sales have become necessary for many companies marketing to large retail outlets. Topiaries must be sheared multiple times to obtain an acceptable Christmas-tree shape. Most production greenhouses use hand pruning shears or hand-held cordless grass shears to shape topiaries free hand or with the aid of a template. Crop size and uniformity can vary with these shearing methods. To create a more uniform rosemary Christmastree topiary for cultivar evaluations, a mechanical shearing device constructed from over-the-counter parts was developed at the University of Illinois. A detailed description of the design and construction of this mechanical shearing device is presented in this report.
Daniel F. Warnock
When breeding floriculture plants, one must have a targeted phenotype and genotype in mind before the initial cross-pollination event is performed. In the case of the floriculture breeding program at the University of Illinois, our initial goal was to develop a commercially acceptable, yet novel, Impatienswallerana(bedding plant impatiens) phenotype with improved resistance to the western flower thrips, Franklinella occidentalis, a significant insect pest in production greenhouses. This study describes the process used to obtain a large impatiens phenotype (>61 cm tall and >125 cm wide) with acceptable branching, leaf color, flower size, flower number, flower display, and flower colors with improved resistance to western flower thrips. A reliable and simple evaluation technique, based on the number of leaves expressing western flower thrips feeding damage after inoculation, was developed and utilized to create more resistant impatiens genotypes based on generation means. Using a 1 to 9 scale, mean damage ratings for the original germplasm populations 1, 2, and 3 were 5.18, 6.02, and 6.11, respectively, with the trend for populations 1, 2, and 3 skewed toward susceptible plants. Germplasm with novel phenotypes were derived from crosses with plants in populations 1 and 3 with commercial cultivars. These novel phenotypes had improved levels of resistance with a mean rating of 5.06 and a normal shaped distribution. The potential for improving resistance to western flower thrips feeding exists within available germplasm and the tools necessary for proper evaluations are available.
Daniel F. Warnock and Heather Lash
Greenhouses contain a vast array of insect, mite, and disease pests primarily managed by applications of conventional and biorational pesticides including insecticides, miticides, and fungicides. However, biorational pesticides have a narrow range of pest activity. As a result, greenhouse producers tank mix to broaden application activity. Research has demonstrated that tank mixing can result in either synergistic or antagonistic interactions for targeted pests. However, the impact of tank mixing insecticides and fungicides on predatory mites, Neoseiulus cucumeris, used to manage western flower thrips, Franklinella occidentalis, is unknown. The objective of this research was to determine how mixtures of four different pesticides (Conserve, Avid, Cleary's, and Decree), alone and in all possible combinations affect predatory mite survival in a laboratory bioassay. Individual 2-day-old adult mites, isolated in a cell of a bioassay tray, were exposed to one of the 15 pesticide treatments, or a water control. Treatments were replicated 15 times. Trays were held in an environmental chamber and mite mortality was assessed after 24 hours. Mite mortality was differentially impacted by some pesticide treatments when compared with the water control. One pesticide mixture, Conserve + Cleary's, significantly reduced mite survival compared to other pesticide treatments or the water control. Up to 70% of the mites exposed to this treatment died. The combination of Conserve + Cleary's should be avoided as a tank mixture when the biological control agent, Neoseiulus cucumeris, is used to manage western flower thrips.
Daniel F. Warnock and Heather Lash
The development of the Renaissance series of cut poinsettias, Euphorbia pulcherrima, presents unique opportunities and challenges to cut flower producers. This series has curled bracts, long stem length, excellent vase life, and is highly marketable. Literature indicates that this crop is suited for pot or bed production, but does not compare how cultural methods impact stem quality. This study assessed the impact of pinching on final stem quality and crop profitability. Uniform rooted cuttings of `Renaissance Red' obtained from a commercial supplier were transplanted into a 1.2 × 2.4 m bed containing a soilless media to obtain two plants per 0.09 m2. A total of 56 cuttings were used and grown using standard production techniques. Transplanting occurred on 29 July 2004 with half of the plants being pinched on 19 Aug. 2004. To minimize border effects, plants in the outside rows were discarded. Upon harvest, stem length, stem diameter, bract diameter, floral development, and number of axillary shoots were determined for 30 interior plants. Both pinched and unpinched plants produced marketable stems; however, unpinched plants produced longer thicker stems with larger bracts. The number of stems obtained per square foot was greater with the pinched plants. While overall quality was reduced, this increase in stem number offset potential lost profit. The production of quality cut stems of `Renaissance Red' poinsettias is possible with either pinched or unpinched plants.
Daniel F. Warnock and Rebecca Loughner
Western flower thrips [Frankliniella occidentalis (Pergande)] are small-bodied insects that prefer tight spaces such as flower buds and young leaves. Western flower thrips (WFT) pose sampling problems when compared with larger insects commonly found in plant canopies. Techniques to wash insects from plant canopies exist; however, plant type, plant age, and spatial distribution of insects within the canopy impact the efficacy of sampling. An experiment was designed to determine if 75% ethyl alcohol (EtOH), 0.1% detergent solution, or deionized water effectively wash WFT from the foliage of six coleus [Solenostemon scutellarioides (L.) Codd] genotypes inoculated with 32 adults and larvae. The number of WFT recovered after filtration through three mesh sizes varied between blocks and extraction solutions. The mean number of thrips recovered from coleus shoots with 75% EtOH solution, 0.1% detergent solution, or deionized water was 6.7, 8.4, or 0.8, respectively. The number of thrips recovered did not vary by coleus genotype, indicating the extraction solutions were equally effective on smooth leaf or curly leaf type plants. The 75% EtOH extraction solution is recommended for subsequent experiments.
Daniel F. Warnock and David W. Davis
European corn borer, Ostrinia nubilalis Hübner, is an economic pest of sweet corn. Consumer demand for high-quality, insect-free produce with minimal pesticide residue necessitates exploitation of various control options. Ear feeding resistance could reduce insecticide inputs. The inheritance of ear feeding resistance and silk channel length in the F1 derived from a diallel cross (Griffing's model I, method 2) of eight breeding stocks describing a wide range of feeding resistance was investigated in field experiments. Feeding damage, based on a 1 (no damage) to 9 (>10% ear damage) visual rating scale, and silk channel length of ears that had been manually infested at the ear tip with O. nubilalis were recorded. A significant (P ≤ 0.05) year by location interaction was found for ear feeding damage and silk channel length. Genotype ear feeding damage and silk channel length differences were significant (P ≤ 0.01) beyond genotype by environment (year and location) interactions. Mean feeding damage ranged from 2.5 (parents 1 × 7) to 8.8 (parent 2) and mean silk channel length ranged from 1.9 cm (parents 2 × 7) to 9.0 cm (parent 3). Ten of the 28 possible crosses (reciprocals combined) and 1 parent were classed as resistant (damage rating < 3.0). Eleven crosses, including all 7 involving parent 2, and 2 parents were susceptible (damage rating > 4.0). Pearson's correlation analysis indicated lower damage levels were weakly to moderately associated with increased silk channel length for both parents (r = –0.18) and progeny (r = –0.44). The general combining ability (GCA) component was significant (P ≤ 0.01) for ear feeding damage, suggesting additive effects control ear feeding damage. GCA and specific combining ability (SCA) effects did not account for silk channel length variability, suggesting strong environmental influences. Improved ear feeding resistance should be possible via recurrent selection with recombination.
B. Bejie Herrin and Daniel F. Warnock
Western flower thrips are an ever-increasing problem in greenhouse floriculture crops. Thrips resistance to pesticides as well as tighter regulations on pesticide use are making thrips management in the greenhouse more difficult. To improve host plant resistance, a study was conducted to determine if impatiens cultivars varied in their susceptibility to western flower thrips feeding damage. In a replicated study, nine impatiens cultivars were inoculated with about 30 thrips. Thrips were allowed to feed on individual plants during an 8-week period of growth. During plant growth, visual evaluations to estimate thrips feeding damage were conducted every 2 weeks. At the conclusion of the experiment, a final visual evaluation was made and thrips numbers were determined. Cultivars varied in estimates of thrips feeding damage. Several cultivars exhibited significantly reduced levels of thrips feeding damage. Of these cultivars, some had high thrips population levels, indicating tolerance, while other cultivars had low thrips population levels, an indication of antibiosis. One cultivar was determined to be highly susceptible to thrips feeding damage. This cultivar was so damaged by the end of the study, remaining plant material was unable to support thrips populations. Variability was found in the levels of thrips feeding damage and thrips population levels indicating the presence of tolerance and/or antibiosis. Because of detected variability, the potential for improving impatiens resistance to thrips feeding damages exists.
Daniel F. Warnock and Charles E. Voigt
Greenhouse production of rosemary (Rosmarinus officinalis L.) as small potted Christmas tree topiaries for holiday sales has become necessary for many companies marketing to large retail outlets. Topiaries must be sheared multiple times to obtain an acceptable Christmas tree shape. Cultivars vary in physical attributes, suggesting that they may respond differentially to mechanical shearing during production. This study assessed sixteen rosemary cultivars for their potential as potted Christmas tree shaped topiaries. Beginning July 2001, rosemary plants derived from vegetative propagation of shoot tips were provided high fertility and maximum light in a greenhouse. From August to October, plants were pruned monthly for a total of three shearing events. The crop was considered mature on the targeted market date of 5 Dec. Final plant quality was visually assessed using a 1 to 5 scale that accounted for taper, plant-to-pot ratio, canopy density, foliage quality, and overall appeal, with one point being removed for each factor not meeting industry expectations. The cultivars varied in their performance as Christmas tree shaped topiaries with most being unacceptable due to minimal basal branching or excessive leaf burn that negatively impacted shape, taper, and aesthetics. Six of the cultivars, `Taylor's Blue', `Herb Cottage', `Joyce DeBaggio' (Golden Rain), `Shady Acres', `Rexford' (Rex), and an unnamed clone, were suitable for commercial use having visual ratings ranging from 3.8 to 4.5. These cultivars had equally healthy foliage with little damage. `Taylor's Blue', `Shady Acres', `Joyce DeBaggio' (Golden Rain), the unnamed clone, and `Herb Cottage' had foliar damage ratings ranging from 3.3 to 3.8 and were not significantly different from the most healthy cultivars, `Logee White' (Thinleaf White), `Salem', and `Hill Hardy', all of which had mean ratings of 4.0. These cultivars should be examined for additional attributes that may enhance their performance as Christmas tree shaped topiaries.