Effects of Tissue Phosphorus and Nitrogen in Impatiens wallerana on Western Flower Thrips (Frankliniella occidentalis) Population Levels and Plant Damage

Host-plant nutritional status may affect the incidence and development of western flower thrips (WFT; Frankliniella occidentalis Pergande). Two greenhouse experiments were conducted to determine the responses of WFT population levels on impatiens (Impatiens wallerana Hook.f.) when plants were fertilized with commercially practiced rates of nitrogen (N) and phosphorus (P). Impatiens `Dazzler Violet' were grown with nutrient treatment combinations of 2 N rates (8 and 20 mm) by 2 P rates (0.32 and 1.28 mm). Individual plants grown in thrips-proof cages were inoculated with WFT at 2 or 4 weeks after transplant, in separate experiments, representing vegetative or reproductive stages of plant growth, respectively. Plants were destructively sampled weekly for 4 weeks following inoculation. Plant tissue N and P concentrations were significantly different across treatments: 8 and 20 mm N resulted in 4.9% and 6.3% N in tissue, respectively; 0.32 and 1.28 mm P resulted in 0.37% and 0.77% P in tissue, respectively. Nitrogen rates had no effect on WFT population levels. However, 4 weeks after inoculation with adult female WFT during the vegetative growth stage, plants fertilized with 1.28 mm P had more adult WFT than those fertilized with 0.32 mm P. Feeding damage varied depending on whether plants were inoculated in the vegetative stage with adult WFT or during reproductive growth with immature WFT. Plant size and number of flowers were lower in plants inoculated during the vegetative growth stage with adult WFT but were not affected when inoculation with immature WFT occurred during the reproductive stage, as most WFT were found feeding inside the nectariferous spurs of the flowers. Tissue N was lower in WFT-inoculated plants compared to noninoculated plants in both experiments.

Growth of Bedding Plants in Substrates Amended with Compost and Fertilized with Three Different Release Rates of a Controlled-release Fertilizer Product

Growth of `Aladdin Peach Morn' petunia (Petunia × hybrida) and `Accent White' impatiens (Impatiens wallerana) was compared in substrates containing 0%, 30%, 60%, or 100% compost made from biosolids and yard trimmings and fertilized with Nutricote Total 13-13-13 (13N-5.7P-10.8K) Types 70, 100, and 140 incorporated at rates of 0.5x, 1x, 2x, or 3x (x = standard application rate for a medium-feeding crop). Petunia shoot dry weight of plants fertilized with Type 70 incorporated at 0.5x increased as the percentage of compost in the substrate increased from 0% to 60% and then decreased, while shoot dry weight of plants fertilized with Type 70 incorporated at 1x, 2x, or 3x increased as the percentage of compost increased from 0% to 30% and then decreased. Impatiens shoot dry weight of plants fertilized with Type 70 incorporated at 0.5x and 1x also increased as the percentage of compost increased from 0% to 30% and then decreased, while shoot dry weight of plants fertilized at 2x and 3x decreased as the percentage of compost increased from 0% to 100%. Both petunia and impatiens shoot dry weight of plants fertilized with Type 100 and Type 140 incorporated at 0.5x, 1x, 2x, or 3x increased as the percentage of compost increased from 0% to 60% and then decreased.

Resistance to Western Flower Thrips Feeding Damage in Impatiens Populations from Costa Rica

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.

Resistance of Impatiens Germplasm to Western Flower Thrips Feeding Damage

Western flower thrips (WFT) [Frankliniella occidentalis (Pergande)] are an ever-present problem in greenhouse floricultural crops. To determine if host plant resistance varied in impatiens [Impatiens wallerana Hook. f.] nine genotypes were evaluated for resistance to WFT feeding damage. Individual insect-free plants of each genotype were inoculated with ≈30 laboratory-reared WFT. Thrips were allowed to feed on individual plants for a 4-week period during which visual evaluations were conducted every 2 weeks to estimate feeding damage. Feeding damage varied among genotypes and increased with time. At 4 weeks after inoculation, `Cajun Carmine' and `Super Elfin Lavender' had significantly less feeding damage than all other genotypes. The San Vito Wild-type germplasm was determined to be highly susceptible to thrips feeding damage based on visual evaluations. Because WFT feeding damage varied among genotypes, the potential for improving impatiens resistance to WFT exists within commercially available germplasm.

Mulching Reduces Water Use of Containerized Plants

Colorful baskets of flowering annuals are popular with home gardeners, but these containerized plants require frequent waterings. Mulching of field soils is a proven way to conserve soil moisture. This study was conducted to see if mulching would reduce the need to irrigate containerized plants. Adding either pine bark or sphagnum moss mulch to potted `Impulse Rose' impatiens (Impatiens wallerana) plants reduced the frequency of irrigations when the plants were small and had not yet reached canopy closure. Mulching had no effect on plant height or flowering.