Potted Chrysanthemum Research Articles

Efficacy of Entomopathogenic Nematode <I>Steinernema feltiae</I> (Rhabditida: Steinernematidae) as Influenced by <I>Frankliniella occidentalis</I> (Thysanoptera: Thripidae) Developmental Stage and Host Plant Stage

Entomopathogenic nematodes were investigated as an alternative biological control strategy for western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), in ornamental greenhouse crops, by using potted chrysanthemum as a model crop. The susceptibility of various life stages of F. occidentalis to different concentrations of the nematode Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae) was investigated in petri dish bioassays. This was followed with trials using potted chrysanthemums comparing the efficacy of nematode application to plants in vegetative (exposed habitat) versus flowering (cryptic habitat) stages. In both trials, the effect of the wetting agent Agral 90 (nonylphenoxy polyethoxyethanol), which is used in combination with the nematode spray, on F. occidentalis mortality was assessed. In petri dish trials, the prepupae and pupae were the most susceptible developmental stages of F. occidentalis to infection by S. feltiae. First and second instars were killed by very high rates of nematodes (> or =20,000 infective juveniles per milliliter), but corrected mortality was only approximately 28-37%. No significant mortality was observed for adult thrips. Results from the petri dish trials were confirmed on chrysanthemum plants. Foliar application of S. feltiae did not result in significant mortality in larvae or adults. No significant differences in efficacy were detected by application of nematodes on vegetative versus flowering chrysanthemum. Agral 90 had a significant impact on mortality on the first stage larvae and prepupae in the petri dish trials but not in the plant trials. Thrips control by S. feltiae in greenhouses may be partly or completely due to prepupal and pupal mortality.

Efficacy of Entomopathogenic Nematode Steinernema feltiae (Rhabditida: Steinernematidae) as Influenced by Frankliniella occidentalis (Thysanoptera: Thripidae) Developmental Stage and Host Plant Stage

Entomopathogenic nematodes were investigated as an alternative biological control strategy for western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), in ornamental greenhouse crops, by using potted chrysanthemum as a model crop. The susceptibility of various life stages of F. occidentalis to different concentrations of the nematode Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae) was investigated in petri dish bioassays. This was followed with trials using potted chrysanthemums comparing the efficacy of nematode application to plants in vegetative (exposed habitat) versus flowering (cryptic habitat) stages. In both trials, the effect of the wetting agent Agral 90 (nonylphenoxy polyethoxyethanol), which is used in combination with the nematode spray, on F. occidentalis mortality was assessed. In petri dish trials, the prepupae and pupae were the most susceptible developmental stages of F. occidentalis to infection by S. feltiae. First and second instars were killed by very high rates of nematodes (> or =20,000 infective juveniles per milliliter), but corrected mortality was only approximately 28-37%. No significant mortality was observed for adult thrips. Results from the petri dish trials were confirmed on chrysanthemum plants. Foliar application of S. feltiae did not result in significant mortality in larvae or adults. No significant differences in efficacy were detected by application of nematodes on vegetative versus flowering chrysanthemum. Agral 90 had a significant impact on mortality on the first stage larvae and prepupae in the petri dish trials but not in the plant trials. Thrips control by S. feltiae in greenhouses may be partly or completely due to prepupal and pupal mortality.

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

AbstractWe 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.

(69) Effects of Photoselective Shadecloths on Growth and Flowering of Potted Chrysanthemum

Controlling plant height is an important practice in the ornamental plant industry. Though commonly used, growth regulators are expensive, and there are concerns about environmental consequences and safety of workers. Alternative ways of controlling growth may be advantageous. The objective of this study was to determine the effects of photoselective shadecloths on the growth and flowering of `Arezzo' chrysanthemum. One-month-old potted `Arezzo' chrysanthemum plants were grown in a saranhouse in chambers built with PVC (polyvinyl chloride) pipe covered with 30% shadecloths—red, blue, gray, and black (control). The blue shadecloth was more effective in reducing plant height, with no differences among the other shadecloths. Plant canopy dimensions—greatest canopy width and average canopy width—did not show any differences among the shadecloths. The red shadecloth was more effective in hastening flowering, followed by the blue shadecloth. This was evident by flowering first occurring with the red shadecloth and initially the greatest number of buds showing color. Additionally, the red shadecloth had the highest proportion of the number of flowers to the combined number of flowers and buds showing color. Specifically, the total number of flowers was similar to the total number of buds showing color. In contrast with the other shadecloths, there was a greater number of buds showing color than the number of flowers. The most buds showing color occurred with the gray shadecloth. The three shadecloths resulted in a greater number of the combined buds showing color and flowers than the black shadecloth. In conclusion, photoselective shadecloths may provide an alternative to controlling plant height and altering the flowering pattern of potted chrysanthemums.

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.

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.

The Assessment of Ozone Treatment for Control of Fungal Diseases of Floriculture Crops in Greenhouses and Cold Storages

Ozone treatment has many advantages for control of fungal diseases. There are no residue concerns, no registration is required, and it is non-specific, therefore potentially effective against a broad spectrum of pathogens. However, ozone is known to cause plant damage. There is little information available on either the ozone tolerance of floriculture crops or the levels required to kill plant pathogens under commercial conditions. Nine floriculture crops (begonia, petunia, Impatiens, Kalanchoe, pot roses, pot chrysanthemums, lilies, snapdragons and Alstroemeria) were subjected to increasing levels of ozone. Trials were conducted at 5 and 20 °C (90% to 95% RH) and ozone exposure was for 4 days for either 10 hours per day (simulating night treatment) or for 10 minutes every hour. Damage was assessed immediately after treatment and after an additional 3 days at room temperature in ozone-free air. Trials were terminated for the crop when an unacceptable level of damage was observed. Trials to determine the lethal dose for actively growing pathogens (Alternaria alternata, Alternaria zinniae and Botrytis cinerea) and fungal spores were conducted under identical conditions. Ozone tolerance varied with plant type and ranged between <0.2 and 3ppm. Generally, the crops surveyed were more susceptible to ozone damage at the low temperature. As a group, the bedding plants were the least tolerant. Fungal spores were killed at treatment levels between 0.8 and 2 ppm ozone. The actively growing fungal mycelium was still viable at 3 ppm ozone when the trial had to be terminated due to ozone-induced structural damage in the treatment chambers. Under the trial conditions, only the Kalanchoe would be able to tolerate the high levels of ozone required to kill the fungal spores.

Manejo da irrigação na cultura do crisântemo em vaso, cultivar rage, cultivado em ambiente protegido

Dentre as dificuldades que os produtores têm encontrado ao adotarem o cultivo em ambiente protegido, destaca-se a falta de dados específicos sobre o uso racional da água e o desconhecimento da quantidade e do momento de irrigar. Esta pesquisa foi desenvolvida na propriedade de um produtor, no Distrito de Holambra II, região de Paranapanema - SP, em cultivos rotineiramente desenvolvidos pelo produtor, buscando melhor representatividade dos dados obtidos. O objetivo principal deste experimento foi identificar a tensão de água no solo que pudesse resultar em melhor qualidade comercial da cultivar de crisântemo "Rage", cultivado em vaso e mantido em ambiente protegido. O delineamento experimental foi o inteiramente casualizado, com duas repetições. Os tratamentos foram definidos por seis níveis de tensão de água: -2; -3; -4; -6; -10 e -30 kPa. Para cada tensão, foram calculadas a altura correspondente na coluna de mercúrio do tensiômetro, as lâminas e o tempo de irrigação. Os resultados obtidos demonstraram que a cultivar Rage obteve a maior porcentagem de vasos de alta qualidade (A1) no tratamento irrigado com a tensão de -4 kPa. O tratamento irrigado, quando atingia -30 kPa, resultou na menor porcentagem de vasos A1.

ESTIMATION OF AVAILABLE WATER AND EVAPOTRANSPIRATION OF POTTED PLANTS WITH A FREQUENCY-DOMAIN SENSOR

The relation between volume fraction water () of different peat-based growing media and permittivity (or dielectric constant, ) was determined using a frequency-domain (FD) sensor. After calibration in two organic mixes, could be estimated in rooted mixes in pot volumes ranging from 0.5 to 4 liter. Marketable plants had a within the range 0.5-0.65 after a subirrigation period of 10 minutes ( at capacity). Wilting point was at 0.12-0.20 for the potted ornamental plants Spathiphyllum, Chrysanthemum, Chamaecyparis and Viburnum. With the use of FD measurements, evapotranspiration of potted plants was determined under different transport and consumer conditions. Evapotranspiration varied between 7 and 91 g pot-1 day-1 for the crops. By dividing the amount of available water (derived from pot volume and difference between at capacity and at wilting point) with evapotranspiration data, potential transport time of potted plants was estimated to be at least 8 days. Both increased relative humidity (70 versus 40%) and decreased temperature (5 versus 15°C) decreased evapotranspiration during transport simulation up to 50%. Given the standard deviation in of 0.03-0.06 and desired accuracy (e.g. 0.05) it was calculated that 7-23 pots had to be measured in order to obtain a reliable sample estimation of water content. Application of the FD-sensor include quality control in the grower-retailer-consumer chain and on-line feed-back irrigation control

Produção de crisântemo (Dendranthema grandiflora Tzvelev.) 'Snowdon' em vaso I: doses e freqüências de aplicação de daminozide

O trabalho teve como objetivo avaliar a resposta de crisântemo através da análise de parâmetros fenométricos, ao redutor de crescimento Daminozide, pulverizado na cultivar de crisântemo de corte "Snowdon", cultivada em vaso. O estudo foi formado por dois ensaios com cinco repetições, usando delineamento experimental inteiramente casualizado em esquema fatorial 4 x 2, sendo formado por quatro doses de Daminozide (0, 2.000, 4.000 e 6.000 mg.L-1) e duas freqüências de aplicações (semanal e bissemanal). Os resultados evidenciaram que as diferentes doses e freqüências de aplicações reduziram a altura da planta, o número de nós, o comprimento de entrenós, o diâmetro da inflorescência e o comprimento do pedúnculo floral. Entretanto, constatou-se aumento dos diâmetros da haste e do pedúnculo floral. Na dose 4.000 mg.L-1 aplicada semanalmente, produziram-se os vasos de melhor qualidade, com altura da planta nos padrões recomendados para comercialização.

Pupation behaviour of western flower thrips (Thysanoptera: Thripidae) on potted chrysanthemum

Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is a serious pest of greenhouse vegetable and ornamental crops across Canada (Broadbent et al. 1987). Upon completing larval development, F. occidentalis either pupates on their host plant or drops to the ground before pupation occurs (Lewis 1973). Because several soil-dwellers prey on or infect F. occidentalis pupae (Gillespie and Quiring 1990; Helyer et al. 1995), assessing the proportion of individuals that pupate on the ground is of critical importance for developing pest management strategies. The present study provides the first quantitative assessment of the pupation behaviour of F. occidentalis.

MANIPULATING THE GIBBERELLIN RESPONSE TO REDUCE PLANT HEIGHT IN CHRYSANTHEMUM MORIFOLIUM

The aim of this work is to produce a dwarf (pot) chrysanthemum without the need for growth retardant sprays, by heterologous expression of the mutant gai (gibberellic acid insensitive) gene from Arabidopsis thaliana. The wildtype GAI gene encodes a repressor of gibberellin responses which is derepressed by gibberellin itself. The mutant GAI gene from Arabidopsis, gai, has lost the ability to be derepressed by gibberellin and thus continually suppresses gibberellin responses causing a dwarf phenotype. Several transgenic chrysanthemum lines have been produced, which are expressing the transgene and exhibit a range of dwarf phenotypes. Physiological measurements of growth, chlorophyll content and flowering time have demonstrated the extent of the transgene effects. Evidence so far suggests that gai could be used to produce novel pot Chrysanthemum varieties. Further genes are under consideration, which may also be used to change morphological characteristics and flowering time in chrysanthemum.

EFFECT OF NITROGEN AND SULFUR APPLICATIONS ON POT CHRYSANTHEMUM PRODUCTION AND POSTHARVEST PERFORMANCE. II. PLANT GROWTH RESPONSES

Chrysanthemums are one of the most important flowering plants produced internationally year round. The objectives of this research were to evaluate the effects of reducing nitrogen (N) applications by adding sulfur (S) and to determine if N * S interactions occur during the production and postharvest longevity of pot chrysanthemums. Pot chrysanthemum ‘White Diamond’ was grown in a peat-based medium following a typical production schedule except for fertilization. Plants received N at 50, 100, 150, or 200 mg L−1 in combination with S at 0, 5, 10, 20, or 80 mg L−1. Variables evaluated were leaf N and S concentrations, plant height, leaf area, days to bud set, and first flower color and inflorescence anthesis as well as size and longevity under simulated interior conditions. N * S interactions were significant for significantfor all plant growth response variables. Applications of 50 mg N L−1 resulted inpoor leaf N and S concentration and plants of questionable quality, yet maximal postharvest longevity. Nitrogen applied at 100, 150, or 200 mg L−1 in combination with at least 10 mg L−1 S had acceptable leaf N and S concentrations and produced plants of commercial quality with adequate postharvest longevity. Thus, N applied at 100 mg L−1 was the minimum acceptable fertilizer rate. Thus, N applications can be reduced by half when S is applied during commercial production without compromising postharvest longevity.

EFFECT OF NITROGEN AND SULFUR APPLICATIONS ON POT CHRYSANTHEMUM PRODUCTION AND POSTHARVEST PERFORMANCE. I. LEAF NITROGEN AND SULFUR CONCENTRATIONS

Chrysanthemums are one of the most important flowering plants produced internationally year round. The objectives of this research were to evaluate the effects of reducing nitrogen (N) applications by adding sulfur (S) and to determine if N* S interactions occur during the production and postharvest longevity of pot chrysanthemums. Pot chrysanthemum ‘White Diamond’ was grown in a peat-based medium following a typical production schedule except for fertilization. Plants received N at 50, 100, 150, or 200 mg L−1 in combination with S at 0, 5, 10, 20, or 80 mg L−1. Variablesevaluated were leaf N and S concentrations, plant height, leaf area, days to bud set, and first flower color and inflorescence anthesis as well as size and longevity under simulated interior conditions. In this article, leaf N and S concentrations are the variables discussed. In general, N* S interactions were significant for leaf S, but not leaf N concentration. Applications of 50 mg N L−1 resulted in poor leaf N and S concentration and plants of questionable quality. Nitrogen applied at 100, 150, or 200 mg L−1 in combination with at least 10 mg S L−1 had acceptable leaf N concentrations and produced plants of commercial quality. Thus, N applications can be reduced by half when S is applied during commercial production.

Phosphate and Potassium Retention and Release during Chrysanthemum Production from Precharged Materials: I. Alumina

Soilless root media have little capacity to retain PO4 or K, and this contributes to leaching of these nutrients during greenhouse crop production. The objective of this research was to evaluate the suitability of precharged alumina as a sole source of PO4 and K during greenhouse production of potted chrysanthemum [Dendranthema ×grandiflora Kitam. (syn. Chrysanthemum ×morifolium Ramat.)]. Phosphate and K adsorption and desorption curves were created at 25 °C for two particle sizes (0.5 to 0.9 and 1.8 to 3.2 mm) of alumina (Al2O3; acid-washed and unwashed), and a medium of 7 peat: 3 perlite (v/v) using solutions of KH2 PO4 (P at 0 to 20,000 mg.L-1). Based on these curves, 1.8 to 3.2 mm, unwashed alumina was selected for use in the studies. Precharged alumina was tested in two greenhouse studies at 10% and 30% (v/v) of a peat-perlite medium used to produce `Sunny Mandalay' chrysanthemum. Phosphate, K, and pH were determined on unaltered root medium solutions collected throughout the 10-week cropping cycle, and foliar analyses were conducted on tissue collected at the middle and end of the cycle. Potassium release was adequate to meet chrysanthemum demand for 4 weeks, but inadequate for the remainder of the production cycle. Precharged alumina retained and released PO4 at sustained concentrations (P at <2 mg·L-1) over the course of a 10-week cropping cycle. Growth of plants receiving PO4 from precharged alumina was not significantly different from the controls receiving liquid fertilizer (P at 46.5 mg·L-1) at each watering when precharged alumina comprised 30% of the medium, and only slightly less when precharged alumina comprised 10% of the medium. A phosphorus budget showed that while 36% (103 mg) of the applied PO4-P was lost in the leachate of the controls, only 0.1% (2 mg) was lost from plants produced with alumina-P. This research demonstrates that in a soilless medium with physical properties similar to standard commercial mixes, low but adequate PO4 concentrations can be achieved and sustained using current production practices.

Effects of air humidity on growth, flowering, keeping quality and water relations of four short-day greenhouse species

The short-day plants Begonia × cheimantha, Chrysanthemum morifolium (one pot and one cut cultivar), Euphorbia pulcherrima (poinsettia) and Kalanchoe blossfeldiana were grown at vapour pressure deficits (VPDs) of 155, 420 and 660 Pa (corresponding to 93, 81 and 70% relative air humidity, respectively). The lowest VPD delayed time to flowering by three to four days in pot and cut chrysanthemum but did not affect the other species. When decreasing VPD from 660 to 420 Pa, plant height was increased in chrysanthemum, Kalanchoe and poinsettia. A further increase in humidity increased the height in chrysanthemum and poinsettia, but not in Begonia. Leaf size in poinsettia and chrysanthemum was increased when VPD was decreased, but was reduced in Kalanchoe at the lowest VPD. High humidity enhanced the plant dry weight of poinsettia and Kalanchoe, decreased it in Begonia and had no significant effect in chrysanthemum. The highest plant quality was generally produced under the lowest humidity, with the development of more compact plants. Keeping quality as tested under indoor conditions was the same irrespective of humidity in Begonia, poinsettia and pot chrysanthemum, highest at 660 Pa VPD in Kalanchoe and at 155 Pa VPD in cut chrysanthemum. The water consumption per leaf area unit during growth was decreased by 39–58% in chrysanthemum, Kalanchoe and poinsettia when VPD was decreased from 660 to 155 Pa. Water loss from detached leaves generally increased with decreasing VPD during growth, particularly in Begonia and poinsettia.

The effect of night temperature on chrysanthemum flowering: heat-tolerant versus heat-sensitive cultivars

The effect of night temperature on the flowering of heat-tolerant and heat-sensitive cultivars of potted chrysanthemum ( Chrysanthemum xgrandiflorum) was examined in four experiments over a period of 4 years. Temperature reductions were imposed only while the plants were under black cloth using a combination of air-conditioning and under-cloth ventilation. The two heat-sensitive cultivars tested were ‘Yellow Mandalay’ and ‘Coral Charm’ and the two heat-tolerant cultivars were ‘Iridon’ and ‘Dark Bronze Charm’. Differences in time-to-flower (TTF) between heat tolerance classifications were less than anticipated. TTF was affected the most in ‘Iridon’, a heat-tolerant cultivar, decreasing by an average of 4.2 days/°C as mean diurnal temperatures (MT) decreased from about 26°C to about 23°C. TTF was affected the least in ‘Coral Charm’, a heat-sensitive cultivar, decreasing by an average of 2.8 days/°C over the same range. Inflorescence diameter, on the other hand, increased by as much as 9% in the two heat-sensitive cultivars but by only about 4% in the heat-tolerant cultivars. The results suggest that the heat-tolerant cultivars tested here may have been classified based on consistency of flower quality rather than TTF.

132 Fertilization Methods to Match Nutrient Supply with Demand for Potted Chrysanthemum

A greenhouse study was conducted in Autumn 1998 using standard cultural practices for potted chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura] to determine how fertilization affected plant growth and quality and nutrient leaching. Fertilization treatments included constant liquid fertilization until anthesis (LFA), constant liquid fertilization until disbud (LFD), slow-release resincoated fertilizer (SRF), and no-fertilizer control. Frequency of irrigation was determined gravimetrically, and leaching fractions maintained near 0.2. Plant growth and quality for LFA, LFD, and SRF met commercial crop standards. Nearly 60% of the total nitrogen applied with LFA was applied during the 4 weeks between disbud and anthesis, due to increased water demand. During the same period when liquid fertilization was discontinued for LFD, leachate electrical conductivity (EC) levels dropped from 4 to <1 dS·m-1. Leachate EC levels for LFA at anthesis remained high, but were <1 dS·m-1 for the other treatments. LFD and SRF drastically reduced the total amount of nutrients applied during the course of production compared with LFA. Use of an appropriate slow-release fertilizer or discontinued use of liquid fertilizer at disbud allow soluble salt levels to decrease during the latter weeks of the mum production cycle, when nutrient demand is low and water demand is high.

416 Blended Composts and N Rates on Growth of Potted Chrysanthemum

Potted `Boaldi', `Red Akron', and `Yellow Boaldi' growth performance were evaluated in eight substrates and four N rates. The substrates included Sunshine Mix 1, Pro Gro 300S, and six compost blends. The compost feedstocks were polymer dewatered biosolids (PDB) blended with poultry litter (PL) or yard wastes (YW) and peat:perlite at final ratios of 4:2:1:1, 3:3:1:1, and 2:4:1:1. Plants received N at 75, 100, 150, or 200 mg•L-1 from 21N-2.2P-16.6K twice a week. Number of flowers, height, diameter, and grade of plants that received N at 200 mg•L-1 treatment were significant better than those received the other N treatments. For all compost blends, premium-quality plants were produced with N at 200 mg•L-1 treatment and good-quality plants were obtained with the remaining N treatments. The control substrates produced good quality plants with N treatments at 150 and 200 mg•L-1, the remaining N treatments resulted in plants that were only salable at reduced price. `Red Akron' is a free-branching spray cultivar, had more flowers and branches than the other two cultivars.

Dispersal and Dispersion of Aphids (Homoptera: Aphididae) and Selected Natural Enemies in Spatially Subdivided Greenhouse Environments

Matrices of potted plants within greenhouses generate spatially subdivided habitats that may influence the spread of arthropod pests and the abilities of natural enemies to locate them. Thus, the goals of current research were to quantify dispersal of the aphids Myzus persicae (Sulzer) and Aphis gossypii (Glover) in potted chrysanthemum [ Dendranthema grandiflora (Tzvelev)] greenhouses; assess the relationship between dispersal capabilities and population dispersion of aphids; and determine the influence of spatial structure on the behavior of 2 aphid natural enemies, Chrysoperla rufilabris (Burmeister) and Aphidius colemani Viereck. Replicated studies conducted in greenhouses revealed no significant differences between M. persicae and A. gossypii displacement distances, diffusion constants, and dispersion indices. Studies of the effects of localized aggregations on M. persicae population dynamics revealed decreasing rates of population increase with increasing aphid densities. Natural-enemy displacement distances and diffusion constants were significantly greater for adult A. colemani compared with 3rd instars of C. rufilabris . In addition, the percentage of A. colemani observed to be actively searching for aphids was significantly higher than the percentage of C. rufilabris larvae. Differences in dispersal capability and searching activity may explain why A. colemani successfully located 97% of all aphid-infested pots compared with the 49% located by C. rufilabris within 10 h of their release. These results suggest that aphid biological control in chrysanthemum greenhouses may be enhanced by releasing sufficient numbers of natural enemies from points ≈2 times their displacement distance 10 h after their releases. These distances are 325 cm apart among benches for A. colemani and 68 cm apart within benches for C. rufilabris .