Effects of vermicomposts produced from food waste on the growth and yields of greenhouse peppers

Vermicomposts, produced commercially from food wastes, were substituted at a range of different concentrations into a soil-less commercial bedding plant container medium, Metro-Mix 360 (MM360), to evaluate their effects on the growth and yields of peppers in the greenhouse. Six-week-old peppers (Capsicum annum L. var. California) were transplanted into 100%, 80%, 60%, 40%, 20% or 10% MM360 substituted with 0%, 10%, 20%, 40%, 60%, 80% and 100% vermicompost. All plants were watered three times weekly with 200 ppm Peter's Nutrient Solution from the time of transplanting up to 107 days. Peppers grown in potting mixtures containing 40% food waste vermicomposts and 60% MM360 yielded 45% more fruit weights and had 17% greater mean number of fruits than those grown in MM360 only. The mean heights, numbers of buds and numbers of flowers of peppers grown in potting mixtures containing 10-80% vermicompost although greater did not differ significantly from those of peppers grown in MM360. There were no positive correlations between the increases in pepper yields, and the amounts of mineral-N and microbial biomass-N in the potting mixtures, or the concentrations of nitrogen in the shoot tissues of peppers. Factors such as: an improvement of the physical structure of the potting medium, increases in populations of beneficial microorganisms and the potential availability of plant growth-influencing-substances produced by microorganisms in vermicomposts, could have contributed to the increased pepper yields obtained.     

Pig manure vermicompost as a component of a horticultural bedding plant medium: effects on physicochemical properties and plant growth

This experiment was designed to characterize the physical, chemical and microbial properties of a standard commercial horticultural, greenhouse container, bedding plant medium (Metro-Mix 360), that had been substituted with a range of increasing concentrations (0%, 5%, 10%, 25%, 50% and 100% by volume) of pig manure vermicompost and to relate these properties to plant growth responses. The growth trials used tomatoes (Lycopersicon esculentum Mill.), grown in the substituted media for 31 days under glasshouse conditions, with seedling growth recorded in 20 pots for each treatment. Half of the tomato seedlings (10 pots per treatment) were watered daily with liquid inorganic fertilizer while the other half received water only. The percentage total porosity, percentage air space, pH and ammonium concentrations of the container medium all decreased significantly, after substitution of Metro-Mix 360 with equivalent amounts of pig manure vermicompost; whereas bulk density, container capacity, electrical conductivity, overall microbial activity and nitrate concentrations, all increased with increasing substitutions of vermicompost. The growth of tomato seedlings in the potting mixtures containing 100% pig manure vermicompost was reduced, possibly as a result of high soluble salt concentrations in the vermicompost and poorer porosity and aeration. The growth of tomato seedlings was greatest after substitution of Metro-Mix 360 with between 25% and 50% pig manure vermicompost, with more growth occurring in combinations of pig manure vermicompost treated regularly with a liquid fertilizer solution than in those with no fertilizer applied. Some of the growth enhancement in these mixtures seemed to be related to the combined effects of improved porosity, aeration and water retention in the medium and the high nitrate content of the substrate, which produced an increased uptake of nitrogen by the plant tissues, resulting in increased plant growth. When the tomato seedlings were watered daily with liquid inorganic fertilizer, substitution of Metro-Mix 360 with a very small amount (5%) of pig manure vermicompost resulted in a significant increase in the growth of tomato seedlings. Such effects could not be attributed solely to the nutritional or physical properties of the pig manure vermicompost. Therefore, it seems likely that the pig manure vermicompost provided other biological inputs, such as plant growth regulators into the container medium, that still need to be identified fully.     

The influence of humic acids derived from earthworm-processed organic wastes on plant growth

Some effects of humic acids, formed during the breakdown of organic wastes by earthworms (vermicomposting), on plant growth were evaluated. In the first experiment, humic acids were extracted from pig manure vermicompost using the classic alkali/acid fractionation procedure and mixed with a soilless container medium (Metro-Mix 360), to provide a range of 0, 50, 100, 150, 200, 250, 500, 1,000, 2,000, and 4,000 mg of humate per kg of dry weight of container medium, and tomato seedlings were grown in the mixtures. In the second experiment, humates extracted from pig manure and food wastes vermicomposts were mixed with vermiculite to provide a range of 0, 50, 125, 250, 500, 1,000, and 4,000 mg of humate per kg of dry weight of the container medium, and cucumber seedlings were grown in the mixtures. Both tomato and cucumber seedlings were watered daily with a solution containing all nutrients required to ensure that any differences in growth responses were not nutrient-mediated. The incorporation of both types of vermicompost-derived humic acids, into either type of soilless plant growth media, increased the growth of tomato and cucumber plants significantly, in terms of plant heights, leaf areas, shoot and root dry weights. Plant growth increased with increasing concentrations of humic acids incorporated into the medium up to a certain proportion, but this differed according to the plant species, the source of the vermicompost, and the nature of the container medium. Plant growth tended to be increased by treatments of the plants with 50-500 mg/kg humic acids, but often decreased significantly when the concentrations of humic acids derived in the container medium exceeded 500-1,000 mg/kg. These growth responses were most probably due to hormone-like activity of humic acids from the vermicomposts or could have been due to plant growth hormones adsorbed onto the humates.     

Numbers of pink sugarcane mealy bug, Saccharicoccus sacchari (Cockerell) (Hemiptera: Pseudococcidae), differ within seasons and among regions and stages of the sugarcane crop cycle

Abstract  The pink sugarcane mealy bug (PSMB; Saccharicoccus sacchari ) is widespread on sugarcane globally. PSMB infest above-ground storage tissue as it develops, feeding on phloem and producing exudate. It is not known, however, whether the level of infestations is the same in different sugar growing regions, or how population size varies year to year within a region. Field surveys of the number of nodes infested were conducted over five seasons in three mill-regions in northern Australia (Macknade, Kalamia and Marian) on plant and ratoon crops. The pattern of infestation was very similar across seasons (only in 1 year of very low rainfall was the increase in population delayed). In all three regions the proportion of nodes infested was similar but reached the maximum 1 month later in the Marian region compared with the Kalamia and Macknade regions. The Kalamia region was distinguished by the rapid decline in the number of nodes infested down to a very low level by March. In the Macknade region mealy bugs persisted at higher levels than the other two regions. The PSMB infestation started earlier and was much greater in ratoon crops than plant crops throughout the sampling period. The differences were more pronounced in the Macknade and Marian districts. These observations provide a firm basis from which future strategies to control PSMB can be developed.     

Starving Aphelinus asychis negatively affects host feeding and parasitism on Myzus persicae

Aphelinus asychis (Walker) is an effective biological control agent for many species of aphids found on various crops. To provide strategies for releasing these parasitoids into a crop ecosystem, the effects of a short-duration starvation experiment on A. asychis were measured under laboratory conditions using Myzus persicae (Sulzer) as the host on cabbage and chili pepper plants. The survival rate of starved A. asychis female adults decreased sharply as the starving time increased, and the longevity of the starved parasitoids also decreased significantly. The number of aphids killed by the parasitoids decreased gradually with the extended duration of starvation. In addition, the number of aphids on chili peppers and cabbages killed by starved A. asychis females over their lifespan was significantly lower than that in the control group. Our results indicated that a short period of starvation might not cause significantly negative effects on the parasitoids and may be beneficial for the control of M. persicae at low densities after 1?day; however, starvation for >1?day seriously affected the performance of A. asychis females over their entire lifespan. The parasitoids performed similarly when aphids were fed chili pepper or cabbage plants.     

The influence of earthworm-processed pig manure on the growth and productivity of marigolds.

The effects of additions of earthworm-processed pig manure (vermicompost) on the growth and productivity of French marigold (Tagetes patula) plants were evaluated under glasshouse conditions. Marigolds were germinated and grown in a standard commercial greenhouse container medium (Metro-Mix 360), substituted with 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% (by volume) pig manure vermicompost. The control consisted of Metro-Mix 360 alone without vermicompost. Plants were supplied regularly with a complete mineral nutrient solution for 121 days. The greatest vegetative growth resulted from substitution of Metro-Mix 360 with 30% and 40% pig manure vermicompost, and the lowest growth was in the potting mixtures containing 90% and 100% vermicompost. Most flower buds occurred in the potting mixtures containing 40% pig manure vermicompost (19.4 buds), and fewest in the potting mixtures containing 100% vermicompost. Marigolds grown in Metro-Mix 360 substituted with 90% and 100% pig manure vermicompost had the fewest and smallest flowers. After substitution of Metro-Mix 360 with 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% vermicompost, the marigold roots were larger than those of plants grown in the Metro-Mix 360 controls. Substitution of Metro-Mix 360 with any concentration of pig manure vermicompost, with all needed nutrients provided, increased the overall nitrate-nitrogen concentrations of the marigold leaf tissues at flowering stage. Some of the marigold growth and productivity enhancement, resulting from substitution of Metro-Mix 360 with pig manure vermicompost, may be explained by nutritional factors; However, other, factors, such as plant-growth regulators and humates, might have also been involved since all plants were supplied regularly with all required nutrients.     

Infestation by pyrethroids resistant bed bugs in the suburb of Paris,France

Bed bugs are hematophagous insects responsible for a re-emerging and challenging indoor pest in many countries. Bed bugs infestations may have health consequences including nuisance biting, cutaneous and systemic reactions. This resurgence can probably be attributed to factors such as increased international travel and development of resistance against insecticides. Resistance against pyrethroids has been reported several times from the USA and rarely in Europe. In France, very few data on bed bugs are available. The present study aimed to assess the infestation by bed bugs of a complex of two high-rise apartment buildings in the suburb of Paris and to evaluate their susceptibility to pyrethroid insecticides. We inspected for bed bugs 192 out of 198 apartments units (97%) and interviewed their residents. 76 (39.6%) apartments were infested. Among the 97 residents living in infested apartments, 53 (54.6%) reported bed bug bites. A total of 564 bed bugs were collected in the infested units. Bioassays showed that 54 out of 143 bed bugs were resistant to pyrethroids (37.8%; 95% confidence interval: 29.9-45.7%). DNA sequencing showed that all bed bugs tested (n = 124) had homozygous L925I kdr-like gene mutation. The level of pyrethroid resistance found indicates that this phenomenon was already established in the site and prompts the need to reevaluate the wide use of pyrethroids to control bed bugs.     

Glasshouse evaluation of systemic compounds, derivatives of dithiocarbamic acid and other fungicides for the control of clubroot

Seventy-one fungicides were mixed with an artificially infested soil/peat mixture in which cabbage seedlings were subsequently grown in pots in a glasshouse. The incidence and severity of clubroot and any toxic effects on the plants were recorded. Carbendazim, chloraniformethan, maneb, ferbam, zinc N-methyl dithiocarbamate, zinc diethanolamine dithiocarbamate and ziram were selected as suitable for further evaluation as they gave disease control as good as the standard calomel treatment and were of comparably low phototoxicity.     

Yield response of dual-toxin Bt cotton to Helicoverpa zea infestations

Field cage experiments were conducted to determine the impact of bollworms, Helicoverpa zea (Boddie), on yields of Bollgard II and Widestrike cotton, Gossypium hirsutum L. One-day-old bollworm larvae were infested in white flowers of Bollgard II and in white flowers and terminals of Widestrike cotton. The infestation levels included 0, 50, and 100% of white flowers for each type of cotton. Terminal infestations included one or two larvae per terminal on Widestrike cotton. Larvae were placed in flowers of Bollgard II cotton each day for 1 to 4 wk during the first 4 wk of flowering during 2003, 2004, and 2005 seasons and in the flowers or terminals of Widestrike cotton each day for 1 to 3 wk. Averaged across years and durations of infestation, yields of Bollgard II cotton were significantly reduced compared with noninfested Bollgard II cotton when 100% of white flowers were infested. For Widestrike cotton, there was a reduction in yield when 100% of white flowers were infested in 2005, but not in 2006. There was a significant relationship for cumulative numbers of white flowers infested on seedcotton yield of Bollgard II during one of the 3 yr of the experiment. The regression equation during that year had a slope of -0.77. No significant relationships were observed for cumulative numbers of white flowers infested on yields of Widestrike cotton. Results of the current experiment suggest bollworms will rarely cause yield losses of Bollgard II and Widestrike cotton. Future research will need to focus on developing specific thresholds for bollworms on Bollgard II and Widestrike cotton.     

Predation capacity and prey preference of <Emphasis Type="Italic">Chrysoperla carnea</Emphasis> on <Emphasis Type="Italic">Pieris brassicae</Emphasis>

The predation capacity and prey preference of larvae of Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae) on eggs or larvae of Pieris brassicae (Linnaeus) (Lepidoptera: Pieridae) in the absence and presence of cabbage aphids as an alternative prey were evaluated in laboratory experiments at 25°C. Both instars preyed upon butterfly eggs and larvae as well as on cabbage aphids with the third instar being the most voracious. The lacewings had a strong preference for caterpillars to butterfly eggs. In the presence of the aphids the predation on P. brassicae eggs or larvae was either completely abandoned or reduced by about 70%, respectively, by second instar lacewings and either reduced by about 80% or maintained, respectively, by third instar lacewings. Both instars thus had a clear preference for aphids compared to eggs of P. brassicae. However, second instar lacewings preferred aphids to caterpillars whereas the opposite was the case for third instar lacewings. The results indicate that 3rd instar C. carnea has a potential as biocontrol agent against P. brassicae.     

Shoot-feeding Aphids Promote Development of Gremmeniella abietina, the Fungal Pathogen Causing Scleroderris Canker Disease in Conifers

We tested experimentally whether shoot feeding aphids Cinara pinea (Mordv.) can promote the development of Gremmeniella abietina (Lagerb.) Morelet, a fungus which causes Scleroderris canker disease in conifers. Pine seedlings were infested with aphids at two different times, and subsequently inoculated with conidia of G. abietina at two different times. The degree of infestation was classified into three groups based on the number of aphids/seedling: none, one (low level), and three (high level). Because of parthenogenetic reproduction, the number of aphids increased during the summer, so we also used aphid numbers to explain the development of the symptoms. Necrosis caused by G. abietina was more prevalent in seedlings infested by aphids in June, and inoculated with fungus in July. Expressed as percents of the total length of the shoots, the necrosis had advanced 50%, 70%, and 95% with no, low, and high aphid levels, respectively. Canker formation was significantly greater when G. abietina conidia were inoculated in July, compared to August. In August, there were no statistically significant differences in the intensity of disease between aphid infestation levels, but the mean number of aphids was related to disease intensity. In the spring following infection, seedlings with aphids had more dead and fewer healthy terminal buds compared to seedlings without aphids.     

Leptodictya tabida (Hemiptera: Tingidae): a potential threat to sugarcane production in Lower Rio Grande Valley of Texas

Areawide surveys and replicated cultivar trials were conducted in 2001 and 2002 in sugarcane (Saccharum spp.) fields in the Lower Rio Grande Valley of Texas to assess the distribution and incidence of the sugarcane tingid Leptodictya tabida (Herrich-Schaeffer). L. tabida was found in all fields surveyed during both years, infesting 60 and 68% of the plants, respectively. The average percentage of leaves infested was 11% in 2001 and 15% in 2002. In 2001, 'CP70-1133' was the most infested, 'CP72-1210' was the least infested, and intermediate infestation levels were evident in 'CP70-321' and 'TCP87-3388'. In 2002, however, TCP87-3388 and CP70-321 were more heavily infested, and CP71-1240 and CP71-1405 were the least infested. Mean densities of L. tabida recovered per plant varied between 1.2 bugs on CP72-1210 and 5.1 on CP70-1133 in 2001, and in 2002, from zero bugs on CP71-1240 and CP71-1405 to 5.3 on CP72-1210. In the cultivar trials, cultivar differences also were evident in both plant and leaf infestation levels, and the proportion of immatures to total L. tabida populations; 'HoCP91-555' had the lowest L. tabida infestations and 'NCo-310' had the greatest levels in both years. Although >5000 L. tabida from the field were collected and kept in the laboratory, no parasitoids were found. The distribution of the infestations during the surveys and in the field trial evaluations suggested that L. tabida populations have been spreading in sugarcane across the Lower Rio Grande Valley. Potential varietal resistance mechanisms are discussed.     

Short-term effects of infestation by two aphid species on plant growth and shoot respiration of three legumes

The short-term effects of infestation by cowpea aphids ( Aphis craccivora Koch) and pea aphids [ Acyrthosiphon pisum (Harris)], both Homoptera: Aphididae, on plant growth and respiration of excised, intact shoots of cowpea [ Vigna unguiculata (L.) Walp. cv. Caloona], broad bean ( Vicia faba L. cv. Aquadulce) and garden pea ( Pisum sativum L. cv. Victory Freezer) seedlings were investigated, but not all plant-aphid combinations were utilized. Root, shoot and plant dry weights were significantly reduced within 10 days in the infested plants. Rates of total shoot respiration were significantly greater in infested plants within 10 days, and the increase was not due to increased alternative pathway activity but, rather, to increased cytochrome pathway activity. It is suggested that the aphid-induced increase in shoot respiration may be due to increased rates of photosynthesis, to substances injected into the phloem by the aphids and/or delayed senescence. These data indicate that aphid-infested shoots had a decreased carbon use efficiency.     

The potential of three native insect predators to control the rosy apple aphid, Dysaphis plantaginea

The potential of three aphidophagous predators, Adalia bipunctata, Aphidoletes aphidimyza, and Episyrphus balteatus to control the rosy apple aphid, Dysaphis plantaginea Pass., a major pest on apple in Europe, was assessed by means of laboratory and field cage experiments in Northern Switzerland. Under laboratory conditions, all three predators efficiently preyed upon D. plantaginea on apple seedlings. The searching success of larvae of A. bipunctata for individual aphids was not dependent on the size of branches of apple trees varying in leaf surface area from 150 cm² to 960 cm². Fifty and 70% of individual aphids were found and killed 6 hours and 48 hours, respectively, after release of single second instar larva of A. bipunctata. In a first field cage experiment in 1996, A. bipunctata, and to a lesser extent E. balteatus, proved to be effective and consistent predators of D. plantaginea during spring conditions, being little affected by cool temperatures and wet weather. In a subsequent field cage experiment in 1997, larvae of A. bipunctata and E. balteatus were released singly and in combination on aphid infested apple seedlings to study interactions between these two promising control agents. Both species had a significant negative effect on aphid population increase. The two species did not significantly interact and thus, their joint effect is best explained by an additive model. Combined releases of the two predator species reduced aphid densities to 5% of the control. This indicates the potential for augmentative releases of these native aphid predators to control D. plantaginea.     

Efficiency of variable-intensity and sequential sampling for insect control decisions in cole crops in the Netherlands

A total of 24 commercial fields of cabbages and Brussels sprouts were sampled in a grid fashion with 20–25 equally spaced cells with four plants per cell. Using this data base of 80–100 plants, we conducted computer stimulations to compare the treatment decisions that would be made for the major insect pests using published sequential sampling programs and a newly developed variable-intensity sampling program. Additionally, we compared the number of samples required to make the decision. At low thresholds (10–20%) for both Lepidoptera and cabbage aphids, variable intensity-sampling required a smaller sample size and provided more reliable decisions, while at high thresholds (40–50%) sequential sampling provided more reliable decisions. In both procedures, the occurrence of incorrect decisions was minimal. The number of cases in which a decision would not be reached after a 40-plant sample was lower for variable-intensity sampling. Considering the number of samples required to make a correct decision and the greater need for reliable decisions at lower thresholds, variable-intensity sampling was superior to sequential sampling. Additionally, variable-intensity sampling has the advantage of requiring samples to be taken in a greater area of the field and thus increases the probability of detecting localized infestations. Although variable-intensity sampling was not designed to classify pest populations for treatment decisions but rather to achieve sampling precision around the population mean, our present studies indicate that it can also be an effective method to aid in treatment decisions.     

Survival and Infectivity of Bursaphelenchus xylophilus in Wood Chip-Soil Mixtures

To determine the effect of soil environment on the life stages and total numbers of Bursaphelenchus xylophilus, nematode-infested wood chips alone and mixed with soil were incubated at 12 and 20 C. Nematodes were extracted at 2-week intervals for 12 weeks. Numbers of nematodes and percentage of third-stage dispersal larvae were greater at 12 C and in chips without soil. Percentage of juveniles of the propagative cycle was greater at 20 C and in chips with soil. Although B. xylophilus survived in chips with soil for 12 weeks, nematode numbers and life stage percentages changed little over time. To determine if B. xylophilus was capable of infecting wounded roots, infested and uninfested chips were mixed with soil in pots with white and Scots pine seedlings. Trees were maintained at 20 and 30 C and harvested at mortality or after 12 weeks. Only seedlings treated with infested chips contained nematodes. In field experiments, planted seedlings were mulched with infested chips to determine if nematodes would invade basal stem wounds. Among these trees, Scots pine was more susceptible than white or red pines to infection and mortality.     

Survey of bed bugs in infested premises in Malaysia and Singapore

A total of 54 bed bug‐infested sites (hotels, public accommodations, and residential premises) in Malaysia and Singapore was surveyed between July, 2005 and December, 2008. Only one species of bed bug was found, the tropical bed bug Cimex hemipterus (Fabricius). Bed bug infestations were common in hotels and public accommodations when compared to residential premises. The three most common locations of infestation within an infested premise were the bedding (31.1%), the headboard (30.3%), and cracks and crevices surrounding the baseboard, wall, or floor (23.5%). We speculate that the route of movement of bed bugs in hotels and public accommodations is more direct than in residential premises.     

Influence of vermicompost and cucumber cultivar on population growth of Aphis gossypii Glover

The melon aphid, Aphis gossypii Glover (Hem., Aphididae), is one of the most important pests of cucumber throughout the world. This aphid has a short generation time and high fecundity that result in an enormous reproductive potential, especially in cucumber‐growing greenhouses. Vermicomposts, which are produced by exploiting interactions between earthworms and microorganisms, may enhance plant growth and plant resistance against some pests and disease. In this study, the effects of vermicompost and cucumber cultivar (Cucumis sativus L.) on infestation levels with A. gossypii were evaluated. We conducted a factorial experiment with two cucumber cultivars (Royal and Storm) and five concentrations of vermicompost in the soil, including 0% (control), 10%, 20%, 30% and 50%, employing a randomized complete block design with four replicates. The experiment was conducted in a growth chamber at 25 ± 2°C, 65 ± 10% RH and a photoperiod of 14 L: 10 D h. The number of aphids was counted 3, 5, 7, 9, 12, 15, 18 and 21 days after infestation of cucumber seedlings by aphids. We found that in all vermicompost‐amended treatments, aphid numbers were lower than when plants were grown in soil without any vermicompost. The highest and lowest aphid counts occurred in the control treatment on cucumbers of the Royal cultivar and in the 30% and 50% vermicompost treatments on the storm cultivar, respectively. Overall, our study showed that the application of vermicompost has a high potential for reducing A. gossypii populations in cucumber cultures.     

Preliminary glasshouse and field tests of soil partial sterilants for clubroot control

Experiments were made on field plots and in individually dosed pots to investigate the effects of ten soil partial sterilants on percentage infection of cabbage with clubroot. Additionally, cores of naturally-infested soil or samples of artificially infested and buried soil removed from some treated plots were also sown with cabbage in a glasshouse and the seedlings then assayed for the presence of clubroot. There was evidence that the partial sterilants were optimally effective at different depths. Dowfume M.C.2 and Basamid having the unique properties of effectiveness at deep and shallow horizons of the soil respectively. Chloropicrin at 60 ml/m² and Dowfume M.C.2 at 98 g/m² were the most effective partial sterilants in controlling clubroot while Basamid and Telone were also considered to merit further testing. All other partial sterilants reduced percentage infection in pot experiments and field crops to varying extents although formaldehyde was least effective.     

EFFECTS OF RELATIVE HUMIDITY AND TYPE OF CONTAINER ON THE GROWTH OF F1 HYBRID ANNUALS IN CONTROLLED ENVIRONMENTS

The effects of three levels of relative humidity (40%, 65%, and 90%) and two types of containers (clay and plastic) on the seedling growth of three F₁ hybrid annuals were determined after 14 days of controlled-environment treatment. Forty percent relative humidity was severely limiting to the seedling growth of ‘Blue Blazer’ ageratum (Ageratum houstonianum Mill.), ‘Pink Cascade’ petunia (Petunia hybrida Vilm.), and ‘Double Eagle’ marigold (Tagetes erecta L.). Raising the relative humidity to 65% resulted in striking increases in fresh weight, dry weight, and leaf area, especially when clay containers were used. Height of the main shoot was increased significantly at 65% relative humidity but node number was influenced only slightly. Increasing the relative humidity further to 90% had no significant effect on fresh weight, dry weight, or percent dry weight for any of the three species, in either container. Leaf area was increased significantly at 90% only in ageratum seedlings grown in clay pots. Each species responded differently to the type of container used. The fresh weight and dry weight of petunia seedlings were significantly greater in plastic pots at every level of humidity while those of marigold seedlings were unaffected by the type of container used. Ageratum seedlings, on the other hand, had significantly greater fresh weights and dry weights in clay pots only at 90% relative humidity.