Five antitranspirant materials, a horticultural oil, the fungicide chlorothalonil, and an untreated control were applied to rose plots using one of four application schedules. After 12 weeks, treatments were evaluated for their effectiveness in control of blackspot. Disease (P=0.0022) and defoliation (P=0.0008) showed significant treatment differences, while vigor and flowering were unchanged. Two antitranspirants, Stressguard 0.05% applied every 2 weeks and NuFilm17 1% alternated with chlorothalonil around rain events, gave similar disease control to weekly chlorothalonil applications. One antitranspirant, Vapor Gard, 1 % alternated with chlorothalonil around rain events, gave similar defoliation control to weekly chlorothalonil applications. These results indicate that blackspot disease can be effectively managed with fewer applications of chlorothalonil.
The pressure microprobe was used to measure cell turgor (ψp) in tomato pericarp tissue, and also to sample vacuolar fluid for the measurement of cell osmotic potential (ψs) in a nanoleter freezing point osmometer. In fresh tissue, cell ψs agreed well with the ψs of frozen-thawed whole tissue measured with a vapor pressure osmometer. Under a wide range of ripeness conditions however, and for both intact fruit and discs of fruit tissue, fruit cell turgor was consistently lower than expected, based on the values of cell ψs. When tissue discs were hydrated in aerated distilled water, disc fresh weight increased substantially (20 - 50+%), and both cell turgor and tissue ψs increased. Cell ψs however, remained relatively constant. These and other observations suggest that the turgor increase during hydration was largely due to losses of solute from the apoplastic space, partly by direct losses from the tissue, and partly by cell solute accumulation.
`Marsh' white grapefruit (Citrus paradisi Macf.) harvested from exterior canopy positions were less tolerant of 0.5 or 1.0 kGy irradiation than were interior fruit. Irradiation at 0.0, 0.5, or 1.0 kGy resulted in 0.0%, 24.3%, and 37.5% surface pitting of fruit, respectively. Pitting was reduced 30% by temperature conditioning with vapor heat at 38 or 42 °C for 2 hours. Exterior canopy fruit had ≈2-fold more pitting, had greater weight loss, and were firmer than interior canopy fruit. Fruit weight loss increased and firmness decreased as conditioning temperature and irradiation dose increased. Total soluble solids, titratable acidity, and flavor decreased with increasing irradiation dose. The peel of exterior canopy grapefruit was damaged more by irradiation than was that of interior fruit, but irradiation damage was reduced by temperature conditioning.
A commercially available cryoprotectant (50% propylene block copolymer of polyoxyethylene, 50% propylene glycol; trade name FrostFree) and an antitranspirant (96% di-1-p-menthene, i.e., pinolene, a terpenic polymer, 4% inert; trade name Vapor Gard) were evaluated for their ability to protect `Pik Red' tomato (Lycopersicon esculentum Mill.) and `Keystone Resistant Giant #3' pepper (Capsicum annuum L.) plants during frost and freeze occurrences in the field. Tests were conducted during four spring and two fall seasons. Protection from these products was not observed under field conditions when minimum air temperature reached -3.5C and -l.0C on separate occasions. Yields for treated and untreated plants were similar. Neither cryoprotectant injured the foliage in the absence of cold events.
The effectiveness of antitranspirant type and concentration on the leaf water relations of Saliva splendens F. `Firebird and Petunia × hybrida Juss. `Comanche'. Two film-forming antitranspirants, Cloud Cover and Folicote, were tested at three different concentrations in two different environments. The leaf water potential, stomatal conductance, and relative water content were evaluated. Transpiration per unit vapor pressure deficit and stomatal conductance for both crops decrease slightly but there was no trend with respect to the film type, environment or concentration rate. The leaf water potentials and relative water content did not show significant difference after antitranspirant application. In order for antitranspirant application to be of benefit to the growth of herbaceous plants, a more durable coating that remains semipermeable would have to be utilized.
Experiments were conducted in four independently controlled greenhouses. The purpose of these experiments was to measure the effect of humidity on transpiration and yields. Four different humidity treatments were evaluated: 1) high night and high day humidity levels (vapor pressure deficits <0.4 kPa), 2) high night and low day humidity levels (VPD >0.8 kPa), 3) high night and low day humidity levels, and 4) variable greenhouse humidity to maintain a set hourly transpiration rate. Transpiration rates were measured in the four greenhouses at 15-min intervals from Nov. 1993 to May 1994. Results show that high humidity reduces the hourly and daily transpiration levels significantly and has an impact on crop yields. Results also show that it is possible to regulate crop transpiration by calculating the transpiration rate for a set of VPD and solar radiation levels.
The benefit of applying an antitranspirant for protection of cranberry (Vaccinium macrocarpon Ait.) vines exposed to desiccating conditions was evaluated at four different sites, two sites per year, for a period of 1 year each. Overall, plots receiving one fall application of an antitranspirant produced more berries and greater total fruit mass the following year than did nontreated plots. Overall dry leaf mass was not significantly affected. At one site, treated plots had more flowering uprights and more flowers per upright per unit of ground area than the nontreated plots. For cranberry growers who cannot maintain a winter flood, one fall application of pinolene (Vapor Gard) may offer some protection against winter injury. Further research is needed to document long-term yield effects as well as to clarify the role of the antitranspirant in protecting exposed vines and floral buds against adverse winter conditions. Chemical name used: di-1-p-menthene (pinolene).
Three different rain protective covering methods for sweet cherry (Prunus avium) trees were tested with uncovered trees as control. The covers were a pitched cover mounted permanently, a similar cover mounted only when raining, and a permanent umbrella type enveloping the top and sides of single trees. Covers were mounted 3 weeks before and throughout the harvest period in two seasons with different weather conditions. All three covering methods increased the amount of marketable fruit from 54% on uncovered to 89% on covered trees in mean of 2 years. Fruit from umbrella covered trees had lower soluble solid content, lower juice color and lower ripeness compared with fruit from all other trees, reflecting the different microclimate in these trees such as frequently higher maximum temperatures and greater vapor pressure. The two pitched covers produced no significant changes in microclimate or internal fruit quality compared with uncovered trees.
Minimizing environmental stress in bedding plant and greenhouse and seedling development has occupied many researchers in academia and industry for many years. The dependence on single plant germination units (plugs) for bedding plant production and high value hybrid seed demand high rates of germination and successful seedling establishment. Pre-germinating or priming of seed is an important method of germination enhancement and methods and benefits of “priming” will be discussed. Environmental options to enhance seed germination of non-primed seed include control of vapor pressure deficit (VPD) and temperature.
Enhancement of seedling establishment through growth room and greenhouse technology includes the optimal use of CO2, temperature and light. Carbon dioxide fertilization on seedlings is receiving serious study and will be further elucidated.
`Karlo' and `Rosana', two Boston-type lettuce (Lactuca sativa L.) cultivars, were subjected to various light treatments in greenhouses equipped with one of two propane heating systems. Photoperiods of 16, 20, 24, or 24 hours for 2 weeks after transplanting and then 16 hours (24–16) and photosynthetic photon flux of 50 or 100 μmol·m–2·s–1 provided by supplementary lighting (high-pressure sodium vapor lamps) were compared to natural light during four experiments performed in greenhouses between Sept. 1989 and May 1990. Using supplementary lighting resulted in significant increases in biomass (≤270%), head firmness, and tipburn incidence and decreases in production cycle length (≈30%). Treatment effects were most pronounced during the months when natural-light levels were low. Fresh weights were higher for `Karlo' than `Rosana'; however, `Rosana' was less susceptible to tipburn than `Karlo'. In general, the radiant heating system resulted in earlier crop maturity and a higher incidence of tipburn than the hot-air system.