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Pik-Off (PO), a Ciba-Geigy Corp. product, has been field evaluated under an Environmental Protection Agency (EPA) experimental permit. Although PO does not usually produce as good abscission as some other chemicals, it appears satisfactory for many uses. From a cost and residue standpoint, PO appears to be in an advantageous position, and it is compatible with the ‘Valencia’ cultivar (Citrus sinensis (L.) Osbeck). PO should not be used with surfactants. Its effect is decreased by rain (within 24 hours of application) and low temperatures. PO is restricted by label as to total quantity which can be applied per ha. However, results of a series of volume versus concentration field tests showed that increased amounts of material per ha substantially improved abscission performance, particularly on larger trees.

Open Access
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Sprays of 3-[2-(3,5-dimethyl-2-oxocyclohexyl)-2hydroxyethyl]-glutarimide (cycloheximide) for abscission of early and midseason oranges loosen fruit, but utilizing this response with a shaker + pickup machine harvest system generally show economic gain only on very large trees. Abscission chemicals (abscisors) lend to overloosen the oranges that are easiest to remove, yet fail to loosen adequately those that are normally most difficult to remove. In Florida, current economic conditions do not justify fruit removal much less than 100%. Fruit drops of up to 80% will probably result if abscisors are used to reduce pull forces of nearly all fruits on a given tree to 2.2 kg, the theoretical level desired for mechanical harvesting.

Open Access
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Various weak acids produce citrus fruit abscission in Florida. Erythorbic (ascorbic) acid (1-2%) or hexamic acid (1-2%), alone or combined with citric acid (total concn 1-2%), produced acceptable abscission but only of early and midseason oranges for cannery use. Phosphoric acid (1/2%) and ferric chloride (0.5-2.5%) produced erratic loosening, phytotoxicity, severe peel injury, and sometimes damaged spray equipment. The type of peel injury resulting from weak acid sprays may cause extensive rotting (40% or more) if extended periods of wet weather occur prior to picking. As weather forecasting is not sufficiently accurate to predict conditions more than 48 hr in advance, and fruit abscission normally occurs from 3-7 days following spraying, the periodic economic losses that could be expected under these conditions preclude their use in Florida.

Open Access

Abstract

Factors contributing to genetic differences in low temperature seed germination of tomato (Lycopersicon esculentum Mill.) were examined by comparing the cold germinating (CG) accession PI 341985 the non-cold germinating (NCG) ‘Centennial’ and random F4 lines with varying low temperature germinating abilities. Rate of radicle elongation at 10°C was similar for both parental genotypes indicating that differences in emergence at 10° are not due to growth rates, but rather to more rapid initiation of germination activities in CG. Preincubation of seeds in hypertonic salt solutions enhanced rate of germination at 10°C equally in both lines, but did not substitute for the genetically based cold germinating ability. Low temperature germinating ability is associated with sprouting at high osmotic concentrations, and with a several fold higher rate of increase in peroxidase activity during the first 10 days of incubation at 10°. Germination at 10° of the NCG lines is improved by activated carbon in the germination media whereas no enhancement occurred in CG lines. Inhibition and/or delay in germination at 10° in NCG lines is due, in part, to low temperature induced formation of activated carbon adsorbable inhibitors of seed germination.

Open Access

This research focused on the potential use of common cattails (Typha latifolia) for removing metalaxyl and simazine residues from contaminated water. Specifically, it established toxicity thresholds to the herbicide simazine and characterized the uptake and distribution of simazine and metalaxyl by the plants. Simazine tolerance levels were determined by exposing plants to a series of six concentrations (0 to 3.0 mg/L) in aqueous nutrient media for 7 days. Metalaxyl toxicity was not evaluated because other studies indicated it was relatively non-toxic to plants. Toxicity endpoints measured included fresh mass production after 7 days exposure and 7 days post-exposure. Pesticide uptake and distribution were determined by growing plants in nutrient media amended with C-14-ring-labeled metalaxyl (0.909 mg/L) or simazine (0.242 mg/L) for 1, 3, 5, or 7 days. Plants were dissected and tissues were combusted and analyzed by liquid scintillation counting. Cattail fresh mass production was reduced 84% and 117% at 1.0 and 3.0 mg/L simazine, respectively, after 7 days of exposure. Metalaxyl and simazine activity in solution was reduced 34% and 65%, respectively, after 7 days. By day 7, activity from both pesticides was detected predominantly in the leaves. Uptake of each pesticide was correlated with water uptake throughout the 7 days. These results suggest that the common cattail may be a good candidate for incorporation into a phytoremediation scheme for metalaxyl and simazine.

Free access

Atrazine, simazine, and metalaxyl residues are often present in sprayer rinsates and in runoff water following application of the formulated products. As an initial step in the development of a constructed wetland for the phytoremediation of these pesticides in water, several plant species were evaluated for their tolerances to each. Plant species were chosen based on their aesthetics, tolerance to wetland conditions, and their potential to produce much vegetative growth. Species included: Acorus gramenius, Canna hybrida `King Humbert', Myriophyllum aquaticum, and Pontederia cordata. Plants were exposed to various concentrations of each pesticide dissolved in 10% Hoagland's nutrient media for 7 days. Tests were conducted under metal halide lamps with a light intensity of 400 μmol/m2 per s and a photoperiod of 16 h light: 8 h dark. Test endpoints measured included 7-day fresh mass production and chlorophyll fluorescence. A completely randomized statistical design with four replications of each concentration was utilized for each plant species. These tests indicate that all plant species were susceptible to atrazine and simazine in the 0.1 to 1 μg/ml range. Effected plants displayed concentration-dependent degrees of chlorosis and necrosis. Plants were more tolerant to metalaxyl concentrations in water. However, leaf chlorosis and necrosis did occur at concentrations greater than 25 μg/ml. Future research will quantify the uptake and mineralization potential for these plants and pesticides.

Free access

The Fordhook lima bean is a large-seeded lima bean grown in California for use by vegetable processors as an ingredient in frozen mixed vegetable packs. California represents one of the largest production regions for this bean because of the temperate climate. Unfortunately, as the population of California grows, the land available for producing this relatively low-valued crop continues to diminish. To overcome the loss of productive lands, we have initiated two projects, both focused on an increase in productivity. The first project is the improvement of current lines used by one processor. Due to the method of production of the seed bean, as well as the age of current lines in use, plant vigor and uniformity within the fordhook lima bean population has decreased over time. By using a modified single-seed descent method within the population, a certain level of improvement of production lines should be realized. Our second objective is in the development of a more heat-tolerant line, which could be grown in the inner valleys of California, where more land is available. Because of the limited availability of heat-tolerant Fordhook lima beans, we are currently investigating the possibility of using chemical mutagenesis to produce a more heat-tolerant variety.

Free access

Abstract

Four abscission chemical treatments (Acti-Aid, 20 ppm cycloheximide) (Release, 125 ppm 5-chloro-3-methyl-4-nitro-1H-pyrazole) (Acti-Aid, 5 ppm + Sweep, 250 ppm chlorothalonil + Release, 125 ppm) and (Pik-Off, 300 ppm glyoxal dioxime) were applied to the same orange trees (Citrus sinensis (L.) Osbeck, cv. Hamlin and Pineapple) for 3 consecutive years to aid harvest with a shaker-catchframe system. The treatments had no significant effect on subsequent fruit yield for years not influenced by freezing temperatures.

Open Access
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Abstract

Mechanical harvesting has, of course, long been standard for many annual crops, the “combine harvester” for wheat being an early, and successful, example. In some instances (e.g., tomato, plant breeders have “tailor made” cultivars to adapt them to mechanical harvesting. Typically, such annuals are destroyed in harvesting. The plant must be preserved with perennial crops, although sometimes considerable injury to the plant can be acceptable when (as for grapes or raspberries) the plant is severely pruned annually. Substantial damage to the plant (tree) is not acceptable, in mechanical harvesting of tree crops, but leaf damage is of minor consequence for deciduous tree crops, and the fruit is biologically destined to abscise; if it is not harvested. Damage to the product is not a problem, it will soon fall naturally for some deciduous tree crops (particularly nuts of various kinds). In contrast, mechanical harvesting of citrus fruits involves quite extraordinary problems. The tree is evergreen and substantial leaf damage is not acceptable. The fruit has no clearly defined abscission period. The same grapefruit that might be picked in October can hang on the tree until May. Citrus fruits are extremely subject to decay. ‘Valencia’ (an important cannery orange cultivar) takes 12 to 18 months from bloom to acceptable maturity to complicate matters further. Thus, there are 2 crops on the tree at harvest time; mature fruit that are to be harvested and immature fruit that must not be damaged or removed. It is apparent after 20 years and millions of dollars spent in Florida that the problem (particularly for ‘Valencia’) is as much biological as it is mechanical. The fruit, but not the leaves, must be made to abscise and, for ‘Valencia’, the tree must retain the immature crop while releasing the mature fruit.

Open Access

Plant response to photoselective plastic films with varying spectral transmission properties was tested using lisianthus (Eustoma grandiflorum) `Florida Pink', `Florida Blue', and `Florida Sky Blue'. Films were designated YXE-10 (far-red light-absorbing film) and SXE-4 (red light absorbing film). Light transmitted through YXE-10 films reduced plant height compared to control plants by 10% (`Florida Blue'), and stem dry weight by 19% to 40%, but the response varied by cultivar. Internode length was reduced by 10% to 19% when `Florida Pink' and `Florida Sky Blue' plants were grown under YXE-10 films. Leaf and root dry weights were not affected by YXE-10 films, with the exception that `Florida Sky Blue' plants had a lower leaf dry weight than the control plants. Light transmitted through SXE-4 films increased plant height of `Florida Pink' plants by 15% but not of `Florida Blue' or `Florida Sky Blue.' Regardless of cultivar, dry weight of leaf, stem and root tissue was not affected by SXE-4 films as compared to control films. The average number of days to flower and bud number were not affected by YXE-10 or SXE-4 films, regardless of cultivar. The results suggest that selective reduction of far-red wavelengths from sunlight may be an alternative technique for greenhouse production of compact plants, but the magnitude of the response is cultivar specific.

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