Acute heat stress can denature and aggregate proteins. The objective of this study was to determine how changes in the chemical and physical environment affected high temperature-induced turbidity and precipitation in pepper (Capsicum annuum L.) leaf extracts. High temperature stability of leaf extracts decreased as the tissue concentration increased. Control extracts exhibited a time-dependent change in resistance to turbidity and precipitate development, but the presence of polyvinylpolypyrrolidone stabilized the extracts. Ethylenediamine-tetraacetic acid had a less marked effect on turbidity and precipitation. Solution thermal stability increased as buffer pH increased from pH 6.0 to 7.0 regardless of whether the pH was adjusted before or after tissue extraction. Mannitol strongly stabilized pepper leaf extracts, but a surfactant lowered the thermal stability.
Heinz K. Wutscher
Seven-year-old `Hamlin' orange on Swingle citrumelo rootstock were sprayed with 30% methanol and 0.05% Silwet surfactant. There were four treatments: one spray application 48 days, two spray applications 48 and 32 days, and three spray applications 48, 32, and 20 days before harvest on December 2, 1993, with five untreated control trees. The treatments were arranged in five replications of randomized, complete blocks throughout the orchard. There were no significant differences in fruit weight, fruit diameter, rind color, rind thickness, juice content, soluble solids, total acids, solids/acids ratio, and juice color of 30 fruit samples collected from each tree. Leaf samples collected at harvest and analyzed for 12 elements showed higher Na and Cl levels in the leaves of the trees treated with methanol once than in those treated three times.
L. Cisneros-Zevallos, M.E. Saltveit, and J.M. Krochta
Fruit processing treatments, such as osmotic dehydration, washing, aqueous dips and coatings applications, and even microbial adhesion, depend critically on the surface energy of surfaces. Knowledge of these values can be used as reference targets for treatment formulations when complete wetting is necessary. Unripened and ripened tomato cultivars, `Ace' and `Castlemart', and bell pepper cultivars `California Wonder' and `Garden Sunshine' were characterized by color, firmness, and soluble solids, and evaluated for their surface energy. Calculated surface energy was obtained using Fowkes' equation by measuring contact angles of a series of pure surfactants of different HLB values on the fruit surface and by comparing with a reference paraffin surface of 25.5 dynes/cm. Results indicated that surface energies were similar between both types of fruits, while there were differences between maturity stages for tomato fruits. Surface energy in all cases was lower than 30 dynes/cm, indicating the hydrophobic nature of the epicuticular surface of the fruits tested.
Thomas A. Bewick, William M. Stall, Stephen R. Kostewicz, and Kenneth Smith
Cupric hydroxide, copper ammonium carbonate, basic copper sulfate, mancozeb, and a combination of cupric hydroxide and mancozeb were applied to American black nightshade (Solanum americanum Mill) before treatment with paraquat at 0.6 kg a.i./ha. Paraquat efficacy was reduced by all fungicides/bactericides, except a flowable formulation of basic copper sulfate, when compared to the herbicide only control. Compared to a surfactant only control, efficacy 1 week after paraquat application ranged from 86% with paraquat only to 42% with a combination of mancozeb and cupric hydroxide. Mancozeb and mancozeb in combination with cupric hydroxide resulted in greater shoot dry weight than the paraquat only control when measured 2 weeks after herbicide application. Chemical names used: 1,1'-dimethyl-4-4'-bipyridinium ion (paraquat); Mn, Zn ethylene bis diethyldithiocarbamate (mancozeb).
Peter Nitzsche, Gerald A. Berkowitz', and Jack Rabin
The objective of this research was to develop an effective antitranspirant formulation for reducing transplant shock (transitory water stress) in bell pepper (Capsicm annuum L.) seedlings. A formulation with a paraffin wax emulsion (Folicote at 5%) and a spreader/sticker type surfactant (Biofilm at 0.5%) was effective as an antitranspirant. This formulation was less phytotoxic than other formulations tested. Application of the formulation led to increased leaf water potential (Ψ w) i in transplanted seedlings for several days as compared with untreated transplants. When this, (relatively) nonphytotoxic formulation was used in a field study for 1 year, increased seedling Ψ w during a period of imposed water stress led to less leaf abscission and increased plant growth throughout the growing season. Chemical names used: alkylarylpolyethoxyethanol (Biofilm).
V. Esensee, D.I. Leskovar, and A.K. Boales
Nonomura and Benson (1992) reported that foliar applications of dilute solutions of methanol caused growth and yield increases and reduced water use in several crops. The request from commercial growers for explicit information regarding this report prompted our experiments using the same procedures. Growth of cantaloupe, pepper, cabbage, cauliflower and onion seedlings and mature plants were evaluated in the laboratory and greenhouse in 1993 and in the field in 1993 and 1994. Treatments of 0%, 10%, 20%, 30%, or 40% methanol (v/v water) with 0.1% surfactant generally did not cause significant growth differences. Stem diameters or lengths, shoot fresh and dry weights, or root fresh and dry weights of seedlings were unaffected as a result of methanol treatment. In the field, cabbage head weight was slightly higher after methanol application only in 1993, whereas cantaloupe fruit weight and number were significantly lower in 1993, but not in 1994.
Matthew W. Fidelibus and Frederick S. Davies
In Florida, gibberellic acid (GA3) is applied to citrus in the late summer or early fall to reduce senescence-related peel disorders of fresh fruit and to increase juice yield of processing oranges. Heavy rainfall may occur daily during this time that could reduce the efficacy of GA3 sprays. Experiments were conducted in 1998-99 and 1999-2000 to test the effect of timed “wash off” treatments on the peel color and peel puncture resistance (PPR) of `Hamlin' orange (Citrus sinensis [L.] Osb.) fruit that were previously treated with GA3. In Oct. 1998 and 1999, the canopy of 14- or 15-year-old trees were sprayed to runoff (≈10 L) with GA3 (45 g a.i./ha) and a non-ionic surfactant (Silwet, 0.05%). For the next 4 (1998-99) or 5 (1999-2000) h, three different GA3-treated trees each hour were then sprayed with ≈20 L of tap water to simulate rainfall that might remove or dilute the GA3. An additional three trees did not receive a GA3 or a washoff treatment. Fruit were harvested in Nov. 1998 and Jan. 1999 and Dec. 1999 and Jan. 2000 and evaluated for PPR and color. Data were subjected to regression analysis to determine the relationship between peel variables and time until washoff. In 1998-99, PPR and peel hue (level of green color) increased linearly with time until washoff, indicating that some GA3 uptake was still occurring after 4 h. In 1999-2000, PPR and hue increased linearly until about 3 h before washoff. Therefore, heavy rainfall within 3 to 4 h of application may reduce GA3 effectiveness, even when a surfactant is used.
David A. Bender, J. Wayne Keeling, and Roland E. Roberts
Large weeds, particularly amaranths, are a serious impediment to mechanical harvesting of jalapeno peppers. Several herbicides were applied in 1998 and 1999 postemergence topical (PT) to commercial fields when peppers had four to six leaves, or postdirected (PD) with a shielded sprayer ≈1 month later, and evaluated for crop injury, weed control, and effects on yield. Treatments were applied to four-row plots 9 m long with a CO<subscript>2 backpack sprayer. PT treatments included pyrithiobac sodium at 0.036, 0.053, or 0.071 kg·ha–1 a.i. with nonionic surfactant or crop oil concentrate, metolachlor at 1.68 kg·ha–1 a.i., and oxyfluorfen at 0.14 or 0.28 kg·ha–1 a.i.. PD treatments consisted of the same rates of pyrithiobac sodium with nonionic surfactant only, and the same rates of oxyfluorfen. Pyrithiobac sodium PT caused significant chlorosis (reduction in SPAD chlorophyll) in new foliage and reduction in plant height after 1 week, but plants recovered with no effect on final plant height, chlorophyll, or yield. No significant difference was observed between the two adjuvants. Metolachlor had no measurable effect on pepper growth or yield. Oxyfluorfen PT killed young apical tissue and caused chlorosis of immature leaves. Plants recovered, but plant height was reduced by 14% to 28% and yield by 11% to 43%. PD treatments had no effect on pepper growth or yield. All herbicides provided adequate weed control under light pressure. Pyrithiobac sodium appears to have potential as a postemergence herbicide for control of amaranth in jalapeno peppers.
Larry Kuhns and Tracey Harpster
Though glyphosate is considered to be a nonselective herbicide, conifer growers have long known that under certain conditions, they could contact the lower branches of their trees with the herbicide Roundup without injuring them. Species, time of application, rate of application, surfactant, method of application, and pruning wounds are all factors affecting conifer tolerance to glyphosate. Because Roundup was widely used by conifer growers, they were very concerned when the formulation of Roundup was changed to contain a more active surfactant. The new product was marketed under the name Roundup Pro. This change increased its herbicidal activity and raised the possibility that it could damage trees if applied in the same way as Roundup. To determine the tolerance of conifers grown in the northeast to a variety of glyphosate formulations, and sulfosate, a set of studies was established. Roundup, Roundup Pro, Glyfos, Accord, and Sulfosate were all applied to field grown hemlock, white fir, Canaan fir, fraser fir, douglas fir, Colorado spruce, and eastern white pine. Rates of 1 to 3 lb active ingredient/A were applied in the fall after new growth was hardened off. In general, it was found that the risk of injuring trees with Roundup Pro is greater than with the old formulation of Roundup. However, in all cases in which Roundup Pro caused more injury than Roundup, the Roundup Pro was applied at 3 lb active ingredient/A. This rate is double the rate recommended for this use. In calibrated, directed spray applications at 1.5 lb active ingredient/A or less, Roundup Pro should be safe for use around the species tested after their growth has fully hardened in the fall.
Wesley R. Autio, James Krupa, Jon M. Clements, and Duane W. Greene
In 2004, at full bloom, 3-year-old `Cameo'/G.16, `Gala'/M.9 NA-KBT337, `Gala'/G.16, and `Redmax'/B.9 apple trees were treated with naphthalene acetic acid (NAA, 1.5% in latex paint) in a 7.5-cm band completely around the central leader at the base of 2-year-old wood. NAA treatment reduced 2004 extension growth of the central leader by 14% and total shoot growth above the treatment area by 32%. `Cameo'/G.16 trees also were sprayed with prohexadione-Ca (250 ppm with surfactant and water conditioner) at full bloom, and additional trees were sprayed with ethephon (500 ppm with surfactant) 1 week after full bloom. These spray treatments were made only to the stems and foliage from the base of the central leader's 2-year-old wood to the top of the canopy. Ethephon reduced total shoot growth in 2004 by 26%, and prohexadione-Ca reduced it by 63%. Prohexadione-Ca also reduced fruit set of `Cameo' in 2004. Scoring (single knife cut completely around the circumference of the trunk) at the base of the 2-year-old wood in the `Cameo' trees resulted in a 23% reduction in leader growth and a 22% in totals shoot growth in the upper canopy in 2004. In 2005 at full bloom, 4-year-old `Golden Delicous'/B.9 trees were treated with NAA similarly to trees in 2004, except treatment at the base of 2-year-old wood was compared to treatment at the base of 1-year-old wood. Treating the base of 1-year-old wood reduced growth to a greater degree than comparable treatment at the base of 2-year-old wood. For the 1- and 2-year-old-wood treatments, the number of laterals produced from the 1-year-old wood was reduced 42% and 17%, and total shoot growth from 1-year-old wood was reduced by 49% and 31%, respectively.