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Peter D. Petracek, Moritz Knoche, and Martin J. Bukovac

Despite the widespread use of surfactants to enhance the performance of foliar applied chemicals, the mechanisms for this enhancement are poorly understood. The penetration of surfactant per se through the cuticular membrane (CM) may play a pivotal role. Thus, we examined CM penetration by octylphenoxy surfactants (Triton X series) using a finite dose (Franz) diffusion cell. The effect of hydrophile length was studied using 14C surfactant (15.9 mm in 20 mm citrate buffer: pH 3.2) with 3, 9.5, 12, 16, and 40 ethylene oxide units per molecule (EO). One 5-μl droplet of surfactant solution was applied to the outer morphological surface of CM enzymatically isolated from mature tomato fruit. The inner CM surface remained in contact with stirred buffer at 25°C. The buffer was sampled periodically through a side portal over 648 h. Penetration curves (time vs. % penetrated) for all surfactants were characterized by three phases: lag, linear, and asymptotic. Lag: There was no effect of EO on the length of the lag phase (average 5 h) Linear: Steady state penetration (0.6 to 1.1% / h) was inversely related to log EO content. Asymptotic: About 70% of applied short EO (3 to 16) surfactants penetrated while 25% of the 40 EO penetrated in 648 h.

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Peter D. Petracek, Moritz Knoche, and Martin J. Bukovac

Despite the widespread use of surfactants to enhance the performance of foliar applied chemicals, the mechanisms for this enhancement are poorly understood. The penetration of surfactant per se through the cuticular membrane (CM) may play a pivotal role. Thus, we examined CM penetration by octylphenoxy surfactants (Triton X series) using a finite dose (Franz) diffusion cell. The effect of hydrophile length was studied using 14C surfactant (15.9 mm in 20 mm citrate buffer: pH 3.2) with 3, 9.5, 12, 16, and 40 ethylene oxide units per molecule (EO). One 5-μl droplet of surfactant solution was applied to the outer morphological surface of CM enzymatically isolated from mature tomato fruit. The inner CM surface remained in contact with stirred buffer at 25°C. The buffer was sampled periodically through a side portal over 648 h. Penetration curves (time vs. % penetrated) for all surfactants were characterized by three phases: lag, linear, and asymptotic. Lag: There was no effect of EO on the length of the lag phase (average 5 h) Linear: Steady state penetration (0.6 to 1.1% / h) was inversely related to log EO content. Asymptotic: About 70% of applied short EO (3 to 16) surfactants penetrated while 25% of the 40 EO penetrated in 648 h.

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R.E. Byers, J.A. Barden, and D.H. Carbaugh

Terbacil applied to whole-spur `Delicious' apple (Malus domestica Borkh.) trees reduced photosynthesis and fruit set. The addition of the surfactant X-77 to terbacil sprays increased fruit thinning and leaf injury. Terbacil sprays applied to leaves only (fruit covered with foil) were as effective as when applied to leaves plus fruit. Dipping fruit alone in a terbacil solution did not cause abscission. Shading trees for 4 days with 92% polypropylene shade material reduced fruit set =50%. Spraying trees with carbaryl reduced fruit set by 25%. The combination of shade + carbaryl spraying reduced fruit set by 89%. Chemical names used: l-naphthalenyl methylcarbamate (carbaryl); 3-tert- butyl-5-chloro-6-methyluracil (terbacil); 2-chloroethylphosphonic acid (ethephon); alkaryl polyoxyethylene alcohols (X-77).

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Joshua D. Klein and Shlomo Cohen

Thinning of nectarines and peaches is largely an expensive manual task. We investigated the use of organosilicone surfactants as thinning materials that can be applied by mechanized sprayers. Of the surfactants tested, Silwet-408 (Witco) and Boost (Dow-Elanco) were the most effective thinning agents. Spray concentrations of 0.1% or 0.25% (v/v) applied at 30% and 60% full bloom, or 0.5% applied at 80% to 90% bloom, reduced by 50% the mass of fruitlets that had to be hand-thinned and increased the average weight of harvested fruit by up to 20%. When 0.75% to 1% surfactants were applied at 80% to 100% full bloom, fruit yield was reduced by up to 90%. The sprays did not affect fruitlets that had set already, nor did they cause damage to leaves or young shoots. Open flowers were more susceptible to the surfactants than were flowers at tight-bloom or balloon stage. Ion leakage from both petals and flower bases increased in proportion to concentration of surfactant applied, but there was no increase in lipid peroxidation.

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R.A. Neja, N.K. Dokoozlian, and N.C. Ebisuda

Field experiments conducted in 1994 (low-chill winter) and 1995 (high-chill winter) examined the effects of surfactants on the efficacy of hydrogen cyanamide (H2CN2) applied to `Perlette' grapevines (Vitis vinifera L.) in the Coachella Valley of California. In 1994, when surfactants were not used, vines treated with 1% and 2% H2CN2 exhibited similar rates of budbreak and grew more rapidly than vines treated with 0.5% H2CN2. When 1% or more of the surfactant Armobreak was used, budbreak was generally similar among all H2CN2 concentrations. The number of days after treatment required for 70% budbreak declined as H2CN2 and Armobreak concentrations were increased. Results were similar in 1995, however, budbreak was inhibited when vines were treated with 2% H2CN2 + 2% Armobreak. A separate experiment conducted in 1995 revealed that two other surfactants, Activator 90 and Agridex, had similar effects on the efficacy of H2CN2 as Armobreak. The results indicate that, when 2% surfactant is used, the standard commercial H2CN2 concentration used in California may be reduced 75% while maintaining treatment efficacy. Chemical names used: hydroxypolyoxyethylene polyoxypropylene ethyl alkylamine (Armobreak); alkyl polyoxyetheylene ether (Activator 90); paraffin petroleum oil (Agridex).

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Bruce W. Wood, Jerry A. Payne, and Michael T. Smith

A 4-year field study on pecan [Carya illinoinensis (Wangenh.) K. Koch] provided indirect support of the supposition held by some U.S. pecan growers that air-blast foliar sprays of potassium nitrate (KNO3) plus surfactant enhances nut yield. While these treatments did not measurably influence yield components, foliar K nutrition, or net photosynthesis, they did suppress “yellow-type” aphid populations. While air-blast sprays of water alone suppressed aphid populations, the inclusion of KNO3 plus surfactant provided an additional level of suppression.

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N.K. Dokoozlian, N.C. Ebisuda, and R.A. Neja

The effects of surfactants on the efficacy of hydrogen cyanamide (H2CN2) applied to `Perlette' grapevines (Vitis vinifera L.) grown in the Coachella Valley of California were examined in 1994 and 1995. Vines were pruned in mid-December in both years and treatments applied at 1000 L·ha-1 the following day to dormant spurs and cordons using a hand-held spray wand. In 1994, H2 CN2 was applied at 0.5%, 1%, or 2% by volume in combination with 0%, 0.5%, 1%, 2%, or 3% by volume of the amine-based surfactant Armobreak. In 1995, H2CN2 was applied at 0.5%, 1%, or 2% by volume in combination with Armobreak at 0% or 2% by volume. In 1994, budbreak rate was highly dependent upon H2CN2 concentration when 0 % to 1 % Armobreak was used; budbreak was generally most rapid for vines treated with 2% H2CN2 and slowest for vines treated with 0.5% H2CN2. When 2% or 3% Armobreak was used, however, little effect of H2CN2 concentration was observed. Results were similar in 1995, but the budbreak of vines treated with 2% H2CN2 + 2% Armobreak lagged behind that of vines treated with 1% H2CN2 + 2% Armobreak. The number of days after treatment required for 70% budbreak generally declined as the concentrations of H2CN2 and Armobreak were increased. A separate experiment conducted in 1995 revealed that several surfactants varying in chemical composition, Armobreak, Activator 90 and Agridex, had similar effects on H2CN2 efficacy. The results indicate that the addition of surfactants to H2CN2 solutions can significantly reduce the amount of active ingredient necessary for maximum efficacy on grapevines. Chemical names used: hydroxypolyoxyethylene polyoxypropylene ethyl alkylamine (Armobreak); alkyl polyoxyethylene ether (Activator 90); paraffin petroleum oil (Agridex).

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Bruce W. Wood, W. Louis Tedders, and James Taylor

Aphids cause major annual economic losses to the U.S. pecan [Carya illinoinensis (Wangenh.) K. Koch] industry and are becoming harder to control with standard pesticides. An evaluation of efforts by certain growers to suppress aphid populations using air-blast sprays of 0.05% Silwet L-77, a non-ionic super-wetting organosilicone surfactant, indicated that: 1) reductions in blackmargined aphid [Monellia caryella (Fitch)] levels were mostly attributable to the air-blast spray effect rather than to the Silwet L-77 component; 2) a 0.05% solution of Silwet L-77 reduced net photosynthesis (A) of foliage by 5% for at least 14 days post-treatment; and 3) the efficacy of 0.05% Silwet L-77 sprays is not substantially increased by doubling the volume of spray per tree (1868 L·ha-1). However, higher Silwet L-77 concentrations were highly effective in killing aphids, although there was little or no residual activity. A response curve indicated that air-blast sprays of orchard trees with 0.30% (v/v) Silwet L-77 (at 934 L·ha-1) are capable of reducing yellow pecan aphid (Monelliopsis pecanis Bissell) populations by at least 84% while only reducing A by ≤10%. Chemical names used: silicone-polyether copolymer (Silwet L-77).

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Stephen M. Southwick, Kitren G. Weis, and James T. Yeager

Hand thinning fruit is required every season to ensure large fruit size of `Loadel' cling peach [Prunus persica (L.) Batsch] in California. Chemical thinning may lower costs of hand thinning. A surfactant, Armothin {[N,N-bis 2-(omega-hydroxypolyoxyethylene/polyoxypropylene) ethyl alkylamine]; AKZO-Nobel, Chicago; AR}, was sprayed at 80% of full bloom (FB), FB, and FB + 3 days. The spray volume was 935 liters/ha. Concentrations of AR were 1%, 3%, and 5% (v/v). An early hand thinning in late April, a normal hand thinning at 13 days before standard reference date (early May), and a nonthinned control were compared to bloom-thinned trees for set, yield, and fruit quality. AR resulted in no damage to fruit; however, slight leaf yellowing and burn and small shoot dieback were seen at the 5% concentration. Fruit set, and therefore, the number of fruit that had to be hand thinned, were reduced with 3% AR applied at 80% FB and 5% AR applied at all bloom phenophases (stages of bloom development). Thinning time was reduced by 37% (5% AR applied at 80% FB), 28% (5% applied at FB), and by 20% (3% applied at 80% of FB), compared to the normally hand-thinned control. Although AR resulted in early size (cross suture diameter and weight) advantages, at harvest there were no significant differences in fruit size among all AR treatments and the normally hand-thinned control. Total and salable yields of AR treatments and the normally hand-thinned control were equal. Armothin shows promise for chemical thinning of peach when used as a bloom thinner.

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Bruce W. Wood

Of 18 commonly used adjuvants evaluated on pecan [Carya illinoinensis (Wangenh) K. Koch], a few exhibited potential for substantially suppressing net photosynthesis (A) and the conductance of foliage to water vapor (g sw) when used within their recommended concentration range; however, most provided no evidence of adversely influencing A or g sw. Suppression of gas exchange by certain adjuvants persisted at least 14 days after a single application. The recently developed organosilicone-based surfactants generally exhibited the greatest potential for suppression. These data indicate that orchard managers should consider the potential adverse influence of certain adjuvants when developing orchard management strategies.