Picloram Absorption Research Articles

Adjuvant Effects on Imazethapyr, 2,4-D and Picloram Absorption by Leafy Spurge (Euphorbia esula)

Laboratory experiments were conducted to identify adjuvants that improve absorption of imazethapyr, 2,4-D amine, and picloram by leafy spurge. Adjuvants (0.25% v/v) included crop oil concentrate (COC), methylated seed oil (MSO), nonionic surfactant (NIS), organosilicones (Silwet L-77®, Sylgard® 309, Silwet® 408), 3:1 mixtures of acetylinic diol ethoxylates (ADE40, ADE65, ADE85) with Silwet L-77, ammonium sulfate (2.5 kg ha−1), and 28% urea ammonium nitrate (UAN, 2.5% v/v). Adjuvants were combined with14C-herbicide and commercially formulated herbicide product. Leaves were harvested 2 DAT, rinsed with 10% aqueous methanol to remove surface deposits of herbicide, and dipped in 9:1 hexane:acetone to solubilize cuticular waxes. Imazethapyr absorption increased by 38 to 68% when UAN was combined with COC, NIS, or MSO. Total absorption of imazethapyr plus COC, MSO, or NIS exceeded 86% 2 DAT when UAN was added. Urea ammonium nitrate reduced the amount of imazethapyr associated with the cuticular wax by 2.0%. Imazethapyr absorption was similar on both the abaxial and adaxial leaf surface when UAN was not added; however, 12% more imazethapyr was absorbed from the abaxial leaf surface than from the adaxial leaf surface when UAN was combined with Sylgard 309. Uptake of 2,4-D ranged from 54 to 78% and was greatest with Silwet 408 and 3:1 mixture of ADE40: Silwet L-77. Picloram absorption ranged from 3 to 19%. Buffering picloram treatment solutions to pH 7 and including 2.5 kg ha-1ammonium sulfate increased picloram absorption to 37%.

Picloram Absorption by Broom Snakeweed (Gutierrezia sarothrae) Leaf Tissue

Foliar absorption of picloram by broom snakeweed, a rangeland shrub, was investigated. Picloram uptake into leaf, axillary bud, and stem tissues was similar. In addition, picloram uptake by leaf tissue from greenhouse- and field-grown broom snakeweed did not differ. Picloram accumulated rapidly and absorption saturated between 15 min and 1 h of application; no further absorption occurred through 72 h with maximum uptake ca. 15% of applied picloram. Picloram content increased linearly with increasing external picloram concentration, implying that movement of the herbicide across the cuticle is via diffusion. Absorption was dependent on relative humidity and temperature with the greatest uptake at 94% relative humidity and 35 C, respectively. Absorption was pH dependent; picloram absorption was greatest at pH 4 and least at pH 8. In addition, picloram absorption was less at pH 3 compared to pH 4. These results provide evidence that picloram is absorbed across the cuticle via simple diffusion and absorption is dependent on environmental conditions and solution pH at and following application.

Environment and Spray Additive Effects on Picloram Absorption and Translocation in Leafy Spurge (Euphorbia esula)

Relative humidity after application, spray additives, and solution pH affected both foliar absorption and translocation of14C-picloram to leafy spurge roots.14C-picloram absorption increased from 11 to 34% and translocation increased from 5 to 21% as time at posttreatment humidity increased from 0 to 48 h. Absorption and translocation were not different when pre- or posttreatment temperatures were 30/18 or 18/10 C (day/night).14C-picloram absorption and translocation to the roots were 18 and 6%, respectively, when applied alone, and increased to 46 and 12%, respectively, when applied with ammonium sulfate at 2.5 kg/ha. Absorption and translocation were unaffected by ammonium nitrate. Foliar absorption and translocation of14C-picloram in leafy spurge were unaffected by pH of unbuffered spray solution but increased at least 50% when applied in a solution buffered at pH 4.8 with trisodium citrate. Foliar absorption in detached leafy spurge leaves increased from 26 to 51% of applied14C as the citrate buffer concentration increased from 0.01 to 0.1 mM, respectively.

Absorption and Translocation of Picloram by Lindheimer Pricklypear (Opuntia lindheimeri)

Removing the epicuticular wax from mature pads (cladophylls) of Lindheimer pricklypear increased picloram absorption by four- to sixfold in the laboratory, while the addition of surfactant had little effect on absorption. Absorption decreased with increasing pH of the picloram solution, indicating that picloram diffused through the cuticle as the undissociated molecule. Picloram entered detached pads at the areoles more readily than through the surrounding cuticle. In the glasshouse, whole plants consisting of an old, mature pad supporting a young, growing pad absorbed picloram very slowly whether picloam was applied as a spray to old or young pads or to the soil. About 90 and 80% of the applied picloram remained on the waxy surface of old and new pads, respectively, and about 2% of the applied picloram was recovered from within the epicuticular wax after 30 days. Picloram concentrations within pads treated in the glasshouse were greater when the herbicide was applied to new pads (4.6 μg/g) than old pads (1.9 μg/g) after 30 days. More picloram was translocated basipetally from treated new pads to untreated old pads than in the opposite direction, but concentrations in untreated pads were low (<1 μg/g). Little picloram was absorbed by roots, compared to pads, and little was translocated into or out of roots. These results conflict with the view that the effectiveness of picloram for pricklypear control is attributable to extensive root uptake and acropetal transport. However, observations of plants 6 months after treatment indicated that soil applications were more effective than sprays in the glasshouse.

Some aspects of the absorption of picloram by gorse (Ulex europaeus L.)

Summary:Plants of Ulex europaeus were grown from cuttings and studies made of the absorption of 14C‐picloram applied with unlabelled 2,4,5‐T. In vivo experiments in a growth chamber showed that absorption ceased after 10 h, but was resumed on wetting. In in vitro experiments the Q10 and the activation energy for uptake decreased with increasing temperature. Absorption was increased by addition of non‐ionic surfactants, by lowering the pH and by removal of cuticular wax. Gorse shoots were shown to have a high wax content but scanning electron microscopy revealed no obvious wax structures and the contact angle of spray droplets was less than 900, indicating that the surfaces were not difficult to wet.

Uptake of picloram by roots of alfalfa and barley

Uptake of [14C] picloram (4-amino-3,5,6-trichloropicolinic acid) from culture solution by alfalfa (Medicago saliva L.) and barley (Hordeum vulgare L.) seedlings was investigated to determine to what extent passive and (or) active mechanisms are involved in the uptake of the herbicide by roots of intact plants. The roots of both species had similar absorption patterns consisting of rapid initial uptake lasting 1 to 2 h, followed by continuing absorption at a markedly lower rate during the rest of a 12-h treatment period. Initial uptake both by roots and whole plants was not significantly reduced by 1.0 mM NaN3, whereas continuing absorption was depressed by this inhibitor. Q10 values were 1.4 for alfalfa and 1.0 for barley for the first 1–2 h of uptake, whereas for subsequent periods the values were consistently greater than 2.0. Evidently, uptake during the initial phase of entry is governed by passive processes, while continuing absorption is controlled, at least in part, by active mechanisms. Much of the picloram taken up by alfalfa and barley roots during a 4-h treatment period was released rapidly to unlabelled nutrient solution. Uptake by both species was decreased in the dark and enhanced in the presence of sucrose. The results of inhibitor studies suggest that picloram absorption by alfalfa plants is more dependent on a supply of metabolic energy than is uptake by barley plants. In most instances, total accumulation of picloram in 4 h was much greater in alfalfa plants than in barley plants of nearly equivalent mass. This difference may account for at least part of the difference in susceptibility of alfalfa (sensitive) and barley (tolerant) to the herbicide. Alfalfa roots always contained a much greater proportion of the total amount of picloram in the plant than did barley roots.

Ammonium Sulfate Enhancement of Picloram Activity and Absorption

Picloram (4-amino-3,5,6-trichloropicolinic acid) herbicidal activity on seedlings of guava (Psidium guajavaL.), strawberry guava (Psidium cattleianumSabine), and dwarf beans (Phaseolus vulgarisL. ‘Bountiful’) was increased by adding ammonium sulfate to the spray solution. Picloram activity tended to increase with increasing ammonium sulfate concentration up to 10% (w/v), but by the end of each experiment ammonium sulfate concentrations above 0.5% were generally equally effective. The absorption of14C-picloram by strawberry guava leaves was increased about five-fold by 0.5% and 10% ammonium sulfate. There was about four times more14C-picloram in the upper stem and attached leaves when ammonium sulfate was added than with picloram alone. Ammonium sulfate at 0.5% increased picloram absorption by four-fold in guava, but there was no increase in the amount of picloram translocated acropetally. Picloram absorption by dwarf beans, measured by difference between the amount of picloram applied and the amount recovered, was increased by 0.5% and 10% ammonium sulfate by a similar magnitude as on guava species.

Ammonium Sulfate Enhancement of Picloram Absorption by Detached Leaves

Ammonium sulfate increased the magnitude and rate of14C-picloram (4-amino-3,5,6-trichloropicolinic acid) absorption in detached strawberry guava (Psidium cattleianumSabine) leaves. Absorption of14C-picloram with or without ammonium sulfate leveled off at 6 to 12 hr. The magnitude of the ammonium sulfate-induced increase in14C-picloram absorption was not affected by picloram concentration in the range 250 to 2000 ppmw, or by leaf age. The absorption of14C-picloram was increased by 0.1, 0.5, 1.0, and 10% ammonium sulfate; 0.01% had no effect. Increased14C-picloram absorption resulted from adding the ammonium salts of sulfate, nitrate, chloride, or dibasic phosphate, but ammonium sulfate was the only one of six sulfate salts to increase picloram absorption. A pH adjustment of the external solution from 6 to 4 increased picloram absorption, whereas a pH change from 6 to 8 had no effect. Both ammonium dibasic phosphate at a solution pH of 7.7 and ammonium monobasic phosphate at pH 4.6 increased picloram absorption, whereas potassium dibasic phosphate at pH 9.5 had no effect, and potassium monobasic phosphate at pH 4.6 did increase absorption.

Comparative Effects and Concentration of Picloram, 2,4,5-T and Dicamba in Tissue Culture

In nutrient agar comparative concentrations (10−3 to 10−5M) of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) were generally more inhibitory to the growth of tissue cultures of soybean (Glycine max (L.) Merrill cv. Acme) and cottonwood (Populus deltoides Marsh.) than were either 4-amino-3,5,6-trichloropicolinic acid (picloram) or 3,6-dichloro-o-anisic acid (dicamba). Compared to untreated tissue dicamba or picloram at 10−6M in the nutrient agar resulted in a 200 % increase in the growth of soybean tissue. At 10−5 and 10−6M dicamba also produced an increase in the growth of cottonwood tissue. Greatest absorption of picloram and dicamba by tissue cultures from agar occurred during the first 24 h after treatment. However, absorption remained nearly static thereafter for 14 days. More dicamba was absorbed by soybean and cottonwood tissue cultures than either picloram or 2,4,5-T.

Absorption and Penetration of Picloram and 2,4,5-T into Detached Live Oak Leaves

Detached live oak (Quercus virginianaMill.) leaves were immersed in aqueous solutions of 4-amino-3,5,6-trichloropicolinic acid (picloram) or (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) for periods up to 4 hr. Herbicide concentration ranged from 10−3to 10−6M; solutions were adjusted to either pH 4, 6, 7, or 8. Absorption of picloram in the presence of equimolar concentrations of 2,4,5-T exceeded that noted for picloram alone. The presence of picloram in the treating solutions had no effect on absorption of 2,4,5-T. This technique allows evaluation of absorption and penetration characteristics of mixtures of herbicides, solvents, and adjuvants.

Effect of Stage of Growth of Field Bindweed on Absorption and Translocation of14C-Labeled 2,4-D and Picloram

The effect of stage of growth of field bindweed (Convolvulus arvensisL.) on absorption and translocation of14C-labeled 2,4-D and picloram was studied. Three stages of growth investigated weres-week old seedlings, and 7-week old and 16-week old vegetatively propagated plants. One middle leaf of each plant was treated with either14C-labeled (2,4-dichlorophenoxy)-acetic acid (2,4-D) or 4-amino-3,5,6-trichloropicolinic acid (picloram). Treated plants were harvested after 48 hr and assayed for radioactive14C. The percent of 2,4-D applied which was absorbed by seedlings was less than that absorbed by adult plants. Picloram absorption was not different in seedlings and 7-week old adult plants, but the 16-week old adult plants absorbed more picloram than either the 5-week old seedlings or 7-week old adult plants. More picloram than 2,4-D was absorbed at all stages of growth. Translocation of both 2,4-D and picloram was greater in seedlings than in older plants. No difference was found in amounts of 2,4-D and picloram translocated by adult field bindweed plants. More 2,4-D than picloram was translocated by seedlings.

Absorption and Penetration of Picloram in Potato Tuber Discs

Discs of potato (Solanum tuberosum L.) tuber tissue were immersed in buffered (pH 4.0 to 8.0) solutions of 4-amino-3,5,6-trichloropicolinic acid (picloram) (5 × 10−4M to 5 × 10−3M) for 1 to 36 hr. Uptake of picloram during incubation, and leakage after return of the discs to untreated buffer, were determined by gas chromatographic analysis of extracts of the tissue and ambient buffer. Picloram absorption increased with concentration and with time up to 24 hr. Maximum uptake occurred at pH 4.0 and very little picloram was absorbed at pH 7.0 and 8.0. Both absorption and leakage were temperature dependent. The rate and extent of leakage was greatest at the highest concentration. Typically, more than 90% of the picloram absorbed from 5 × 10−3M was lost to fresh buffer within 12 hr.