Rodney W. Bovey

Determining Exposure to Auxin-Like Herbicides. I. Quantifying Injury to Cotton and Soybean

Crop injury caused by drift of auxin-like herbicides has been a concern since their development. Research was conducted to describe a method of quantifying injury from auxin-like herbicides as a first step in determining crop damage. Reduced rates of 2,4-D, dicamba, and triclopyr were applied to cotton and soybean plants in the three- to six-leaf stage in field and greenhouse studies. Injury to leaves and stems were evaluated separately, and the values were combined so that one injury estimate was obtained for each individual plant rated. Injury symptoms were typical for auxin-type herbicides and ranged from slight bending of stems or petioles and wrinkled leaves to necrosis. Specific descriptions of leaf and stem injury levels were used to describe plant injury consistently. These descriptions were very detailed for the lower injury levels, but the characterizations became more general as the injury increased because of the prominence of factors such as necrosis. The injury evaluation method provided repeatable results for each herbicide and herbicide rate used. This injury evaluation method has many possible uses in auxin-like herbicide research and lays the foundation for forecasting the impact of early-season injury to cotton and soybean yield. Nomenclature: 2,4-D; dicamba; triclopyr; cotton, Gossypium hirsutum L. ‘Delta Pine 50’ #3 GOSHI; soybean, Glycine max (L.) ‘Delta Pine 415’ Merr. # GLYMA. Additional index words: Epinasty, method, plant injury, rating scale. Abbreviation: DAT, days after treatment.

Wheat and Italian ryegrass (Lolium multiflorum) competition as affected by phosphorus nutrition

Abstract A greenhouse experiment used a replacement series design to compare the vegetative growth 6 wk after emergence in pure cultures and mixtures of winter wheat and Italian ryegrass, with phosphorus (P) levels recommended by soil testing. The planting proportions of wheat and Italian ryegrass were 100 and 0%, 75 and 25%, 50 and 50%, 25 and 75%, and 0 and 100%, respectively. There was no alleopathic interaction between the species. Both species in all pure and mixed cultures had substantially less growth in the low-P than in the recommended P treatment. However, the relative performance of the two species differed between P treatments. In the recommended P treatment in pure culture, Italian ryegrass had more tillers and greater root weight and length than wheat. Pure culture wheat in the low-P treatment exceeded pure culture Italian ryegrass in leaf area, weights of leaves, stems, and roots, and root length. Thus, the growth of wheat was inhibited less by P deficiency than the growth of Italian ryegrass in pure culture. In the 50:50 mixture of the recommended P treatment, wheat had greater leaf, stem, and root weights than Italian ryegrass. In the 50:50 mixture of the low-P treatment, the two species were very similar in growth, except that Italian ryegrass had about three times more tillers than did wheat. Whereas P deficiency limited the growth of wheat less than Italian ryegrass in pure culture, P deficiency did not affect the relative competitiveness of Italian ryegrass as much as wheat in mixed cultures. The ability of Italian ryegrass to compete with wheat when P was limiting may result from a difference in root growth. Italian ryegrass had a greater fresh root length to fresh root weight ratio than did wheat in the low-P treatment in pure culture and in the 50:50 mixture. The greater surface area of Italian ryegrass roots likely enhanced the competitiveness of Italian ryegrass relative to wheat under P-deficit conditions. Thus, the use of the recommended P nutrition from soil testing may be a key component to diminish Italian ryegrass competition in wheat fields. Nomenclature: Italian ryegrass, Lolium multiflorum Lam. LOLMU; wheat, Triticum aestivum L.

Determining Exposure to Auxin-Like Herbicides. II. Practical Application to Quantify Volatility'

Volatility and drift are problems commonly associated with auxin-like herbicides. Field and greenhouse studies were conducted at Texas A & M University to develop a method of quantifying volatility and subsequent off-target movement of 2,4-D, dicamba, and triclopyr. Rate–response curves were established by applying reduced rates ranging from 4 × 10−1 to 1 × 10−5 times the normal use rates of the herbicides to cotton and soybean and recording injury for 14 d after treatment (DAT) using a rating scale designed to quantify auxin-like herbicide injury. Injury from herbicide volatility was then produced on additional cotton and soybean plants through exposure to vapors of the dimethylamine salt of 2,4-D, diglycolamine salt of dicamba, and butoxyethyl ester of triclopyr using air chambers inside a greenhouse and volatility plots in the field. Injury resulting from this exposure was evaluated for 14 d using the same injury-evaluation scale that was used to produce the rate–response curves. Volatility-injury data were then applied to the rate–response curves so that herbicide rates corresponding with observed injury could be calculated. Using this method, herbicide volatility rates estimated from greenhouse-cotton injury were determined to be 3.0 × 10−3, 1.0 × 10−3, and 4.9 × 10−2 times the use rates of 2,4-D, dicamba, and triclopyr, respectively. Greenhouse-grown soybean developed injury consistent with 1.4 × 10−2, 1.0 × 10−3, and 2.5 × 10−2 times the normal use rate of 2,4-D, dicamba, and triclopyr, respectively. Under field conditions, cotton developed injury symptoms that were consistent with 4.0 × 10−3, 2.0 × 10−3, and 1.25 × 10−1 times the recommended use rates of 2,4-D, dicamba, and triclopyr, respectively. Field soybean displayed injury symptomology concordant with 1.6 × 10−1, 1.0 × 10−2, and 1.1 × 10−1 times the normal use rates of 2,4-D, dicamba, and triclopyr, respectively. This procedure provided herbicide volatility rate estimates that were consistent with rates and injury from the rate–response injury curves. Additional research is needed to ascertain its usefulness in determining long-term effects of drift injury on crop variables such as yield. Nomenclature: 2,4-D, dicamba, triclopyr, cotton, Gossypium hirsutum L. ‘Delta Pine 50’, #3 GOSHI, soybean, Glycine max (L.) Merr. ‘Delta Pine 415’, # GLYMA. Additional index words: Injury modeling, plant injury, rate of exposure. Abbreviations: BEE, butoxyethyl ester; DAT, days after treatment; DGA, diglycolamine; DMA, dimethylamine; WAE, weeks after emergence.

Potential herbicides for brush control.

Several new herbicides and herbicide combinations were evaluated in the greenhouse for control of honey mesquite, huisache, whitebrush, live oak and Texas persimmon. Sprays of picloram, triclopyr ester and 3,6-dichloropicolinic acid at 0.56 kg/ha were the most effective herbicides in reducing the canopy of honey mesquite. Picloram at 0.14 to 0.56 kg/ha effectively defoliated huisache. At 1.12 kg/ha tebuthiuron, buthidazole, hexazinone and 3,6_dichloropicolinic acid also defoliated huisache. Whitebrush was effectively controlled with picloram, triclopyr ester, tebuthiuron, buthidazole, hexazinone, dicamba and ethidimuron at 0.56 kg/ha. None of the treatments was effective against live oak or Texas persimmon. Certain combinations of picloram plus triclopyr effectively defoliated whitebrush and honey mesquite. Picloram plus 3,6-dichloropicolinic acid was also effective for honey mesquite control. Development of herbicides for woody plant control is expensive, requires relatively large land areas and several years of investigation. Use of a woody plant nursery (Bovey et al. 1979) can hasten the evaluation of herbicides, but also requires large material and labor inputs. The greenhouse offers a more rapid method to evaluate potential herbicides for woody plant control (Bovey and Meyer 1974; Bovey et al. 1967; Bovey et al. 1968). The greenhouse also allows a large number of herbicide treatments to be evaluated in a relatively limited space. Evaluations at 2 and 6 months after treatment in the greenhouse is a valid indication of herbicide effectiveness, whereas field evaluations may take 2 to 3 years or longer (Bovey and Meyer 1978; Meyer et al. 1969; Meyer and Bovey 1979a, 1979b, and 1979~; Scifres 1975). Several herbicides that have become available since 1972 were evaluated alone and in mixtures in the greenhouse for their potential to control undesirable woody plants. The objective of this paper is to present the relative efficacy of those compounds to expedite selection of potential treatments for brush control which warrant continued evaluation under field conditions. Materials and Methods Honey mesquite [Prosopis juliflora (Swartz) DC var. glandulosa (Torr.) Cockerell], huisache [Acacia farnesiana (L.) Willd.], live oak (Quercus virginiana (Mill.), and Texas persimmon (Diospyros zexana Scheele) plants were grown in the greenhouse for 1 to 2 4years in 12.7-cm-diam pots containing 1:l: 1 Houston black clay:sand:peat moss mixture. Woody stems ranged from 20 to 40cm in Authors are research agronomist, plant physiologist and plant physiologist, respectively, U.S. Department of Agriculture, Science and Education Administration, Agricultural Research, Department of Range Science, Texas A&M University, College Station, TX 77843. This paper reports results of research only. Mention ofa pesticide in this paper does not constitute a recommendation by the USDA nor does it imply registration under FIFRA. Manuscript received September 13, 1979. 144 height, with one primary stem per plant. Usually, one to three plants were grown per pot. Propagation methods for these woody plants are given elsewhere (Bovey et al. 1979). All herbicides were applied as foliar-soil sprays at rates ranging from 0.14 to 4.48 kg/ha in water at the equivalent of 93.5 l/ha with a laboratory spray chamber described by Bouse and Bovey ( 1967). After treatment, plants were returned to the greenhouse and topwatered after 24 hours and watered daily thereafter. Herbicide formulations consisted of the propylene glycol butyl ether ester of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), the ethylene glycol butyl ethel ester and the triethylamine salt of [(3,5,6trichloro-2-pyridinyl)oxy] acetic acid (triclopyr), the potassium salt of 4-amine-3,5,6-trichloropicolinic acid (picloram), the dimethylamine salt of 3,6dichloro-+anisic acid (dicamba), the ammonium salt of ethyl hydrogen (aminocarbonyl)phosphonate (fosamine), the isopropylamine salt of N-(phosphonomethyl)glycine (glyphosate) the alkanolamine salt of (2,4_dichlorophenoxy)-acetic acid (2,4-D), 3[5-( 1, I-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4hydroxyl-1-methyl-2-imidazolidinone (buthidazole), N-[5-( 1, Idimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N’-dimethylurea (tebuthiuron), 3-Cyclohexyl-6-(dimethylamino)-l-methyl-l,3,5-triazine-2,4( lH, 3H)-dione (hexazinone), 1,2,-dihydro-3,6_pyridazinedion (MH), rert-butylcarbamic acid ester with 3(m-hydroxyphenyl)-1, ldimethylurea (karbutilate), 5-bromo-3-see-butyl-6-methyluracil (bromacil), N-[5-(ethylsulponyl)-1,3,4-thiadiazol-2-yl]-N,N’-dimethylurea (ethidimuron), and N3,N3-Di-n-propyl-2-4-dinitro-6trifluoromethyl 3-m-phenylenediame (prodiamine) and 3,6-dichloropicolinic acid. Coded materials included N-[5-(Zchlorol,l-dimethylethyl)1,3,4-thiadiazol-2-yl]-N,N’dimethylurea (“EL-l 12’11, N’(2,5difluorophenyl)-h!N’-dimethylurea (DS-17338)1, N-(2,5-difluorophenyl)-N-methylurea (DS-18507)‘,6-(l,l-dimethylethyl)-3-( 1 methylethyl)iSothiazolo-[3,4-d]pyrimidin-4(5~)-one (NIA19873)‘, N-(2,2dimethoxyethy1)-N’-[5-(1,l-dimethylethyl)-1,3, 4thiadiazol-2-yl]-N-methylurea (HCS-3510)‘, N-(2,Zdimethyoxyethyl)-N’-methyl-~~5~trifluoromethyl)-1,3,4-thiadiazol-2-yl]urea (HCS-3438)1, 4-hydroxy-l-methyl-3-[5-(trifluoromethyl)-1,3,4-thiadiazol-2-yl]-2-imidiazolidinone (VEL-5028)1, 2-chloro-N-(2,6dimethylphenyl)-N-( 1,3-dioxolan-2-yl methyl)acetamide (VEL 5052)‘. An experimental growth regulator, N,N-dimethylcocoamine succinate salt (1: 1) (TD-692)’ was also included. Treatments were evaluated by visually estimating canopy reduction (defoliation) of leaves of each plant at approximately 1 week and 1 to 6 months after treatment. Data reported are from evalua‘Mention of trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture or Texas A&M University and does not imply their approval to the exclusion of other products that may alSO be suitable. Trademark names are used only for those herbicides which have not been assigned a common name, and for ease of presentation only. JOURNAL OF RANGE MANAGEMENT 34(2), March 1981 Table 1. Percent canopy reduction of lto 2-year-old honey mesquite, 3 to 6 months after spraying with various herbicides and rates in the greenhouse.1 Herbicide 0 0.14 0.28 Herbicide rate (kg/ ha)

Droplet size and spray volume effects on honey mesquite mortality with clopyralid.

The effects of droplet size and spray volume (spray-mixture application rate) on honey mesquite (Prosopis glandulosa Torr.) mortality were evaluated using 0.55 to 0.58 kg ae (acid equivalent) ha-1 clopyralid (3,6 dichloro-2-pyridinecarboxylic acid). A factorial combination of 3 spray volumes (19, 37, and 75 liters ha-1) and droplet sizes of 325 +/- 25, 475 +/- 25, and 625 +/- 25 micrometers nominal volume median diameter were replicated 3 times at both Andrews and Big Lake, Tex., during June 1989. The experiment was repeated in 1990 at Big Lake and Campbellton, Tex., without the 75 liters ha-1 spray volume. Honey mesquite mortality and canopy reduction 16 months after application were significantly less on the 625 micrometer droplet treatments in 2 of 4 experiments, when compared to plots treated with smaller droplet sizes. Mortality increased with larger spray volumes, particularly with 625 micrometer droplets. Relative mortality data from the 4 experiments clearly demonstrated that larger droplet sizes require larger spray volumes for greatest efficacy.

Rice Response to Clomazone as Influenced by Application Rate, Soil Type, and Planting Date

Clomazone is an effective herbicide widely used for PRE grass control in rice. However, use of clomazone on sandy textured soils of the western Texas rice belt can cause serious rice injury. Two field experiments at three locations were conducted in 2002 and 2003 to determine the optimum rate range that maximizes barnyardgrass and broadleaf signalgrass control and minimizes rice injury across a wide variety of soil textures and planting dates. At Beaumont (silty clay loam), Eagle Lake (fine sandy loam), and Ganado (fine sandy loam), TX, PRE application of 0.34 kg ai/ha clomazone applied to rice planted in March, April, or May optimized barnyardgrass and broadleaf signalgrass control and rice yield while minimizing rice injury. Data suggest that, although injury might occur, clomazone is safe to use in rice on sandy textured soils. Nomenclature: Clomazone, barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, broadleaf signalgrass, Brachiaria platyphylla BRAPP, rice, Oryza sativa L

Control of honey mesquite with clopyralid, triclopyr, or clopyralid:triclopyr mixtures.

Greenhouse and field experiments were conducted to evaluate clopyralid formulations and triclopyr ester alone and in mixtures with clopyraiid for control of honey mesquite. In the greenhouse, mixtures of the butoxyethyi ester of triclopyr enhanced the activity of the 2-ethylhexyl ester, the monoethanolamine salt and the free acid of clopyraiid when applied in l:l, 1:2 or 1:4 clopyralid:triclopyr mixtures at total rates of 0.07,0.14, and 0.28 kg se/ha. The activity of triclopyr was not enhanced by addition of clopyralid. In the field, mixtures of the 1-decyl ester of clopyralid + the butoxye thyi ester of triclopyr were usually more effective than either herbicide applied alone. Addition of 0.14 kg/ha of triclopyr to clopyralid applied at 0.28 kg/ha markedly increased canopy reduction and mortality by at least 47% compared to either herbicide applied alone. Basal pours of diesel oil alone at 0.9 L/tree were usually as effective as diesel oil fortified with esters of clopyraiid, 2,4,5-T or triclopyr at 4.8 or 9.6 g/L. Basal sprays of diesel oil + esters of clopyralid, 2,4,5-T or triciopyr in concentrations of 4.8 or 9.6 g/L applied at 0.5 L/tree caused high mortality of honey mesquite trees similar to basal pours. Triclopyr or clopyralid at 4.8 g/L were less effective in diesel oil:water carrier (1:4 or 1:3), respectively, than in diesel oil carrier.

Phytotoxicity and transport of clopyralid from three formulations in honey mesquite.

Foliar sprays of the monoethanolamine salt, oleylamine salt, and 1-decyl ester of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were about equally effective in killing greenhouse-grown honey mesquite (Prosopis glandulosa Torr.). Treated leaves absorbed more clopyralid within 15 min after pipet application of the oleylamine salt compared to the other formulations. After 24 h, treated leaves absorbed and transported more clopyralid into the plant after application of the salt formulations compared to that of the 1-decyl ester. There were no consistent differences among clopyralid formulations in transport of clopyralid from foliar sprays at 4 h or 1, 3, or 8 days after treatment. Only the acid form of clopyralid was transported from the site of application of either ester or the amine formulation.

Seasonal response of Macartney rose and huisache to herbicides.

Highlight: Picloram granules and sprays were applied to Macartnev rose (Rosa bracteata Wendl.} and huisache (Acacia farnesiana (L.) Willd.) in the claypan area of Texas. Monthly granule applications to Macartney rose were generally least effective in the summer. Rates of 1, 2, and 3, lb/acre of picloram as granules reduced the canopy 53, 68, and 86% and killed 14, 32, and .5 7% of the plants, respectively. Foliar sprays of picloram were about equally effective as granules. Huisache was not as highly responsive to picloram as to either granules or soil sprays at rates up to 4 lb/acre. However, picloram at 2 lbfacre as a foliage spray in May or September killed 90% or more of the plants. A 1 lb/acre foliage spray of picloram combined with a 1 lb/acre spray of 2,4,S-T, dicamba, or picloram in the soil also killed 53% or more of the huisache plants.

Subsurface herbicide applicator for brush control.

Highlight: A tractor-drawn machine was designed to apply soil-active herbicides subsurface to experimental brush control plots. The applicator was constructed with a large coulter, 32 inches in diameter, to penetrate soil to a depth of 0 to 8 inches and to cut through woody vegetation. An injector-knife immediately behind the coulter supported a spray nozzle to apply herbicide into the bottom of the slice made by the coulter. The injector applies herbicides in continuous narrow bands spaced on 6-inch ten ters at 3to 6-ft intervals and requires low energy input to operate. Spacing of herbicide bands depends upon type and size of brush being treated.