Glufosinate (Ignite): a New Promising Postemergence Herbicide for Citrus

Glirus Section

Proc. Fla. State Hort. Soc. 100:58-61. 1987.

GLUFOSINATE (IGNITE): A NEW PROMISING POSTEMERGENCE HERBICIDE FOR CITRUS

Megh Singh and D. P. H. Tucker ported that the pattern of plant responses to glufosinate University of Florida, IFAS and glyphosate was distinctly different. Glufosinate has li Citrus Research and Education Center mited translocation to rootstocks and rhizomes, etc. of per 700 Experiment Station Road ennial weeds as compared to glyphosate. Therefore, even Lake Alfred, FL 33850 tual regrowth from these plant parts will occur. Glufosinate may be a useful herbicide for weed control Additional index words. Basta, Buster, Conquest, Finale, in no-tillage systems, for orchards and vineyards, and for HOE-00661, HOE-39866, glufosinate-ammonium. general weed control in rangeland and non-cropland situ ations. Kapusta (6) reported effective control of several weed species using glufosinate in no-till fields. Glufosinate Abstract. Glufosinate [ammonium (3-amino-3-carboxypropyl) at 1.0to 2.0 kg/ha provided effective control of several methyl phosphinate] is a non-selective postemergence her annual and perennial weeds in vineyards, citrus, and other bicide for the control of a broad spectrum of grasses and fruit orchards as well as in uncultivated areas (3). Lawson broad leaf weed species. It is known worldwide by various names such as Basta, Buster, Conquest, and Finale. Glufosi and Wiseman (9) reported satisfactory runner control in nate controls both annual and perennial weeds. The activity strawberries without the adverse effect on the growth and of glufosinate is somewhat slower than paraquat but dis yield of the crop. Glufosinate at 4.0 kg/ha provided tinctly faster than that of glyphosate. The effect on perennial adequate control of cogangrass (Imperata spp.) (10) and at weeds is longer lasting than paraquat but not as long as the 2.0 kg/ha provided 93% control of purple nutsedge (7). control exhibited by glyphosate. Glufosinate inhibits thesyn Wilson et al. (11) reported the control of rye and horse- thesis of glutamine synthetase which is required for the fixa weed with glufosinate. Glufosinate at 1.0 kg/ha controlled tion of ammonia in plant cells. Without the activity of a broad spectrum of annual and perennial weeds in or glutamine synthetase, ammonia (NH3) concentration in chards in Europe, though some species required higher creases to toxic levels in the plants. Glufosinate is a herbicide rates. In most cases two applications were adequate to pro of relatively low toxicity; the oral LD50 in female rats is 1620 vide full season weed control. The summer application in mg/kg. It is rapidly degraded biologically in soil. Glufosinate many cases was more effective than the spring one. This is being developed in the United States for no-tillage crops, may be due to weeds which were not fully emerged at the orchards, vineyards and for non-cropland situations. Evalua time of early application. The leaves of stone and pome tion of glufosinate for the control of bahia (Paspalum fruit trees which were directly sprayed showed necrotic notatum Fluegge), bermuda [Cynodon dactylon (L) Pers.], symptoms but no signs of translocation were found (8). guinea (Panicum maximum Jacq.), para [Brachiaria mutica Glufosinate shows excellent potential as a herbicide for (Forsk.) Stapf], torpedo (Panicum repens L.) and signal weed control in citrus. Thus, it is appropriate to review the [ Brachiaria piligera (F. Muell.) Hughes] grasses indicated that information from the manufacturer's technical informa glufosinate will be a useful herbicide for weed control in cit tion bulletins (1, 2) for the benefit of citrus industry per rus. Further work needs to be done on its compatibility as a sonnel. tank mix with residual herbicides. Chemical and Physical Properties Glufosinate is a primary amine with an extended car Chemical Name: Ammonium (3-amino-3-carboxypropyl) bon chain. The parent acid of glufosinate was first discov methylphosphinate ered as a microbial metabolite of Streptomyces viridoc- Common Name: Glufosinate hromogenes in 1972 and was named phosphinothricin or Chemical Structure: bialophos (5). Glufosinate is a non-selective, foliar applied herbicide for the control of a broad spectrum of grasses and broadleafweeds. Glufosinate controls both annual and perennial weeds (1). In general, lower rates of glufosinate are needed to control dicot weed species. NH, CH - p - CH-CH-CH - COOH Glufosinate acts more slowly than paraquat and faster 5 I 2 d\ than glyphosate. It controls perennial weeds longerthan paraquat but not as long as glyphosate. Bellinder and Wil son (4) reported the effective control of several weed species using glufosinate. The symptom response to glufosinate occurred within 36 hr, whereas response to Trade Name: The trade name in the U.S.A. is IGNITE. glyphosate was observed after 4 to 7 days. They also re- Molecular Weight: 198.19 Appearance: Crystalline powder Florida Agricultural Experiment Station Journal Series No. 8630. Color: White to light yellow

58 Proc. Fla. State Hort. Soc. 100: 1987. Odor: Slightly pungent duction, photorespiration and amino acid metabolism) is Solubility: Soluble in water bound to glutamic acid to form glutamine. This process is Vapor Pressure: Not determinable due to decomposition catalyzed by the enzyme glutamine synthetase. Glufosi- Stability: Two years in original sealed containers stored at nate-ammonium inhibits the activity of this enzyme. Am 25 ± 5 C. monium metabolism in the plant is disturbed shortly after Formulation: It is a blue color liquid containing 200 g/liter application of the product so that ammonia (NH3), a strong active ingredient. phytotoxin, accumulates and kills the cells. Photosynthesis is also inhibited. Toxicological Properties Since ammonia is produced mainly during the reaction linked with photosynthetic electron transport, its accumu Aute Oral Toxicity: LD50 Male Rat—2000 mg/kg body lation is higher in treated plants exposed to light than in weight those kept in darkness or shade. Exposure to light also Female Rat—1620 mg/kg body accelerates the development of phytotoxic symptoms, weight which begin with the development of pale yellowish discol Acute Dermal Toxicity: LD50 Male Rat—4000 mg/kg body oration of the green plant parts. Plants wilt and die within weight 1 to 2 weeks. Female Rat—approximately 4000 mg/kg body weight Metabolism in Soil and Plants Skin and Eye Irritation: No primary irritation of skin and eye mucosa was observed in rab Physical and chemical properties of the active ingre bits. dient glufosinate-ammonium are very similar to those of Subchronic Toxicity: This is based on a 90-day feeding test. protein compounds synthesized by living organisms. The No effect level—rats—18 mg/kg body weight/day active ingredient is highly stable as a chemical compound dogs—2 to 8 mg/kg body weight/day but its degradation is rapid in a microbiologically active Embryo Toxicity: No observable effect level— environment such as soil or surface water. Consequently, rats—10 mg/kg body weight there should be no accumulation of the substance in the rabbits—6.3 mg/kg body weight food chain. Model tests carried out in the laboratory Mutagenicity: Mutagenic tests in vitro and vivo did not suggested that the active ingredient could leach into the show any mutagenic activity. deeper layers of the soil. Field studies, however, de Neurotoxicity: No signs of neurotoxic effects in hens have monstrated that under natural conditions there is no been observed. movement into the soil layers deeper than 15 cm. Because Ecological Data: glufosinate is a relatively new herbicide, there are no de Toxicity to Fish: LD50 (96 hr) for Rainbow trout is > tailed studies on its mobility in different soils under differ 320 mg/liter water. ent environmental conditions. Such studies are needed to Bees: Non-toxic to bees. clearly establish its leaching behavior in soil. This suggests rapid biodegradation of glufosinate-ammonium. Further Biological Properties tests with radioactive labelled material showed that glufosi nate-ammonium is rapidly decomposed to 3-methyl phos- Glufosinate must be applied postemergence to the phinicopropionic acid and finally to carbon dioxide. No weeds. Annual grasses and broadleaf weeds should have residues of the active ingredient have been detected using developed sufficient foliage to allow uptake of the her the commercial formulation in any of the major crops bicide. Perennial weeds are most sensitive when treated at treated for weed control (fruits, grapes, vegetables, etc.); the time of maximum translocation of photosynthetic however, traces of the metabolite, 3-methyl phosphinicop- products to the storage plant parts, i.e., beginning of flow ropionic acid were detected. ering to full flowering stage. Favorable environmental con ditions for active plant growth are preconditions for effec Spectrum of Herbicide Activity tive weed control with glufosinate. Cold and dry weather reduce plant metabolic activity and thus, the product effi Glufosinate is effective against a wide range of monocot cacy. Lower light intensity may increase the activity of and dicot annual and perennial weeds. Generally, peren glufosinate. Since the spray deposit of glufosinate is likely nial weeds require a higher rate than annual ones. Major to be washed off by rain, no precipitation should fall dur weeds controlled by glufosinate are listed in Table 1 ing the first 6 hr after application to ensure adequate up (monocot) and Table 2 (dicot) (1). take of the herbicide (2). We have evaluated glufosinate for the control of annual and perennial grasses in citrus groves. The grasses in our study included bahia, bermuda, para, guinea, torpedo, and Mode of Action signal. The rates tested were 1.12 and 2.25 kg a.i./ha. The active ingredient of Ignite, glufosinate-am- Glufosinate provided excellent burn down of all grasses at monium, is a non-selective, partially systemic contact her both rates. Signal grass was most sensitive, para and tor bicide. After uptake, the compound is active in the leaf. pedo were most tolerant, with other species being inter No activity in the roots could be detected in plants after mediate in response. Regrowth of perennial grasses varied emergence and no damage is caused to seedlings before with rate of application and species. It appears from our emergence (2). results that glufosinate will be a useful herbicide for weed Under normal conditions, ammonia produced during control in citrus. Further work needs to be done on its various metabolic processes in the plant cells (nitrate re- compatibility as a tank mix with residual herbicides.

Proc. Fla. State Hort. Soc. 100: 1987. 59 Table 1. Monocot weeds controlled by glufosinate. Table 2. Dicot weeds controlled by glufosinate.

Common name Scientific name Common name Scientific name

velvetleaf Agropyron repens quackgrass Abutilon theophrasti Agrostis stolonifera creeping bentgrass Achillea millefolium common yarrow redroot pigweed Agrostis tenuis colonial bentgrass Amaranthus retroflexus Alopecurus myosuroides slender foxtail Ambrosia artemisiifolia common ragweed corn chamomile Avenafatu wild oats Anthemis arvensis Brachiaria platyphylla broadleaf signalgrass Arctotheca calendula capeweed Bromus mollis soft brome Artemisia vulgaris mugwort Bromus sterilis poverty brome Bellis perennis English daisy hairy geggarticks Bromus tectorum downy brome Bidens pilosa Calamagrostis epigeios bushgrass Cadaria draba hoary cress shepherdspurse Carex spp. sedges Capsella bursa-pastoris Cynodon dactylon bermudagrass Chenopodium album common lambsquarters Cyperus esculentus yellow nutsedge Chrysanthemum vulgare common tansy Cyperus rotundus purple nutsedge Cirsium arvense Canada thistle Dactylis glomerata orchardgrass Convolvulus arvensis field bindweed Deschampsia flexuosa wavy hair grass Convolvulus sepium hedge bindweed Digitaria sanguinalis large crabgrass Datura stramonium jimsonweed Echinochloa cms. galli barnyardgrass Equisetum arvense field horsetail Eleusine indica goosgrass Erigeron canadensis horseweed Festuca pratensis meadow fescue Eupatorium odoratum thoroughwort spp. Holcus lanatus common velvetgrass Euphorbia hirta garden spurge Hordeum murinum wall barly Fumaria officinalis fumitory Imperata cylindrica cogongrass Galinsoga parviflora smallflower galinsoga Lolium multiflorum Italian ryegrass Galiu aparine catchweed bedstraw Lolium perenne perennial ryegrass Glechoma hederacea ground ivy Panicum dichotomiflorum fall panicum Helianthus annuus common sunflower Panicum maximum guineagrass Hypericum perforatum common St. Johnsworth Panicum texanum Texas panicum Ipomea spp. morningglory Paspalum conjugatum sour paspalum Lamium amplexicaule henbit ' Paspalum dilatatum dallisgrass Lamium purpureum purple deadnettle Paspalum distichum knotgrass Lithospermum arvense corn gromwell Pennisetum clandestinum kikuyugrass Malva neglecta common mallow Phalaris spp. canarygrass Matricaria chamomilla wild chamomile Phragmites communis giant reed Matricaria maritima false chamomile Poaannua annual bluegrass Physalis angulata cutleaf groundcherry Poa pratensis Kentucky bluegrass Plantago lanceolata buckhorn plantain Poa trivialis roughstalk Plantago major broadleaf plantain

Secale cereale rye Polygonum amphibium water smartweed Setaria faberi giant foxtail Polygonum aviculare prostrate knotweed Setaria lutescens yellow foxtail Polygonum convolvulus wild buckwheat Setaria viridis green foxtail Polygonum pensylvanicum Pennsylvania smartweed Sorghum halepense johnsongrass Polygonum persicaria ladysthumb Portulaca oleracea common purslane Pteridium aquilinum brackenfurn Carolina falsedandelion Relatively lower acute toxicity and control of a wider Pyrrhopappus carolinianus Ranunculus repens creeping buttercup spectrum of weeds make glufosinate a useful addition to Raphanus raphanistrum wild radish presently available herbicides for citrus. It will be a useful R ubus fruticosus European blackberry foliar applied herbicide to control weeds which escape or Rubus idaeus European red raspberry are tolerant to preemergence herbicides. In addition, post- Senecio vulgaris common groundsel Sida spinosa prickly sida emergence herbicides such as glyphosate are needed to Sinapis arvensis wild mustard control weeds where there is a potential injury to young Solanum carolinense horsenettle citrus trees from residual herbicides. Its application in cit- Solanum nigrum black nightshade riculture will not require any modification in present prac Solidago spp. goldenrod tices. Glufosinate is not presently registered for citrus in Sonchus arvensis perennial sowthistle Sonchus oleracea annual sowthistle Florida but is expected to be soon. Spergula arvensis corn spurry Stellaria media common chickweed Literature Cited Taraxacum officinale dandelion Thlaspi arvense field pennycress 1. American Hoechst Corporation. 1982. Technical Information Bulle Trifolium arvense rabbitfoot clover tin. Somerville, NJ p. 4. Trifolium repens white clover 2. American Hoechst Corporation. 1983. Basta: The new non-selective Urtica dioica stinging nettle herbicide. Somerville, NJ p. 27. Urtica wrens burning nettle 3. Bahat, A. 1985. Glufosinate-ammonium for general weed control in Veronica hederaefolia ivyleaf speedwell vineyards, citrus and other fruit orchards and uncultivated areas. Veronica persica persian speedwell Phytoparasitica 13:239. Vicia spp. vetch 4. Bellinder, R. R. and H. P. Wilson. 1983. Comparison of several non- Viola tricolor pansy selective herbicides in reduced tillage systems. Proc. Northeast Weed Xanthium pensylvanicum common cocklebur Sci. Soc. 37:20-26.

60 Proc. Fla. State Hort. Soc. 100: 1987. 5. Bellinder, R. R., K. K. Hatzios, and H. P. Wilson. 1985. Mode of control and crop tolerance in orchards. Proc. British Crop Prot. Conf. action investigations with the herbicides Hoe 39866 and SC-0224. Weeds (1985). 3:1047-1057. Weed Sci. 33:779-785. 9. Lawson, H. M. and J. S. Wiseman. 1985. Evaluation of glufosinate- 6. Kapusta, G. 1981. Hoe-661: A new herbicide for the control of veg ammonium for runner control in strawberries. Proc. British Crop etation in no till fields. Proc. North Centr. Weed Contr. Conf. 36:92. Prot. Conf. Weeds (1985). 3:1081-1085. 7. Labrada, R., J. Hernandez, and J. Baez. 1987. Evaluation of her 10. Twitrosoedirdjo, S. 1984. The conversion oilmperata dominated veg bicides for Cyperus rotundus control. Weed Abstr. 36:159. etation into productive systems. Trop. Newsletter 45:6-7. 8. Langeluddeke, P., W. Bubl, H. P. Huff, U. Kotter, and F. Wallmuller. 11. Wilson, H. P., T. E. Hines, R. R. Bellinder, and J. A. Grande. 1985. 1985. Glufosinate-ammonium (Hoe 39866): New results on weed Comparisons of Hoe-39866, SC-0224, paraquat and glyphosate in no-till corn (Zea mays). Weed Sci. 33:531-536.

Proc. Fla. State Hort. Soc. 100:61-64. 1987.

GROWTH OF YOUNG 'HAMLIN' ORANGE TREES USING STANDARD AND CONTROLLED-RELEASE FERTILIZERS

T. E. Marler, J. J. Ferguson, and F.S. Davies Controlled-release fertilizers have been used on many University of Florida, IFAS horticultural crops (10), including citrus. These sources in Fruit Crops Department creased fruit production on mature citrus (7) and growth Gainesville, FL 32611 of young containerized citrus (3, 6) when compared to more soluble fertilizer sources. In contrast, growth of Abstract. Controlled-release fertilizers were compared with young 'Orlando' tangelo trees was comparable for control a standard fertilizer on 1- and 2-year 'Hamlin' orange led-release sulfur-coated urea and soluble sources, but fre [ Citrus sinensis (L.) Osb.] on sour orange (C. aurantium quency of application was reduced by 50% (4). Neverthe L.) trees planted on double-row beds. All fertilizers con less, acceptance of controlled-release fertilizers by the sisted of an 8N - 2.6P - 6.6K - 2Mg - 0.2Mn - 0.12Cu - Florida citrus industry has been limited (5), primarily be 0.2Zn - 1.78Fe formulation. No differences were found in cause of higher fertilizer costs and lack of grower experi tree growth over two years in two separate experiments ence with these materials. for comparisons between the following treatments: (A) Current fertilizer recommendations (8) for young cit isobutylidene diurea (IBDU) and Wonder Gro (WG) rus trees have been based on previous studies (1, 11), ob applied twice per year (year 1, 2 lb./tree/application; year servations, and industry trends. Recommendations call for 2, 4 lb./tree/application); (B) standard fertilizer applied 0.06 to 0.10 lb. N/tree (average = 0.08 lb.) for newly- four times/year (year 1, 1 lb./tree/application; year 2, 2 lb./ planted citrus, applied five to six times per year (8). Fer tree/application). In a separate study, standard fertilizer tilizer is usually broadcast evenly in a 3 ft diameter circle, was applied four times/year in one experiment and five which translates to ca. 3,000 lb. N/year per treated acre. times/year in another experiment at 0.5, 1.0, or 1.5 lb. of Young citrus trees require an adequate supply of nutrients material/tree/application (middle rate equivalent to aver to optimize growth; however, this rate is 10 times more age recommended rate). No differences were found in than recommended levels for mature trees and may be growth, suggesting that optimum fertilizer rates may be excessive under some circumstances. Rasmussen and lower in some cases than those currently recommended Smith (11) also expressed concern that young trees were being over-fertilized and recommended reduced applica for young citrus trees. tion frequency and rates. Objectives of this study were to compare the effects of Efficiency of fertilizer use can be expressed as the per commonly available controlled-release and standard fer centage of applied nutrients recovered by the crop. Nitro tilizers on growth of young citrus trees, and to determine gen is the most important nutrient in a citrus fertilization the effects of three rates of application of standard fer program and the nutrient with the most variability in effi tilizer on leaf nutrient levels and tree growth. ciency of recovery. Nitrogen losses due to erosion, leach ing, denitrification, and volatilization reduce N availability for plant uptake. Sandy soils and heavy rainfall in Florida Materials and Methods are frequently associated with substantial N losses, espe cially through leaching. The problem is greater in areas Four field experiments were conducted at the Horticul where high water tables limit rooting depth. Concerns over tural Unit NW of Gainesville, Florida, using 'Hamlin' energy conservation and ground water pollution, com orange on sour orange rootstock. Double row beds, 55 ft bined with the competitive pressure to reduce production wide and 2-2.5 ft in height, were constructed in March, costs in the Florida citrus industry (2) make reduction of 1985. Soil type was Kanapaha sand (loamy, siliceous, applied fertilizer losses desirable. hyperthermic, Grossarenic, Paleaquult) underlain by a Controlled-release fertilizers potentially reduce N los hardpan. Two tree rows 25 ft apart were used on each bed ses, improving efficiency of plant recovery (6, 10). Fewer with trees set 11 ft apart. Irrigation was applied by 90 applications are needed (4, 7, 10), which reduces labor and degree, 10 gallons-per-hour microsprinklers located ca. equipment costs and soil compaction by equipment. 3.25 ft NW of tree trunks. Available soil moisture was maintained at optimum conditions (20% soil moisture de

Florida Agricultural Experiment Station Journal Series No. 8559. pletion; Marler, T.E., Univ. of Florida, unpublished).

Proc. Fla. State Hort. Soc. 100: 1987. 61