Barry J. Brecke

Competition for water in a pecan (Carya illinoensis K. Koch) - cotton (Gossypium hirsutum L.) alley cropping system in the southern United States

Understanding the belowground interactions between trees and crops is critical to successful management of agroforestry systems. In a study of competition for water in an alley cropping system consisting of pecan (Carya illinoensis) and cotton (Gossypium hirsutum) in a sandy loam soil (Rhodic Paleudult) in Jay, Florida, root systems of the two species were separated by trenching to 120 cm depth. A polyethylene barrier was installed in half of the plots. Spatial and temporal variations in soil water content, root distribution and water uptake by both species, and leaf area development and height of cotton were measured. Interspecific competition for water was greater in the non-barrier treatment near tree rows than at the alley center. Competition became evident 3 to 4 weeks after emergence of cotton and increased during the following 7 to 8 weeks. Compared with the non-barrier treatment, the barrier treatment had higher soil water content and better growth of cotton (height, leaf area, and fine root biomass). Cotton lint yield in the barrier treatment (677 kg ha–1) was similar to that in a sole-crop stand, but higher than in the non-barrier (502 kg ha–1) treatment. Lint production efficiency of plants was higher in the interior rows in the non-barrier treatment (0.197 kg lint per square meter of leaf area, compared to 0.117 kg in the barrier treatment). The results suggest that trenching or even deep disking parallel to the tree row may reduce competition for water, but the impact on tree growth cannot be established from this study.

A proposal to standardize soil/solution herbicide distribution coefficients

Abstract Herbicide soil/solution distribution coefficients (Kd) are used in mathematical models to predict the movement of herbicides in soil and groundwater. Herbicides bind to various soil constituents to differing degrees. The universal soil colloid that binds most herbicides is organic matter (OM), however clay minerals (CM) and metallic hydrous oxides are more retentive for cationic, phosphoric, and arsenic acid compounds. Weakly basic herbicides bind to both organic and inorganic soil colloids. The soil organic carbon (OC) affinity coefficient (Koc) has become a common parameter for comparing herbicide binding in soil; however, because OM and OC determinations vary greatly between methods and laboratories, Koc values may vary greatly. This proposal discusses this issue and offers suggestions for obtaining the most accurate Kd, Freundlich constant (Kf), and Koc values for herbicides listed in the WSSA Herbicide Handbook and Supplement. Nomenclature: Readers are referred to the WSSA Herbicide Handbook and Supplement for the chemical names of the herbicides.

Factors affecting seed germination of tropical signalgrass (Urochloa subquadripara)

Abstract Tropical signalgrass is one of the dominant weeds in the Florida turfgrass industry and is potentially troublesome for the southeastern turfgrass industry. Tropical signalgrass is especially problematic for St. Augustinegrass sod producers because of lack of control options. The objectives of our research were to determine the effect of light, pH, temperature, water potential, and planting depth on tropical signalgrass germination and emergence. Tropical signalgrass germination does not require light and is optimum at pH 5 to 6, temperature 25 C, and water potentials greater than − 0.4 MPa. Tropical signalgrass shoots emerged from depths of 0 to 7 cm, with maximum germination when placed on the soil surface. Tropical signalgrass seedlings emerged in the field during the second week of March in Ft. Lonesome, FL. Weekly mean soil and ambient air temperatures at the time of emergence were 20 C. Tropical signalgrass emergence was first observed at 118 and 73 growing degree-days (GDD) (13 C base temperature), with a peak emergence period at 222 and 156 GDD for 2001 and 2002, respectively. Nomenclature:  Tropical signalgrass, Urochloa subquadripara (Trin.) R. D. Webster BRASU; St. Augustinegrass, Stenotaphrum secondatum (Wait.) Kuntz.

Fumigant Alternatives for Methyl Bromide Prior to Turfgrass Establishment1

Potassium azide (PA) (112 kg/ha), oxadiazon + 1,3-dichloropropene (1,3-D) (168 kg/ha + 140 L/ha), dazomet (392 kg/ha), dazomet + chloropicrin (392 + 168 kg/ha), dazomet + 1,3-D (392 kg/ha + 140 L/ha), iodomethane (IM) (336 kg/ha), metam-sodium (MS) (748 L/ha), MS + chloropicrin (748 L/ha + 168 kg/ha), and MS + 1,3-D (748 + 140 L/ha) were evaluated at Jay and Arcadia, FL, in 1998 and 1999 as alternatives to methyl bromide (MeBr) fumigation for the management of common turfgrass weeds. Potassium azide was as effective as MeBr in controlling ‘Coastal’ bermudagrass, yellow and purple nutsedges, alexandergrass, broadleaf signalgrass, tall and sharppod morningglories, and various winter annual broadleaf weeds, but it failed to provide acceptable control of redroot pigweed. 1,3-Dichloropropene + oxadiazon did not control yellow nutsedge, purple nutsedge, or Coastal bermudagrass. Similarly, this combination treatment failed to control carpetweed but did provide 83% control of the winter annual weed species, 71% control of alexandergrass and broadleaf signalgrass, and ≥ 80% control of tall morningglory, sharppod morningglory, and redroot pigweed. Dazomet + combination treatments provided control of Coastal bermudagrass at Jay; however, control of common bermudagrass, alexandergrass, and broadleaf signalgrass was not acceptable at Arcadia. Sedge species control with dazomet + combinations was poor (< 63%) at both sites. Iodomethane, a treatment not yet registered by the U.S. Environmental Protection Agency (EPA), controlled weedy grass species, sedge species, and broadleaf weeds present at the two locations under different environmental conditions. Metam-sodium alone and MS + chloropicrin, tarped and untarped, and MS + 1,3-D provided acceptable weed control; however, MS + chloropicrin covered with a plastic tarp for 48 h was the best MS treatment. Metam-sodium + chloropicrin, with plastic tarp, controlled weedy grass and broadleaf species equal to MeBr; however, unacceptable sedge species control at Jay and Arcadia was 56 and 79%, respectively. Metam-sodium applied alone failed to control redroot pigweed; however, MS + combinations provided control. These studies confirm that no EPA-registered fumigant alternative to MeBr, applied alone or in combination for preplant turf soil fumigation, exists. Consequently, until such time that an effective alternative is identified, turf managers will be forced to forego fumigation, or they will have to choose a less-effective alternative and accept the consequences of contamination. Nomenclature: Chloropicrin (trichloronitromethane); dazomet; 1,3-dichloropropene; iodomethane; metam-sodium; methyl bromide; oxadiazon; potassium azide; alexandergrass, Brachiaria plantaginea (Link) A.S. Hitchc. #3 BRAPL; bermudagrass, Cynodon dactylon (L.) Pers. # CYNDA; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash # BRAPP; carpetweed, Mollugo verticillata L. # MOLVE; purple nutsedge, Cyperus rotundus # CYPRO; redroot pigweed, Amaranthus retroflexus L. # AMARE; sharppod morningglory, Ipomoea cordatotriloba Dennstedt # IPOTC; tall morningglory, Ipomoea purpurea L. # IPOPU; yellow nutsedge, Cyperus esculentus L. # CYPES. Additional index words: Fumigation, sod, turf. Abbreviations: 1,3-D, 1,3-dichloropropene; EPA, Environmental Protection Agency; IM, iodomethane; MeBr, methyl bromide; MITC, methyl isothiocyanate; MS, metam-sodium; PA, potassium azide; WAT, weeks after treatment.

Nitrogen mineralization in a pecan (Carya illinoensis K. Koch)–cotton (Gossypium hirsutum L.) alley cropping system in the southern United States

Information on temporal and spatial patterns of N mineralization is critical in designing tree-crop mixed systems that could maximize N uptake while minimizing N loss. We quantified N mineralization rates in a pecan (Carya illinoensis K. Koch)–cotton (Gossypium hirsutum L.) alley cropping system in northwestern Florida with (non-barrier) and without tree-crop belowground interactions (barrier separating the root systems of pecan and cotton). Monthly rates of mineralization were estimated using buried bag incubations over a 15-month period. In addition, seasonal mineralization rates and cotton lint yield on soils supplied with two sources of N—inorganic fertilizer and organic poultry litter—were assessed. Results indicated that temporal variations in net NH4 and NO3 accumulation and mineralization rates were driven primarily by environmental factors and to a lesser degree by initial soil NH4 and NO3 levels. Mineralization varied by belowground interaction treatment during the initial growing season, when the non-barrier treatment exhibited a higher mineralization rate than the barrier treatment, likely due to reduced nutrient uptake by cotton in the non-barrier or a higher degree of immobilization in the barrier treatment. Mineralization during the second growing season was similar for both treatments. Source of N had no effects on N transformation in the soil. Lint yield reductions were observed in the non-barrier treatment during both years compared to the barrier treatment, likely due to interspecific competition for water. Yield differences between treatments in the second growing season were likely compounded by a diminishing pre-study fallow effect. Source of N was found to have a significant effect on cotton yield, with inorganic fertilizer resulting in 39% higher lint compared to poultry litter in the barrier treatment.

Control of Purple Nutsedge (Cyperus rotundus) with Herbicides and Mowing1

Purple nutsedge management with herbicides (halosulfuron, imazaquin, MSMA, S-metolachlor, and sulfentrazone) and mowing was investigated in a bare ground homogenous purple nutsedge field site. Mowing at 5 cm increased control of purple nutsedge by 6% compared to not mowing. Sequential applications of halosulfuron, MSMA, and sulfentrazone provided at least 80% control of purple nutsedge shoots, whereas imazaquin controlled purple nutsedge shoots less than 65%. All herbicide treatments reduced purple nutsedge total and viable tuber densities at least 40%. S-metolachlor PRE reduced total and viable tuber densities 65 and 69%, respectively. Sequential applications of sulfentrazone or MSMA reduced total and viable tubers 80%. Early postemergence (EPOST) or EPOST followed by late-postemergence applications of halosulfuron and imazaquin reduced total and viable tuber densities 52 and 59%, respectively. Data indicate that S-metolachlor PRE and sequential applications of MSMA and sulfentrazone may be viable treatments for control of purple nutsedge shoots and tubers. Nomenclature: Halosulfuron; imazaquin; MSMA; S-metolachlor; sulfentrazone; purple nutsedge, Cyperus rotundus L. #3 CYPRO. Additional index words: Purple nutsedge control, purple nutsedge tuber viability. Abbreviations: EPOST, early postemergence; LPOST, late-postemergence; WALP, weeks after late-postemergence; WAT, weeks after treatment.

Field Efficacy of Dactylaria higginsii as a Bioherbicide for the Control of Purple Nutsedge (Cyperus rotundus)1

Abstract: An isolate of the fungus Dactylaria higginsii obtained from purple nutsedge in Florida was highly pathogenic to Cyperus spp. The potential of this isolate as a bioherbicide was field tested in natural populations of purple nutsedge in Gainesville and Jay, FL. The fungus was applied in 0.5% Metamucil® as a carrier, and the treatments were: carrier only, 105 conidia/ml + carrier, and 106 conidia/ml + carrier. Treatments were applied as single, double, or triple postemergence (POST) sprays at biweekly intervals. The disease and secondary infections developed in about 5 and 15 d after inoculation, respectively, killing most of the infected leaves. All weed growth parameters and disease progress rates were affected by inoculum dosage and inoculation frequencies. Three inoculations, each at 106 conidia/ml, provided effective control of purple nutsedge compared to a single inoculation, as measured by shoot dry weight, tuber numbers, and tuber dry weight. Higher rates of disease progress and disease levels, defined by the area under the disease progress curve (AUDPC), occurred with three inoculations at 106 conidia/ml. Disease progress was slower and the level of weed control was lower at 105 conidia/ml compared to the higher inoculum level. Three applications of 106 conidia/ml provided >90% nutsedge control. Dactylaria higginsii appears to be an effective bioherbicide candidate deserving further development for commercial use. Nomenclature: Purple nutsedge, Cyperus rotundus L., #3 CYPRO, Dactylaria, D. higginsii (Luttrell) M. B. Ellis. Additional index words: Mycoherbicide, biological control of weeds, fungal pathogen. Abbreviations: AUDPC, area under the disease progress curve; PDA, potato dextrose agar; POST, postemergence; rG, disease progress.

The Persistence of Imazapic in Peanut (Arachis hypogaea) Crop Rotations1

Field studies were conducted at Yoakum and Stephenville, TX; Jay, FL; and Midville and Plains, GA, to determine the persistence of imazapic applied to peanuts at 0, 70, 140, and 210 g ai/ha. The following year, cotton, sorghum, and corn were planted in the treated plots in Texas, cotton was planted in Florida, and corn and cotton were planted in Georgia and evaluated for carryover injury. Data collected to determine injury included plant heights and weights. In 1999 in Texas and in Florida and Georgia, there was no significant carryover injury to rotational crops from any of the imazapic rates. Data on cotton and sorghum plant height from Texas in 2000 showed height reductions for the 210-g/ha rate on cotton and the 140- and 210-g/ha rates on sorghum. These data showed no significant carryover effects to rotational crops from the 70-g/ha rate of imazapic applied to peanuts the previous year. Nomenclature: Imazapic; cotton, Gossypium hirsutum L.; corn, Zea mays L.; peanut, Arachis hypogaea L.; sorghum, Sorghum bicolor L. Additional index words: Carryover injury, herbicide persistence, herbicide residue. Abbreviations: DAP, days after planting; EPOST, early postemergence; MAP, months after planting; PPI, preplant incorporated.

Response of seven peanut (Arachis hypogaea) cultivars to sulfentrazone.

Abstract: Field studies were conducted to evaluate the tolerance of peanut cultivars ‘Florunner’, ‘Georgia Green’, ‘Sunoleic 95R’, ‘AgriTech GK7’, ‘NC-7’, ‘ViruGard’, and ‘Spanco’ to sulfentraone. Herbicide treatments included sulfentrazone applied as a single treatment preemergence (PRE) at 0.14, 0.21, 0.28, 0.35, or 0.42 kg ai/ha or as a PRE followed by (fb) an at cracking (AC) application (0.14 kg ai/ha PRE fb 0.14 kg ai/ha AC, 0.21 kg ai/ha PRE fb 0.14 kg ai/ha AC, 0.21 kg ai/ha PRE fb 0.21 kg ai/ha AC, 0.28 kg ai/ha PRE fb 0.07 kg ai/ha AC, or 0.28 kg ai/ha PRE fb 0.14 kg ai/ha AC). Imazapic and paraquat applied early postemergence (EPOT) were included along with a weed-free control. NC-7 exhibited higher early-season injury (ranging from 1 to 29%) than other cultivars across all sulfentrazone applications. However, this injury did not affect yield when compared with the untreated weed-free check. Overall, peanut tolerance to sulfentrazone was high across all varieties. Nomenclature: Imazapic, (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid); paraquat-dichloride, 1,1′-dimethyl-4,4′-bipyridinium dichloride; sulfentrazone, N-[2,4-dichloro-5-[4-(difluoromethyl)]-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl]phenyl]methanesulfonamide; peanut, Arachis hypogaea L., ‘AgriTech GK7’, ‘Florunner’, ‘Georgia Green’, ‘NC-7’, ‘Sunoleic 95R’, ‘Spanco’, ‘ViruGard’. Additional index words: Peanut injury, peanut cultivar, peanut yield, herbicide susceptibility. Abbreviations: AC, at cracking; ALS, acetolactate synthase; EPOT, early postemergence; fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Torpedograss (Panicum repens) Control with Quinclorac in Bermudagrass (Cynodon dactylon × C. transvaalensis) Turf1

Torpedograss is a serious problem in southern turfgrass, especially along the U.S. gulf coast. Studies were conducted during 1998, 1999, and 2000 to evaluate quinclorac for torpedograss control in bermudagrass turf. Three applications of quinclorac at 0.6 kg/ha spaced 21 d apart provided better torpedograss control (88%) than two applications at 0.8 kg/ha (69%) or one application at 1.7 kg/ha (69%). Two applications of quinclorac (0.8 kg/ha) plus diclofop (0.8 kg/ha) provided better torpedograss control (82%) than either herbicide applied alone when evaluated after a single season of application. Increasing the mowing interval prior to quinclorac application to allow for more foliage to be present did not improve control. Nitrogen application prior to quinclorac treatment did not improve torpedograss control. Long-term control will most likely require quinclorac applications for more than one season. Nomenclature: Diclofop; quinclorac; bermudagrass, Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davey ‘Tifway’; torpedograss, Panicum repens L. #3 PANRE. Additional index words: Application frequency, cultural practices, mowing interval, nitrogen fertility, turfgrass. Abbreviations: LSD, least significant difference; POST, postemergence; WAIT, weeks after initial treatment.