Nathan S. Boyd

The effects of depth and fluctuating soil moisture on the emergence of eight annual and six perennial plant species

Abstract Weed seedling emergence is partially dependent on biotic and abiotic conditions directly surrounding the seed. When environmental conditions are appropriate, seed germination and emergence occurs. We studied the impact of seeding depth (surface, 1 to 2, 3 to 4, and 6 to 7 cm) and fluctuating soil moisture regimes (field capacity [FC]–1/3FC–FC; FC–1/6FC–FC) on percent weed emergence in a greenhouse. At FC, wild mustard and field pennycress had the greatest percent emergence when seeds were placed on or near the soil surface, whereas percent emergence of barnyardgrass and round-leaved mallow was unaffected by seeding depth. All the perennials tested had the greatest percent emergence at FC when seeds were placed near or on the soil surface, except for common milkweed which only emerged below the soil surface. When soil moisture levels fluctuated, surface seeds of barnyardgrass, catchweed bedstraw, green foxtail, wheat, and wild oat had less emergence than seeds below the soil surface; field pennycress had increased emergence when the seeds were placed on the surface; and round-leaved mallow and wild mustard emergence was unaffected by seeding depth. The emergence of curly dock, dandelion, and perennial sowthistle was unaffected by seeding depth, whereas foxtail barley and quackgrass emergence was reduced when seeds were placed on the surface and soil moisture fluctuated. Nomenclature:  Barnyardgrass, Echinochloa crus-galli L. ECHCG; catchweed bedstraw, Galium aparine L. GALAP; common milkweed, Asclepias syriaca L. ASCSY; curly dock, Rumex crispus L. RUMCR; dandelion, Taraxacum officinale Weber in Wiggers TAROF; field pennycress, Thlaspi arvense L. THLAR; foxtail barley, Hordeum jubatum L. HORJU; green foxtail, Setaria viridis (L.) Beauv. SETVI; perennial sowthistle, Sonchus arvensis L. SONAR; quackgrass, Elytrigia repens (L.) Nevski AGGRE; round-leaved mallow, Malva pusilla Sm. MALSU; spring wheat, Triticum aestivum L. ‘AC Barrie’ wild mustard, Brassica kaber (D.C.) L.C. Wheeler SINAR; wild oat, Avena fatua L. AVEFA.

Stale Seedbed Techniques for Organic Vegetable Production

Weed control in organic vegetable production systems is challenging and accounts for a large portion of production costs. Six methods to prepare a stale seedbed were compared on certified and transitional organic land in Salinas, CA, in 2004. Weed control operations occurred on raised beds 2 to 3 d before planting baby spinach or a simulated vegetable planting. A flamer and an herbicide application of 10% v/v of a clove oil mixture (45% v/v clove oil) at 280 L/ha (iteration 1) or 15% v/v of a clove oil mixture (45% clove oil) at 467 L/ha (iterations 2 and 3) were used to control weeds without disturbing the soil. Top knives on a sled, a rolling cultivator, and a rotary hoe were used to control weeds while tilling the bed top. A bed shaper–rototiller combination was also used, which tilled the entire bed. Broadleaf weed control was 36% with clove oil, 63% with the rotary hoe, and significantly higher (87 to 100% control) with the remaining treatments in iteration 1. Broadleaf weed control was consistently lower (72 to 86% control) with the flamer than all other treatments (95 to 100% control) in iterations 2 and 3. The difference between sites can probably be attributed to differences in weed size. The flamer and the clove oil herbicide had the lowest number of weeds emerging with the crop following stale seedbed formation. The most expensive technique was clove oil at

Hexazinone and Fertilizer Impacts on Sheep Sorrel (Rumex acetosella) in Wild Blueberry

1,372/ha. The estimated cost of forming the stale seedbed with the remaining weed management tools ranged from

Impact of Wild Blueberry Harvesters on Weed Seed Dispersal within and between Fields

10 to

The Impacts of Fertilizer and Hexazinone on Sheep Sorrel (Rumex acetosella) Growth Patterns in Lowbush Blueberry Fields

43/ha. Nomenclature: Spinach, Spinacia oleracea L. #3 SPQOL. Additional index words: Flaming, cultivation, weed emergence, irrigation, stale seedbeds, vegetables. Abbreviations: USDA-ARS, U.S. Department of Agriculture–Agricultural Research Service.

Effect of Dry Heat, Direct Flame, and Straw Burning on Seed Germination of Weed Species Found in Lowbush Blueberry Fields

Abstract Sheep sorrel is an invasive, creeping perennial weed of lowbush blueberry fields. It is one of the most prominent weeds in blueberry fields in Nova Scotia and is responsible for decreasing yields. Three levels of fertilizer (0, 20, 40 kg N ha−1) and two levels of hexazinone (0 or 1.92 kg ai ha−1) were applied to experimental plots to determine their effects on sheep sorrel density. Sprout-year hexazinone reduced sheep sorrel densities, which led to increased yields. Fertilizer increased weed density in the absence of herbicides, had no effect on density in the presence of herbicides, tended to have no impact on floral buds, and did not increase yields. Fruiting-year hexazinone decreased sheep sorrel densities in some situations, but did not result in yield increases. Nomenclature: Hexazinone, Velpar; sheep sorrel, Rumex acetosella L.; lowbush blueberry, Vaccinium angustifolium Ait. and Vaccinium myrtilloides Michx.

Clopyralid Dose Response for Two Black Medic (Medicago lupulina) Growth Stages

Abstract Agricultural equipment can disperse weed seeds over large distances. Efforts to minimize or prevent equipment-mediated dispersal should be a key component in any integrated weed management plan. Several experiments were initiated in commercial wild blueberry fields to examine the potential impact of harvesting equipment on weed seed dispersal within and between blueberry fields. Seed loads were examined on harvesting equipment between fields and results suggest that harvesting equipment is a major vector of seed dispersal. Seed loads were 397,000 in 2006 and 194,000 in 2007. Of all seeds located on the harvester, 66 to 79% were located on the belts or affiliated components. In 2006, a second experiment was established to examine within-field seed dispersal. A sampling grid was established over multiple distinct poverty oatgrass patches with seed heads at 44% of all sampling points. Following harvest, seeds were located at 67% of all sampling points. In 2006 and 2007, short-distance secondary dispersal of poverty oatgrass by harvesting equipment was measured. The relationship between distance from patch perimeter and seeds per unit area on the side approached by harvesting equipment and the far side of the patch was adequately modeled with an exponential decay model. Secondary dispersal within blueberry fields by harvesting equipment is inevitable. Dispersal may be reduced by avoiding dense weed patches, or altering harvest timing. Periodic cleaning of harvesting equipment between fields will help prevent the spread of weed seed. Nomenclature: Poverty oatgrass, Danthonia spicata (L.) Beauv. ex Roemer & J. A. Schultes DANSP; wild blueberry, Vaccinium angustifolium Ait. and Vaccinium myrtilloides Michx.

Spreading Dogbane (Apocynum androsaemifolium) Development in Wild Blueberry Fields

Abstract Sheep sorrel is an invasive, creeping perennial weed of lowbush blueberry fields that decreases yields and hinders harvest. Much of the basic phenology of sheep sorrel in blueberry fields is unknown and not documented in peer-reviewed journals. Three levels of fertilizer (0, 20, and 40 kg N ha−1) and two levels of hexazinone (0 and 1.92 kg ai ha−1) were applied to three vegetative-year blueberry fields to determine their effects on root and shoot growth, biomass allocation, and seed production of sheep sorrel plants. Hexazinone efficacy varied widely between sites, but suppressed shoot biomass, achene number and weight, and reproductive biomass, as well as the reproductive ∶ shoot biomass ratio. Fertilizer tended to increase achene number and increased sheep sorrel shoot biomass in the absence of hexazinone, but had no effect on achene weight, root biomass, or reproductive biomass. When fertilizer was applied, sheep sorrel allocated resources to sexual reproduction at the expense of vegetative growth. Nomenclature: Hexazinone; Velpar; sheep sorrel, Rumex acetosella L.; lowbush blueberry, Vaccinium angustifolium Ait. and Vaccinium myrtilloides Michx.

Weed Management in a Legume-Cereal Cover Crop with the Rotary Hoe1

Experiments were conducted to determine the effects of dry heat, direct flame, and straw burning on germination of several weed species from lowbush blueberry fields. Dry heat experiments were designed as factorial arrangements of temperature (100, 200, and 300 C in experiment 1 and room temperature, 100, 200, and 300 C in experiment 2) and exposure time (0, 5, 10, 20, 40, and 80 s in experiment 1 and 2, 5, 10, and 20 s in experiment 2) to determine the exposure time required to reduce germination for each temperature. Susceptibility to dry heat varied across species tested, but germination of spreading dogbane, meadow salsify, fireweed, and hair fescue seeds collected from lowbush blueberry fields in Nova Scotia, Canada generally declined exponentially as a function of duration of heat exposure at the temperatures tested. Germination decreased more rapidly at higher temperatures in all species, although the duration of heat exposure required to reduce germination by 50 and 90% varied across temperatures and species. Exposure of seeds to direct flame rapidly reduced germination, with less than 1 s of exposure required to reduce seed germination of witchgrass, spreading dogbane, and meadow salsify by > 90%. Straw burning did not consistently reduce germination of hair fescue or winter bentgrass, indicating that a surface burn occurring above weed seeds may not be consistently effective at reducing seed viability. These results provide important estimates of the temperature and exposure times required to reduce viability of weed seeds in lowbush blueberry fields and suggest that thermal technologies that expose weed seeds to direct flame will be the most consistent in reducing seed viability. Nomenclature: Fireweed, Chamerion angustifolium (L.) Holub CHAAN; hair fescue, Festuca filiformis Pourret FESTE; meadow salsify, Tragopogon pratensis L. TROPR; spreading dogbane, Apocynum androsaemifolium L. APCAN; winter bentgrass, Agrostis hyemalis (Walt.); witchgrass, Panicum capillaire L. PANCA; lowbush blueberry, Vaccinium angustifolium Ait. Experimentos fueron realizados para determinar los efectos de calor seco, llama directa, y la quema de paja sobre la germinación de varias especies de malezas en campos de arándano de arbusto bajo. Los experimentos con calor seco fueron diseñados como arreglos factoriales de temperatura (100, 200, y 300 C en el experimento 1, y temperatura ambiente, 100, 200, y 300 C en el experimento 2) y de duración de exposición (0, 5, 10, 20, 40, y 80 s en experimento 1, y 2, 5, 10, y 20 s en experimento 2), para determinar el tiempo de exposición requerido para reducir la germinación en cada temperatura. La susceptibilidad al calor seco varió entre las especies evaluadas, pero la germinación de semillas de Apocynum androsaemifolium, Tragopogon pratensis, Chamerion angustifolium, y Festuca filiformis colectadas en campos de arándano de arbusto bajo en Nova Scotia, Canada, generalmente declinó exponencialmente en función de la duración de la exposición al calor a las temperaturas evaluadas. La germinación disminuyó más rápidamente a temperaturas más altas en todas las especies, aunque la duración de la exposición al calor requerida para reducir la germinación en 50 y 90% varió entre las temperaturas y las especies. La exposición directa de semillas a llamas rápidamente redujo la germinación, con menos de 1 s de exposición requerida para reducir en >90% la germinación de las semillas de Panicum capillare, A. androsaemifolium, y T. pratensis. La quema de paja no redujo consistentemente la germinación de F. filiformis o de Agrostis hyemalis, indicando que una quema superficial sobre las semillas de malezas no sería consistentemente efectiva para reducir la viabilidad de las semillas. Estos resultados brindan estimados importantes de la temperatura y los tiempos de exposición requeridos para reducir la viabilidad de las semillas de malezas en campos de arándano de arbusto bajo y sugiere que las tecnologías termales que exponen directamente las malezas de semillas a llamas serán las más consistentes para reducir la viabilidad de las semillas.

Impact of Application Time and Clopyralid Rate on Strawberry Growth and Yield

Black medic is a troublesome weed in commercial strawberry fields in Florida. It emerges during crop establishment from the planting holes punched in plastic mulches that are installed on raised beds. Clopyralid is registered for posttransplant applications at 140 to 280 g ae ha−1 but growers typically report suppression, not control. An outdoor potted experiment was designed to model the black medic dose-response curve and determine the effect of plant size at application on control. Two plant sizes were selected: designated small (0.5- to 1-cm stem length) and large (3- to 6-cm stem length). Dose-response curves were generated using a log-logistic four-parameter model. At 22 d after treatment (DAT), there was a significant interaction between clopyralid rate and black medic growth stage on both epinasty (P = 0.0022) and chlorosis (P = 0.0055). The effective dosage to induce 90% (ED90) epinasty were 249.5 and 398.3 g ha−1 for the small and large growth stages, respectively. The ED90 for chlorosis was 748.2 for the small growth stage, whereas the estimated value for the large was outside the measured range. For necrosis there was no significant effect of growth stage, and the ED90 was 1,856.3 g ha−1. The aboveground dry biomass ED90 for the small growth stage was 197.3 g ha−1, and the estimated ED90 value for the large was not within the measured range. Results indicate that clopyralid adequately controls black medic when applied at maximum label rates when stems were 0.5 to 1 cm long but not when plants were larger. Poor efficacy typically observed in commercial fields is likely due to black medic plant size or lack of herbicide coverage via shielding by strawberry plants. Nomenclature: Clopyralid; black medic, Medicago lupulina L. MEDLU. Medicago lupulina es una maleza problemática en campos comerciales de fresa en Florida. Esta maleza emerge durante el establecimiento del cultivo en los huecos hechos para el cultivo en la cobertura plástica sobre las camas de siembra. Clopyralid esta registrado para aplicaciones pos-trasplante a 140 a 280 g ae ha−1, pero los productores típicamente reportan supresión y no control de esta maleza. Se diseñó un experimento al aire libre en potes para modelar la curva de respuesta a dosis de M. lupulina, estimar la dosis de clopyralid requerida para alcanzar 90% de control, y determinar el efecto sobre el control del tamaño de planta al momento de la aplicación. Se seleccionaron dos tamaños de planta designados: pequeño (0.5 a 1 cm de longitud del tallo) y grande (3 a 6 cm de longitud del tallo). Las curvas de respuesta a dosis fueron generadas usando un modelo log-logístico de cuatro parámetros. A 22 d después del tratamiento (DAT), hubo una interacción significativa entre la dosis de clopyralid y el estadio de crecimiento de M. lupulina con respecto a epinastia (P = 0.0022) y clorosis (P = 0.0055). La dosis efectiva para inducir 90% (ED90) de epinastia fue 249.5 y 398.3 g ha−1 para los estadios pequeño y grande, respectivamente. La ED90 para clorosis fue 748.2 para el estadio pequeño, mientras que el valor estimado para el grande estuvo fuera del rango estudiado. Para necrosis, no hubo un efecto significativo del estadio de crecimiento, y la ED90 fue 1,856.3 g ha−1. La ED90 para biomasa aérea seca para el estadio pequeño fue 197.3 g ha−1, y el valor estimado de ED90 para el estadio grande no estuvo dentro del rango medido. Los resultados indican que clopyralid controla adecuadamente M. lupulina cuando se aplica a las dosis máximas de la etiqueta a tallos de 0.5 a 1 cm de longitud, pero no cuando las plantas son más grandes. La pobre eficacia típicamente observada en campos comerciales se debe probablemente al tamaño de planta de M lupulina o a una cobertura del herbicida limitada producto de la interferencia de las plantas de fresa.