Milton J. Haar

Evaluation of Integrated Practices for Common Purslane (Portulaca oleracea) Management in Lettuce (Lactuca sativa) 1

Studies were conducted to develop a weed management strategy for common purslane in lettuce based on available cultural and chemical control methods and an understanding of common purslane biology. A wide-band application of bensulide or pronamide reduced common purslane emergence compared with the standard narrow band. Both narrow and wide bands of pronamide as well as a wide band of bensulide reduced the time required to thin and hoe lettuce. The wide-band pronamide treatment reduced thinning time more than did the narrow band. Overall, none of the herbicide weed management expenses were lower for pronamide treatments than for bensulide and the control. Wide-band bensulide reduced weed management expenses compared with the control, whereas narrow bands did not. Common purslane plants uprooted 1 or 2 wk after emergence (WAE) did not produce any viable seed. Plants uprooted 3 WAE produced from 1 to 60 viable seeds, and seed production increased rapidly from 4 to 6 WAE. Flame and 2% (v/v) glyphosate treatments reduced seed production by uprooted common purslane. Nomenclature: Bensulide; pronamide; common purslane, Portulaca oleracea L. #3 POROL; lettuce, Lactuca sativa L. Additional index words: Banded herbicide, weed seed production. Abbreviations: DAT, days after treatment; GDD, growing degree day; WAE, weeks after emergence.

Temperature and Relative Humidity Affect Weed Response to Vinegar and Clove Oil

Abstract Nonsynthetic herbicides offer a potentially useful addition to the suite of weed management tools available to organic growers, but limited information is available to guide the optimal use of these products. The objectives of this research were to (1) evaluate the efficacy of clove oil– and vinegar-based herbicides on weeds across multiple states, and (2) assess the potential role of temperature, relative humidity (RH), and cloud cover in explaining inter-state variations in results. From 2006 to 2008, a total of 20 field trials were conducted in seven states using an identical protocol. Seeds of brown mustard were sown and herbicides applied to both mustard and emerged weeds when mustard reached the three- to four-leaf stage. Treatments included clove oil at 2.5, 5, 7.5, and 10% v/v concentrations at 54 L ha−1, and vinegar at 5, 10, 15, and 20% v/v concentrations at 107 L ha−1. Results varied widely across trials. In general, concentrations of at least 7.5% for clove oil and 15% for vinegar were needed for adequate control of mustard. Both products were more effective at suppressing mustard than Amaranthus spp. or common lambsquarters. Poor control was observed for annual grasses. No significant effects of cloud cover on the efficacy of either product were detected. In contrast, RH was positively correlated with control of brown mustard by both clove oil and vinegar with improved control at higher RH. Temperature had no detectable effect on the efficacy of clove oil, but higher temperatures improved control of brown mustard by vinegar. Nomenclature: Clove oil; vinegar; common lambsquarters, Chenopodium album L.; redroot pigweed, Amaranthus retroflexus L.; brown mustard, Brassica juncea L. Czerniak. Resumen Herbicidas no-sintéticos ofrecen potencialmente una adición útil a la variedad de herramientas para el manejo de malezas, disponible para productores orgánicos. Sin embargo, hay poca información disponible para guiar el uso óptimo de estos productos. Los objetivos de esta investigación fueron (1) evaluar, en diferentes estados, la eficacia de herbicidas a base de aceite de trébol y de vinagre sobre malezas, y (2) evaluar el papel potencial de la temperatura, humedad relativa (RH), y la cobertura nubosa para explicar variaciones inter-estatales en los resultados. De 2006 a 2008, un total de 20 experimentos de campo fueron realizados en siete estados usando un protocolo idéntico. Semillas de mostaza (Brassica juncea) fueron sembradas y los herbicidas aplicados a la mostaza y malezas emergidas cuando la mostaza alcanzó el estado de desarrollo de tres a cuatro hojas. Los tratamientos incluyeron aceite de trébol a concentraciones de 2.5, 5, 7.5 y 10% v/v a 54 L ha−1, y vinagre a concentraciones de 5, 10, 15 y 20% v/v a 107 L ha−1. Los resultados variaron ampliamente entre experimentos. En general, concentraciones de al menos 7.5% para el aceite de trébol y 15% para el vinagre fueron necesarias para el control adecuado de la mostaza. Ambos productos fueron más efectivos para suprimir la mostaza que Amaranthus spp. o Chenopodium album. Se observó un control pobre de gramíneas anuales. No se detectaron efectos significativos de la cobertura nubosa sobre la eficacia de ninguno de los productos. En cambio, la RH estuvo positivamente correlacionada con el control de la mostaza por el aceite de trébol y el vinagre con un mejor control a RH más altas. La temperatura no tuvo efectos detectables sobre la eficacia del aceite de trébol, pero las temperaturas altas mejoraron el control de la mostaza con vinagre.