Richard J. Heerema

Resistance to Glyphosate in Palmer Amaranth (Amaranthus palmeri) Populations from New Mexico Pecan Orchards

Abstract Two populations of Palmer amaranth suspected of being resistant to glyphosate have been reported since 2007 in pecan orchards in Doña Ana County, New Mexico. The objectives of the study were to confirm and evaluate the level of resistance, to evaluate the effectiveness of alternative herbicide mechanisms of action, and to compare the cost of effective alternative herbicides for weed management in pecan orchards. Greenhouse experiments indicated that the resistant populations were able to survive glyphosate at 736 g ae ha−1. Compared with a susceptible (S) population, one of the resistant (R) populations had sevenfold resistance to glyphosate. POST application of 12 herbicides, with five different mechanisms of action, all provided at least 88% control of both R and S populations when applied at their recommended field rates. PRE application of trifluralin and metolachlor also provided more than 99% control of R and S populations. The results of field studies indicated that the financial benefit of season-long weed management with glyphosate, in pecan orchards, was comparable with some of the tested alternative herbicides. Nomenclature: 2,4-D; atrazine; carfentrazone-ethyl; dicamba; flumioxazin; glyphosate; glufosinate; imazethapyr; imazamox; metolachlor; oxyfluorfen; primisulfuron; prosulfuron; pyrithiobac; trifluralin; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; pecan, Carya illinoinensis (Wangenh) K. Koch. Resumen Dos poblaciones de Amaranthus palmeri sospechosas de ser resistentes a glyphosate han sido reportadas desde 2007 en plantaciones de pacana en el condado Doña Ana en New Mexico. Los objetivos de este estudio fueron confirmar y evaluar los niveles de resistencia, evaluar la efectividad de herbicidas con mecanismos de acción alternativos, y comparar la eficacia y el costo de herbicidas alternativos efectivos para el manejo de malezas en plantaciones de pacana. Experimentos de invernadero indicaron que las poblaciones resistentes fueron capaces de sobrevivir a glyphosate a 736 g ae ha-1. Comparada con una población susceptible (S), una de las poblaciones resistentes (R) tuvo una resistencia a glyphosate siete veces mayor. Aplicaciones en pos emergencia (POST) de 12 herbicidas, con cinco mecanismos de acción diferentes, proporcionaron un control de al menos 88% para ambas poblaciones R y S cuando se aplicaron a sus respectivas dosis de campo recomendadas. La aplicación en preemergencia (PRE) de trifluralin y metolachlor también brindó mas de 99% de control de poblaciones R y S. Los resultados de estudios de campo indicaron que en plantaciones de pacana, el beneficio monetario de realizar el manejo de malezas a lo largo de todo el ciclo productivo con glyphosate, fue comparable con algunas de los herbicidas alternativos evaluados.

Remote sensing used to detect moisture status of pecan orchards grown in a desert environment

Remote-sensing techniques can detect and up-scale leaf-level physiological responses to large areas, and provide significant and reliable information on water use and irrigation management. The objectives of this study were to screen leaf-level physiological changes that occur during the cyclic irrigation of pecan orchards to determine which responses best represent changes in moisture status of plants and link plant physiological changes to remotely sensed surface reflectance data derived from the Landsat Thematic Mapper and Enhanced Thematic Mapper Plus (ETM+). The study was conducted simultaneously on two southern New Mexico mature pecan orchards. For both orchards, plant physiological responses and remotely sensed surface reflectance data were collected from trees that were either well watered or in water deficit. Remotely sensed variables included reflectance in band 1, the ratio between shortwave infrared (SWIR) bands (B5:B7), the normalized difference vegetation index, and SWIR moisture indices. Midday stem water potential (Ψsmd) was the best performing leaf-level physiological response variable for detecting moisture status in pecans. The B5:B7 ratio positively and significantly correlated with Ψsmd in five of six irrigation cycles while multiple linear regression weighted with six remotely sensed surface reflectance variables revealed a significant relationship with moisture status in all cycles in both orchards (R2 > 0.73). Because changes in the B5:B7 band ratio and multiple regression of spectral variables correlate with the moisture status of pecan orchards, we conclude that remotely sensed data hold promise for detecting the moisture status of pecans.

Comment on “Evolutionary transitions between beneficial and phytopathogenic Rhodococcus challenge disease management”

We would like to address a number of concerns regarding this paper (Savory et al., 2017)