- Author: Marie Jasieniuk
- Author: Maor Matzrafi
Italian ryegrass is a major weed in orchards, vineyards, field crops and fallow fields of California (Figure 1). Several different herbicides are used to control ryegrass and had been effective in reducing infestations until resistance evolved in many populations following repeated use of the herbicides. To date, resistance to glyphosate, paraquat, and some ACCase and ALS inhibitors has been confirmed in ryegrass infestations across the agricultural landscape of California. To make matters worse, resistance to multiple postemergence herbicides with different modes of action has been confirmed within the same orchard, vineyard, or field in some areas. Consequently, management of Italian ryegrass in California annual and perennial cropping systems has become a major challenge.
Glufosinate is an alternative non-selective postemergence herbicide that can still be used to control herbicide-susceptible and most herbicide-resistant Italian ryegrass in California, as only two populations with resistance to glufosinate have been documented to date. However, the higher cost of glufosinate relative to other herbicides may drive farmers to apply glufosinate at reduced rates, as has occurred in other cropping systems, such as the Australian wheat belt, with other herbicides. The lower rates and other drivers such as herbicide applications at non-optimal weed size, inappropriate weather conditions, and insufficient spray coverage may result in sublethal rate selection of ryegrass by glufosinate.
To evaluate the potential for low glufosinate rates to select for reduced susceptibility to the herbicide, and to determine if selected populations are cross-resistant to herbicides with other modes of action as has been observed in a few studies, we conducted a greenhouse study using a herbicide-susceptible parent population originally collected from a vineyard in Sonoma County. Plants were grown in the greenhouse to the 3-4 leaf stage and treated with low glufosinate rates for three generations. For the first round of selection, plants were treated with glufosinate at 1/8X, 1/4X, and 1/2X of the labelled field rate (984 g ai ha-1). Surviving plants were grown to reproductive maturity and allowed to cross-pollinate. Seeds were harvested from all plants, pooled, germinated, and plants grown in the greenhouse for the next round of selection at slightly higher rates (1/2X, 3/4X, and 1X). For the third round of selection, plants were treated at 3/4X, 1X, and 1.25X of the labelled field rate.
Results showed that susceptibility to glufosinate was reduced in offspring in comparison with the susceptible parent population following only three generations of selection (Figure 2). Comparing the susceptible parent population with the offspring from the second and third selection cycle, the percentage of surviving plants increased to values of LD50 (1.31 and 1.16, respectively) and LD90 (1.36 and 1.26, respectively).
Figure 2. Dose-response of the Italian ryegrass susceptible parent population (P0) and three successive generations (P1, P2, P3) of offspring following selection with low glufosinate rates in the greenhouse. Lines are the predicted values for percent survival. Red arrow indicates the labelled field rate (984 g ai h-1). Adapted from Matzrafi et al., 2020 (https://www.biorxiv.org/content/10.1101/2020.07.04.182733v1).
When treated with alternative postemergence herbicides (glyphosate, paraquat, or sethoxydim), no plants of either the parental or successive offspring populations survived treatment with 0.75X or higher rates of these herbicides (see Matzrafi et al., 2020 (https://www.biorxiv.org/content/10.1101/2020.07.04.182733v1).
The magnitude of increases in resistance levels over three generations of recurrent low-rate glufosinate selection observed is relatively low compared with higher levels of resistance observed in response to low-rate selection with other herbicides (three-fold and greater). However, under field conditions, even low levels of resistance within weed populations may reduce control. This study shows that repeated selection with glufosinate at low rates can reduce the susceptibility of Italian ryegrass populations to glufosinate, and points to the importance of incorporating a diversity of approaches, both chemical and non-chemical, in the management of ryegrass in annual and perennial cropping systems of California.
This article was originally published in the Weed Science blog.
- Author: Kathy Keatley Garvey
A super weed commonly known as Palmer amaranth or Palmer pigweed (Amaranthus palmeri) may soon not be so super.
In first-of-its-kind research, a 10-member international team of scientists, led by Maor Matzrafi of the Hebrew University of Jerusalem, Ittai Herrmann from Ben-Gurion University of the Negev, and UC Davis agricultural entomologist Christian Nansen, used hyperspectral technologies to successfully predict the viability of the weed seeds and herbicide response.
The research, published in the current edition of Frontiers of Plant Science, (https://doi.org/10.3389/fpls.2017.00474) offers growers of cotton, soybean, corn, watermelon and other crops a new tool in their toolbox to thwart the growth of the herbicide-resistant Palmer amaranth, a fast-growing and highly aggressive weed which cripples crop yields.
The newly published research indicates that through hyperspectral technologies and analysis, growers may soon more accurately predict seed germination and response to the herbicide trifloxysulfuron-methyl (sold as Envoke and Monument). Correlation between leaf physiological parameters and herbicide response (sensitivity/resistance) was also demonstrated.
The weed, native to the desert regions of the southwest United States and northern Mexico, and now found throughout much of the world, has developed resistance in many areas to glyphosate, a broad-spectrum herbicide. The summer annual is especially troubling to cotton and soybean farmers in the southern United States. The weed can grow several inches a day and up to 8 to 10 feet in height. A single plant can produce between 100,000 and 500,000 seeds.
“Weed infestations in agricultural systems constitute a serious challenge to agricultural sustainability and food security worldwide,” the researchers wrote in their abstract, pointing out that weeds are responsible for more than 34 percent of crop yield losses throughout the world. “The ability to estimate seed viability and herbicide susceptibility is a key factor in the development of a long-term management strategy, particularly since the misuse of herbicides is driving the evolution of herbicide response in various weed species.”
In the research, they “demonstrated that hyperspectral reflectance analyses can provide reliable information about seed germination and levels of susceptibility in Amaranthus palmeri,” the researchers wrote. “The use of reflectance-based analyses can help to better understand the invasiveness of A. palmeri, and thus facilitate the development of target control methods. It also has enormous potential for impacting environment management in that it can be used to prevent ineffective herbicide applications.”
Their research showed high levels of accuracy. Using hyperspectral data, they successfully distinguished between germinating and non-germinating seeds, showing an accuracy of 81.9 percent and 76.4 percent, respectfully. Also, using a classification model that distinguishes between the three classes of herbicide response (sensitive, moderate response and resistant), they identified sensitive and resistant plants with high degrees of accuracy, 85.5 percent and 90.9 percent respectfully, from leaf hyperspectral reflectance profiles acquired prior to herbicide application.
Using less herbicide is a win-win situation: a win for the growers and a win for the environment.
Researcher Nansen, an assistant professor in the UC Davis Department of Entomology and Nematology, and also part of the State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, Zhejiang Academy of Agricultural Sciences, Hangzhou, China, contrasted the seeds hyperspectral imaging system and analyzed the data.
Lead author Matzrafi, currently a post-doctoral researcher in the UC Davis Department of Plant Sciences, is with the Hebrew University of Jerusalem's Robert H. Smith Faculty of Agriculture, Food and Environment as are co-authors Tom Kliper, Yotam Zait, and Baruch Rubin.
Other co-authors:
- Ittai Herrmann and Arnon Karnieli of the Remote Sensing Laboratory, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Beersheba, Israel
- Timea Ignat of the Institute of Agricultural Engineering, Agricultural Research Organization, Volcani Center, Rishon LeZion, Israel
- Hanan Eizenberg, Department of Plant Pathology and Weed Research, Agricultural Research Organization, Newe Ya'ar Research Center, Newe Yaar, Israel
The study was funded in part by the Office of the Chief Scientist, Israel Ministry of Agriculture and Rural Development.
Nansen said his lab in the UC Davis Department of Entomology and Nematology is pursuing a wide range of applications of image-based classifications of “objects” – such as seeds, insects, and growing plants. “These applications are part of a growing appreciation for imaging at high spatial and spectral resolutions under controlled laboratory conditions--sometimes referred to as ‘proximal remote sensing'--to describe objects, he said. “As portions of the surface reflectance features penetrate into objects, this technology can be used non-invasively to quantify traits, which are associated with physiological stages – including viability of seeds and/or metabolic processes in growing leaves.”