Posts Tagged: resistance
Article written by UC Davis PhD student Caio Brunharo from his dissertation research. It was originally posted in the September 2017 "Weed Management Notes" newsletter from the UC Cooperative Extension office in Glenn County by new weed science and agronomy Farm Advisor Mariano Galla (also a UCD PhD student in weed science!).
Take care, Brad
Italian ryegrass management in perennial crops in California
Caio Brunharo1 and Brad Hanson2
1PhD Candidate, UC Davis; 2UCCE Weed Science Specialist, UC Davis.
Italian ryegrass (Lolium perenne L. spp. multiflorum (Lam.)Husnot) causes yield losses in a variety of cropping systems around the world (Figure 1). This species is highly competitive with annual crops but may also compete with perennial crops particularly during the establishment years when they are most vulnerable to direct competition. In orchards and vineyards, ryegrass infestation can also interfere with cultural practices during the bearing years.
Repeated herbicide use has selected Italian ryegrass populations resistant to a variety of herbicide mode of actions across the world. Glyphosate-resistant Italian ryegrass populations were first reported in California in 2008, and the evolution and spread of these populations in the state made alternative postemergence herbicides an important management strategy against this troublesome species.
Recently, poor control of Italian ryegrass with Gramoxone 2.0 SL was reported in a prune orchard near Hamilton City, California. Greenhouse dose-response experiments and field trials were carried out to evaluate Italian ryegrass response to several postemergence and preemergence herbicides.
Our greenhouse studies confirm that the Italian ryegrass population from Hamilton City is resistant to Gramoxone 2.0 SL, Envoy Plus, Roundup PowerMAX and Osprey, whereas Fusilade DX, Rely 280, Simplicity CA, Matrix and Poast controlled both a known-susceptible and resistant Italian ryegrass population (Table 1). (note: Osprey and Simplicity CA, which are not registered in perennial crops, were included in the study for comparison purposes). Our criteria were that whenever the resistance index (RI) was larger than two and the comparison between biotypes was statistically different (P <0.05), the population was considered as resistant to that particular herbicide. Matrix is an exception, however, because this herbicide controlled both biotypes at well below its recommended field rate.
The field experiment with postemergence herbicides corroborates with data from the greenhouse studies, since glyphosate and paraquat did not adequately control the herbicide-resistant population from Hamilton City. On the other hand, most of the treatments containing Rely 280 were effective for control of the resistant population (Figure 2).
From the preemergence herbicide trial, all treatments containing Alion controlled the resistant population up to 150 days after herbicide application. Chateau, Surflan AS, GoalTender, Prowl H2O, and the tankmixes of Chateau + Prowl H2O and Chateau + Surflan AS exhibited control percentages above 90% with long lasting residual activity (up to 150 days after treatment; Table 2).
Even though several postemergence herbicides controlled Italian ryegrass in our research, it should be noted that ryegrass populations resistant to Fusilade DX, Rely 280 and Poast have been reported elsewhere in the state (data not shown), and overreliance on these herbicides will increase the chances of selection of further cases of resistance. A chemical weed management program in areas infested with Italian ryegrass should include a preemergence herbicide with long residual sprayed in the winter (Alion, Chateau, Surflan, GoalTender or Prowl H2O are possible options) tankmixed with an effective postemergence herbicide. In areas where herbicide-resistant weeds are known to be present, alternative herbicide chemistries should be adopted (rather than increasing the herbicide rate sprayed) in both the winter and spring application. In some cases, a short residual grass herbicide included with the post-harvest burndown application may help reduce recruitment of early-germinating Italian ryegrass plants which will reduce weed pressure and densities to be managed later in the season.
Three citrus trees that produce inedible fruit at the UC Lindcove Research and Extension Center in Visalia may be a game-changer for the citrus industry, reported Ezra David Romero on Valley Public Radio.
The trees are thought to be resistant to huanglongbing, a severe disease of citrus that has devastated the Florida industry and could become a serious problem in California. The citrus-saving potential of the three 34-year-old trees was outlined in an article by UC Agriculture and Natural Resources writer Hazel White in the most recent issue of California Agriculture journal.
UC Riverside citrus breeder Mikeal Roose collected seed from the trees and will test seedlings as soon as they are large enough.
"So what (breeders) have to do is cross this with some edible varieties and eventually create something that has the gene for resistance, but also the genes for good fruit," said Beth Grafton-Cardwell, Lindcove director and research entomologist.
Huanglongbing disease has cut citrus production in Florida by more than half. It's been found in residential citrus trees in Southern California, but hasn't reached the state's vast commercial orchards yet. Grafton-Cardwell said she expects the disease will arrive in 4 or 5 years.
From the UC Weed Science Blog
A repost and link today to a recent Weed Science Society of America press release entitled: "About Weed Seeds and Their Longevity" Click the link to go to the full article.
An excerpt from the press release and links to the free download:
Did you know some weed seeds can lie dormant in the soil for more than a century and then sprout when conditions are right? A new factsheet available for free download from the Weed Science Society of America (WSSA) dives into the topic of weed seed longevity, as well as how weed seeds travel, when and why they germinate, and ways they can be eliminated.
“Understanding weed seeds and their lifespan is critical for both farmers and backyard gardeners alike,” says WSSA member Greta Gramig, Ph.D., associate professor of weed science at North Dakota State University. “Seeds can remain viable in the soil for extended periods of time. That means if even a single weed is allowed to go to seed, you may be battling the aftermath for years to come.”
Here are just a few of the many facts about weed seeds that are covered in the new WSSA fact sheet:
- Moth mullein seeds buried by a researcher in 1879 were still able to germinate more than 130 years later.
- Weed seeds can easily be spread and transported far from their original location. Some have found their way into the earth's planetary boundary.
- Earthworms are known to collect weed seeds and move them into their burrows.
- Weed seeds that remain dormant in the soil will often germinate in response to changes in temperature, moisture, oxygen or light.
- Carabid beetles are voracious eaters and can consume large quantities of weed seeds that drop to the soil.
In addition to its fact sheet on weed seeds, WSSA offers a variety of other free fact sheets and educational materials online, including infographics and presentations on herbicide resistant weeds and their management./span>
Ed Stover and crew at USDA, Fort Pierce in Florida have been studying the response of different scions and rootstocks that have been inoculated with the HLB bacteria. As reported in the Proceedings of the International Citrus Conference (http://www.icc2016.com/images/icc2016/downloads/Abstract_Book_ICC_2016.pdf), they have found some scion/rootstock combinations more tolerant or less susceptible to the disease six years after they have been inoculated. It turns out scions with a citron pedigree have more resistance. Also those with a Poncirus (trifoliate) background also had lower populations of the bacterium.
What this means is that there is resistance and possible immunity out there and there is breeding/genetic engineering material out there that can be used to improve the whole of the citrus family to HLB. Of course, this will take time, but there is hope.
HLB symptoms and trifoliate leaves
From the Topics in Subtropics blog ∴ June 15, 2016 Researchers have now confirmed that...