Posts Tagged: weeds
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.
Here's the latest from the UC ANR Topics in Subtropics blog written by Ben...
It really has gotten out of hand - Hairy Fleabane and Horseweed which are both Conyza weed species that have run rampant this year because of the extra rain. It's also because they have become resistant to glyphosate herbicide. The problem has shown up all over the US and other parts of the world. Gradually as resistance has grown and their resistant fairy seeds have floated wherever the winds go, the weed is having a field day everywhere in your backyard, in your orchard, in the sidewalk. It's not just abandoned areas, but in actively managed areas where Cal Trans is doing its best.
Citrus growers who have not used preemergents in years or never used them have turned to various cocktails to knock it out.
A good description of the biology and care of Conyza can be found at:
And we along with others have written about this problem in the past -
http://ucanr.edu/blogs/topics/index.cfm tagname=Conyza ,
But this year has been exceptional in the ubiquity of this plant. Something more than glyphosate is called for at this point. Glufosinate is a postemergent herbicide somewhat similar to glyphosate in name only and more expensive. It is a broadspectrum herbicide that is effective with thorough coverage on younger stages of conyza and other weeds. It will take some learning to get the best effect out of it. Citrus growers have been able to use it for several years now and have enjoyed its effectiveness. We are currently working on an IR-4 registration (http://ir4.rutgers.edu/) for avocados. It is currently not registered for use in avocado.
Mature avocados are pretty good about controlling any weeds in their own orchards through ground shading and self mulching, but conyza has become a problem in young orchards. And this new herbicide could help.
There was a post written a few months ago by Rebecca Ozeran entitled “A Tale of Two...
Rain is unusual in that it germinates weed seeds and then the need to manage them in some fashion arises. Many subtropical tree growers do not like the potential impact of pre-emergent herbicides on tree growth due to potential damage to shallow roots. Lemon growers rely fairly heavily on the post-emergent glyphosate, especially since there are cheap generic versions available. I don't know of many avocado growers who use a pre-emergent, using the natural mulching effects of fallen leaves, introduced mulch, the natural shading of the canopies and glyphosate.
I am not aware of any field studies that have shown that pre-emergents can cause root damage or reduction of tree growth or yield. There are a number of registered chemicals with different modes of action, so one would expect to see more use as practiced in other tree crops, but there is a reluctance that is based on some possible damage to trees. So, a lot of glyphosate is used and to some extent another material, glufosinate, is also used in citrus.
One of the issues that has arisen with glyphosate use has been the resistance of some weed species to this material. There are some thirty-seven species of resistant weeds in the world. In California orchards, the biggies are Hairy Fleabane, Horseweed and Johnson grass. Resistance means that you can spray the plants, even in their small stages and there's little or no effect. A non-resistant species would just wither, turn yellow and die down to the roots.
There are always plants like horsetail or purslane which have a surface that does not absorb material very well. They appear to be resistant, but aren't. Once you use the maximum dose, with a spreader-sticker or another adjuvant, the herbicide gets into the plant and it dies. Also, the key is timing, young plants being much more susceptible than bigger plants with a less absorptive surface.
This year, though with all the rains, there've been calls about not just horseweed being tough to get, but also nutsedge. Nutsedge, as far as I know, has no documented resistance, but it does have a waxy surface that gets thicker with the age of the plant. With all the weeds, people have gotten behind and the weeds have gotten out of hand and the older plants are harder to spray out. It takes more tact to get at them when they get older.
Nutsedge also reproduces from swollen underground stems called tubers or “nuts”. They aren't nuts – seeds – and some people mistake them for a grass, which they are not. They are a sedge. They reproduce primarily through the “nut” and they form lots of “nutlettes”, each of which can form a new plant. If you pull the plant up and don't get all those nutlettes, you are actually increasing the number of plants that will form. It is tricky to deal with and a good thorough spraying can control them, if done at the right stage.
It turns out that these nuts are eaten by lots of animals – pigs, chickens, humans. In the South, pigs and chickens have been used to clear fields of nutsedge before planting rice. The presents of nutsedge around the world is quite likely due to humans having spread it around the world as a food. A poor person's nut.
So, this brings me to the title of this article. Why not grow it for sale? Intercrop it with lemon. Drip irrigate the nutsedge separate from the trees and figure out the pesticide schedule and other management issues and there's a new crop for sale. Foraging for malva, nettle, mustard, pursalane, dandelions and other unconventional edible plants has become a big deal in urban agriculture. You see “wild plants” for sale in the farmers markets. Euell Gibbons has become not just fashionable but commercial. Kale has taken the country by storm. Who would have thought it?
Root System of Yellow Nutsedge