Here's the latest from the UC ANR Topics in Subtropics blog written by Ben Faber, Farm Advisor, UCCE Ventura County.

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: https://anrcatalog.ucanr.edu/pdf/8314.pdf

And we along with others have written about this problem in the past - 

• http://ucanr.edu/blogs/topics/index.cfm tagname=Conyza, 
• Herbicide resistant weeds in your neighborhood: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=10648, 
• What is that in my grove, Horseweed or Hairy Fleabane?: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=20061

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.

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.