Subtropical Fruit Crops Research & Education
University of California
Subtropical Fruit Crops Research & Education

Posts Tagged: roundup

Glyphosate Resistance in Orchards

There has been a good overall discussion of herbicide resistance found in plants and how they can affect orchard management.  Check out this presentation by UC Cooperative Extension Weedologist, Brad Hanson, in the "past Webinars" section:

And read more about glyphosate resistance in orchards:

Preventing and Managing Glyphosate-Resistant Weeds in Orchards and Vineyards
Rely too much on any one herbicide and you end up with weeds that will resist its effects—and that's just what is happening now with glyphosate (Roundup®). See how you can increase effectiveness by diversifying your weed-management strategies.
Publication Number:: 8501
Managing Glyphosate-Resistant Weeds in Glyphosate-Resistant Crops
Glyphosate-resistant crops made farming a lot easier when they first came out, but many weeds have developed resistance. Herbicide-tolerant crops will only work as part of a more comprehensive, Integrated Pest Management plan.
Publication Number:: 8494

hairy fleabane 1
hairy fleabane 1

Posted on Monday, May 6, 2019 at 6:22 AM
Tags: glyphosate (6), herbicides (18), resistance (13), roundup (2), weeds (32)

You See It Here, You See It There - That Elusive Hairy Fleabane Everywhere

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 - 

// tagname=Conyza , 

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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 ( 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.



Posted on Friday, August 18, 2017 at 4:51 AM
Tags: avocado (287), citrus (335), grapefruit (27), herbicide resistance (2), lemon (100), mandarin (68), orange (69), roundup (2), weed control (8), weeds (32)
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