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Posts Tagged: invasive weeds

Cal Ag article: Predicting invasive plants in California (by Brusati et al.)

Link to a recent (July 2014) research article in California Agriculture (link to table of contents for volume 68)


The article by E.D. Brusati, D.W. Johnson, and J.M. DiTomaso is entitled "Predicting Invasive Plants in California" focuses on risk assessment modeling of plants under consideration for importation through the horticultural industry.


Preventing plant invasions or eradicating incipient populations is much less costly than confronting large well-established populations of invasive plants. We developed a preliminary determination of plants that pose the greatest risk of becoming invasive in California, primarily through the horticultural industry. We identified 774 species that are invasive elsewhere in Mediterranean climates but not yet invasive in California. From this list, we determined which species are sold through the horticulture industry, whether they are sold in California and whether they have been reported as naturalized in California. We narrowed the list to 186 species with the greatest potential for introduction and/or invasiveness to California through the horticultural trade. This study provides a basis for determining species to evaluate further through a more detailed risk assessment that may subsequently prevent importation via the horticultural pathway. Our results can also help land managers know which species to watch for in wildlands.

Link to full article in California Agriculture


arundo donax from CalAg68 pg89 DiTomaso
arundo donax from CalAg68 pg89 DiTomaso

Posted on Tuesday, August 5, 2014 at 3:40 PM

The Cooperative Mule

From the Invasive Plants in Southern California blog :: Nov. 22, 2013


Hi All. In my last blog the subject was about what I had learned regarding the use herbicides as a tool for effective passive restoration of CSS and native grassland habitats. As an Extension Advisor my job is to not only develop new information, but to also try to move it forward into practice.

In this case that means educating land managers and related professionals on how to efficiently and accurately apply herbicides to large areas. That's what the Cooperative Mule is all about, so sit back, I hope you enjoy the show. By the way, Ryan Krason, our Digital Media Specialist produced this video and came up with the name; I really think he did a great job, so thanks Ryan.

The video [CLICK HERE] is just a general introduction to the potential to use an UTV or ATV for restoration work. I have captured the same information in a PDF that is available on my website at -- look for UTV Sprayer System. As always, if you have questions or comments, please post them below or email them to me at And if you are finding this blog useful, please subscribe and please send me ideas for blog topics.

Please follow me on twitter @CarlEBell.

Posted on Saturday, June 21, 2014 at 11:14 AM

Weed Seed Germination

I'm sure you've noticed that different years have dominant weed species. For example this year in Southern California Russian thistle (aka tumbleweed Salsola tragus among other Salsola species) is abundant in many areas. Other years it is only moderately abundant and some years it seems to hardly hang on. The obvious question is why? Why is there so much variation in abundance between years?


Fortunately for us people have been working on this issue for a while and have a few general answers for us. Since the bulk of weeds in California are annuals I'll limit my discussion to those plants.


The seeds of annuals germinate only under a certain range of environmental conditions. For example, many winter annuals in California germinate when temperatures are cool or cold. Sahara mustard (Brassica tournefortii) does not germinate well when the temperatures are above about 85F. Other plants do not germinate when the temperatures are cold. You can see this pattern on THIS page of common garden vegetables by Cooperative Extension in Alabama. There are cold season plants (onion) and warm season plants (tomato, melon).


Although we have only one rainy season in California, and sometimes less than that, we still have cool season weeds and warm season weeds. Most of our weedy grasses (like bromes) are cool season, and our late season weeds (like tumbleweed) are warm season. Of course there can be overlap, warm temperatures in the fall can provide suitable conditions for warm season weeds, even though they ‘normally' germinate in the spring.


Our ability to predict which weeds will be abundant is hampered by many things; most of all is insufficient data. We know plants respond to soil moisture, soil temperature, oxygen levels in the soil, light levels (seeds can ‘see' light!), scarification (abrasion of the seed coat), soil salinity, age of seed, age of parent plant, and many other factors.


Imagine we tested to the germination conditions of 3 weed species for 3 factors (moisture, salinity and light) and each factor at just 3 different levels (high, medium or low), and we replicated this test in 3 different soil types (sandy, loam, silt). In the end, we would have 81 different trials for this simple experiment (weed #1 at high light in loam = 1, …). Barring a large infusion of money to conduct experiments to predict weed germination, and thus examine one factor in the spread and increase in weeds, we will be using coarse measures to figure out the population of weeds.


Back to my original question, why was there a lot of tumbleweed this year? Because tumbleweed germinates better in conditions of high light or disturbed soil, with relatively warm temperatures and the seed germinates rapidly, effectively using small amounts of moisture. Given there was limited rainfall early in the winter, which limited production of many cool season weeds, and moderate moisture in the mid spring coupled with a relatively warm winter, conditions were rife for the establishment of tumbleweed.

UC IPM page for tumbleweed is HERE

Posted on Wednesday, June 18, 2014 at 11:29 AM

New book helps pros manage invasive weeds in California forests

Scotch broom: A beautiful plant, but a forest nightmare.
Beautiful but unwelcome in California wildlands, brooms are shrubs introduced into North America from Europe in the mid-1800s. Common species include Scotch broom (Cytisus scoparius) and Portuguese broom (Cytisus striatus). Brooms were introduced as ornamentals, but also were used extensively for erosion control along roadsides and in mined areas.

Now growing profusely in California forests, on roadsides, and wildlands, brooms:

  • Crowd out out desirable vegetation
  • Form impenetrable thickets that limit access to some areas
  • Shade out tree seedlings, and make reforestation difficult
  • Burn readily, increasing the intensity of fire, and carry fire to the tree canopy
  • Are toxic to cattle and horses and unpalatable to most wildlife
  • Produce abundant, long-lived seed
  • Are able to fix atmospheric nitrogen, giving broom a competitive advantage over native plants

Management of these and other weeds are presented in the recently published second edition of Forest and Right-of-Way Pest Control. Invasive species that create a dangerous wildfire hazard and crowd out desirable vegetation and wildlife are examples of why this book emphasizes vegetation management and pesticide handling, including correct equipment calibration and effective herbicide application. The second edition also provides broader coverage of insects, plant pathogens, vertebrate pests, and the various practices to manage them, recognizing that lands commonly have multiple uses and when and how pests are managed depends on many considerations with sometimes conflicting goals.

Second edition of 'Forest and Right-of-Way Pest Control.'
One of many new features in this edition is a section with expectations and review questions, which will help professionals pass DPR's tough applicator certification examinations. The book may be used as a guide to safe and effective pest management on public and private forests, tree plantations and nurseries, and along roads, railways, utility corridors, biking and hiking trails, and other rights-of-way. Nearly 200 photos and illustrations, 56 tables and sidebars, and 11 main chapters aid in pest identification and problem diagnosis and provide users with pesticide and nonpesticide solutions.

Experts with Cal-Fire, Caltrans, PG&E, USDA Forest Service, private industry, the University of California (UC) Berkeley and Davis campuses, UC County Cooperative Extension offices, and the California Department of Pesticide Regulation (DPR) contributed to Forest and Right-of-Way Pest Control, prepared by UC ANR's Statewide Integrated Pest Management Program.

Forest and Right-of-Way Pest Control is available for $35 online in the UC ANR Catalog. The table of contents and more information about the book are available on the UC IPM website. You can also preview and electronically search the contents on Google Books.

Posted on Wednesday, March 5, 2014 at 8:46 AM

Tips on grazing for invasive plant control

Some tips on grazing for invasive plant control

Using livestock for controlling invasive plants has a lot of appeal; the animals seem like a natural, green method; they're cute; and at times they can be a very inexpensive way to do some weed control. But there are also various difficulties and issues with using livestock that should be understood before you jump into a grazing program, I've discussed some below. 

Livestock have different eating preferences and needs; Cattle (photo of cattle courtesy of Jack Kelly Clark, UCANR) like grass, sheep like grass and forbs, goats like browse (foliage on stems of woody shrubs, young stems and bark, like photo), and horses like grass.

They eat differently; cattle pull up plants with their tongues, sheep and horses clip off plants close to the ground, and goats pull foliage off of stems with their tongues.

The owner of the livestock (called the grazier) usually has a different goal for the animals then you do. The grazier wants the animals to fatten up for the market. You want them to eat weeds. If the weeds are what the animals want to eat and they are nutritious, then your goals are compatible. It is more often the case that the weeds are not desirable and the animals will try to eat everything else instead.

The grazier wants the animals to wander freely over a large area. You probably want the animals to be confined to a smaller area to maximize weed control. This requires fencing, which is a cost to the grazier. It also means the animals are being forced to eat plants they may not want to eat (Kind of like being forced to stay at the table and finish all of your lima beans when you were a kid).

 The grazier wants to turn the animals out to graze when she/he arrives at your site. You want the animals to stay in a penned area for 2-4 days eating hay and voiding all of the weed seed from their last site. You also want the pen in case of rain, rather than allowing the animals to wander around in the mud and trample small plants.

Livestock do not often eradicate weeds; they just remove above ground stems and foliage. The San Diego Weed Management Area tried goats for control of perennial pepperweed (Lepidium latifolium) a few years ago. The grazier promised that the goats would eradicate the weed if they were allowed to graze it twice in the summer for two weeks each time. They rented the goats to the WMA for $300/acre. The goats removed about ½ of the stems and foliage and a year later it looked like it had never been grazed.

Graziers are used to driving hard bargains, so make sure you know what you want and are ready to insist on it.

Don't get me wrong, livestock can be very effective and useful in large-scale weed management if they are suitable consumers of the target weed(s) and they are managed properly. I collaborated with several UC scientists to study sheep grazing as a weed control practice in newly planted alfalfa in the low desert. The sheep were very successful, as good as the herbicide alternative. Citations for three of our papers are on this website page (near the bottom). This short blog only presents some of the issues, especially those I have personal experience with. After spending eight years studying sheep grazing, I like to say that I know far more about sheep than I ever wanted to.

And they really are cute.
Posted on Monday, February 24, 2014 at 3:36 PM

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