How to Control Locoweed and Friends

Recently the University of Arizona’s cooperative extension published a watchout for Locoweed in southeast Arizona. I myself have had some experience with this weed this spring and wanted to provide some potential solutions I have learned throughout my career in agriculture and with herbicides. This issue comes up every year or every other year depending on our prior year’s moisture. We are then faced with the dilemma of `being reactive instead of proactive. As the Extension publication noted, there are many species (friends) of Locoweed and often it’s hard to tell which one is which. As it concerns chemical treatment of this weed, the type doesn’t really matter. I would advise folks who are curious as to what type they are seeing to reference Circular 557, A Guide to the Common Locoweeds and Milkvetches of New Mexico. The recent University of Arizona Extension publication focused on the weeds affect on livestock, the symptoms the livestock could have, and the treatment of livestock. Here, I will focus on some basics of Locoweed in general, and some potential options one may have aside from mechanical or manual removal.

The Astragalus genus is the largest genus of flowering plants in Arizona with over 70 species, plus 2 species of Oxytropis, a species that closely resembles locoweed in both appearance and poisonous principle (Ruyle 2008). We know that if it’s an annual or perennial species that most of the species of Locoweed tend to be noticed when there are generally wet conditions. Overall, Locoweed seed can lay dormant in the soil for long periods of time and pop-up plants when conditions are favorable. This year may not seem like a year where we have “favorable conditions,” however in a lot of these areas where we see Locoweed there is adequate soil moisture.

Astragalus genus

When it comes to treating Locoweed with a herbicide you must always consider all of the options and follow the herbicide label and the law. The method in which the herbicide is applied matters in a lot of cases on your needs and severity of your issue. For example, if there is a large-scale problem, aerial treatments may be ideal. On the other hand, if the problem is isolated to water tanks and other small areas a hand treatment may be sufficient. A lot of these herbicides will leave grasses safe and eliminating your weed problem may even allow your grass to flourish. Most all plants when treated with a foliar herbicide need to be in good condition at the time of application. In addition, the weather should be temperate and not windy, overly cold, or overly hot. The timing for spraying Locoweed can be anywhere from late March until mid-May. You can see below that there are several options that are effective in the treatment of Locoweed (McDaniel, Duncan and Graham, 2015).

Grazon P+D

Picloram + 2,4-D

Grazon P+D

Trusted for years, Grazon P+D herbicide delivers broad-spectrum, season-long control of tough weeds that’s more effective and longer lasting than mowing or shredding.

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Tordon 22K

Picloram

Tordon 22K

Tordon 22K herbicide provides all-purpose noxious weed control as well as basic invasive weed management.

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Chaparral

Aminopyralid + metsulfuron

Chaparral

Chaparral herbicide is the broadest-spectrum weed and brush control product available for rangeland and pastures.

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GrazonNext HL

Aminopyralid + 2,4-D

GrazonNext HL

GrazonNext HL herbicide is the easiest way to get broadleaf weeds out of the way of pasture production. It provides a simple, lasting solution for the toughest pasture and rangeland weeds and clears the way for more forage.

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Surmount

Picloram + fluroxypyr

Surmount

Surmount herbicide provides excellent broad-spectrum broadleaf weed control without 2,4-D. Surmount® herbicide also delivers outstanding pricklypear and cholla cactus control.

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Escort XP

60% Metsulfuron methyl

Escort XP

Escort XP is a postemergence herbicide that cost-effectively controls many annual and perennial weeds, plus tough woody plants.

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Several of these herbicides require you to have a REGULATED GROWER PERMIT (PGP) by the Arizona Department of Agriculture. My suggestion would be to contact myself or one of my colleagues in the agriculture chemical industry for more information on how and when to spray one of these chemicals.

Spring is upon us and my advice in this environment of supply disruptions would be to decide and look into what you want to do sooner rather than later.

~Grow Your Know article written by Tyler Bowen

McDaniel, K., Duncan, K. and Graham, D., 2022. NMSU: Locoweed Control: Aerial Application or Ground Broadcast. [online] Aces.nmsu.edu. Available at: <https://aces.nmsu.edu/pubs/_b/B823/welcome.html> [Accessed March 18 2022].

Ruyle, G.B. 2008. Locoweeds. University of Arizona Cooperative Extension publication Backyards and Beyond: Rural Living in Arizona(link is external), 2(1), 11. Accessed March 18, 2022

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