Yikes! Stinknet is Here!

Stinknet Has Reached Dewey-Humboldt, Arizona

Yesterday (June 14, 2019), I discovered a new invasive weed growing in Humboldt. The plant’s small yellow flowers caught my attention as I walked along Old Black Canyon Highway. Roads are common dispersal routes for invading weeds. First the roadsides, next the yards and hillsides.

Stinknet (Oncosiphon piluliferum), an invasive desert weed.

The first thought produced by Stinknet is that its bright yellow flowers are beautiful. The next thought, however, is that something stinks. Stinknet produces resinous sap that smells like a rotten pineapple. The odor plus the tendency for the plants to grow in tight formation create real impediments to outdoor activity. Even worse, Stinknet is a strong competitor that replaces native plants. But worse still, the plants are highly flammable and encourage destructive wildfires. If Stinknet invades, the quality of natural habitats will decline and many soil organisms, native plants, and native animals will disappear.

Stinknet is spreading across the hot deserts of California and Arizona. I’ve known about the weed since 2008 when Andrew Salywon of the Phoenix Botanical Garden ranked it as one of four weeds posing the greatest threats to Agua Fria National Monument 20mi south of Humboldt. The plant has not been reported above 2300ft in Arizona, and I assumed that at 4500ft, Lonesome Valley winters would be too cold for Stinknet. I did not even include it in the list of possible future weeds in Weeds of Dewey-Humboldt, Arizona. Let’s hope that other dangerous weeds that I did not list will not reach Lonesome Valley.

Stinknet is a member of the Sunflower family. It’s small round yellow flower heads are composed of 100 to 250 flowers packed into a ball no more than 1cm (1/2in) in diameter (Copyright 2019, Garry Rogers).

Stinknet is a small plant rarely more than 2ft tall. This plant is about 6 1/2in (Copyright 2019, Garry Rogers).

 

Treatment: How to Control Stinknet

Though people have carried Stinknet thousands of miles from its South African home, and though the plant has dispersed rapidly along Arizona highways, Stinknet may not survive and spread in Dewey-Humboldt. However, that’s not a safe bet. Like medical doctors, weed professionals practice EDRR (Early Detection Rapid Response). Now’s the time to begin watching for the plant along the highway and town streets. At this early point in Stinknet’s invasion of Dewey-Humboldt, the best control tactic is pulling and bagging the complete plant including the roots. If the plant spreads, control will become much more difficult and expensive. Like any disease, weed invasions are easier to cure when discovered early.

Stinknet (Copyright Max Licher).

Identification

Stinknet (Oncosiphon piluliferum) Daisy Family—ASTERACEAE.
Annual with persistent roots. Small, less than 2ft tall. One to five or more thin stems arising from base, sparse alternate leaves, striking yellow flowers in small tight balls less than 10mm diameter. Stinky.

Weeds of Coldwater Farm | Photo Gallery

Illustrations of the Weeds of Coldwater Farm

All invasive plants are weeds but not all weeds are invasive.

In fact, a great majority of weeds aren’t invasive. Most are native plants that respond to natural and human-made disasters by covering and protecting exposed soil. They do not invade native vegetation by spreading among the longer-lived, shade-casting plants that make up what we call climax vegetation. Here are illustrations of the 153 weed species observed or expected to appear at Coldwater Farm. Click images to see weed names and image creators. If there is no name or creator given, or if you want information on a weed’s characteristics including its value as medicine and food, refer to the bookWeeds of Dewey-Humboldt, Arizona available from Amazon,and Gifts and Games in Humboldt.

Drawings, Paintings, and Photographs

Plant identification is easier with drawings made by an experienced botanical illustrator than with photographs. In photographs, important features aren’t always distinct on a particular leaf or flower. An illustrator can emphasize the appropriate features. Photographs are useful for showing plant colors and typical settings with other plants.

For each weed, I tried to present the best illustrations available. Many of the drawings are by Lucretia Breazeale Hamilton from the book An Illustrated Guide to Arizona Weeds by Kittie Parker published in 1972. In the gallery, they are usually identified as “Parker”. They are included with the generous permission of the University of Arizona Press. Most of the photographs have Creative-Commons licenses that allow reproduction only requiring attribution to the photographer (CC BY 2-4 and BY-SA 2-4). I did not alter the photographs except as needed to fit them on the page and make them suitable for printing. Some of the drawings and photographs are from U. S. government web sites and are in the public domain. Paintings were available for some of the weeds. The ones I used are over 100 years old and are in the public domain. For all images, Weeds of Dewey-Humboldt, Arizona has the names of creators in the captions and in an Index of Illustrators, Painters, and Photographers just before the General Index.

You can find more works by the photographers by entering their names or the names of the plants they depicted in the search box at Wikimedia Commons, Wikipedia, or Flickr Creative Commons. “GR” in a caption identifies photos by me. You can use my photos as long as you attribute them as “© Garry Rogers.” Look up Creative Commons BY-SA 4.0 to read the license requirements.

 

 

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Prioritizing Weed Species and Sites in Deserts

Prioritizing Weed Species and Sites

Along with budgeting and seeking public support, determining priorities is an essential element of weed-control strategy. This article considers natural vegetation and does not deal with weeds in irrigated crops.

Prioritizing Species

Cost effective weed management focuses resources on the most dangerous species and the most valuable sites. Less than 10% of the hundreds of native and introduced alien weed species present in deserts will invade native vegetation. Many invasive species have little impact when they do. Because of financial limitations, this has prompted greater emphasis on passively monitoring weed infestations to learn whether they will cause problems. Prioritization equips weed managers for immediate response when aggressive species appear.

Locating information on the ecology, distribution, and control of weeds requires literature searches for each species. Though the information produced by the searches is variable and may not cover local conditions, it provides a first approximation of the relevant characteristics and control treatments for species that are present.

Weed scientists have developed many prioritization systems. For example, Byers et al. (2002) provide a risk-assessment guide that ranks species according to potential for:

  • Arrival (risk associated with entry pathways)
  • Establishment (risk of forming viable, reproductive populations)
  • Spread (risk of expanding into native vegetation)
  • Impact (risk of having a measurable effect on existing species or plant communities)

Species distribution information by country is available online from the Global Register of Introduced and Invasive Species (http://www.griis.org).

The risks are uncertain for many species, populations, and places. And even after weed managers learn a species’ characteristics and the conditions of a site, a significant level of uncertainty remains. Environmental fluctuations, land-use changes, and species adaptations require frequent adjustments of prioritization systems.

According to Rew and Pokorny (2006), the ideal prioritization system combines weed and site ranking integrating ecological knowledge of species with site conditions, and adjusts with observed results of treatments.

Prioritizing Sites

Species information is often be useful across regions, but every site requires direct observation. Here is a sample recipe for the process.

First, divide large or complex sites into homogenous Weed Control Areas (WCAs) aligned with administrative or environmental boundaries. Next, use information from an initial inventory to subdivide the WCAs into Weed Control Zones (WCZs) based on weed distribution and planned treatments. Use the site categories outlined below to rank the WCZs.

Priority Site Categories

Hobbs and Humphries (1995) propose four categories of management action based on resource value and the level of site disturbance. Thus, parks, wilderness areas, critical habitats, etc. are in the highest category.

Desert streams and riparian areas play such an important role in arid ecosystems they have high value even though they are at high risk of invasion. Besides providing critical habitat, riparian vegetation occupying floodplains is an important natural shock absorber that reduces flooding, erosion, and sediment transport.

Highest Priority Sites

  • Upland sites that are relatively undisturbed, where entry pathways are controllable, and few weeds are present.
  • Moderately disturbed perennial stream segments with riparian vegetation on either bank that extends over 20-m laterally from the center of the stream channel. Weeds are a minor part of the vegetation. Entry pathways are limited, and managers can control human-caused disturbances from recreation and livestock grazing. Applies to hydrophytic shrub, woodland, and gallery forests in wildernesses and monuments. Such streams are rare and may no longer exist.

Objectives for Highest Priority Sites:

  1. Maintain weed-free by eradicating existing and new weed populations.
  2. Prevent disturbances and weed establishment by altering land use, managing access, and conducting frequent monitoring and rapid response to eliminate new populations.
  3. Restore native vegetation to increase invasion resistance and stabilize floodplains.

Highest priority areas include national parks, species and habitat conservation areas, research reserves, other important natural areas.

High Priority Sites

  • Upland sites moderately disturbed and susceptible to invasion.
  • Moderate to highly disturbed ephemeral stream segments with patches of native riparian vegetation extending more than 20m from either side of the stream. Weeds may be abundant. Apply this category only if access and human disturbances such as hiking and livestock grazing are controllable. Examples: willow thickets and hydrophytic woodland and gallery forests in parks and conservation areas.

Image:  Highly disturbed site with heavy weed infestation. Wide (>20m) riparian vegetation also highly disturbed and infested. Human disturbances are controllable.This is a perennial stream of critical importance for wildlife, but weed control is unlikely (photo by GR).

Objectives for High Priority Sites:

  1. Manage weeds by eradicating high-priority species and controlling others.
  2. Limit weed introductions and establishment by managing access and altering land use to eliminate disturbances.
  3. Restore native vegetation in treated areas.

High priority areas may include boundary areas next to highest priority areas.

Medium Priority Sites

  • Upland sites of subject to frequent disturbance including livestock grazing, wood gathering, and recreation.
  • Highly disturbed ephemeral stream segments with narrow (<20m) bands of riparian vegetation at least 20m long measured along the mean course of the stream. Human access and disturbances such as recreation and livestock grazing are controllable.

Image:  Highly disturbed site with heavy weed infestation. Wide (>20m) riparian vegetation also highly disturbed and infested. This is a perennial stream of critical importance for wildlife, but weed control is unlikely.

Objectives for Medium Priority Sites:

  1. Monitor likely areas and control high priority weeds.
  2. Poorly accessible upland areas lightly grazed by livestock and ephemeral stream segments outside high-value management units fit this category.

Low Priority Sites

Repeatedly burned, heavily grazed, almost total weed cover. Former diverse woodland lost. Restoration would be difficult and very expensive (GR).

  • Upland sites subject to high levels of disturbance. These sites have so many weeds that restoration of native communities is unlikely. Roadways and transmission rights of way fit this category well. Hobbs and Humphries (1995) recommend that these sites receive no action.
  • Ephemeral stream channels with discontinuous riparian vegetation occurring in segments <20m. These sites are of higher concern when they contain high-priority species.

Objectives for Low Priority Sites:

  1. Monitor likely areas for new weed invasions and control high-priority weeds.

After initial inventories, analyze each WCZ using criteria in the prioritization table below and place it in a Management Priorities List. The Management Priorities List denotes the order and principal categories of management action and forms a core element of the regional weed management plan.

Many countries have developed prioritization systems and have weed management plans in place. I prepared the table below to illustrate the issues involved, not serve as a working system.

  • Table Explanation:  Following initial inventories, this table uses species and site prioritization to guide monitoring, and treatment.
  • Numbers in the left column show the minimum search frequency in years to detect new infestations. Highest-priority sites receive two or more visits each year because some species germinate throughout the growing season and others germinate during spring or summer.
  • Numbers in cells (not including the left column) indicate the recommended frequency in years for monitoring of existing infestations. The “0” in the cells for highest and high priority sites and the weed designations “Highest” and “High” show rapid response instead of monitoring. The seasonal timing of observations should follow maturation of the weeds. For weeds that germinate throughout the growing season, this would be autumn. The term “withdraw” indicates intervention to limit human disturbances. Monitor sites in the cells at lower right to detect appearances by high-priority species. Depending on resources and proximity to high-value sites, managers might eradicate such species.

Relevant Websites

Sources Cited

Byers, J. E., et al. 2002. Directing research to reduce the impacts of nonindigenous species. Conservation Biology 16: 630-640.

Hobbs, R.J. and Humphries, S.E. 1995. An integrated approach to the ecology and management of plant invasions. Conservation Biology 9: 761-770.

Rew, L. J., and M. L. Pokorny, eds. 2006. Inventory and survey methods for nonindigenous plant species. Montana State University Extension Service, Bozeman, MT. 75 p.