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).


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 book Weeds of Dewey-Humboldt, Arizona available from Amazon.

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.




Protected: Desert Weeds – Draft – Comments Welcome

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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.


Controlling Invasive Weeds in Deserts: Strategic Concepts

Strategic Concepts for Invasive Weed Control in Deserts

This is the first in a series of articles on methods for preventing the devastation caused by weeds invading desert ecosystems.


Weed control efforts are more successful when strategy and tactics are carefully planned in advance. Strategy includes these concepts:

Adaptive Management

Weed managers can build periodic reviews into their plans so they can benefit from results and insights generated by the plan’s implementation. Adaptive management, also known as ecological management, uses analytical techniques to assess results of actions and provide feedback for improving methods. Adaptive management is useful when outcomes are uncertain but weed treatments are clearly defined. Analysis of outcomes may contribute new general knowledge, and it will help adjust policies and tactics.

Priority Weeds

Building a list of problem weeds for management units is an essential part of weed-control planning. Private and government organizations provide lists of known invasive species for countries and regions worldwide. These sources will provide a baseline list that will expand as observations and experience accumulate. The place to begin is the Invasive Species Compendium hosted by the Center for Agriculture and Biosciences International.

Public Perception and Support for Weed Management

The field of Weed Science developed in response to the measurable economic costs of weed invasions of farms. Measuring economic costs of weed invasions on non-agricultural wildlands is more difficult. Aldo Leopold argued that applying economics to ecosystems was not appropriate.

“One basic weakness in a conservation system based wholly on economic motives is that most members of the land community have no economic value. Wildflowers and songbirds are examples. Of the 22,000 higher plants and animals native to Wisconsin, it is doubtful whether more than five percent can be sold, fed, eaten, or otherwise put to economic use. Yet these creatures are members of the biotic community, and if (as I believe) its stability depends on its integrity, they are entitled to continuance” –Leopold, 1949, 210.

Example weed-prevention poster by U. S. State of Minnesota

During the years since Leopold wrote the above comment, environmental economics has made substantial progress. For instance, weed reductions in species richness and diversity and harvests of wildland plants have been measured (e.g., Costanza, R., d’Arge, R., de Groot, R. et al., 1997), and benefit-cost analysis supports stringent weed control strategies (Naylor, R. L., 2000).

As weed management has progressed toward integrating complex tactics and ecosystem concepts, the issues may have become opaque to nonscientists. Conducting weed-management discussions within a framework of human economic and environmental security can awaken public interest.

An effective strategy for encouraging public support is to provide examples that involve local communities. Field trips to view fire scars or transmission corridors dominated by weeds will illustrate how weeds are transforming desert vegetation. Community leaders can use the illustrations to create weed prevention and eradication programs within their community.

No one wants to lose the value and character of the land, but many users of the land are unaware of the full significance of the weed invasion. Weed managers can find partners willing to help publicize weed problems among organizations, such as native plant societies and wildlife conservation organizations. Weed problems will also interest recreation users, ranchers, hunters, and others spending time outdoors. School visits, field demonstrations, films, and tours for individuals and groups of users should be an initial element in weed control plans. Education materials are available online from the North American Invasive Species Management Association.


Prevention planning and execution precedes or is concurrent with initial weed inventories. This is necessary, because continual appearance of weeds erases the effectiveness of eradication, control, or restoration efforts. Weed prevention is much less expensive than any form of treatment. Regional and national plans listed on the U. S. National Invasive Species Information Center website present techniques for preventing weed invasions and spread. The focus of the plans is on movement of people, livestock, and equipment, and on restoration of native vegetation. Major prevention strategies include:


National and regional restrictions can limit introduction of invasive plants. Regulation is most effective if there is public awareness and participation.

Ecosystem Health and Invasive Weeds

Biological soil crusts block invasive weeds in deserts. Livestock grazing damages crusts and heavy trampling can eliminate them. (Collema spp. In Colorado Plateau division of the Great Basin Desert. © GR.

Supporting and restoring native plant communities and ecosystems increases resistance to invasion while reestablishing lost biodiversity and ecosystem value (Blumenthal, D. M., Jordan, N. R. & Svenson, E. L., 2003). Habitats and ecological processes can suffer cumulative impacts from the direct and indirect effects of invasive species. Ecological relationships that have evolved over evolutionary timescales are at risk. Invasive species cause disturbances that have multiple effects throughout an ecosystem, and human alterations of the environment can exacerbate them. Healing these disturbances is difficult. Thus, restoration treatments are an integral part of control and management efforts. They help guard against future re-infestations and the potential for further harm.

Minimizing Disturbance

Strict fire-control programs and grazing management to allow recovery of soil microorganisms and native vegetation removed by fires or excessive grazing are essential.

Ecological Restoration

Healthy native vegetation resists weed invasions. The Society for Ecological Restoration supplies information with examples and techniques on the organization’s website.

Early Detection, Rapid Monitoring and Response

Effective weed control requires rapid responses to invasive weeds. Early detection is essential. It requires preliminary inventories and regular monitoring to discover new populations. The later section on inventory describes monitoring tactics. Management responses including mechanical, chemical, biological (including grazing), and fire treatments are described in the section on treatment tactics.

The appearance of a non-native species does not always signal the onset of an invasion. Unfavorable environmental conditions, inherent demographic and biological limits, and resistance of native vegetation can prevent spread or cause demise of a weed. Because of the uncertain survival of new weeds, the first response to most species should be monitoring. This does not apply to weed species known to be invasive in similar sites nearby. Since it is possible for a static weed patch to serve as a source population, monitoring must include a thorough survey of the surrounding area. Repeated observations of existing populations is ‘type-two’ monitoring in the discussion below.


Monitoring comprises repeated observations to detect new weed infestations, to keep track of changes in an existing weed patch, and to test the results of management activities. When effort is evenly divided between monitoring and treatment, weed control becomes more efficient. I recognize three types of monitoring. Type-one comprises repeated searches of sites for new infestations, type-two comprises repeated observations of existing infestations, and type-three comprises repeated observations to learn the results of management actions.

Type-one monitoring

Periodic visits to likely sites for new infestations are the primary defense against new weed invasions. Variations in weed visibility and elevated threat levels associated with highest priority sites and weed species might require multiple visits each year, but most areas can be visited yearly or every two or three years. Because desert precipitation is often irregular, monitoring schedules must be flexible. Some weeds germinate in spring when there is sufficient moisture; and others germinate after summer rain. If the weed list for a particular management unit includes species from both groups, two visits each year are required. Single yearly visits should follow summer rains when winter annuals are still standing and summer annuals are likely to have germinated. Recommended frequencies are included in Table 1.

Table 1. Decisions Based on Combined Weed Species and Site Priorities.
Weeds Across

Sites Down









Highest (<1) (0) withdraw, eradicate, restore (0) withdraw, eradicate, restore (2) monitor, treat if expanding, restore (3) monitor, treat if expanding, restore
High (1) (0) withdraw, evaluate for eradication or control, treat, restore (1) withdraw, evaluate for eradication or control, treat, restore (2) monitor, treat if expanding, restore (3) monitor, treat if expanding, restore
Medium (2) (0) withdraw, evaluate for eradication or control, treat, restore (2) monitor, treat if expanding, restore (3) monitor (4) monitor
Low (3) (1) withdraw, evaluate for eradication or control, treat, restore (3) monitor, treat if expanding, restore (4) monitor (5) monitor


This table shows management actions for sites with varying weed threats and resource values. Managers use it to set inventory and monitoring schedules after the initial weed inventory is complete.

Numbers in the left column of Table 1 are the minimum frequency in years for type-one monitoring to detect new infestations. Schedule highest-priority sites for two or more visits each year to spot species that develop differentially during spring and summer.

Numbers in cells (not including the left column) are the recommended frequency in years for type-two monitoring of infestations. Zero (0) in the cells for highest and high priority sites and the weed designations “Highest” and “High” indicate that rapid response instead of monitoring is required. Highly invasive weeds are eradicated as soon as possible after discovery. Seasonal timing of type-two monitoring should match the maturation of individual weed species. Withdraw indicates intervention to limit human disturbances. The term “monitor” refers to type-two monitoring. Type-three monitoring will follow all treatments and restorations. Eradicate refers to the immediate management response for new or small areas of weeds. Eradication of widespread weeds requires a preliminary effort to secure financial and public support.

Type-two monitoring

Type-two monitoring applies to new and existing infestations. It is used to determine stability and potential threat. Since weeds often establish in plant communities and on soils that are not optimal for their survival and growth, many patches found along roads or around disturbed areas may never spread into adjacent vegetation. It is cost effective to monitor them while devoting resources to treating infestations of species of highest concern in high-value areas and infestations known to be spreading. Recommended frequencies are included in Table 1.

Type-three monitoring

Type-three monitoring gauges ecosystem responses to natural and human-caused disturbances, weed treatments, and restorations. Landuse such as livestock grazing, weed treatments, and restoration projects incorporate measurements made at regular intervals. Type-three monitoring will often occur more than once during growing seasons.

Satellite Populations

Weed populations grow by expanding their boundary and by long-distance dispersal to establish outlying or satellite populations. Where habitat conditions and dispersal vectors are spatially uniform, propagule dispersal from each plant follows a simple curvilinear process to create a circular pattern with decreasing propagule density in all directions from the center. As the area of an infestation grows, the proportion of each plant’s propagules falling among the plants within the occupied area will increase and the proportion falling outside the area will decline. Thus, the rate of expansion will decrease as the infested area grows. Since the rate of expansion is greater for small populations, satellite populations should be treated first.

Horehound (Marrubium vulgare) beside a fresh road cut through weed-free oak-dominated Interior Chaparral. Each plant produces thousands of hooked seed pods.

Since a single plant can produce thousands of seeds, very small satellite populations of one or a few plants can serve as significant sources for further invasion. Searches in concentric circles around the source population should find fewer satellites as the circles are enlarged. Of course, neither available germination sites nor dispersal vectors such as wind vary with topography, vegetation, and transient air pressure. However, without preliminary data on vectors and preferred habitats, the more refined and accurate analytical techniques geographers use (e.g., R. Abler, J. S. Adams, and P. Gould, 1971) to calculate rates of spread and predict the impact of barriers (absorbing, filtering, reflecting), shapes of source areas, hospitable sites, and so forth cannot be used. Thus, the inventory system presented below assumes symmetrical dispersal and is appropriate for general use to locate satellite populations. Information about a particular species’ dispersal mechanisms and response to vectors and barriers in particular locations can be developed and used to modify the search pattern (see M. B. Soons and J. M. Bullock 2008).

Coordination with Neighbors

Property boundaries do little to influence weed dispersal and establishment. Fences may stop the first wave of tumbleweeds, and they may create rows of bird-dispersed weeds, but they are not an effective barrier. Coordinating prevention, inventory, and control with neighboring agencies and private landowners is essential.

Control vs. Eradication

Immediate eradication is sometimes more cost effective than the various other treatment options. Annual costs to control weeds increases as new species arrive and existing species establish satellite populations. Eradication of a widespread species is difficult and costly, but might be essential to protect native ecosystems and reduce long-term costs. Mack, R. N. & Foster, S. K. (2009) found that eradication of a widespread species requires most of the following conditions.

  1. An effective prevention plan is in place.
  2. An exhaustive inventory is available.
  3. The target species are readily detectable. Failure to find all individuals creates opportunities for new seed banks to form.
  4. Terrain is accessible and easily inventoried and monitored.
  5. Target species’ seed bank is short lived (no more than 3 years).
  6. Target species’ current range is small enough that available resources are adequate for inventory, eradication, and monitoring.
  7. Concurrent treatment of satellite and source populations is possible.
  8. Monitoring will continue well past the expected duration of the seed bank. Otherwise, seedlings and other individuals missed in inventories, treatments, and subsequent monitoring will produce new seed banks.
  9. Public and financial support is constant.


  • Abler, R., Adams, J. S. & Gould, P. (1971). Spatial organization: The geographer’s view of the world. Englewood Cliffs, NJ, Prentice-Hall.
  • Blumenthal, D. M., Jordan, N. R. & Svenson, E. L. (2003). Weed control as a rationale for restoration: example of tallgrass prairie. Conservation Ecology 7, 1.
  • Costanza, R., d’Arge, R., de Groot, R., et al (1997). The value of the world’s ecosystem services and natural capital. Nature 387, 253-260.
  • Mack, R. N., & Foster, S. K. (2009). Eradicating plant invaders: Combining ecologically-based tactics and broad-sense strategy. In Inderjit, (ed.) Management of invasive weeds. Pp 35-60. Dordrecht: Springer.
  • Leopold, A. 1949. A Sand County almanac and sketches here and there. New York: Oxford University Press.
  • Naylor, R. L. (2000). The economics of alien species invasions. In Mooney, H. A. & Hobbs, R. J. (eds.) Invasive species in a changing world. Pp 241-259. Washington, D. C.: Island Press.
  • Soons, M. B. & Bullock, J. M. ( 2008). Non-random seed abscission, long-distance wind dispersal and plant migration rates. J. Ecology 96, 581-590.

List of Relevant Websites

Some Weed Problems

Some Weed Problems Introduction

Giant Hogweed (Heracleum mantegazzianum) by Walter J. Pilsak

We know and love weeds for their ability to spread to and cover bare soil exposed by fires and floods, but we hate them when their natural abilities spread them into crops and gardens. In nature, weeds are like band-aids on skinned knees, protecting soil from erosion by wind and water. This is good, and should be good enough for us to be selective (not stereotyping) in our attitude toward weeds. But it isn’t. The reason for our persistent hatred is that weeds can compete with and replace crop and garden plants, they can replace native vegetation, and they can block vision and even travel. And, as you will see in the first article below, some weeds have toxic chemicals for defense and aggression and can inflict serious injury to grazers or innocent passersby.

Giant Hogweed (by Appaloosa)

People used to use the techniques of organic gardening to prevent and eradicate weeds. However, in the middle of the last century, science gave us herbicides, chemicals that interfere with weed growth and reproduction. What a pleasure to wave our spray wand over weeds and watch them shrivel and die. For decades, agricultural scientists have improved herbicides. They have even paired them with genetically modified crop plants that aren’t hurt by the magic spray that kills invading weeds.

Herbicides disrupt nature and cause cancer in humans. The chemical industry claims that reduced cost of food production justifies herbicide use. However, herbicides are growing stronger and farmers are applying them more heavily. This increases the harm to nature and human health.

Weeds are not defenseless against herbicides. Most of them produce seeds for the next generation in a single year, and this allows natural selection of herbicide-resistant plants within a few years. As described in the second article below, weed resistance is exceeding the power of the herbicides. As the gap between herbicide efficacy and weed resistance grows, farmers will return to the old organic gardening techniques. Though this will be less harmful to nature and people, it will increase the cost of farmed produce. Consequently, we may have to reduce meat production, a major consumer of farm crops, and, eventually, we will have to reduce human population size.

The articles below include recent discussions of weed problems.

Some Weed Problems References

Click for more on weeds.

Weeds, Nature’s First Responders

My weed book is in print. It focuses on the weeds in Dewey-Humboldt, a small town in central Arizona. There are 40 families, 163 genera, and 214 species of weeds present in Dewey-Humboldt now, or expected soon. The book includes descriptions and illustrations of 149 species. Buy from Amazon and most other bookstores. You may also down a free PDF copy.


NATIONAL WEED APPRECIATION DAY – March 28 | National Day Calendar

GR: Today is National Weed Appreciation Day. Yay weeds!

The following is from the National Day Calendar. The weeds mentioned are present in D-H and everywhere else.

“Did you know that some weeds are beneficial to us and our ecosystem?  National Weed Appreciation Day is observed on March 28 of each year, and it is a good day to learn more about weeds and their benefits.

“Humans have used weeds for food and as herbs for much of recorded history. Some are edible and nutritious while other weeds have medicinal value.

“Do you remember as a small child the fun you had with dandelions? Well, these bright yellow flowers serve a purpose.  Dandelions are a food source for insects and some birds.  Humans eat young dandelion leaves and enjoy tea and wine made from the leaves and flower.  The Native Americans used dandelions to treat certain ailments.  Nutritionally, dandelions contain a source of vitamin A and C, calcium, iron and fiber.

“There are also other edible and medicinal weeds, some of which include: Yellow Dock/Burdock: The taproot of young burdock plants can be harvested and eaten as a root vegetable. Immature flower stalks may also be harvested in late spring before flowers appear.  The flavor of the young stalk resembles that of an artichoke. It is a good source of dietary fiber and certain minerals, including calcium and potassium. It is also used as a medicinal herb.

“Lamb’s Quarter: (also known as goosefoot) The leaves of lamb’s quarter are excellent added to lettuce salads or cooked and used as a replacement for spinach. Lamb’s quarter seeds are also edible. They are a good source of protein and vitamin A.

“Amaranth: (also known as pigweed)  Amaranth species are cultivated and consumed as a leaf vegetable in many parts of the world.  The leaves can be cooked, and its seeds can be harvested and cooked the same as quinoa. The root of mature amaranth is a popular vegetable. It is white and usually cooked with tomatoes or tamarind gravy. It has a milky taste and is alkaline.  It is high in vitamins and minerals, including vitamins A, K, B6, calcium and iron, and the seeds are a good source of protein.

“Purslane:  It may be eaten as a leaf vegetable, but is considered a weed in the United States. It has a slightly sour and salty taste.  The stems, leaves and flower buds are all edible. Purslane may be used fresh as a salad, stir-fried or cooked as spinach is, and because of its sticky quality, it also is suitable for soups and stews.   It is an excellent source of vitamins, minerals and antioxidants and is high in omega-3 fatty acids.  Purslane can be found growing in all 50 states.” Source: NATIONAL WEED APPRECIATION DAY – March 28 | National Day Calendar

This article by Marcus Schneck describes more weeds found at Coldwater Farm in Dewey-Humboldt and elsewhere.

Eat your lawn on National Weed Appreciation Day

Switch to Renewable Energy

Storm Coming (NASA)

GR–Ode to concerned scientists: They see the danger, they blow the horns and clang the bells, and they wait. But the ramparts remain empty. They turn to their family and friends, but dreamlike their voices are too soft and none respond.

“Fifteen thousand scientists have issued a dire warning to humanity about impending collapse but virtually no-one takes notice. Ultimately, our global systems, which are designed for perpetual growth, need to be fundamentally restructured to avoid the worst-case outcome.

“For a moment, the most important news in the entire world flashed across the media like a shooting star in the night sky. Then it was gone. In November, over fifteen thousand scientists from 184 countries issued a dire warning to humanity. Because of our overconsumption of the world’s resources, they declared, we are facing “widespread misery and catastrophic biodiversity loss.” They warned that time is running out: “Soon it will be too late to shift course away from our failing trajectory.”

“This is not the first such notice. Twenty-five years ago, in 1992, 1,700 scientists (including the majority of living Nobel laureates) sent a similarly worded warning to governmental leaders around the world. In ringing tones, they called for a recognition of the earth’s fragility and a new ethic arising from the realization that “we all have but one lifeboat.”

“This second warning contains a series of charts showing how utterly the world’s leaders ignored what they were told twenty-five years earlier. Whether it’s CO2 emissions, temperature change, ocean dead zones, freshwater resources, vertebrate species, or total forest cover, the grim charts virtually all point in the same dismal direction, indicating continued momentum toward doomsday. The chart for marine catch shows something even scarier: in 1996, the catch peaked at 130 million tonnes and in spite of massively increased industrial fishing, it’s been declining ever since—a harbinger of the kind of overshoot that unsustainable exploitation threatens across the board.” –Jeremy Lent (What Will It Really Take to Avoid Collapse?).

How Many of You Switched to Renewable Energy?

In recent posts, I described the warnings of impending disaster. I didn’t expect to have an impact, and I wasn’t wrong. As Jeremy Lint points out in the article above, the media avoidance of unappetizing topics is too complete. And of course, our leaders in power avoid the subject in their subservience to wealth. My first hint that good advice for avoiding collapse would be futile was the minimal response to my discovery of the simple and inexpensive means for everyone to switch their homes from fossil fuel energy to renewable energy. Like Pangloss, I’ve remained hopeful. But I read that book, and now I’ve turned to a more practical concern; the post-anthropocene survivors, the weeds, have absorbed my attention. Today’s weed is Shepherdspurse, a foreign but familiar little mustard that feeds butterflies and yields medicines for us humans.

Plants of the Post Anthropocene: 5. Barnyard Grass

Weed No. 5. Barnyard Grass (Echinochloa crus-galli)

Farmers detest this European grass for its ready invasion of most crops. The plant can also invade and destroy native grassland vegetation. This appears to be true only of areas disturbed by grazing livestock. Otherwise, Barnyard Grass serves as a colonizer and successional species that is steadily replaced by longer-lived species. In one research study, other species replaced it in about 10 years.

In the arid climate of central Arizona, the plant survives only along moist stream banks and in bare spots in and beside watered lawns and gardens. Here, the plant is easy to control by mowing or withholding water. However, if you allow a few clumps to grow, you will get to enjoy watching the acrobatics of Lesser Goldfinches that relish Barnyard Grass seeds. The small birds hang (often upside down) on drooping seed tops steadily removing mature seeds until all are gone. The birds must drop some seeds, however, as new plants appear in the same spots every spring.



Barnyard Grass (Echinochloa crus-galli). This strong summer annual matures at ½ to 6 feet tall and often spreads from its base to form large clumps. The leaves are 4 to 20 inches long and ¼ to ¾ inches wide. Flowering occurs along the top 3 to 10 inches of the stem. Flowering branches are 1 to 2 ¼ inches long with short green or purple spikelets 1/8 inch long with bristles up to 1 ½ inches long. A single plant can produce 40,000 of the pale yellow shiny seeds. A. Spikelet spread open. B. Two spikelets with short and long awns. C. Grain. Image used with permission of the University of Arizona Press.