question: what is the difference between plant resistance and plant tolerance?

Plant tolerance is the characteristic of a plant that allows a plant to avoid, tolerate or recover from attacks from insects, among other things, under conditions that would typically cause a greater amount of injury to other plants of the same species. These inheritable characteristics are what influence the ultimate degree of damage caused by a pest. Tolerance in terms of agricultural production means that despite stress from a pest or disease, the production levels will remain above the economic threshold.

Resistance means that a plant completely immunizes itself from a particular stress.  This is typically a biotrophic pathogen infection. The host has a resistance gene which prevents the proliferation of the pathogen. The pathogen typically contains an avirulence gene which triggers plant immunity.

Resistance and tolerance are the best defense mechanisms of plants against pests. 

developing new plants that are resistant to freezing  photo credit:

There are two main types of resistance: ecological resistance/pseudo-resistance and genetic resistance. Ecological resistance is resistance related to favorable environmental conditions at a given location at a particular time. This type of resistance can be broken down into 3 forms:

  1. Host evasion – this phenomenon occurs when a host passes through the susceptible stages very quickly or during a period when pests are fewer.  This type of resistance applies to an entire species population.
  2. Induced resistance – this type of resistance is the result of some type of changed condition for the plant, such as an increase in available nutrients or water
  3. Escape – this is more or less luck as there is an absence of infestation or injury to a host plant as a result of incomplete infestation.

Genetic resistance is resistance related to (you guessed it) plant genetics.  There are several types of genetic resistance:

Resistance based on the number of genes

  • Monogenic – controlled by a single gene which makes it easy to both incorporate and exclude in plant breeding programs
  • Oligogenic – controlled by a few genes
  • Polygenic – controlled by several genes
  • Major Gene Resistance – controlled by one or a few major genes (vertical resistance) 
  • Minor Gene Resistance – controlled by many minor genes; the cumulative effect of minor genes is called adult/mature/field/horizontal resistance

Resistance based on biotype reaction

  • Vertical Resistance – specific resistance against specific biotypes
  • Horizontal Resistance – effective against all known biotypes; nonspecific resistance

Resistance based on miscellaneous factors

  • Cross-Resistance – when resistance against a primary pest results in resistance to a secondary pest
  • Multiple-Resistance – different environmental stresses (e.g. insects, diseases, nematodes, heat, drought, etc.) results in a new resistance

Resistance based on evolution

  • Sympatric Resistance – resistance that is acquired through the coevolution of a plant and insect (which is why it is important to protect our native pollinators!); governed by major genes
  • Allopatric Resistance – not governed by a co-evolution; governed by many genes

There are three mechanisms of resistance in plants.

Antixenosis (non-preference) resistance mechanisms are those by which host plant has characteristics that result in non-preference for insects in terms of shelter, oviposition, feeding, etc. There are morphological or chemical factors that influence insect behavior and results in the poor establishment of insects. Plant shape and color can also be an important influencing factor.

Antibiosis is the negative effect of a host plant on the biology of an insect. This can include decreased rates of survival, development and/or reproduction and is a result of biochemical and biophysical factors. Antibiosis may be a result of the presence of toxic substances, the absence of essential nutrients or a nutrient imbalance. Physical factors, such as thick cuticles, glandular hairs and silica deposits, also contribute to antibiosis.

Tolerance is a plant’s ability to grow and produce an acceptable yield despite a pest attack. Tolerance is typically attributed to plant vigor, regrowth of damaged tissue and a plant’s ability to produce additional stems/branches.

Both plant tolerance and plant resistance are extremely important to IPM efforts as it helps to reduce costs and amount of other control tactics that need to be implemented. This includes improving the efficacy of insecticides and promoting non-chemical benefits like shifts in predator-prey relationships and reduced pest populations.

The benefits of the use of resistant cultivars are numerous as this method has a high level of specificity, is eco-friendly, lower cost and adaptable to a given situation. The benefits are limited only by the amount of time required to develop new cultivars in breeding programs and by a lack of known resistance genes that can be used. To identify and capture relevant genes, crop wild relatives are often used.

an introduction to integrated pest management (IPM)

Integrated pest management (IPM) is a long-term pest prevention program that focuses on ecosystem-based strategies for the control of pest related issues. This is accomplished through a combination of techniques including biological control, habitat manipulation, modification of cultural practices and the use of resistant cultivars. The use of chemical pesticides is then restricted to applications only after strict monitoring that is based on established guidelines indicates that stronger measures are required for pest management. In the event that chemical agents are required, they are applied in a targeted manner intended to minimize risks to the environment, other organisms (especially beneficial and non-target organisms) and to human health.

The 8 principles of IPM are as followed:

  1. In an effort to prevent and/or combat pests, the following intelligent production practices shall be used: crop rotation, sustainable cultivation techniques, resistant/tolerant cultivars and certified seed production systems, balanced fertilization, irrigation and drainage techniques, proper hygiene measures and the protection and proliferation of beneficial organism.
  2. The use of biological, physical and non-chemical control methods must be preferred to chemical options as long as the non-chemical options provide acceptable pest control.
  3. In the event that pesticides must be applied, they shall be target-specific and strategically applied in an effort to reduce negative health outcomes.
  4. Pesticides shall be used only on an as-needed basis and the frequency and intensity of use  should be minimized in order to reduce the risk of resistance populations.
  5. In cases where pest resistance has been established and repeat pesticide application is necessary, anti-resistance strategies should be integrated into control efforts.  
  6. Record keeping is essential and should be based on detailed records in order to determine the efficacy of pest control programs – especially in the case of chemical inputs.
  7. Monitoring efforts are essential in order to track pest presence.  This can be accomplished via observations, forecasting and early diagnosis systems and information, as well as information from professionally qualified .  
  8. The information garnered by monitoring efforts shall be used to determine when and which plant protection measures will be taken.  There should be scientifically supported threshold values upon which to base decision making.  Said values should be adapted to local conditions including climate, crop type and topographical qualities.




question: how is a beautiful lawn the “perfect antithesis of an ecological system”?


According to the Barbara Stein, author of Noah’s Garden, a perfect lawn perpetually requires intensive inputs due to the fact that it is completely cut-off from the natural system that would otherwise support it. Additionally, the roots that grow from lawn grass become a “feltlike mat” that is between 2 and 4 inches deep. The tangled roots inhibit the growth of other plants and require large amounts of water input during the hot summer months, as well is 5 “feedings” of nitrogen, phosphorous and/or potassium. With so many inputs, including additional herbicides to remove any potential invaders, the grass grows rapidly which requires that it be cut frequently which in turn encourages the growth of new blades because the plant is never able to flower. In turn, the carrying capacity of the lawn extremely low because there is a lack of biodiversity that is necessary to support fauna.

As grass has evolved to endure grazing it grows sideways below the reach of grazers (or lawnmowers) in order to protect the nodes from consumption and/or destruction and the tillers of the plant grow from the root of the plant, as opposed to the stalk itself. Furthermore, grass is defensive in nature – there is silica in the blades, needled awns in the seeds, and the ability to use leftover nutrients in the roots in order to toughen the cellulose in preparation for the following growing season. There is also an indication that different grasses “green” sequentially as an adaptation to grazers.

As a result of these adaptations, grass looks best in the spring because that is when it is naturally vibrant, has had enough time to “rest” and it is not going against its natural cycle of “tanning” and relaxing in the summer when the weather is hot. It is suggested that an inch of water be applied to lawns along with various fertilizers, herbicides and pesticides in order to maintain the youthful, green spring glow. These inputs need to applied because “lawn” grass engages in C4 photosynthesis which incorporates CO2 with a 4 carbon compound. This form of photosynthesis takes place in the inner cells and occurs much more rapidly than C3 photosynthesis under high light intensity and temperatures because of the compound PEP Carboxylase delivering the CO2 more rapidly. C3 photosynthesis incorporates CO2 with a 3 carbon compound. This form of photosynthesis takes place in the leaves and is most effective in cool and moist locations with normal light conditions.

For more information on the effects of chemical inputs, check out this post on eutrophication.

community gardens discussed and analyzed

“The greatest fine art of the future will be the making of a comfortable living from a small piece of land.”

– Abraham Lincoln

Agriculture is defined as the science, art, and business of cultivating soil, producing crops and raising cattle. It is more commonly referred to as farming. Without it, society as we know it would not exist. It has enabled people to put down roots which provided the means for the world’s population to expand. Unfortunately, it has also been transformed by industrialization into a widely abused system that is dependent on government subsidies and environmentally unsound practices in order to produce food products with less nutritional value and poorer taste. Furthermore, the existing agriculture system is controlled by an increasingly small number of international firms.

However, grassroots efforts and individuals are choosing to look at food in a different way, a way that seems to be able to co-exist with ecosystems. A viable option that has been employed in the past, but since forgotten, is the community garden.

A community garden is any vacant land that is used for growing food and is accessible to community members. Not only do these gardens provide healthy food to demographics that many not otherwise have access, but it improves the overall quality of life in the community by reducing crime, encouraging exercise, and encourages people to have pride in their neighborhood. However, the benefits of community gardens are not limited to the community. Instead, the effects impact the whole ecosystem.

Many community gardens have strict rules about the methods members can employ, and choose to model organic farming methods. Those rules include limiting or banning synthetic pesticides and fertilizers. Some community gardens also ban certain species of plants that have been proven to attract pests or have no predators to limit spreading.

Community gardens limit non-organic pesticides and fertilizers, because of the effects that they can have on human, animal, and environmental health which allows for the natural qualities of soil and the ecosystem to shine.


Soil is an essential part of the growing environment and without healthy soil, one would not be able to produce healthy plants. Ideal soil for plants is composed of 25% air, 45% minerals, 25% water and 5% organic material. This mix allows for plant roots to efficiently breathe and absorb nutrients and water. However, different plants prefer different mixes of minerals and will tolerate varying degrees of acidity and moisture.

To create ideal soil that is rich in nutrients, well-aerated, and free from disease, many community gardens employ composting methods. Compost is the process of breaking down organic material. The result is a very dark, rich addition to any garden.

Compost is created by putting Nitrogen rich items (greens-vegetable scraps, lawn cuttings, and coffee grounds) and Carbon-rich items (browns-shredded cardboard, sawdust, and leaves) together into a well-ventilated space and mixing with water. The ideal ratio of Carbon to Nitrogen is 25-30:1. This mixture can heat up to 150 degrees from the work of macro and micro-organisms. The increased heat speeds up the breakdown process, and when coupled with Red Wiggler Worms, can reduce the decomposition time to only a few weeks.

Finished compost helps to reduce water use because it is will hold 6X’s more water than traditional soil. It also provides nutrients that would not otherwise be available to plants. This reduces and/or eliminates the need for any non-organic fertilizers, reducing cost and environmental impact while gardeners enjoy similar, if not better results.

Another benefit of compost is that it creates stronger plants, and can help to eliminate the need for pesticides. Pesticides include anything designed to destroy fungus, weed, insect or disease. These synthetic killers are non-discriminatory in their effects, and could just as easily kill family pets as insects. This harm could come from direct consumption, water-run off or from residual traces of chemicals in the soil.

compost 101

To further reduce the needs for pesticides, community gardens encourage and use “beneficial” pests. These are insects that are carnivorous and indigenous to the area. The most popular versions of these bugs are Praying Mantises, spiders, Ladybugs and Lacewings. It must also be noted that one should not introduce too many of one species or too many in general in order to maintain a balance.

When gardens choose not to introduce beneficial pests into the garden, they often choose to use other methods to protect their plants. Covering plants in light-weight netting can deter all insects but does not allow for pollination.

Another option is companion planting, such as putting onions or garlic with almost any plant, or celery with plants in the cabbage family. By planting certain plants together, the smells naturally detract invasive species. Marigolds, nasturtiums, and rosemary are also very pungent smelling and deter many pests.

As in any scenario, some problems arise with community gardens, including issues with existing soil, cultural sensitivities, unfavorable weather and the question of sustainability.

Since community gardens use whatever space is available, and the modern version originated in urban areas where the environmental impact of humans is greater than in rural areas. One of the biggest problems community gardens find is the presence of lead in the soil. Lead is devastating to life and is not easy to remove from soil.

Cultural sensitivities are also difficult to deal with, as they are generally historically rooted. In cities such as Chicago and Detroit, some groups are associating community gardening with slavery. This is difficult to deal with because community gardens are dependent on community involvement.

Weather can also impact the effectiveness of community gardens, especially in cooler climates. To deal with weather problems, community gardens use cold frames and wind tunnels. These structures help to regulate temperature and keep out harsh winds and snows. Sometimes, community gardens will couple these methods with cold hardy plants to lengthen the growing season.

The biggest concern that surrounds community gardens is their capacity to feed a large number of people since the population is not getting smaller and everyone needs to eat. There is a large amount of unused space in cities throughout America, but it is unclear if people are willing to utilize it for food production and put forth the effort needed to transform dilapidated neighborhoods.

While the concept of community gardens is not a new idea, society is in a unique situation that could revitalize their presence in towns and city throughout the country. This revival could help improve ecosystems everywhere, redistribute wealth and resources, encourage and the American agricultural system as a whole, or at least I think so!

For more information, check out this website about the steps needed to start a community garden:


Environmental Working Group. (n.d.) Farming: Farm Subsidies. Retrieved from

Pidwirny, Michael. (2013). Soil. Retrieved from

Runk, David. (2010). Lead, other chemicals taint some urban gardens. Times Union

Smith, Edward C. The Vegetable Gardener’s Container Bible. North Adams: Storey, 2010.

eight influential agricultural figures


Eli Whitney (December 1765 – January 1825)

cotton ginIn 1794 US born inventor Whitney patented the cotton gin which revolutionized cotton production by dramatically increasing the speed of seed removal from the fiber. This was accomplished by running the cotton through a wooden drum fitted with a number of hooks that caught the fibers and pulled them through mesh fiber too fine for the seeds. Unfortunately, this invention provided southern farmers with justification for continuing and even expanding the practice of slavery – despite growing favor for its abolition. However, due to patent infringement issues, Whitney was unable to economically profit from his invention. Despite not providing the desired economic outcomes, his invention of the cotton gin garnered him a solid reputation that he was later able to use to secure a government contract for musket building. This resulted in the development of standardized interchangeable parts. Due to these advances, he is credited with being one of the pioneers of American manufacturing.


Cyrus McCormick  (February 1809 – May 1884)

mechanical reaperFor twenty years Cyrus McCormick’s father Robert attempted to build a mechanical reaper to no avail. Cyrus adopted his father’s work and reconfigured his father’s concepts to create a properly working machine in 1931 that he patented shortly after in 1834. This invention revolutionized harvesting techniques that had not being updated in approximately 5,000 years. Previously crops were reaped by hand using a scythe. This labor was backbreaking and often resulted in crop loss because of the limited time for harvest before the product began to decay. However, at first, the product was not particularly popular. It was not until he developed a business plan that allowed for the use of credit and offered guarantees of harvest improvements that the machine gained acceptance and eventually popularity. His development of the traveling salesmen to spread the word about the mechanical reaper also revolutionized the world of marketing.

John Deere
(February 1804 – May 1886)

john deer plow bladeVermont native John Deer found that the economic conditions in his home state were unfavorable and opted to move to the Midwest where he quickly built a new forge which enabled him to reestablish himself. He listened to the complaints of farmers stating that their cast-iron plows were unable to effectively manage the local thick, tacky soil. Using this information, he joined forces with fellow Vermonter Major Leonard Andrus to develop the first no-stick plow blade from an old saw blade and a wrought iron moldboard. The new plow was made from steel, rather than cast iron, and polished smooth on both sides to ensure that the damp soil would not stick to the blade. His dedication to innovation transferred to future improvement to his products because he was aware of the fact that if he did not develop the advancements, someone else would.


Fritz Haber (December 1868 – January 1934)

nitrogenNitrogen, one of the most important elements used in agriculture was first solidified by Haber in 1908. This provided a means to utilize the mass amounts of gaseous Nitrogen in the air which was essential to meet the growing demand needed for the rapidly expanding food production system. He accomplished this feat by combining hydrogen and nitrogen at high temperatures in the presence of a catalyst to produce NH3 – more commonly known as ammonia. His success [which is often associated with Carl Bosch] earned him a Nobel Peace Prize. In modern times, 48% of the world’s agricultural production systems are dependent on nitrogen fertilizers.


George Washington Carver (January 1864 – January 1943)

george washington carverAfter several decades of continuous cotton farming in the southern United States, much of the soil became depleted that resulted in diminished crop returns that were devastating to the already poor rural farmers. To combat this issue Carver suggested a diversification of crops include peanuts, sweet potatoes, and cow beans. Each of these plants enriched the soil and allowed for the creation of new economic opportunities for farmers. This led to him to develop more than 300 ways to incorporate peanuts into products like plastics, dyes, and cosmetics and 118 ways to use sweet potatoes in non-food products like rubber and postage stamp glue. His goal was to help eradicate some of the poverty that he had been forced to endure in life, but his quest was not easy due to segregation in the south. Still, he was quite successful in his endeavors and helped to improve the lives of thousands of people and lay the foundation for modern-day organic agriculture.


Rachel Carson (May 1907 – April 1964)

rachel carsonCarson began her studies as an English major but switched to biology shortly after. She completed her graduate work on a scholarship at John Hopkins University in 1929 which at the time was an amazing accomplishment for women. Her hard work and dedication earned her one of the only two positions with the U.S. Bureau of Fisheries where she worked to encourage the implementation of regulations and promote conservation efforts. She was then offered a full-time position as a junior aquatic biologist which allowed her to learn about the culture and economics of the Chesapeake Bay area and collaborate with the US Navy for a project to study underwater sounds, life, and terrain. In 1941 she published her first book Under Sea-Wind which captivated readers’ interest in the natural world. She continued working for the Bureau of Fisheries and authored a variety of series directed at the American public that often included information in laymen’s terms. She published her second book in 1951 which prompted her to leave her position with the government to devote her time to writing. She then published The Sea Around Us in 1952 and The Edge of Sea in 1956. However, it was her book Silent Spring that changed the course of American history by bringing attention to the harmful effects of pesticides – most notably DDT. Her goal was not to eliminate the use of pesticides but to encourage better regulation and safety testing. Regardless, the book caused a great deal of controversy and there were extensive efforts to discredit Carson by the pesticide industry. Despite their efforts, Carson was asked to testify before a congressional committee when a complete review of the United States’ pesticide policy was ordered.


 (1953 – present)

fraleyFraley is currently serving as the Executive Vice-President and Chief Technology Officer at Monsanto. He began working for the company as a research specialist in 1981 where he worked to develop solutions to many of the problems facing farmers, such as pest and disease control. His breakthrough came when he [and his team] isolated a bacterial gene marker that was engineered to express itself in plant cells. The first transgenic organism was developed using Agrobacterium which was used to transfer an immunity trait to tobacco and petunia plants. This development has expanded greatly and genetically modified seeds are now available throughout the world. In 1996 the first Round-Up ready soybean plants [that are resistant to the herbicide glyphosate] were planted in the United States. In his current position, Fraley is working to ensure that genetically modified products are readily available throughout the world with an emphasis on integration GMOs into smaller farm operations.

Joel Salatin (1957 – present)

joel salatinSalatin is a third generation organic farmer who advocates for developing agricultural systems that mimic natural ecological cycles.  On his farm in the Shenandoah Valley, he integrates permaculture and polyculture which enables him to provide food to more than 5,000 families, 50 restaurants, and 10 retail outlets. He is an author and public speaker who brings attention to subjective and burdensome government regulations that encourage large entities and discourages new and smaller producers from entering the market, as well as shares his personal knowledge and experiences with biodiversity and land remediation. Salatin has also attempted to bring his ideas to the government in an effort to reduce the environmental damage from agricultural waste runoff to the Chesapeake Bay area, although his solutions have not been embraced. His body of work includes a variety of books that detail the methods he uses on his farm in an effort to share the information necessary to restructure our food system starting from the farm up, although he also emphasizes the importance of personal responsibility in consumer choices. Due to the innovative nature of his farming practices he has also been featured in several films with the most notable being Food Inc. Salatin is also known for his relationship with Michael Pollen, another very influential advocating for sustainability.


Salatin, J. (2007). Everything I Want to Do Is Illegal. Polyface.