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 Pyrethrum plants

Growing pyrethrum is both a skill and a way of life for many growers. Pyrethrum plants can produce as many as 400 flowers per plant and grow best in locations with well-drained, volcanic soils and temperate climates such as in China, East Africa and Australia/New Zeland. The pyrethrum plant can be highly sensitive to soil and weather conditions, so commercial production of pyrethrum presents numerous challenges to the grower. To learn more about growing pyrethrum, 

  
Pyrethrum has been grown for well over a thousand years. The commercial production of Pyrethrum began in China to supply the demand for pyrethrum along the silk route and in Europe. For reasons unknown, pyrethrum production moved to the Dalmatia coast and again to Japan prior to WWII. Post WWII presented a new era for pyrethrum farming when production was moved to East Africa, Tanzania and Rwanda where soil and temperature conditions are ideal.

Size and Method Relationship

The farm size for pyrethrum can range from less than one acre run by an individual grower to hundreds of acres grown by large grower cooperatives. There are many differences between small scale and large scale growers although the end pyrethrum product is nearly indistinguishable except by scientific methods.   

Small Scale Growers: There are more than 50,000 small scale pyrethrum growers in East Africa and China. Small scale growers grow pyrethrum on fields ranging in size from a quarter acre to 5 acres and typically use organic production techniques such as planting seed by hand and hand-picking the flower heads at harvest. Small scale growers benefit from low input and production costs but typically have a lower yield per acre, on average less than half, than that of a large scale producer.

Large Scale Growers: There are less than a few hundred large scale pyrethrum growers mostly located in Tasmania, Australia. Large scale farmers typically have plots ranging from 10 acres to a few hundred acres.  They apply modern agricultural production techniques that can include treated seeds, fertilizers, fungicides and irrigation.  They rely on modern farming equpment for planting and harvesting.  Although large scale farmers have higher input costs, the result is higher yields and revenue per acre.

A Challenging Crop

Wherever pyrethrum is grown, experience has shown there are numerous challenges to overcome as compared to many other crops.  The balance between the Pyrethrum plant itself, environment, and harvesting issues must be closely optimized in order to produce pyrethrum cost effectively.  The plant can be highly sensitive to soil and temperature conditions along with the usual weather sensitivity common for many crops.  The evidence of the difficulty is shown by the more than a dozen different regions/countries that have tried to grow pyrethrum, yet today it is commercially grown in only three main areas:  East Africa, China, and Australia.   

In East Africa and Australia, Pyrethrum is planted as a perennial and typically left in a particular plot for 3 to 5 years, before crop rotation.  The length of time is often dependant on pyrethrum production volume in a given year.  The first year product is usually about 2/3rds of the 2nd year flower production and Pyrethrum yields.  Years 3 through 5 are similar to the 2nd year, dependent on clones, weather and related environmental conditions.  Typically after 4 or 5 years it is best to rotate a field out of pyrethrum as production yield can drop significantly.  Most vegetable crops do extremely well following pyrethrum.  China has used both perennial cropping and annual cropping via seedlings.

All pyrethrum plants require similar soil conditions regardless of which breeding stock is used. Because pyrethrum is highly susceptible to root rot, the soil must be well draining with a minimum pH of 5.4 to slightly alkaline and rich in nutrients (phosphorus, calcium and magnesium) for a good yield. Pyrethrum is often used to regenerate crop land and can even be instrumental in preventing land erosion

Rainfall at the correct time and amount affects yield per acre significantly for all types of pyrethrum plant clones.  The rainfall or watering requirements range from 30 inches (762mm) spread over the growing season to as much as 50 inches (1270mm).  Pyrethrum is intolerant of excessively wet conditions.  Excessive rains will likely cause root rot and other diseases caused by fungus.  On the other hand, pyrethrum is somewhat drought resistant, and a short dry spell (45 days or less) at the right time can be good for flowering.  A longer dry spell or drought can be disastrous for a given years yield.  Rains or watering, just prior to significant flowering can results in more flowers and increased pyrethrum content.

In East Africa and China, altitude and season are two factors that determine temperature.  In Australia, the season is the main factor in temperature.  Generally speaking Pyrethrum is intolerant of severe frosts, and an entire year’s yield can be wiped out.  If the crop is very young or recently transplanted, a relatively light frost can be equally detrimental and may result in near complete loss of crop.  At the same time, for a healthy mature pyrethrum crop, a light frost during the somewhat dormant stage of the crop seldom does much damage to the pyrethrum plant and or effect on future flowering.  While it is clear frost temperatures [0°C ( 32°F) and below] should be avoided, it is further noted that pyrethrum content is affected by changes in temperatures.  Tests have shown as the average temperature falls with no frost, the pyrethrum content rises, as long as there is no frost.  At the same time flower initiation can also be increased as temperatures fall during the onset of rains.

While different conditions further effect each of these fungi, in general the cause of fungus is usually damp, misty, wet weather conditions.

Some examples of fungus that affect pyrethrum are:

Even though once pyrethrum flowers are dried and ground they are one of the world's best insecticides, while pyrethrum is grown it is as susceptible to insects as any other growing crop.

The most harmful insects to pyrethrum crops include:

•Thrips
•Flower Thrips
•Green Peach Aphids
•Red Spider Mites
•Nematodes
Usually insects don't cause as much harm to pyrethrum crops as fungi do.  Insects tend to be the most harmful to pyrthrum crops during dry seasons.

While sunlight is required for pyrethrum flowers, reports are mixed as to how much or how little is required.  One key acknowledgement is that hours of sunlight in a given day, determines the plant’s flowering pattern.  Namely if the plant flowers most of the year and, or if there is only one or two flowering periods during the year.  For example in East Africa where the hours of sunlight are relatively similar throughout the year, the pyrethrum plants have two major flowerings due to seasons, but also flower a majority of the year, allowing a steady income for many months.  In Australia, the hours of sunlight varies significantly between seasons and the long sunlight hours and warmer weather in the spring and early summer results in near synchronous blooming in late spring, early summer.

There are a wide variety of weed problems with pyrethrum and each are often dependent on country, and regions of country where pyrethrum is grown.  With this said, it is clear that weeds often have a most detrimental effect on pyrethrin production and yield.  Pyrethrum per acre if often less than half normal yields, and perhaps a low as one fourth normal yields if weeds are not controlled.  While Australia uses herbicides to control weeds, East Africa relies mainly on organic methods; that being manual weeding.  It is important that weed management is most problematic the first year.  Once the crop is established, weeds are typically easier to control and have less negative impact on production yields.

Propagation of pyrethrum plants also varies by country and may further vary between regions within a country.  In East Africa and China they grow seedlings in nurseries to produce small plants that are then transplanted into larger acreage.  Australia typically plants seeds directly into large acreage plots, most often referred to as paddocks.

Much attention is paid to the pyrethrum yields when growing pyrethrum, and this is related to different pyrethrum plants, clones and/or breeding programs, and between countries, regions and even between farmers.  There is sometimes confusion and miscalculation of yields. 

There are 2 main yields to consider on a per acre or hectare basis: 

1. Kilos of active pyrethrins 
2. Kilos of flowers

By far the most important yield is kilos of active ingredient per acre/hectare.  It is always better to have higher pyrethrum content per flower head, thereby creating a better opportunity for higher yield per acre/hectare and higher income for the farmers.  Certain clones may produce more flower heads or larger flower heads with lower pyrethrum content and result in reasonable pyrethrum content per acre/hectare.  While the total pyrethrum content can be good, the extra energy to harvest, dry and process the lower pyrethrum content flowers consistently results in higher production costs for farmer and processor.

Pyrethrum Flowers are Processed to produce Pyrethrins

Refined pyrethrum extract has been commercially produced for more than 60 years.  As a natural product, it is not unexpected that pyrethrum presents challenges in both processing and analysis.  The key to extraction and refining is maintaining high recoveries of pyrethrins throughout processing.  To maintain the high recoveries, proper handling of the flowers and extracts must be tracked to insure there are not losses due to fermentation, excessive exposure to heat, or inadequate extractions.

Pyrethrum flowers are harvested by hand in East African countries- Kenya, Tanzania, and Rwanda - and are dried in the open air to avoid fermentation that can lead to pyrethrin losses.  The dried flowers are placed into burlap sacks for transportation to processing facilities where they are ground into powder for extracting.  Good quality dried flowers contain approximately 1.4% to 1.8% pyrethrins. 

The primary extraction from ground pyrethrum flowers results in a crude pyrethrum extract that can vary from semi-solid to a viscous liquid and is similar to a black tarry substance.  In Tasmania, Australia mechanical cultivators are used to cut the pyrethrum flowers and stack the cut flowers and stems in wind rows for drying under the sun prior to collection.  The dried material is collected and pelletized for extraction to produce a crude extract similar to other producers containing approximately 30% pyrethrins.

Crude extract is not suitable for use in formulations as it still contains excessive levels of vegetable waxes and resins and high levels of color bodies that will result in staining.  Therefore further extraction is conducted to remove excess vegetable waxes, resins and color bodies.

Each of the three primary refiners of pyrethrum in the world - Kenya, MGK or BRA - have some unique aspects of their processing, but they all result in a clear, amber liquid that contains anywhere from 20% to 55% pyrethrins.  The standardized pyrethrins solution is typically blended with synergists, emulsifiers and solvents into the various formulations to kill insects

An extensive database of toxicology studies on pyrethrum has been generated by the Pyrethrin Joint Venture of which MGK is a member.  The U.S. Environmental Protection Agency ("EPA") reviewed the studies and determined that the database was acceptable to re-register pyrethrins in 2006 when the Reregistration Eligibility Decision (RED) for pyrethrins was issued. The database consists of a long list of studies including:

 •Acute toxicity studies
•Acute and chronic dietary studies
•Short and intermediate term oral studies
•Short and intermediate term inhalation studies
•Reproductive and fertility studies
•Genotoxicity studies
•Developmental toxicity studies
•Neurotoxicity studies
•Dermal absorption study 
Pyrethrins are relatively low in toxicity to humans and mammals with the toxicity to rats being 4000 times lower than pyrethrins toxicity to the house fly.  There were no reproductive, genetic, or mutagenic effects from pyrethrins in these studies.

The Pyrethrin Joint Venture conducted a series of studies looking at the mode of action of pyrethrins on the liver following EPA guidelines.  In 2008, the EPA’s Cancer Assessment Review Committee ("CARC") classified pyrethrins as “Not Likely to be Carcinogenic to Humans” at doses that do not cause a mitogenic response in the liver/cell proliferation.  This is based on a weak liver tumor response seen in female rats only at the high dose.  No tumors were seen in male or female mice.  The weight of evidence supports a non-genotoxic mitogenic mode of action for liver tumors.

As the EPA and the industry investigated exposure modeling and conducted risk assessments, the dermal absorption became a key factor.  The PJV decided to conduct a human dermal absorption study on pyrethrins due to the EPA’s use of a 20% dermal absorption as a default factor.  The dermal absorption study was conducted in Europe under clinical conditions with male volunteers and found a dermal absorption value of 0.21% or two orders of magnitude less than the EPA’s default value.  This value was helpful in showing the low levels of exposure to pyrethrins in the use of our products.  

The EPA has identified neurobehavioral effects and thyroid effects as critical toxicological effects of pyrethrins and has required additional studies to better understand these affects.  The neurobehavioral effects will be eval‎uated by conducting either a developmental neurotoxicity study or alternative studies that the EPA and the pyrethrin/pyrethroid industry have been discussing.  The thyroid effects will be eval‎uated by conducting a comparative thyroid study.  These studies are expected to be started in 2011.  It is expected that pyrethrins caused the formation of tumors in the thyroid through dose-related secondary proliferative stimulation of thyroid follicular cells.  The tumor formation is clearly based upon a dose-threshold by non-genotoxic mechanisms that are unlikely to occur in humans.

The EPA has concerns with adverse affects from pyrethrin containing products involving dermal or inhalation exposures.  The PJV initiated a Stewardship Program in 2010 that will track all adverse affect reports from products containing pyrethrins and conduct follow-ups to better understand these events.  The Stewardship Program will be conducted for five years and yearly reports will be prepared for the EPA to summarize the findings from the previous year.

Botanical vs Laboratory Synthesized

The six esters known collectively as pyrethrins are produced in the Chrysanthemum plant, Chrysanthemum cinerariaefolium. Pyrethrins are found at particularly high concentration within flower structures known as achenes which are located in the flowerhead of the Chrysanthemum. The extract from the Chrysanthemum plant containing pyrethrins is called pyrethrum.     

Pyrethroids are synthetic, or man-made, versions of pyrethrins. There are two major classes of pyrethroids, Type I and Type II pyrethroids. Type I pyrethroids are characterized by their ability to knockdown insects quickly but the Type II pyrethroids will induce higher insect mortality than Type I pyrethroids. While pyrethrum extract is composed of 6 esters which are insecticidal, a synthetic pyrethroid is composed of only one chemically active compound.

One result of the similarities between the chemistry of pyrethrins and synthetic pyrethroids is that have a similar mode of action (i.e. both pyrethrins and pyrethroids induce a toxic effect within the insect by acting on sodium channels; see Mode of Action). Some differences in the chemistry between pyrethrins and synthetic pyrethroids have the result that synthetic pyrethroids have relatively longer environmental persistence than do pyrethrins. Pyrethrins have shorter environmental persistence than synthetic pyrethroids because their chemical structure is more susceptible to the presence of UV light and changes in pH.

One important difference between pyrethrins and synthetic pyrethroids is the behavioral effect they have on insects. Pyrethrins have a unique ability to induce excitation behavior in the target insect. This excitation behavior is characterized by erratic and increased movement by insects. This is sometimes referred to as ‘flushing’ action. This flushing action induced by pyrethrins is highly desirable; because of the increase in movement, it often results in increased insect exposure to pyrethrins

The first record of the pyrethrum daisy was 2000 years ago at the time of China’s Chou Dynasty.  The flower appears to have been traded along the Silk Route and eventually was grown in the Dalmatian region.  There are reports that French soldiers used crushed flowers to control fleas and body lice during the Napoleonic Wars (1804-1815).  In 1860, pyrethrum powder was introduced to the United States, but whole flowers later replaced the powder as the desired imported product.  In 1881, pyrethrum cultivation was introduced to Japan from England and when World War I broke out in 1914, Japan became the principle supplier of pyrethrum flowers to the United States.

 McLaughlin Gormley King Company (MGK) was formed in 1902 and by 1910 was importing spices that were packed in dried pyrethrum flowers.  MGK began importing pyrethrum powder in 1915 for insect control that was applied with a bellows-type device.  In 1919, kerosene extracts of pyrethrum became available and by 1928, the use of pyrethrum powder had nearly ceased.  A paper by Staudinger and Ruzicka on pyrethrum identification in 1924 and a paper by Gnadinger, an MGK employee, on a method to quantitate pyrethrum in 1929 awakened new interest in the product and it became possible to assay pyrethrum and produce a pyrethrum extract of standardized active content. 

Japan was supplying 82% of pyrethrum flowers sold to the United States in 1926 and by 1931 they were supplying 91% of the US needs.  In 1928, pyrethrum cultivation was introduced to Kenya and by 1932 commercial production of pyrethrum flowers began.  MGK initiated a project to grow pyrethrum flowers in Colorado in 1933 while efforts to develop commercial production of pyrethrum flowers in Brazil were also underway.  In 1938 the first pyrethrum flowers were imported from Tanganyika (now Tanzania) and in 1939 MGK assisted with the construction of a pyrethrum extraction plant in South Africa.  With significant contributions from Gnadinger, AOAC published the first method for quantification of pyrethrum in 1940.

In 1990 MGK began collaboration with a group in Australia that eventually evolved into Botanical Resources Australia (BRA).  BRA grew pyrethrum flowers using modern agricultural practices and soon supplied MGK with crude pyrethrum extract for refining.  In approximately 1998 BRA began refining pyrethrum extract using a super critical fluid process.  Due to social and economic problems in Kenya in 2006 – 2008, supplies of refined pyrethrum drastically dropped to almost non-existent and BRA became the largest supplier of pyrethrins in the world market.  In 2006 MGK purchased controlling interest in TPPMCL, a company that extracted pyrethrum flowers in Tanzania.  Most recently, the company’s name was changed to Pyrethrum Company of Tanzania (PCT).  MGK has undertaken a long term project to improve the extraction facility in Tanzania, to coordinate the pyrethrum flower growers and the annual collection of flowers

Special Places to Grow a very Special Flower

The pyrethrum flower is a hearty perennial that thrives in interesting and challenging environments.  As a result, pyrethrum is grown commercially in some of the most interesting places in the world.  

Throughout history, pyrethrum has been grown in many places, from the Balkans to China.  During the post-World-War II era, however, for several political and economic reasons, Pyrethrum growing has flourished in East Africa and Australia. 

Pyrethrum in East Africa

English and American interests introduced pyrethrum cultivation to East Africa during World War II to replace flower production lost during fighting in China.  As a result, Kenya and Tanzania became prime growing regions. MGK licensed extraction and refining technology to the Pyrethrum Board of Kenya (“PBK”), which became a leading producer of pyrethrum in East Africa.  PBK’s headquarters and production facility is located in Nakuru, Kenya.  PBK collects flowers from growers in several regions in Kenya.

In Tanzania, in the early 1960s MGK formed a joint venture with Mitchell-Cotts, and established a pyrethrum extraction plant in Arusha, Tanzania, in the Northern part of the country, near Mount Kilimanjaro.  Tanzania ultimately consolidated the pyrethrum industry under the Tanzania Pyrethrum Board (“TPB”).  TPB moved the extraction plant to the Southern Highlands area of Tanzania, where it remains today.  In 1998 Tanzania privatized the pyrethrum sector, selling the pyrethrum operation to a private company now known as Pyrethrum Company of Tanzania (“PCT”).  In 2006 MGK invested in PCT and is its majority owner.  PCT is leading a multi-year expansion program to revitalize pyrethrum growing in the Southern Highlands as well as the Arusha region. PCT is also investing in its extraction plant in Mafinga, Tanzania, so that PCT will be able to process the expanded harvest of flowers now growing across Tanzania. 

Rwanda also began to cultivate pyrethrum and sell its extract through OPYRWA.  In 1996 the Rwandan government privatized the pyrethrum sector in Rwanda, transferring the business to SOPYRWA, a private company with its operations in Ruhengeri, Rwanda.  Rwanda has made great strides to recover from the genocide and to rebuild its pyrethrum production capacity.

Producers in East Africa succeeded in growing pyrethrum for several reasons.  The pyrethrum plant thrives at high altitudes and in volcanic soil.  There are many growing regions in East Africa with good combinations of altitude, rainfall and soil conditions.  Additionally, the people living in many of these areas are not able to grow crops to sell for cash.  Pyrethrum provides a cash crop that supplements subsistence farming.  The cash earned from pyrethrum funds school uniforms, books, supplies and other essentials. 

Pyrethrum is, therefore, a vital component to rural life in the countries and villages where pyrethrum is cultivated.  MGK sees this as an important factor in maintaining a sustainable and reliable supply of pyrethrum.  Pyrethrum also gives farmers in remote villages access to cash from a crop that is important to the developed world.  By accessing this value chain, rural African villagers become important participants in a global market.

Pyrethrum in Australia

Pyrethrum is also cultivated on a commercial scale in Tasmania, Australia.  Tasmania has long been an agricultural center for Australia and Asia.  In the 1980s, however, the Tasmanian government sought high-value crops to improve the standard of living of farmers living on Tasmania. This led to many years of research and trials to grow and harvest pyrethrum using the technology of mechanized farming.  Out of this program came a commercial pyrethrum industry led by Botanical Resources, Australia (“BRA”).  BRA has its headquarters in Hobart, Tasmania, and its operations, extraction and refining facility in Ulverstone, Tasmania, on the Northern coast of the island, where most of the pyrethrum farms are located.     

BRA employs the latest in agricultural technology.  On its own farms and on farms under contract with BRA, the company plants pyrethrum flowers by mechanical means.  Crop managers keep a close eye on production and advise farmers as to appropriate weed control measures and other steps necessary to protect the crop.  Starting in January of each year, BRA manages the agricultural equivalent of a major battlefield operation, coordinating a fleet of harvesters and trucks to collect and deliver the crop to its extraction facility.  As a result of its investment in modern technology, BRA has become a major supplier of pyrethrum to the world market. 

MGK has been a partner with BRA from the beginning.  MGK saw the need for diversified supplies for the world market and supported BRA’s program.  MGK is a minority owner of BRA.

Where does pyrethrum come from?

Pyrethrum is found in the Chrysanthemum plant, Chrysanthemum cinerariaefolium. Pyrethrum is found at particularly high concentration within flower structures known as achenes which are located in the flowerhead of the Chrysanthemum.

What are the differences between pyrethrum, pyrethrins and pyrethroids?

Pyrethrum is the extract from the flowerhead of the Chrysanthemum plant.  The six esters known collectively as pyrethrins are found within the pyrethrum extract.  The pyrethrins are the active ingredient in pyrethrum that kills insects. 

Pyrethroids are synthetically produced compounds with a chemical structure that is similiar to the structure of one of the pyrethrin esters.  They kill insects by a similiar mode of action, but do not come from flowers.

How does pyrethrum kill insects?

Pyrethrum induces a toxic effect in insects when it penetrates the cuticle and reaches the nervous system. The pyrethrins that compose pyrethrum bind to sodium channels that occur along the length of nerve cells. Sodium channels are responsible for nerve signal transmission along the length of the nerve cell by permitting the flux of sodium ions. When pyrethrins bind to sodium channels, normal function of the channels is obstructed thereby resulting in hyperexcitation if the nerve cell and, consequently, a loss of function of the nerve cell. The shutdown of the insect nervous system and insect death are most often the consequences of insect exposure to pyrethrins.

What happens to pyrethrum in the environment?

Pyrethrum does not persist for a long time in the environment. The active chemicals in pyrethrum, pyrethrins, are degraded by high temperature and UV light.

What kind of insects can be controlled with pyrethrum based products?

Pyrethrum is a broad spectrum insecticide.  Meaning it will affect a wide range of insects; including beneficials.

How long have pyrethrins been used for insect control?

Pyrethrins have been used in insect control for more than 160 years.

Will pyrethrum/ins degrade or become less potent during storage?

Most products are packaged in containers that do not let UV light through, and indicate they should be stored in a cool, dry place.  Under these conditions most products should maintain their potency for a couple of years.  If the product is subjected to high temperature or UV light, there can be some degradation of the pyrethrins.  As with most products, you should only purchase what you need, and for best results use it within the season it is purchased.

How safe is Pyrethrum?

Pyrethrum has been extensively studied for its effects on people and the environment. Like all insecticides, pyrethrum is used to have a toxic effect on insects. Thus it is not correct to say that pyrethrum is "safe." At the same time, we are confident that pyrethrum has a very good toxicity profile. For mammals, doses that elicit toxic reactions are significantly larger than the exposures people typically experience in using pyrethrum based products