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Updated May, 2011 |
Growing the Blue Agave
Recommended Temperature Zone: USDA:
9b-10 (hardiness zone means the average annual minimum temperature range
is: 9b: 25 to 30F (-1.2 to -3.8C - examples: Brownsville, Texas;
Fort Pierce, Florida) to 10a: 30 to 35F (1.6 to -1.1C - examples:
Naples, Florida; Victorville, California).
The blue agave was classified by German botanist F. Weber in 1905. It's commonly - and mistakenly - called a cactus, but it is really a succulent that belongs to the lily (amaryllis) family. It is sometimes known as cabuya, maguey mezcal, mexic, pita and teometl. The agave used in mezcal, although similar, is harvested younger than the tequila agave.
The agave plants are grown in cultivated orchards called potreros (pastures, also called agave fields, or campos de agave - also called huertas, or groves, in Los Altos).
The harvested shoots are anywhere from the size of an onion to the
size of a grapefruit. In a plant's lifetime it will produce 10-20
shoots.
This
creates a cycle of harvesting and replanting that continues year-round. The rainy
season in the summer usually sees a cessation of field work because the
plants are more difficult to harvest and because of the rain are heavier and
fatter - although with no more sugar. The best harvesting is at the end of
the dry season when the sugar content is at its highest.
Agave grow best in the sun, and in places where they received direct and reflected sun - such as near a stone wall - may be noticeably larger. Weeding is done not merely to remove competitors for nutrients, but to remove sources of shade.
The size of the agave head (piña) is not as important as its sugar content. Technicians test the agaves to be sure the sugar content of the plant is high enough to harvest (at least 24% but higher is preferred). There is a short window of only a few months between the optimum sugar level and the over-ripening of the agave. The rainy season may lower the sugar percentage because the agaves soak up extra water to carry them through the long period until the next rainy season.
During the growing period, the plants are pruned (barbeo), cutting the points of the leaves with machetes to encourage the piña to grow. Some farmers also use a technique called 'shotgun plowing' (barbeo de escopeta) to induce premature ripening of plants, but most fields are hand grown and cultivated, using traditional methods passed down from generation to generation.
Like any other crop or plant, agaves are threatened by a variety of insects, fungi and other natural predators. Included among these are the larvae of several butterflies, and beetles (some, like the black weevil, attack several species).
Today's field hands must be as conversant in the use of chemicals and farm equipment as in the traditional practices.
The agave has both male and female plants. Both produce a tall, fast-growing stalk called the quiote, which looks like a tall asparagus spear prior to flowering. If left to mature, this stalk will produce flowers that will begin the sexual reproduction cycle. A mature field may start to produce quiotes after five to six years, but maybe later depending on local growing conditions. These fields are tended every two weeks because the quiotes grow rapidly - about one metre per week. If left to grow, the flowering quiotes will take sugars and nutrients from the piña and the plant will put all of its energy into the flower production.
The quiote may take longer to appear in the highlands, where agave are slower-ripening because of the cooler climate, sometimes not until the eighth year.
The dried quiote may also be used as wood, for posts, furniture, and
similar household uses. In the past, natives may have used hollow
quiotes as musical instruments, and today an entrepreneur in British
Columbia, Canada, is making didgeridoos with them. Another is using the
wood to make surfboards.
Researchers in the University of Guadalajara and other universities in Mexico have been working to develop fusarium-resistant strains of agave, but even if successful, this does not solve the problems of the monoculture. Other researchers have found that the blue agave develops natural inhibitors against some aspergillus mycotoxins, and suggested it might be worthwhile to 'scale up' such natural inhibitors in the plant.
Most of Jalisco state where tequila is made is a high plateau that averages 7,500 feet above sea level, with sandy, mineral-rich red soil in the highlands, and black earth in the valleys. It is a mountainous, hilly region - but agave grows best above 1,500 metres.
According to some, the best agave plants grow on the slopes of the extinct volcano near the town. Others say the best tequila is made from agave taken from the highlands to the east because highland agave tend to grow larger.
One variety, the Arandas agave, is very large and considered a premium plant that commands more money. Another term for large agave is mano larga or long hand. It may also be that highlands distillers tend to use more traditional production methods to manufacturer smaller quantities of tequila, while those around the town are more modern and produce more mixto (made with cane sugars added to the fermenting agave juices to increase the alcohol content).
One highland grower claims his 2006 agave crop has an average weight from 60-65 Kilos and the sugar content is consistently 41 Brix units.
While most of the blue agave has been planted in the two main production zones, there are other plantations in Jalisco, and farmers in the southern part of the state have expressed concern by the expansion of the blue agave, worried it will replace other traditional food crops like maize and beans, encourage soil erosion in their region, and push out other types of agave still used locally for food, mezcal and pulque.
Other methods of propagating agave have been explored, although not necessarily with the Blue Agave. According to Springerlink, scientists at the Institute of Biology, NCSR Vietnam, Hanoi, grew agave in an agar solution: Abstract A procedure for rapid propagation of Agave (A. cantala Roxb., A. fourcroydes Lem. and A. sisalana Perrine, (Agavaceae) have been developed. The explants were excised from stolon plantlets, sterilized and cultivated on Murashige and Skoog (MS) basal medium containing 2% sucrose, 10% coconut water and 0.8% agar. The addition of following combination of growth substances—0.075 mgl-1 naphthalenacetic acid (NAA)+0.1 mgl-1 indolylbutyric acid (IBA)+0.5 mgl-1 kinetin (KIN) caused an extensive proliferation of multiple shoot primordia. Subcultures of these on the same medium were successful for the multiplication with an index of 3–4 times per 4 weeks subculture period. Shoots were rooted on hormone free MS medium and then transferred into a sand bed for acclimation before field planting.
In Oaxaca, an alternate method of cloning is sometimes used (as described by Lopez in Oaxaca Tierra de Maguey y Mezcal) in which the quiotes are allowed to grow and blossom, but the flower petals are pinched off before they can open for pollination. At this point, the plant will produce a tiny agave shoot - called a bulbul - instead of the flower. These can be collected and replanted. However, because this method is labour-intensive, and the younger shoots are more vulnerable than the hijuelos, it is not commonly practiced any more.
Diseases and Pests of the Blue Agave
This infection and inevitable plant death is collectively known as
TMA ("Tristeza y Muerte de Agave", the wilting and death of the agave). What is interesting is that Fusarium may not always be harmful to all agaves, and may have a beneficial symbiotic relationship. As noted in Springerlink (emphasis added): Abstract A unique non-pathogenic strain of Fusarium oxysporum was isolated from field-collected plants of Agave victoria-reginae Moore. It was then re-introduced into micropropagated plants of the same species under greenhouse conditions. The fungic inoculation induced a 225% increase in the length of roots, 50% in the number of root branches and 50% in the number of stomata on the adaxial surface of leaves. Also, an increment of 167% in nocturnal acidity and a 122% in malic acid was observed and nocturnal pH was significantly more acid in the inoculated plants. Total chlorophyll and sugar content increased 14 and 172%, respectively. These results indicate a higher photosynthetic efficiency of the plants inoculated with the fungus than those plants which were not inoculated; therefore the association of this unique F. oxysporum strain with A. victoria-reginae Moore was considered as a beneficial symbiosis.
This cycle will likely see another shortage of agave in 2010-2012 (see the page on the shortage). As well, the neglected fields are breeding grounds for fusarium, and in June 2007, CRT officials estimated at least 20% of this year's crop has a disease. It may grow much higher if those fields continue to sit untended.
Also, the fungus Thielaviopsis paradoxa prevents younger plants
from forming roots.
Fungus gnat adults transported Fusarium oxysporum f.sp. radicis-lycopersici from Petri dish culture and infected host plants to the roots and hypocotyls of healthy tomato and bean plants. The source of the fungus did not affect the ability of fungus gnats to transport the fungus to healthy hosts. The presence of fungus gnat larvae in media in which young tomato plants were grown did not increase the incidence of plant infection by the pathogen. Fungus gnat adults appear to aid in the dissemination of F. oxysporum f.sp. radicis-lycopersici
In other crops, there are many insect vectors for the fungus: the European corn borer, Ostrinia nubilalis, which affects corn Canada and the USA, cotton thrips. There are other caterpillars that infect the maguey: the maguey worm (teria agavis) and chinicuil or chilocuil (bambis agavis) which both eat the leaves of the pulque and manso agaves, causing significant damage.
Other fungi that affect agave include phyophthora, asterina mexicana and pleospora. Parasites include the nematodes pratylenchus, dorylaimus and helicotylenchus.
Some researchers believe humidity can accelerate or facilitate the spread of diseases in agave. Acid soils also affect agave growth and health. And finally, in some areas, domestic cattle and goats eating the agave leaves can be a problem.
Blue Agave are graded as to their health: grade 1 is a healthy plant; grade 2 has 33% of its foliage affected by disease; grade 3 has less than 66% of foliage affected, and grade 4 is more than 66% affected.
Climate change and global warming may be the next big threat, according to an article in Milenio ("El cambio climatico trae focos amarillos al tequila) in 2006. The article suggested changing climate effects could be see by yellow centres in the agave.
Another ongoing threat is the loss of genetic diversity in the agave crops, which gradually is weakening the plant's capability to fight disease and adapt to changing conditions.
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The
blue agave has a lifespan of 8-14 years, depending on soil, climate and
cultivation methods. The typical growth
cycle sees shoots cut annually from plants 4-6 years old. The younger the
agave (but not before three years old), the better and the stronger the
shoot will be. After six years - usually the third year of cutting - the pups are usually considered too weak to be regrown.
The shoots themselves are about a year old when harvested. 
The pups also take moisture and nutrients
from the mother, so even if they are not replanted, they are removed
to let the mother plant develop more fully.
Agave plants take six to 10 years to mature,
depending on soil, weather and environmental conditions. Most are
harvested between 8-10 years but if the sugar content is high enough, some
producers will harvest them earlier. Some may even be left for 12 years. The more mature, the better its natural sugars (agave sazon
means ripened). 
During the growing cycle, the
plants will be weeded, sprayed with fertilizers, herbicides and pesticides, and some of
their leaves trimmed. Most growers use farm hands to meticulously control
the weeds by hand. Fields are not irrigated; the plants depend entirely
on the rainy season for moisture. Experiments with irrigation showed the
larger plants that resulted did not produce any more agave sugars.
The
quiotes are often harvested and eaten, usually cooked or steamed. They are fibrous,
with a slightly sweet sugar-cane flavour. They are very popular, especially among the
children. Sometimes they are sliced and fried with other vegetables. Vendors can be
found in the mercado in Tequila selling slices of cooked quiote for a
small cost.
In the past, agave fields were often inter-planted with crops like
beans and corn, especially when the agave were young and there was more
space between the rows. This practice is not very common today, although
you can still find large agave fields where sections are dedicated to an
alternate crop (particularly noticeable in the highlands region where
the agave density per acre is higher than in the Tequila valley region). 
The
biggest threat to the Blue Agave of late was the wildfire spread of the
fungus, Fusarium oxysporum, which always appears to appear in
conjunction with another disease, 'soft rot' or Erwinia carotovora
(although scientists have also identified Erwinia cacticida, Pantoea
agglomerans and Pseudomonas sp. in the soft rot). 
In
the early-mid 1990s, these two illnesses spread rapidly through the agave fields,
infecting as much as 40% of the crop, and causing a massive shortage in
the agave, at a time when tequila's popularity was on an accelerating
upswing. This in turn led to significant price hikes in the finished
product, record agave prices, and a massive binge in planting fields
with agave in hopes to reap the rewards some eight to ten years down the
road. But that only led to a glut of agave from around 2005, and rapidly
deflating agave prices forced some growers to abandon their fields to
the weeds, and to neglect cutting their leaves or removing the quiotes.
Others simply plowed the agave up and burned the crop so they could
plant more immediate cash crops like beans and corn. 
