Weeds and Allergies
WEEDS AND ALLERGIES Thomas Leo Ogren
Allergy, on the rise in the United States and throughout the
world, is worst in urban areas. In the past thirty years in the
US the percentage of people with allergies has rapidly climbed
from 10 percent, to a staggering 38 percent now affected. There
are many factors involved in this epidemic of allergy including
an increase in the total amount of urban airborne pollen. In
urban areas much of the increase in allergy can be tied to the
over-use of staminate (male ) dioecious cultivars in our urban
landscapes. There is much evidence though, that from years of
constant exposure to pesticides and industrial pollutants, that
people in general have become more susceptible to developing
allergies. As such, people are now often more sensitive to
allergens such as pollen than they were in the past. In most US
cities, especially on the West Coast, some 70 to 80 percent of
the total yearly pollen load has consistently been found to come
from the area's urban landscaping, especially from the trees.
Weeds and grass pollens make up the rest of the yearly pollen
load, however in many cases, the pollen from some of these weeds
and grasses is especially allergenic and causes more than its
share of actual allergic response. Much of the grass pollen in
urban areas comes directly from lawns that are not kept
regularly mowed. Bermuda grass in particular is often the cause
of grass pollen allergy in cities. There are now some very
interesting and useful new types of grass that have been
developed that do not produce any pollen whatsoever. In
particular, certain pistillate ( female ) cultivars of Buffalo
Grass ( Buchloe dactyloides ) are proving to be of great use.
Female Buffalo Grass cultivars grow shorter than male clones and
as such, require much less mowing. Because they are female they
produce no pollen and cause no allergy. Buffalo Grass is also
winter hardy, easily grown under a wide range of soil and
climatic conditions, and is available as sod or from plugs.
Because this native grass is especially deep-rooted it requires
much less fertilizer and water than most sod lawn species more
commonly in use. There is another important reason for the use
of cultivars such as female Buffalo Grass--because they need to
be mowed less often, fewer VOC's ( volatile organic compounds )
are released into the air. The whole issue of VOC production and
methods for its limitation is one that will become increasingly
important in the future as we seek to find more methods of
limiting air pollutants of all types, whether organic or
inorganic. Certain types of weeds and the pollen they shed are
of great importance as the cause of allergy. In much of the
Southern, Midwestern, and Eastern US the worst allergy weeds of
all are the species of Ambrosia, or the Ragweeds. There is a
certain amount of ragweed in the Western states and it is most
commonly found growing alongside highways. Ragweed is a
monoecious species that produces huge amounts of small, very
light and buoyant pollen. The individual grains of pollen are
spiked with many sharp points and under a microscope resemble
tiny balls of cactus. This pollen can and does cause hay fever,
asthma, itching, and skin rash. The number of people allergic to
ragweed pollen is very high. Although there is a species of
ragweed native to Europe, in Europe now, there are many species
of ragweed present, most of them unwanted imports from America.
Likewise, in California we now have many non-native species of
ragweed growing. In the past there have been a few examples of
successful civic actions taken against ragweed. In several areas
of Europe local crusades to wipe out ragweed have had mixed
success. In the 1930's in the Montreal area of Canada the local
citizens banded together to destroy ragweed. Farmers were
encouraged to eradicate it. School children were taught how to
identify it in its juvenile stages and contests were held for
many years: to see who could pull up the most ragweed seedlings.
Eventually ragweed was actually eliminated from large areas due
to this combined civic attack. Unfortunately after many years
passed, attention was not paid to seeing that ragweed did not
regain a foothold and today it is again common in the Montreal
area. It is the feeling of this author that in California, where
so much of our ragweed is concentrated alongside highways, that
with a concerted effort, we could come close to eradicating it
here. At any rate, even partial success at ragweed elimination
would result in large increases in cleaner air and would be
appreciated by the estimated 10 million people in California who
suffer each fall from pollen allergies. There are a number of
other weeds common in California that cause more than their
share of allergies, in particular the Pigweeds ( Chenopodium
species. ), Groundsel ( Senecio spp. ), Plantain ( Plantago spp.
), Poison Oak, ( Rhus Toxicodendron ), and the Castor Bean (
Ricinus communis ). Poison Oak is a dioecious species and is
both insect and wind-pollinated. As such this pollen is often
abundant in Spring in all areas where Poison Oak is common.
Pollen from Poison Oak can land on people's skin and can cause
the exact same symptoms as contact with the leaves of the plant.
Inhalation of Poison Oak pollen can be dangerous for people with
asthma who are also susceptible already to the contact affects
of this species. Castor Bean is a fast-growing annual or
perennial plant with very large, often colorful leaves and
stems. It is monoecious and the female flowers are above the
male flowers, a system that ensures a large amount of
wind-pollination. Native to central Africa, Castor Bean is now
grown as an oil crop or as an ornamental in many areas of the
world. During World War Two a large amount of acreage in the US
was planted to Castor Bean as an oil seed crop and within two
years of these plantings allergy to the pollen suddenly became
both common and severe. Castor Bean is especially common along
highways in many of the coastal communities of California. The
pollen is shed for many months during the year, from early in
the season to late. Whereas most species' pollen usually
triggers hay fever symptoms in people, Castor Bean pollen almost
always directly causes severe attacks of asthma. Castor Bean is
a Euphorbia Family member and as such its pollen is especially
dangerous for certain individuals. Over the years in the US and
in other urbanized areas of the world, millions of cars and
trucks have been driving down the roads and their rubber tires
have been breaking down, due to simple friction between the
tires and the roadways. Billions of tiny particles of this latex
rubber constantly go airborne and in the process millions of
people are exposed to breathing in these minute particles of
rubber. The rubber that the tires are made from comes from the
collected sap of the tropical tree, Hevea brasiliensis, which is
also a member of the notorious Euphorbia family. There has been
another recent addition to allergies from rubber and this has
been caused by the huge increase in the use of latex gloves.
With the spread of AIDS, the wearing of these rubber gloves has
increased rapidly. The gloves are dusted with powder so that
they will not stick together and when they are put on or taken
off, this same powder, now "rubberized," goes airborne. In the
process many more people are exposed to latex particles. In
allergy study cross-reactive responses are frequently seen.
People who are allergic to one particular type of plant, often
become allergic too, to the pollen of that plant's close
relatives. With the huge increases in latex allergies we are now
seeing, it is not surprising that allergy to Castor Bean pollen
is also on the increase. Latex allergies are almost always
severe. Common symptoms include terrible swelling of the face
and head, difficulties in breathing, cough, head ache, skin
rash, and all too often, anaphylactic shock. This is one allergy
that can and does kill. At this conference we have assembled
here many of the finest minds in our State, people with the most
experience at controlling weeds. If from this talk I could
somehow trigger a systematic, coordinated attack on just one of
these highly allergenic weeds, then I would certainly feel that
my time here today was well worth it. If I were to pick two
weeds in California to zero in on to improve air quality and
quality of life for us all, I would pick ragweed and Castor
Bean. Were I to have to pick just one for starters, Castor Bean
would be my weed of choice to see it eliminated from our Golden
State.