indicator of the condition of the s oil. This us eful function is of cours e lost where chemical weed
killers have been used. Thos e who find an ans wer to all problems in spraying also overlook a
matter of great scientific importance—the need to preserve some natural plant communities.
We need thes e as a s tandard agains t which we can meas ure the changes our own activities
bring about. We need the m as wild habitats in which original populations of ins ects and other
organisms can be maintained, for, as will be explained in Chapter 16, the developme nt of
resistance to insecticides is changing the genetic factors of ins ects and perhaps other
organisms. One scientis t has even s ugges ted that s ome s ort of ‘zoo’ s hould be es tablis hed to
pres erve ins ects , mites , and the like, before their gene tic compos ition is furthe r changed. S ome
experts warn of s ubtle but far- reaching vegetational shifts as a result of the growing us e of
herbicides. The chemical 2,4-D, by killing out the broad-leaved plants, allows the grasses to
thrive in the re duced competition—now some of the grasses themselves have become ‘weeds’,
pres enting a new problem in control and giving the cycle anothe r turn. This strange situation is
acknowledged in a recent iss ue of a journal devoted to crop proble ms : ‘With the wides pread
us e of 2,4-D to control broadleaved weeds, grass weeds in particular have increasingly become
a threat to corn and s oybean yields.’
Ragweed, the bane of hay fever sufferers, offers an interesting example of the way efforts to
control nature s ometi mes boome rang. Many thous ands of gallons of chemicals have been
dis charged along roads ides in the name of ragweed control. But the unfortunate truth is that
blanket spraying is resulting in more ragweed, not less. Ragweed is an annual; its s eedlings
requi re ope n s oil to become es tablis hed each year. Our bes t protection agains t this plant is
theref ore the maintenance of dens e s hrubs , ferns , and othe r pe rennial vegetation. Spraying
freque ntly des troys this protective vegetation and creates open, barre n areas which the
ragweed hastens to fill. It is probable, moreover, that the pollen content of the atmos phe re is
not related to roads ide ragweed, but to the ragweed of city lots and fallow fields. The booming
sales of chemical crabgrass killers are another example of how readily unsound methods catch
on. There is a cheaper and better way to remove crabg rass than to attempt year after year to
kill it out with chemicals. This is to give it competition of a kind it cannot s urvive, the
competition of other grass. Crabgrass exists only in an unhealthy lawn. It is a s ympt om, no t a
disease in itself. By providing a fertile soil and giving the desired grasses a good s tart, it is
pos s ible to create an environment in which crabgras s cannot grow, for it re quires ope n s pace in
which it can start from seed year after year.
Ins tead of treati ng the bas ic condition, s uburbanites—advis ed by nurs eryme n who in turn have
been advis ed by the chemical manufacturers—continue to apply truly as tonis hing amounts of
crabgrass killers to their lawns each year. Marketed under trade names which give no hint of
their nature, many of thes e prepa rations contain s uch pois ons as mercury, ars enic, and
chlordane. Application at the recommende d rates leaves tremendous amounts of thes e
chemicals on the lawn. Us ers of one product, for example, apply 60 pounds of technical
chlordane to the acre if they follow directions. If they us e another of the many available
products , they are applying 175 pounds of me tallic ars enic to the acre. The toll of dead birds , as
we s hall s ee in Chapter 8, is dis tress ing. How lethal thes e lawns may be for human beings is
unk nown. The s uccess of s elective s praying for roads ide and right- of-way vegetation, where it
has been practiced, offe rs hope that e qually s ound ecol ogical methods may be devel oped f or
othe r vegetation progra ms for farms , fores ts , and ranges— methods aimed not at des troying a
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