Weed management: a need for ecological approaches - Ecological Management of Agricultural Weeds - page 16

a.i. ha 1 ) during anthesis reduced seed yield 92% and 99%, respectively, com-
pared with untreated plants, whereas height was reduced only 12% and 8%.
Similarly, treatment of cherry trees with low rates of chlorsulfuron reduced
fruit yield but created little or no foliar damage (Fletcher, Pfleeger & Ratsch,
1993).
Other herbicides do not necessarily have such potent effects at low concen-
trations. Rapeseed and soybean were unaffected by applications of atrazine,
glyphosate,and 2,4-D at rates and stages of plant development at which chlor-
sulfuron suppressed reproduction (Fletcher et al ., 1996). None the less, the
experiments with chlorsulfuron indicate that low doses of certain compounds
can profoundly affect plant reproduction, and the results emphasize the
potential for serious off-target damage due to herbicide drift. Currently, data
concerning the impacts of chlorsulfuron and other herbicides on nontarget
plant reproduction are not required for product registration in the USA
(Fletcher et al ., 1996).
Acute and chronic effects of herbicides on human health
Although much remains to be learned about the acute and chronic
health impacts of herbicide use, public health reports and epidemiological
studies indicate that certain herbicides can be responsible for direct, uninten-
tional poisoning and may be associated with increased incidence of cancer and
other disorders. Farmers, farm families, and agricultural workers are exposed
to herbicides at higher concentrations than the general public and conse-
quently may be subjected to greater health risks. Health issues relating to
exposure to herbicides and other pesticides are particularly important in
developing countries, where safe use is difficult because of unavailable or pro-
hibitively expensive protective equipment, inadequate and poorly enforced
safety standards, poor labeling, illiteracy, and insufficient knowledge of
hazards by handlers and applicators (Pimentel et al ., 1992; Repetto & Baliga,
1996, pp.9-16).
Acute symptoms of pesticide poisoning include headache,skin and eye irri-
tation, fatigue, dizziness, nausea, cramping, fever, diarrhea, and difficulty in
breathing (Stone et al ., 1988). Most incidents of pesticide poisoning go unre-
ported (Jeyaratnum, 1990), but it is conservatively estimated that one million
serious accidental pesticide poisonings occur throughout the world each year
(World Health Organization,1990, p.86).Pesticide poisonings of farmers and
agricultural workers occur in industrialized countries, such as the USA (Stone
et al ., 1988), but are more frequent in developing countries (Repetto & Baliga,
1996, pp.9-16).
Public health data from Costa Rica suggest that herbicides may contribute