Agriculture Reference
In-Depth Information
Table 6.1
Estimated potential of weeds, animal pests (arthropods, nematodes, rodents, birds, snails, and slugs), pathogens
(fungi and bacteria), and viruses due to pest groups in six major crops worldwide, in 2001-2003 (Oerke
2006
)
Crop losses (%) due to
Weeds
Attainable production
(million tons)
Crop
Animal pests
Pathogens
Viruses
Total
Wheat
785.0
23.0
8.7
15.6
2.5
49.8
Rice
933.1
37.1
24.7
13.5
1.7
77.0
Maize
890.8
40.3
15.9
9.4
2.9
68.5
Potatoes
517.7
30.2
15.3
21.2
8.1
74.9
Soybeans
244.8
37.0
10.7
11.0
1.4
60.0
Cotton
78.5
a
35.9
36.8
8.5
0.8
82.0
a
Seed cotton
2003 on a regional basis (19 regions) as well as
for the global total. Among crops, the total global
potential loss due to pests varied from about
50 % in wheat to more than 80 % in cotton pro-
duction. The responses are estimated as losses of
26-29 % for soybean, wheat, and cotton and 31,
37, and 40 % for maize, rice, and potatoes,
respectively. Overall, weeds produced the high-
est potential loss (34 %), with animal pests and
pathogens being less important (losses of 18 and
16 %). The effi cacy of crop protection was
higher in cash crops than in food crops. Weed
control can be managed mechanically or chemi-
cally; therefore, worldwide effi cacy was consid-
erably higher than for the control of animal pests
or diseases, which rely heavily on synthetic
chemicals. Despite a clear increase in pesticide
use, crop losses have not signifi cantly decreased
during the last 40 years. However, pesticide use
has enabled farmers to modify production sys-
tems and to increase crop productivity without
sustaining the higher losses likely to occur from
an increased susceptibility to the damaging
effect of pests.
Nationally, pests are estimated to destroy
about one-third of our crops and are an increas-
ingly serious constraint to crop production, in
spite of the advances in pest control technology
over the last half century.
Agricultural trends are infl uencing the inci-
dence and importance of pests. First, the expan-
sion of worldwide trade in food and plant
products is spreading the impact of weeds,
insects, and diseases. Second, changes in cultural
techniques, particularly intensifi cation of crop-
ping, reduction in crop rotations, and increase in
monocultures, encourage the activity of pests.
Many people believe that global warming as
predicted would increase pressure from weeds,
pests, and diseases. Higher temperatures and lon-
ger growing seasons could result in increased
pest populations in temperate regions of Asia.
Warmer winter temperatures would reduce win-
ter kill, favoring the increase of insect populations.
Overall temperature increases may infl uence
crop pathogen interactions by speeding up patho-
gen growth rates which increases reproductive
generations per crop cycle, by decreasing patho-
gen mortality due to warmer winter temperatures
and by making the crop more vulnerable (Cruz
et al.
2007
).
Climate change will affect crop protection
challenges. In cooler latitudes, global warming
brings new species but others may disappear.
Whether or not new species translate into pest
problems is uncertain. Invasive species are often
brought to other places by global trade of food
and goods.
Climate change might have an infl uence on
pesticide use due to presence of weeds, diseases,
pests, and their natural enemies. The latter fac-
tors are infl uenced by the weather and in the
midterm by climatic changes (Goudriaan and
Zadoks
1995
). Tilman et al. (
2001
) foresee a
2.4-2.7-fold increase in pesticide use by 2050.
Chen and McCarl (
2001
) investigated the rela-
tionship of temperature, precipitation, and pesti-
cide costs for several crops in the USA and
concluded that increases in rainfall lead to
increases in average pesticide costs for corn, cot-
ton, potatoes, soybeans, and wheat, while hotter
weather increases pesticide costs for corn, cot-
ton, potatoes, and soybeans but decreases the
cost for wheat.
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