163
(continued)
Table 2 Overview of the active ingredients in commonly used pesticides, target pests, application rates and key environmental factors
Substance group
Active ingredient
(a.i.)
Target pests
Typical application
rates [grams (g) of
active ingredient
(a.i.) per hectare
(ha)] (g a.i. ha
−1
)
Mode of action
Factors determining pesticides fate in the environment
Solubility in
water
(mg L
−1
)
a
Half-life
in soil
(DT50:
days)
b
Organic
carbon
sorption
constant
(K
oc )
c
Dissociation
constant at
25 °C (pKa)
Avermectins
(abamectin)
Arthropod pests:
aphids (Sipha
flava),
thrips and
red spider mites
21.6
Stimulate the chloride
channels that are regulated by
the neurotransmitter
glutamate
Insoluble
1–7
4000
–
d
Organophosphate
(dimethoate)
Aphids
2.2
Acetylcholinesterase (AChE)
inhibitor
39,800
2.6
No dissociation
Organophosphate
(chlorpyrifos)
Soil and foliage
arthropod pests
750
Acetylcholinesterase (AChE)
inhibitor
1.05
21
8151
–
Chloroacetamide
(S-metolachlor)
Grasses and some
broad-leaved weeds
1536
Inhibition of VLCFA
(inhibition of cell division)
480
21
110–369
–
Organometal
(organic arsenical)
Sedges, grasses and
broad-leaved weeds
2160
Inhibition of VLCFAs
(inhibition of cell division)
580,000
200
–
9.02 weak acid
Phenoxyacetic acid
(MCPA)
Annual and
perennial weeds
1080
Synthetic auxin
29,390
25
–
3.73 weak acid
Triazines (ametryn)
(atrazine)
Most annual and
broad-leaved weeds
900–1200
Inhibits photosynthesis
(photosystem II)
200
37
316
10.07 very
week acid
1125–1350
35
29
100
1.7 very weak
base
Phenoxyaliphatic
acids
(fluazifop-p-butyl)
Ripener
55.5
Inhibits acetyl-CoA
carboxylase
0.93
8.2
3394
−
5
Impact of Climate Variability on the Use and Exposure of Pesticides in Sugarcane…