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Publisert:
17.10.2023 | Oppdatert: 24.05.2025
Phytotoxicity
Phytotoxicity
/ afreaction of herbicides
Dr. Oleksii Orlov,
PhD in Agriculture
Phytotoxicity is the toxic effect of a chemical compound / substance on
plant growth and development. Phytotoxicity often results in plant
death.
Phytotoxicity is harm and damage to plants, which
can be caused by a wide range of chemical compounds of natural and
chemical origin, as well as their combined effect: traces of metals,
soil acidity, soil salinity, pesticides, phytotoxins or allelochemicals.
Phytotoxicity of the herbicide acetochlor. Deformation
and death of seedlings of common sunflower. 17.05.2013, Chernihiv region,
Ukraine
On the left is a normal sunflower plant, on the right
is a action of the phytotoxicity of the acetochlor herbicide. The plant is
deformed and will soon die
Phytotoxicity can leads not only
to plant stress, but also create changes in quantitative parametrs - a decrease
in growth energy, a decrease in plant productivity and a decrease in the
quality of the crop.
Phytotoxicity that occurs on crop plants after the application of a
herbicide is called herbicide aftereffect.
The photo on the left shows
wheat by next season after the application of imi-herbicide. The photo on
the right shows normal wheat, where imi-herbicide was not applied. The
photos were taken in the North Kazakhstan region. The death of crops is
caused by the phytotoxicity of imi-herbicides
Phytotoxicity
of natural compounds
and soils
Many natural chemicals found in soil can be toxic to plants. For
example, chemical elements such as aluminum (Al), manganese (Mn), iron
(Fe), and boron (B), which are found in soils, can cause phytotoxicity
and damage roots and kill plants in acidic soils.
Phytotoxicity
/ afteraction
of fertilizers
Phytotoxicity can be observed as a result of the use of fertilizers.
Excessive use of fertilizers can create a high concentration of
mineral salts in the soil or irrigation water, which can cause
phytotoxicity, plant suppression and reduced yield. Many fertilizers can
cause phytotoxicity: urea, liquid ammonia, fresh manure.
Spraying with fertilizers often leads to plant burns.
This is caused by the use of excessive rates of fertilizers and
by using of the wrong fertilizers and their
combinations. Mixing fertilizers and herbicides significantly increases
the phytotoxicity of both fertilizers and herbicides and leads to a
decrease in yield and death of plants.
Phytotoxicity
/ afteraction
of herbicides
Herbicides are needed to kill
harmful plants and provide a great benefit - they are used to
control unwanted plants such as weeds.
Although herbicides are created to kill weeds,
the use of herbicides can cause phytotoxic effects on
main crop plants.
Phytotoxic
effect of herbicide application on sunflower. On the photo: strong
phytotoxicity after herbicide application on herbicide-resistant sunflower
(imazamox 33 g/l + imazapyr 15 g/l, 1.0 l/ha). This resulted in crop
failure. The phytotoxic effect was enhanced by very cold weather
Herbicides can also cause phytotoxic effects if they are applied
incorrectly, at the wrong stage of plant growth, or if the herbicide is
applied at too high
by
rate
/ concentration.
However, herbicides can cause phytotoxic effects in plants with
different types of contact with plants:
-
when drifting outside the area to which the herbicide is
applied, for example, as a result of drift, spray spray, wind, or the
use of a herbicide-contaminated sprayer or materials (such as straw or
manure)
-
as a result of the action of residual amounts of herbicides remaining in
the soil after the application of the herbicide (since some herbicides
decompose in the soil for a long time)
- this
effect is called herbicide afteraction
-
human errors, for example, if herbicides, fields, crops were confused, the
rates are overestimated, the regulations for the application of
herbicides are not followed, etc.
-
when
preparing tank mixtures and spraying plants, in order to avoid
phytotoxicity, herbicides and fertilizers must not be mixed in
the one tank mixture.
Photo © Dr.
Oleksii Orlov
Strong phytotoxicity manifests itself in the form of plant stress, as in
this case - yellowing, stunted growth, deformation of the growing point
after the application of Clearfield herbicide on sunflower, which was
tested for the level of herbicide resistance.
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The phytotoxicity of herbicides must be taken into account when planning
crop rotations - and planning crop rotation, because after the
application of some herbicides, crops can reduce the yield or die.
Often, the harm from phytotoxicity is not visible visually, it manifests
itself only in a decrease in yield.
If the phytotoxicity is strong, then this
manifests itself in the form of plant stress - growth retardation,
changes in growth and color, in which case, even if the plants do not
die, their yield will decrease.
For a successful farmer, it is very
important that herbicides are
applied correctly, so that there is no
phytotoxicity and crop stress, in this case, you can increase work
efficiency, save money and get the greatest profit from the agricultural
business.
What
increases the phytotoxicity / afteraction of
herbicides?
Unfavorable environmental conditions (weather, soil, etc.) can increase
the effect of phytotoxicity.
Herbicide phytotoxicity. Sunflower plant
deformation after application of the herbicide Heliantex (galauxifen-methyl,
68.5 g/l), Dnipropetrovsk
region, Ukraine. The leaves are wrinkled, the growth point has turned
yellow, the stem is bent / deformed, the lower leaves are drooping. In the
photo: left - 1 day after treatment; right - 10 days after treatment.
Sprayed at a rate of 0.045 l / ha + 100 l / ha of water. Spraying date June
8, 2020. It is clear that the herbicide was applied after the maximum
permissible phase of sunflower development. Possible reasons for this
situation: tank mix with graminicide; herbicide of unknown origin or
counterfeit; overgrown sunflower was sprayed; hybrid susceptible to the
herbicide - most likely a non-Pioneer hybrid and without resistance to SU or
IMI
The most common
causes of increased phytotoxicity of herbicides:
- errors (wrong crop, rate, herbicide, wrong
time, wrong mixing, failure to follow instructions and regulations for
herbicide application);
- poor-quality herbicides;
- shallow tillage and plow soles;
- alternation in crop rotation of crops on which
IMI herbicides are used and other strong afteraction herbicides;
- overestimation of the rate and concentration
of the solution when applying the herbicide;
- incorrect adjustment of the sprayer and
poor-quality nozzles and wear of nozzles);
- double or multiple passes of the sprayer over
the same area of the field;
- incorrect phase of herbicide application, for
example, herbicide on wheat should be applied in the tillering phase, if it
is applied on the flag leaf or on the ear, then there will be oppression or
death of crops;
- failure to observe crop rotation, for example,
sowing sensitive crops after IMI herbicides;
- acidic, saline or alkaline soils;
- very wet soils;
- unfavorable weather conditions (cold, heat);
- incorrect selection of herbicide taking into
account the varietal characteristics of the crop (for example, whiskered
peas are more sensitive to herbicides than leaf peas);
- mixing fertilizers and herbicides in one tank
mixture;
- mixing herbicides and growth regulators in one
tank mixture;
- mixing herbicides of different classes in one
tank mixture (for example, graminicides and herbicides against
broadleaf weeds);
- repeated application of herbicide in one
season;
- using the same herbicides with a strong
aftereffect every season. In this case, herbicides do not have time to
decompose in the soil and accumulate in the soil, increasing their
phytotoxicity.
On the left is the
effect of the herbicide (aclonifen 600 g/l) on sunflower plants SU - a
resistant sunflower hybrid variety (classic hybrid, Syngenta) on chernozem
soils when applied in the phase of 2 true leaves, subsequently a very high
yield was obtained. There are enough nutrients (31.05.2017, Nikolaev
region). On the right is the effect of the herbicide
(etamesulfuron-methyl 750 g/kg) on sunflower plants of a regular not
therbicide tollerant variety on poor chernozem with a high sand content
(insufficient nutrition). The phase of application of 6 true leaves of
sunflower, against Chenopódium álbum weed, which had
already outgrown and was not killed by this herbicide, subsequently this
field was overgrown with weeds and the yield was low. When using this
herbicide against Chenopódium álbum weed, it should
be taken into account that this weed can only be killed in the cotyledon
phase. It should also be taken into account that many weeds already have ALS
resistance (10.06.2017, Cherkasy region)
Soil compaction, especially
at a shallow depth of 5-15 cm, greatly increases the concentration of
herbicides (and other pesticides) in the soil layer above the compaction.
Therefore, the decay time
of herbicides in the soil increases due to soil compaction, and their
phytotoxicity / afteraction increases. Thus, soil compaction leads to an
increase in the aftereffect of herbicides and to an increase in
phytotoxicity, as well as to a slowdown in their decay in the soil.
Soil
compaction at a sowing depth of 5-10 cm (no-till, mini-till) leads not only
to drying out of the topsoil and death of crops, but also to increased
aftereffects and phytotoxicity of herbicides, as they are concentrated in
the topsoil. In this photo - death of the root system of wheat due to
drought. Due to lack of moisture in the soil, not only the roots of the
wheat died, but the entire plant died, the grain did not fill out and there
was no yield at all. Such plants do not recover, dry out and die completely
How does soil
type, soil acidity (pH) level affect the breakdown of herbicides in the soil
and the level of herbicide after-effects?
The effect
of herbicides is enhanced in acidic or alkaline soils.
The effect of herbicides is enhanced on sandy
and rocky soils, as well as on saline soils.
A study of the effect of soil acidity and alkalinity on plant growth and
development shows that on highly alkaline soils (as in the photo), plants
grow poorly, and the decomposition of herbicides in the soil slows down and
their phytotoxicity on plants increases. In the photo - a sunflower plant on
highly alkaline soil after the use of a herbicide. Strong inhibition and
phytotoxicity / afteraction are visible
Phytotoxicity
/ afteraction of herbicides and its combination with salinity and
alkalinity (soil acidity) is the most common in agriculture.
Phytotoxicity / afteraction of
imi-herbicide on wheat. Yellowing and strong stress of wheat sown after
sunflower treated with imi-herbicide. There was a lot of moisture, there was
good soil cultivation. But it was cold in the spring and the soils were
poor, sandy. On poor soils, in cold weather, when using generics
formulations of herbicides - the yield of soft wheat is greatly reduced
after using imi-herbicides!
Soft wheat is the most tolerant crop to the
aftereffect and phytotoxicity of imi-herbicides. But it also significantly
reduces the yield when sowing the following year after the use of IMI
herbicides. As in this photo, a field of spring soft wheat is in very poor
condition, the plants are sick, signs of the aftereffect of the herbicide
are visible - the leaves are twisted, bent and dried out, there is yellowing
and burns and necrosis. Imi-herbicide was applied to this field last year.
In the photo - the aftereffect of imi-herbicides in a field in Chistopolye,
North Kazakhstan region, Kazakhstan
How to
reduce or eliminate phytotoxicity if it exists?
Phytotoxicity can be reduced or eliminated
by the following methods:
- avoiding
strong herbicides (e.g. IMI herbicides);
- good tillage,
removing soil compaction;
- crop rotation
(after using IMI herbicides, sow only resistant crops, e.g. soft wheat);
- weed control
by crop rotation, not by using of strong and expensive herbicides (we kill
cereal weeds in broadleaf crop fields, and kill broadleaf / dicotyledonous
weeds in cereal crop fields);
- proper
accounting of herbicide use in all fields (you must know where what was used
and when);
- excluding
from crop rotation those places (spots) where nothing grows;
- liming acidic
soils and gypsuming saline soils;
- other
methods...
Good tillage of soil accelerates the decomposition
of herbicides in the soil and reduces their concentration in the upper soil
layer. Thus, tillage reduces the level of aftereffect of herbicides and
their phytotoxicity by the next crop in crop rotation. On the photo -
chiselization of soil TopDown 300-700
How to
avoid of phytotoxicity of herbicides and fertilizers?
For example, if the
use of IMI herbicides causes an aftereffect on subsequent crops, it is
better to replace them with other herbicides that do not have an
aftereffect.
The use of
liming of acidic soils allows to reduce the phytotoxicity of the herbicides
used and makes it possible to obtain a normal yield.
Phytotoxicity can be avoided by correctly using herbicides and
fertilizers and observing the regulations for their use and by simle and
effective crop rotation!
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Photo ©
Dr. Oleksii Orlov
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