Environmental Conditions Have the Greatest Impact on Crop Injury from Herbicides
Why Reading Herbicide Lable Matters
Applying herbicides under
extreme environmental conditions, especially periods of fluctuating day and
night temperatures can cause significant yield losses. Reading the herbicide
label will help ensure that such yield losses are avoided.
Ultim® herbicide was
applied to four replicated research trials during the first three weeks of June
in 2006. Although this product provided excellent grassy weed control, two of
the trials suffered extensive corn injury as shown in Figures 1 and 2.
 |
 |
|
Figure
1 – Ultim® injury 14 days after application
|
Figure
2 – Ultim® injury 28 days after application
|
The recommendations found
on the Ultim® label indicate that “rapid fluctuations in temperatures
greater than 20 °C within 24-36 hours of application will stress the corn
crop.” It also suggests to “only apply Ultim® when the temperatures
in the 24 hours before and after application range between 5 and 28 °C,
temperatures beyond this range increase the potential for crop injury.”
| TABLE 1. Four Ultim® trial applications including temperatures and times corresponding to visual injury and yield loss | |||||||
|
Trial
#
|
Leaf
Stage at Appln.
|
Temperature
Extremes (C) |
Temperature
Swing (C)
|
Appln.
Timing
|
Visual
Injury %
|
%
Yield Loss
|
|
|
Min
|
Max
|
||||||
|
1
|
5-6
leaf
|
5
|
32
|
27
|
8
pm
|
21
|
22
|
|
2
|
7-8
leaf
|
6
|
32
|
26
|
9
am
|
13
|
8
|
|
3
|
7-8
leaf
|
8
|
28
|
20
|
9
pm
|
0
|
no
yield loss
|
|
4
|
5-6
leaf
|
8
|
25
|
17
|
10
am
|
0
|
no
yield loss
|
|
*Temperature within
36 hour window before and after application |
|||||||
As seen in Table 1, the
two trials that suffered Ultim® injury and yield loss were applied when
temperatures were above 28 °C, and exceeded the 20 °C swing range stated
on the label. Additionally, the minimum temperatures experienced in those trials
were approaching the temperature at which injury from low temperature effects
can be seen. These were clearly off-label applications. When the applications
were made while temperatures were below 28 °C and within a 20 °C swing
range, regardless of the leaf stage (Ultim® can only be applied up to the
6 leaf stage of corn) and the time of day at which the applications were made,
no injury or yield loss was observed. Evening applications, which are often
recommended during times of hot daytime temperatures, did not eliminate the
potential for injury as the trial showing the most injury was sprayed in the
evening.
In order to avoid this
potential for injury from extreme air temperature fluctuations, the Ultim®
label suggests “waiting 48-72 hours before application to allow the corn
plants to acclimatize.” If you cannot wait the recommended 48-72 hours
because the crop stage may exceed the label restrictions or poor weather conditions
are forecast, then
other herbicide options should be considered. Accent® and OptionTM were
also
applied in all four trials and under the same environmental conditions. Both
of these herbicides provided grassy weed control equivalent to Ultim®, with
no visual injury or yield loss observed.
Key findings from this research:
• Off label applications of any herbicide will increase the risk of crop
injury and yield loss.
• Applying Ultim® during periods of air temperature fluctuations greater
than 20 °C resulted in crop injury and yield loss.
x The
product label warns against such applications.
• Applying Ultim® past the maximum labeled corn leaf stage did not
appear to have as great an influence on crop injury as air temperature
fluctuations did.
• Always check the herbicide label before use.