Does Dew Affect Glyphosate?
Chris
Boerboom
It is logical to question if dew might affect glyphosate
performance because we know that glyphosate’s efficacy is
greater when sprayed in 10 gallons/a of water than 20 or 30
gallons/a of water. If glyphosate is sprayed onto leaves with
dew, this would act to dilute the glyphosate similar to spraying
at higher spray volumes. Also, glyphosate spray droplets might
run off dew covered leaves. On the positive side, dew could
increase the hydration or water content of the cuticle of the
leaf and aid glyphosate uptake.
To examine this question further, two Chilean weed scientists
tested glyphosate’s control of oats with different levels of
dew. Specifically, they treated the oats with either 0, 50, or
100% dew and then sprayed with the equivalent of 20 oz/a of
Roundup in either 16, 31 or 47 gpa of water. Fifteen days after
spraying the oat plants were weighed to determine control.
The results that are presented in table 1 support previous
research that glyphosate’s control is greater when sprayed at
lower volumes than at high spray volumes under the no dew
condition. The presence of moderate or high levels of dew at the
low spray volume did not reduce the control of the oats. The
fact that control was not reduced was attributed to the greater
hydration of the cuticle by the dew, which may have compensated
for the less concentrated glyphosate (ie. the concentration in
spray droplets was diluted by the dew). The high dew level
reduced glyphosate’s control of oat when glyphosate was
sprayed in the high spray volume. This may have occurred because
of some spray droplets running off due to the high total load of
water on the leaves.
Table 1. Effect of spray volume and dew on glyphosate’s
control of oats.
|
Spray volume |
Dew Level |
| 0% |
50% |
100% |
| (gpa) |
(% control) |
| 16 |
88 |
89 |
89 |
| 31 |
82 |
88 |
88 |
| 47 |
65 |
65 |
59 |
Overall, the authors concluded that moderate levels of dew
will likely have little effect on the performance of glyphosate
when applied at normal spray volumes. These results are
consistent with research in the 1970's by Caseley and colleagues
who studied the influence of dew on glyphosate’s control of
quackgrass.
Source: Kogan and Zuniga. 2001. Dew and
spray volume effect on glyphosate efficacy. Weed Technol.
15:590-593.
March, 2002 |
