Windy Conditions and Herbicide Drift
Fabian Menalled
MSU Extension Service Cropland Weed Specialist
After a long winter, spring has arrived and crops are emerging. Although soil moisture
conditions in many areas of the state are favorable, the windy conditions we usually
experience in spring could be much less favorable for herbicide applications. Wind and
air currents can carry herbicide far beyond the treated area. In many cases, herbicide drift
could damage sensitive crops, shelterbelts, garden and ornamental plants. They can also
cause water pollution or could result in hazard to people or livestock. Finally, herbicide
drift can result in non-uniform application in a field, with possible crop damage and/or
poor weed control.
Herbicide can drift either as particles or as vapor. Particle drift occurs when herbicides
are applied as small spray droplets and are carried of target by air movement. A good
approach to minimize particle drift is to increase droplet size as small droplets take more
time to fall to the ground and can drift farther. For example, while a very fine droplet of
20 microns in diameter may travel more that 1,000 feet when falling 10 feet in a 3mph
wind, a coarse spray (400 microns in diameter) will only travel 8.5 feet under the same
conditions. Increasing droplet size can be achieved by selecting nozzles that produce
coarse sprays or by lowering spay pressure. For example, switching from standard flatfan nozzles to turbulence-chamber or venturi nozzles increases droplet size and can
greatly reduce the amount of drift. Droplet size can also be increased by utilizing
additives that augment spray viscosity. Research has shown that using a spray thickener
can reduce spray drift by 66 to 90 percent compared to application without thickener.
You can also use specialized equipment and herbicide formulations to create invert
emulsions. This technique is mostly used for spraying noncrop areas such as rights-ofway.
Increasing droplet size could be challenging when using some postemergence herbicides
that require small droplets for optimum performance. Examples of these products are
Fusilade (fluazifop-P), Assure II (quizalofop-P), Betanex (desmedipham), Betamix
(phenmedipham + desmedipham), Poast (sethoxydim), Basagran (bentazon) and Buctril
(bromoxynil). The efficacy of other translocated herbicides such as 2,4-D, MCPA,
Banvel (dicamba), Stinger (clopyralid), Roundup (glyphosate), and Tordon (picloram) is
not so much affected by droplet size, so drift control techniques generally will not reduce
their performance.
Vapor drift occurs when herbicides evaporate or turn into gas and moves with wind
currents. While particle drift occurs while spraying, vapor drift may occur from one hour
to several days after herbicide applications and has the potential of injuring vegetation a
mile or more from the applied point. Luckily, not all herbicides have a high risk of
drifting as vapor. For example, while 2,4-D or MCPA ester formulations may produce
damaging vapors, less volatile ester formulations are less hazardous but can evaporate if
temperatures exceed about 85o F. Finally, 2,4-D or MCPA amines are essentially non-
volatile and can drift only as droplets or dry particles. Thus, these amine formulations
should be used when spraying near sensitive area.
In recent years, much interest has been focused on drift reduction nozzle technology and
the use of drift reduction agents. Also, we know that simple management practices such
as the use of low or nonvolatile pesticides, wide angle nozzles and low boom heights can
reduce the risk of pesticide drift. While these technologies can help reduce the threat of
herbicide drift, they may also give a false sense of security leading to applications under
risky conditions. As a friend of mine says “Increasing gallons of carrier per acre and
lowering spray pressures may help reduce drift. Precluding drift may require keeping the
sprayer in the shop until the wind dies down.”
Disclosure. Common chemical and trade names are used in this publication for clarity by
the reader. Inclusion of a common chemical or trade name does not imply endorsement
of that particular product or brand of herbicide and exclusion does not imply nonapproval.
Categories: Herbicide, Drift
Date: 05/03/2006