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Conservation buffers
can trap and degrade a portion of pesticides that run off fields
either adsorbed to sediment or dissolved in water. However, buffers
are seldom effective in trapping all pesticides in runoff. Buffers
have been described as "the last line of defense" or as
acting to "polish" runoff after it has been treated by
other practices. Other BMPs are needed in a systems approach in
order to adequately protect water quality. Many practices can be
used to reduce off site movement of pesticides. These practices
can be selected and integrated into cropping systems where appropriate
and effective. Although not an exhaustive list, some common pesticide
BMPs and descriptions are listed here.
Integrated Pest
Management.
IPM systems utilize pesticides in concert with non-chemical pest
management techniques. Pest populations are determined and pesticides
or other techniques used only when populations exceed economic thresholds.
The lowest pesticide rate which is effective is used, and pesticide
products selected based on specific pests present and safety to
nontarget organisms.
Pesticide Selection.
Pesticides applied at low rates reduce amounts available to run
off. Products which are strongly adsorbed are less likely to move
off fields dissolved in runoff.
Pesticide Application
Timing. Risk of pesticide runoff is greatest when heavy rains closely
follow pesticide application. Application should be avoided if heavy
rain is imminent. Sometimes long-term weather records can identify
application times when heavy rains are less likely. Postemergence
applications result in less runoff than soil applications, as the
crop and weeds behave in the manner of a buffer, increasing infiltration
and pesticide adsorption by soil and foliage.
Banded Application. Application of herbicides in bands
over crop rows, combined with cultivation to control weeds between
rows, reduces total amounts of chemical applied compared to broadcast
applications.
Soil Incorporation. Some herbicides and insecticides
are effective when mechanically incorporated into the soil (in the
case of herbicides) or placed in crop furrows (in the case of insecticides).
Placing some of the applied chemical below the soil surface protects
it from surface runoff.
Conservation
Tillage.
Surface crop residue reduces erosion and often increases water infiltration,
reducing pesticide runoff. No-till, especially after practiced for
several years, has sometimes dramatically reduced pesticide runoff.
Contour Planting.
Contour rows reduce erosion, slow runoff, and increase infiltration.
Orientation of rows adjacent to buffers may need to be adjusted
to direct runoff as sheet flow across buffers.
Strip Cropping. When strips of densely planted
crops such as forages or small grains are alternated with strips
of row crops, the densely planted crop acts as a buffer. When the
strips are planted on the contour, runoff and erosion are reduced
and more runoff water enters the soil.
Crop Rotation. Rotation of crops can disrupt
life cycles of insects, diseases, and weeds, and reduce the necessity
for pesticide treatments. Pesticides can be rotated as the crop
is rotated, thus reducing the amount of any one pesticide used on
that field.
Terraces/Detention
Ponds.
These structures shorten slope length, trap sediment, and increase
water infiltration, reducing pesticide runoff.
Irrigation Timing.
Irrigation after application of soil-applied herbicides moves the
chemical off the soil surface, improving weed control and protecting
the chemical from later rainfall-runoff events. PAM increases infiltration.
Irrigation Water
Management.
Improved management of the rate and amount of irrigation water can
reduce deep percolation, tailwater, and soil movement.
Compaction Reduction. Correcting compaction problems encourages
water infiltration and reduces runoff.
Subsurface Drainage.
High water tables can result in excessive runoff and pesticide loss.
Improvement of drainage increases water infiltration and reduces
pesticide runoff. As subsurface drainage carries nitrate to streams,
treatment of tile effluent in a constructed wetland or buffer area
may be desirable.
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