When you ride through the potato fields, does your horse come in contact with
the plants? Are they freshly sprayed (spray material has not dried)?
In the United States, all pesticides have reentry restrictions of varying
lengths. This means no one may enter the field after the pesticide has been
applied until this no-entry time has passed. This is a federal law. It may
not be the same in Canada, but the same caution should be exercised.
The length of the restriction is directly related to the potential harm to
humans of the pesticide that was used. Many pesticide labels say fields may
be reentered as soon as the spray has dried. Some have restrictions of
several days. You (and your horse) should not be getting close enough to
treated plants to come in contact with them until after the
reentry-restricted period is up. Once that period is over, it is safe for
you and your horse. Hosing him down afterward would be a good idea because
some people, and possibly horses, do develop allergic rashes to some of the
inert ingredients in pesticides. But don't rely on just hosing your horse
off to remove dangerous pesticide residues.
Some pesticides used on potatoes, such as herbicides and fungicides, are
relatively harmless, even if you should come in contact with freshly sprayed
foliage. There are some insecticides, however, that may pose a hazard. It
would be wise to check with the growers to find out what they are spraying
and when it is safe to enter the fields.
The safest thing to do would be to stay out of the fields. If you don't come
in contact with the plants, you are not at risk, unless you are riding
alongside a row that is just being sprayed!
Hope this helps. I write about pesticide use for agricultural trade journals
in the United States and have learned a lot about pesticide safety.
Linda and Chaco (quit spraying that permethrin + piperonyl butoxide in my
face--I don't care if you do say it's safe!)
San Francisco, Calif.