A citronella spray will be inexpensive and help repel them. An orange oil solution will kill them. Dry diatomaceous earth in a powder rubbed on their coats will also kill them. Use it lightly and don't make a cloud, just sprinkle it on your brush and take it over their body. The spray should be mixed no stronger than 1/4 to 1/2 cup of orange oil to a gallon of water. Spray it directly on the ticks and they will drop off and die. DE works only when dry so don't use the DE and then spray them down. That's an either/or tactic. Any are inexpensive and effective.
Feeding trace minerals in block or bucket form has given indications of helping the horse's immune systems become more resistant to pests of all kinds. Remember that increased biological activity in the soil helps eradicte them too. An investment on spreading of molasses in those pastures might take you a long way toward knocking back the ticks and keeping the horses healthy. Also look at the pasture rotation methods as a way of short-circuiting the pest cycle. We have gotten repeated positive reports from that program. Walt Davis spoke about it breifly at our seminar the 13th. He's really great.
Hope this helps!
Kathe
