from an entomology extension guide
http://extension.missouri.edu/p/g7398
"Avoidance
The best defense against chiggers is to avoid them. Avoid wearing shorts, sleeveless shirts and sandals when going into chigger habitats. Tightly woven fabrics reduce the threat of chiggers penetrating clothing. Tuck pant legs inside boots, and button cuffs and collars tightly to keep chiggers on the outside of clothing. This increases the time that chiggers are exposed to any repellents you have applied to your clothes. Remove clothing as soon as possible after exposure to chigger habitats, and launder it before wearing it again. A warm shower with a vigorous skin massage, taken within an hour or two after exposure, greatly reduces the number of irritating bites. If itching has already started, however, it is probably too late for bathing to do much good.
Repellents
If you must enter chigger-infested areas, chemical repellents can be used with good results.
Any insect repellent containing DEET (diethyl toluamide) or picaradin will be effective. Apply it to clothing from the feet up, and reapply every two to three hours to maintain its effectiveness.
Sulphur powder is also effective when applied to clothing but has a strong odor that makes it less desirable.
Permanone, also sold as Coulston's Permethrin Tick Repellent, contains the pyrethroid insecticide permethrin and should be sprayed on clothing and allowed to dry before the clothing is worn."