Section 524.920 - Fenthion(a)Specifications.(1) The drug is a liquid containing: (i) 3 percent of fenthion; or(ii) 20 percent fenthion.(2) The drug is a solution containing either 5.6 or 13.8 percent fenthion. Each concentration is available in 2 volumes which are contained in single-dose applicators.(b)Sponsor. See sponsors in § 510.600(c) of this chapter:(1) No. 058198 for use of product described in paragraph (a)(1)(i) of this section as in paragraph (d)(1) of this section.(2) No. 058198 for use of product described in paragraph (a)(1)(ii) of this section as in paragraph (d)(2) of this section.(3) No. 058198 for use of products described in paragraph (a)(2) of this section as in paragraph (d)(3) of this section.(c)Related tolerances. See § 556.280 of this chapter.(d)Conditions of use - (1)Beef cattle and nonlactating dairy cattle -(i)Amount. It is used at the rate of one-half fluid ounce per 100 pounds of body weight applied topically on the backline of the animal. Only one application per season should be made for grub control and this will also provide initial control of lice. A second application for lice control may be made if animals become reinfested, but no sooner than 35 days after the first treatment. Proper timing of treatment is important for grub control; cattle should be treated as soon as possible after heel-fly activity ceases.(ii)Indications for use. For the control of grubs and lice in beef and nonlactating cattle.(iii)Limitations. Do not use on animals simultaneously or within a few days before or after treatment with or exposure to cholinesterase-inhibiting drugs, pesticides, or chemicals. Cattle should not be slaughtered within 35 days following a single treatment. If a second application is made for lice control, cattle should not be slaughtered within 45 days of the second treatment. The drug must not be used within 28 days of freshening of dairy cattle. If freshening should occur within 28 days after treatment, do not use milk as human food for the balance of the 28-day interval. Do not treat lactating dairy cattle; calves less than 3 months old; or sick, convalescent, or stressed livestock. Do not treat cattle for 10 days before or after shipping, weaning, or dehorning or after exposure to contagious infectious diseases.(2)Beef cattle and dairy cattle not of breeding age -(i)Amount. It is administered as a single, topical application placed on the backline of animals as follows: For animals weighing 150 to 300 pounds, apply 4 milliliters (mL); for animals weighing 301 to 600 pounds, apply 8 mL; for animals weighing 601 to 900 pounds, apply 12 mL; for animals weighing 901 to 1,200 pounds, apply 16 mL; and for animal weighing over 1,200 pounds, apply 20 mL. For most effective results, cattle should be treated as soon as possible after heel-fly activity ceases. A second application is required for animals heavily infested with lice or for those which become reinfested. A second application should be made no sooner than 35 days after the first treatment.(ii)Indications for use. For control of cattle grubs and as an aid in controlling lice on beef cattle and on dairy cattle not of breeding age.(iii)Limitations. Do not use on animals simultaneously or within a few days before or after treatment with or exposure to cholinesterase-inhibiting drugs, pesticides, or chemicals. Host-parasite reactions such as bloat, salivation, staggering and paralysis may sometimes occur when cattle are treated while the common cattle grub (Hypoderma lineatum) is in the gullet, or while the northern cattle grub (H. bovis) is in the area of the spinal cord. Cattle should be treated before these stages of grub development. Consult your veterinarian, extension livestock specialist, or extension entomologist regarding the timing of treatment. If it is impossible to determine the area from which the cattle came and/or exact stage of the grubs, it is recommended that the cattle receive only a maintenance ration of low-energy feed during the treatment period. This lessens the likelihood of severe bloat which may occur in cattle on full feed when the common grub is killed while in the gullet. Do not treat dairy cattle of breeding age; calves less than 3 months old; sick, convalescent, or severely stressed livestock. Do not treat cattle for 10 days before or after shipping, weaning, dehorning, or after exposure to contagious or infectious diseases. Do not slaughter within 45 days of treatment.(3)Dogs -(i)Amount. Four to 8 milligrams per kilogram of body weight. Apply the contents of the proper size, single-dose tube directly to one spot on the dog's skin.(ii)Indications for use. For flea control on dogs only.(iii)Limitations. Federal law restricts this drug to use by or on the order of a licensed veterinarian. 79 FR 10968 , Feb. 27, 2014, as amended at 84 FR 32993 , July 11, 2019; 86 FR 14821 , Mar. 19, 2021 84 FR 32993, 9/9/2019; 86 FR 14821, 3/19/2021