Manure treatment (larviciding), applied directly to the manure surface to control fly maggots, is discouraged because beneficial arthropods associated with the manure can be killed. Also, adding extra moisture to the manure can result in additional fly breeding with potential fly resistance increased. (Effort should be made to keep all manure as dry as possible, less than a 30 percent moisture level, to greatly reduce or halt fly breeding.) However, if manure cannot be kept dry or removed on a weekly basis, it is possible to use manure sprays.
(a) dimethoate (Cygon): Mix one half pint of Cygon 23.4 percent EC in five quarts of water. Apply finished spray as a coarse spray.
(b) tetrachlorvinphos (Rabon): Mix four pounds of Rabon 50 percent WP in 25 gallons of water. Apply one gallon of finished spray per 100 square feet of manure.
(c) tetrachlorvinphos and dichlorvos (Ravap): Mix one gallon Ravap 28.7 percent EC per 25 gallons of water. Apply one gallon of finished spray per 100 square feet of manure.
Use a hoe or trowel to sample the larvae present in the manure before treatment. Any "hot spots," where water has laid in the manure and containing many fly eggs and maggots, can be spot treated with a low pressure knapsack sprayer or sprinkling can. Apply to wet the manure surface (not soak), and repeat applications as necessary but not more often than once every seven days. Avoid widespread use of manure sprays. Treating the edges of stacked manure before covering it with plastic can be helpful. Do not apply where animals or birds will come in contact with the manure. Do not apply treated manure to crops not approved on the insecticide label.