EFFECTIVENESS OF POISONED BAITS IN ORCHARD MOUSE COOTROL AS DETERIIINED 



BY 

 THE U. S, FISH AND WILDLIFE SERVICE 



Pre-Harvest Baiting : Application of poisoned bait before harvest to prevent 

 orchard mouse damage to apples in cold storaijc plants is not a sound practice. 

 The recommended methods of orchard mouse control do not always result in 100 per 

 cent control of the species in the orchard. Therefore, some mice survive the 

 pre-harvest control and may enter the boxes of apples and still be carried into 

 the cold storage. The pre-harvest poison application will reduce the population 

 of mice in the orchard; competition among the survivors will be greatly reduced; 

 and food and cover v/ill be more than ample. The survivors, under these favorable 

 conditions, will breed and the number of young per litter may be as high as eight. 

 In a very short period of time, the population will build up to its original 

 level, A large number of young mice will be present during the recovery period. 

 These mice, having a short home range, would not be exposed to poisoned baits 

 applied during the normal control season. 



The recommended control season is just prior to freezing temperatures. This 

 is the best time to control the mice present in an orchard to prevent damage 

 during the winter months; and this is the season when population recovery is very 

 slow. Any control program that may lessen the effect of the recommended control 

 program is defeating the purpose for which it was developed. A vigorous, mature 

 apple tree is capable of producing up to 35 bushels of apples per season. The 

 destruction of such a tree, due to girdling by orchard mice during the winter 

 months, certainly is a greater economic loss tlian several bushels of apples in a 

 cold storage. 



Strychnine-treated Steamed-crushed Oats ; These oats do not obtain the 

 desired results for the control of meadow or pine mice in orchards because accep- 

 tance of strychnine by these species of mice is less than with zinc phosphide. 

 Also, a poison tolerance is sometimes developed within individual mice so that 

 doses above normal limits will not kill them. 



Strychnine-treated Steamed-crushed Oats do have an advantage when used in 

 apple storages because they maintain their toxicity for long periods of time 

 under humid conditions. Teaspoonful quantities of this bait should be placed in 

 stations such as cigar boxes, short lengths of pipe, or sections of rolled 

 roofing paper. These stations should be placed under the pallets, along the 

 walls, and, if possible, at frequent intervals within the stacks of boxes. Since 

 mice may not travel more than a few feet during the entire winter, numerous bait 

 stations should be used. A room 20' x 20' should have at least 15 bait stations. 

 One application of this bait ordinarily provides adequate protection for the 

 winter. Strychnine-treated Steamed-crushed Oats may be obtained only from: 

 RODENT CONTROL FUND, University of Massachusetts, 107 Fernald Hall, Amherst, 

 Massachusetts. They are priced at 35 cents per pound and are available in 10, 25, 

 and 50-pound bags. As poisons are not mailable, all shipments are made via 

 Railway Express, with the shipping charges COLLECT. 



Zinc Phosphide-treated Cracked Corn ; The U. S. Fish and Wildlife Service 

 does not recommend Zinc Phosphide-treated Cracked Corn for pine or meadow mouse 

 control because field test results have demonstrated that the degree of control 

 is very erratic; and the results not as good as with Zinc Phosphide- treated 



