Annual report of the Agricultural Experiment Station of the University of Minnesota . ewindward side, and allowed to spread, or it may be sprayed. Anobjection to spraying is the fact that some oil is wasted and thatvegetation is unnecessarily killed. Under some circumstances, how-ever, spraying is certainly the best method, and in the case of low,hummocky land with water in innumerable small holes all overthe field, it would be manifestly a herculean task to pour oil ineach hole, and the spray is resorted to as the best and quickestmethod, new vegetation quickly taking the place of that killed
Annual report of the Agricultural Experiment Station of the University of Minnesota . ewindward side, and allowed to spread, or it may be sprayed. Anobjection to spraying is the fact that some oil is wasted and thatvegetation is unnecessarily killed. Under some circumstances, how-ever, spraying is certainly the best method, and in the case of low,hummocky land with water in innumerable small holes all overthe field, it would be manifestly a herculean task to pour oil ineach hole, and the spray is resorted to as the best and quickestmethod, new vegetation quickly taking the place of that killed bythe oil. 52 INSECTS INJURIOUS IN 1902. How often should one apply the oil ? It would seem that thisis a matter easily determined by observation, for as long as a filmof oil can be seen upon the surface, no further treatment will benecessary, and the volatility of the oil must be dependent in agreat measure upon meteorological conditions. It has been sug-gested that one application every four weeks during the summeris sufficient. I believe that a more frequent treatment, perhaps. Fig. 46.—Pupa of Mosquito killed by fungus, enlarged. once in three weeks is safer in this vicinity. As to the date offirst application, that too is easily determined by observation. Assoon as the wigglers are first seen or even earlier when the adultmosquitoes are noted about the water preparing to lay their eggs,then the oil should be applied. It is claimed that this method canbe used with safety in the case of large tanks, the water in whichis intended for drinking purposes, providing the water is drawnfrom the bottom of the tank, or a better way perhaps is to put ascreen over such tanks. It is very evident that there must be co- INSECTS INJURIOUS IN 1902. 53 operation in this work, for it would profit but little if one citizenshould treat all the stagnant water upon his place, while his neigh-bor across the fence leaves untouched, pools and ditches capableof producing millions of mosquitoes. It
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