June IS, 1915 Soil Moisture and Sugar-Beet Root Louse 



249 



Table X. — Combined records of sugar-beet root-louse increase under different soil-moisture 

 conditions. Irrigation experiments at Huntley, Bozenian, and Edgar, Mont. 



RELATION OF SOIL MOISTURE TO SUGAR-BEET ROOT-LOUSE 



CONTROL 



From the results obtained by field observation, insectary experiments, 

 and irrigation tests it seems safe to assume that soil moisture is a very 

 important factor in controlling the rate of increase in colonies of the 

 sugar-beet root louse. While root lice were in no instance entirely con- 

 trolled by irrigation during the first year's experiments, their number 

 was greatly reduced, and it is hoped that a system of irrigation may be 

 worked out that will reduce root-louse injury to a negligible amount. 

 It is expected that such a system will not interfere with the approved 

 sugar-beet cultural methods, but that in the light of experiments reported 

 in this paper it will rather tend to increase both the sugar content and 

 the tonnage, and will thus perhaps more than pay for the extra labor it 

 may demand. The principal immediate source of root-louse infestation of 

 sugar beets is the cottonwood (Populus balsamifera L. and P. angustifolia 

 James) , upon which the root louse develops galls in the spring. During 

 the latter part of June and early July some of the numerous migrants 

 that have developed within the galls fly to sugar beets, where they deposit 

 living young, which descend to the roots and start new colonies. In 

 studying the life history of the sugar-beet root louse in the insectary it 

 has been found very difficult to induce the progeny of the migrants to 

 colonize upon sugar beets growing in soil the surface of which is at all 

 moist. The only successful attempts in colonization have been where 

 sugar beets were subirrigated and several inches of dry soil were kept 

 at the surface. It therefore seems highly important that sugar-beet 

 fields should not be allowed to dry out during the period when the sugar- 

 beet root louse is migrating from the cottonwoods to the beet fields. All 

 too frequently this is just the time when in ordinary farm practice the 

 beet fields are allowed to become quite dry. The June rains cease, and 

 by July I in an average year nearly all the beet fields in the Yellowstone 

 Valley need water. Many times water is purposely withheld at this time 



