328 Phylum Arthropoda 



to another. The trays are usually staggered 12 high, leaving 2 feet 

 between the top trays and the 8-foot ceiling. 



Each method of handling has its advantages and either may be used 

 with satisfaction. Where racks' are used the trays are more easily placed 

 in position ; poor trays may be easily removed and new ones added ; and 

 less labor is required to keep the sprouts out of the aisles and within the 

 confines of the racks. Where the stacking method is used all of the host 

 plant or host insect material in the entire lot of trays is directly accessible 

 to the mealybugs. 



The average period required for developing the potato sprouts to the 

 point where they are ready for infesting with the mealybug is 60 days. 

 However, this period is considerably lengthened during the winter months 

 when the "new crop" seed tubers are more or less immature, and reduced 

 almost to 30 days in midsummer when fully matured seed from cold 

 storage is used. 



The sprouts are allowed to develop in subdued light in order to 

 promote longitudinal growth and to limit the formation of chlorophyl, 

 which tends to inhibit the settling down of the mealybugs during the 

 period of infestation. A temperature averaging 65 ° F. and a humidity of 

 approximately 70% is maintained during the growing period. The 

 moisture requirements of the growing sprouts necessitate that the trays 

 be watered at 10-day intervals. Top trays and others directly exposed to 

 ventilators dry out rapidly, and must be watered every 5 days. 



Materials, such as sphagnum moss, wood shavings, sawdust, and coarse 

 sand have been used as growing media but with less satisfactory results 

 than with prepared soil mixtures. 



Whole tubers in open trays with no growing medium may be used. 

 Twice the number of tubers are then required, but a proportionate in- 

 crease in production is secured, without any increase in equipment or 

 room space. Other advantages of this method of operation are the ma- 

 terial decrease in the amount of labor involved in the initial planting and 

 in the subsequent care of the room. The necessity for frequent waterings 

 with their attendant troubles from overwatering or drying out is elimi- 

 nated. In addition, the tuber itself serves as a host of the more mature 

 mealybugs. This method, so far as now understood, is limited, however, 

 to late-season use when completely mature seed tubers are available; 

 otherwise the prolonged period of sprout development makes it un- 

 practicable. The development of more effective methods of accelerating 

 sprout growth in new tubers would give this method of host plant culture 

 preference over any other.* 



♦Editor's Note: The Cobbler, Green Mountain, and Russett Rural varieties of 

 potatoes have been sprouted successfully when taken from the field in mid-season and 

 stored at 40°F. for a month. The use of ethylene as an aid in speeding up maturity 

 has also been successful. — G. F. MacLeod, Cornell University. 



