16 MONTANA BULLETIN 150 



tliey will l)e able to hold over in tlic ground from the time the spring 

 plowing is done to the time when the young wheat is coming up to 

 furnish something for them to feed upon. In other words, it is be- 

 lieved that the young worms can be starved out in the spring but that 

 the older worms can not be. 



4. No cultivation practices are of value where winter wheat is 

 grown except when the wheat is seeded after September 15th. 



5. Early irrigation will prove an effective means of preventing 

 damage. Fields known to be infested which can be irrigated should 

 have the water applied to them without delay, 



THE FRUIT-TREE LEAF -ROLLER 



Tlie outbreak of the fruit-tree leaf-roller {Archips argyrospila 

 Walker) in the Bitter Root Valley continued unabated during the past 

 spring and summer. Several hundred acres of orchard were again 

 totally stripped of foliage with the loss of thousands of boxes of ap- 

 ples, while injury of lesser importance extended to over a thousand 

 acres. The pest is now established in four localities in sufficient num- 

 bers to cause noteworthy loss to the fruit crop, namely, at Stf^vens- 

 ville, Victor, Corvallis, and Darby. Control measures carried out by 

 a number of growers the past spring, while greatly reducing the injury, 

 lacked the proper strength and thoroughness and were not sufficiently'' 

 extensive to materially reduce the infestation. 



During the past spring and summer (1922) tests were conducted 

 in some of the worst infested orchards to determine the most effective 

 and economical method of controlling this pest. Of five commercial 

 brands of miscible oil sold on the market for leaf-roller control, only 

 two proved sufficiently effective in these tests to warrant their use for 

 this purpose. The strength i-equired to secure an effective kill was 

 also determined to be above that ordinarily recommended. The influ- 

 ence of high pressure, weather conditions, time of application, etc., 

 on the results of spraying were satisfactorily' worked out, as well as 

 the life cycle for the insect in the Bitter Root Valley. 



It was discovered that in tlie case of severe infestation, serious 

 reduction in llie fruit set and injury to the mature crop could be pre- 

 vented only l)y Hn' use of an effective miscible oil to destroy the eggs 

 before they hat<'li. It was determined by these tests that in the case 

 of mild infestation the pest could be effectively controlled by thorough 

 applications i>f ni-senalo of h'ad, iircferably with a spreader added. 



