THE MONTHLY BULLETIN. 



391 



CONTROL. 



Curly leaf of potatoes has been known in the San Gabriel region for 

 two or three years but it has not heretofore been as serious as it is 

 this season. No attention has been given to the trouble, but some active 

 measures will be necessary if the infestation is as serious next season 

 as this. 



The most important thing is to protect the plants when they are 

 young and actively groAving, for it is only at this stage that the curling 

 results from the thrips injuries. Several growers sprayed their plants 

 with Bordeaux mixture for early blight and reduced the numbers of 

 thrips considerably. One man sprayed about four weeks after planting 

 and his field shows a relatively small amount of curly leaf and almost 



Fig. 79. — Two potato leaves, showing typical "curly leaf." (Original.) 



no serious dwarfing; another sprayed about six weeks after planting, 

 but it was too late to save the plants from curling badly and being con- 

 siderably dwarfed, although the thrips were reduced in numbers. 



It is recommended that tobacco extract be added to the Bordeaux 

 spray, for this will be more deadly to the thrips. "Black Leaf 40" 

 is a commercial extract of tobacco and can be purchased at almost all 

 large drug stores. One pint of this added to 100 gallons of Bordeaux 

 mixture, or to water alone, will be very effective in killing the insects 

 on the leaves. Spray as thoroughly as possible, wetting the under sides 

 of the leaves well, if feasible. 



Most potato growers spray their plants at least once for the early 

 blight, for it paj's well to do so. This should be done early to protect 

 against the first attacks of the blight— 7io^ later than one month after 

 planting. This is just the right time to catch the thrips with the tobacco 

 spray and thus prevent curly leaf. It will help much, both for blight 

 and curly leaf, to spray a second time with the same combination of 

 Bordeaux and tobacco extract, about three weeks after the first time. 

 It pays to spray potatoes. 



