494 STATE BOARIJ OF AGRICULTURE. 



sects.* The method has been put to the test in several other states and 

 is now recognized as the best method of controlling insects in welL built, 

 steam-heated mills. 



In view of the above facts it has seemed to the author that j^erhaps 

 heat might be applied to advantage as an insecticide for many insects 

 in situations where it has never been the ])ractice to use it. A few, more 

 specific suggestions may be made. There have never been any extensive 

 tests carried out (so far as we have been able to find) to determine 

 whether heat might not be used profitably in certain instances to clean 

 some kinds of nursery stock of insect pests. One opportunity was af- 

 forded the author of making a limited test of the possibilities along this 

 line. Forty-four one year old apple-stocks were given by the Department 

 of Horticulture for the test. It had been found by trial that San Jose 

 scale on thickly infested twigs could be killed by submerging them for 

 five minutes in water heated to 130° F. The green apple aphis was killed 

 within one-half minute in water at that temperature. The test with the 

 apple-stocks was carried out, therefore, to learn something of the etfect, 

 upon the stocks themselves, of dipping them in water at certain tem- 

 peratures for different periods of time. The bundle of stocks, wrapped 

 in sphagnum, had been kept all winter in the basement of the cold stor- 

 age plant at the College. They were still almost entirely dormant on 

 May 4th, 1914, when the test was started. Ten average stocks were 

 picked out for a check — not to be treated, but planted just as they came 

 from the storage. The remainder Avere given treatment as follows: — 



(1) 5 stocks — tops, only, dipped at L30° F. for 5 mins. 



(2) 5 stocks — tops, only, dipped at 130° F. for 10 mins. 



(3) 5 stocks — tops and roots dii)ped at 130° F. for G mins. 



(4) 5 stocks — tops, only, dipped at 140° F. for 5 mins. 



(5) 5 stocks — tops, only, dipped at 140° F. for 15 mins. 



(G) 5 stocks — tops and roots dipped at 140° F. for 20 mins. 

 (7) 4 stocks — tops and roots dipped at 150° F. for 10 minutes. 



All the stocks were then planted in a row close together at the same 

 depth in the same kind of soil. 



The checks or untreated stocks leaved out several da3's ahead of the 

 treated plants, but all of the latter finally came into leaf, and were still 

 alive in the fall — except the four stocks which had been treated in 

 water at 150° F. for 10 minutes. Those four plants had been killed, 

 evidently by the treatment. Examined on May 21, 1915, most of the 

 young apple trees were in almost full leaf. The dead and injured trees 

 could be easily recognized. Nine of the trees in the check were alive and 

 one dead. By numbers, the condition of the treated trees was as fol- 

 lows : — 



(1) 5 trees alive. 



(2) 4 trees alive; 1 tree dead. 



(3) 3 trees alive; 2 trees dead. 



(4) 3 trees alive; 2 trees dead. 



(5) 5 trees alive; 3 of them with 3 or 4 inches of stock dead at the 



top. 



•Bulletin No. 189, 1913, Kansas Agr. Expt. Station. 



