dosage necessary to protect elms from infection with 

 Dutch elm disease for the 30 days necessary in Wiscon- 

 sin, Norris concluded. 



We originally planned to place a series of cages 

 on the trees 32 days after treatment, but by that time 

 the crotches in the twigs were so badly damaged by 

 the natural infestation of bark beetles that this pro- 

 cedure proved impractical. However, enough undamaged 

 crotches were found 32 days after treatment to run tests 

 with beetles in jars containing twigs from the treated 

 trees, table 2. These tests showed that the life span 

 of bark beetles placed in jars with twigs from trees 

 treated with 0.5, 1, and 2 ml of technical SD-3562 per 

 inch of tree dbh was about half the normal life span, 

 table 2. Apparently, some of the beetles were killed 

 when exposed to twigs from trees given dosages lower 

 than those required to materially reduce the number of 

 penetrations, while others survived long enough, even 

 on branches from trees given the 2 ml dosage, to 

 produce penetrations in the crotches of twigs. 



TESTS WITH SD-3562 INJECTED INTO ELMS 

 FOR CONTROL OF DUTCH ELM DISEASE 



The preliminary tests with SD-3562 as a systemic 

 insecticide produced several interesting findings. 

 After injection into American elm trees, SD-3562 was 

 translocated throughout the trees and was toxic to 

 bark beetles feeding in the crotches of twigs, where 

 infection with the Dutch elm disease fungus, Cerato- 

 cystis ulmi (Buisman) C. Moreau, takes place. The 

 chemical was toxic to the bark beetles for about a 

 month after the trees had been treated at dosages of 

 0.5 ml per inch of tree dbh. At a dosage of 2 ml per 

 inch of tree dbh, the number of penetrations to the 

 xylem of the twigs was definitely reduced. This 

 dosage, however, caused slight injury to the foliage 

 of elms. There seemed to be little margin between the 

 dosage level required to reduce the number of beetle 

 penetrations and the dosage causing injury to elm 

 trees. 



An important question to answer was whether 

 SD-3562 at nonphytotoxic dosages could provide suf- 

 ficient protection from the bark beetle to control Dutch 

 elm disease. Only comprehensive field experiments 

 could answer this question. 



Experiment on Elms at Sinnissippi Forest. - A 

 field experiment to test the effectiveness of SD-3562 

 for reducing the incidence of Dutch elm disease was 

 started in I960 at Sinnissippi Forest, near the village 

 of Oregon. The test area contained 162 American elm 

 trees that ranged in size from 1.5 to 12.3 inches dbh. 

 On May 13, just after the buds had broken dormancy, 

 half of the trees (81) were treated by injection with 

 SD-3562. Half were left as controls. (No holes were 

 bored and no distilled water was injected into the 

 trees set aside as controls.) The treated and untreated 

 trees were chosen at random throughout the block. Un- 

 diluted technical SD-3562 (30-50 percent alpha isomer) 



Table 3. — Number of elm trees at Sinnissippi Forest 

 showing each of several degrees of chemical damage follow- 

 ing treatment of 81 trees with SD-3562 on May 13, 1960 

 (30-50 per cent alpha isomer), and on May 1, 1961 (75 per 

 cent alpha isomer). SD-3562 was used at the rate of 2 ml 

 per inch of trunk dbh in I960 and 1.5 ml in 1961. 



Number of Trees 



Damage* 



1960 



1961 



None 



Slight 



Moderate 



Severe 



Complete (tree killed) 



3 

 35 

 24 



17 

 2 



31 

 12 

 18 

 17 



1 



*Slight, some cupping of leaves but no dead areas; moderate, 

 cupping of leaves over the greater portion of the tree, accompanied 

 by some marginal leaf bum; severe, cupping and burning of leaves 

 extensive, between the veins as well as marginal, in some cases 

 one or more branches killed. 



was injected into four holes, three-eighths inch in 

 diameter, in each test tree at the rate of 2 ml per inch 

 of tree dbh. 



On May 1,1961, the same trees were again treated, 

 this time with the improved technical SD-3562 (75 per 

 cent alpha isomer) at the rate of 1.5 ml per inch of tree 

 dbh; the holes drilled were five-sixteenths inch in 

 diameter. This dosage of the improved chemical was 

 presumed to have more insecticidal activity than 2 ml 

 of the older product. At seasonal intervals after being 

 treated, the trees were examined for disease symptoms 

 and signs of chemical injury. 



The observations on phytotoxicity for both years 

 are summarized in table 3- None of the untreated trees 

 showed any signs of injury. Two trees treated with 

 the chemical died in I960 and one in 1961. Seventeen 

 showed severe injury in each year. Although only 3 

 trees were free of injury in I960, 31 were without in- 

 jury in 1961. The significance of these figures is a 

 matter of conjecture at this stage of the experiment. 



There was no evidence of Dutch elm disease in 

 the entire block of trees in I960. In 1961, however, 

 eight of the untreated trees and one of the treated trees 

 died of the disease, as verified by laboratory tests. 

 The 1961 losses from Dutch elm disease amounted to 

 1.2 per cent of the treated trees and 9.9 per cent of the 

 control trees. The difference between these per- 

 centages is encouraging, but its significance can be 

 determined only by continuing the experiment for 

 several years. 



Experiment on Elms in Cook County. — In 1961, a 

 block of 500 American elm trees ranging in size from 

 1.0 to 7.4 inches dbh was made available in the Forest 

 Preserve District of Cook County for tests with the 

 improved technical SD-3562 product. Three lots of 

 100 trees each, randomized throughout the entire block, 

 were treated with the chemical at dosages of 1, l l A, 

 and 2 ml per inch of tree dbh, respectively. Treatment 



