25(5 MASS. EXPERIMENT STATION BULLETIN 271 



All of the sprays sjiowed excellent control of scab as compared with 

 unsprayed checks. Combinations containing calcium arsenate controlled 

 scab as well as did those containing lead arsenate, but were slightly less 

 efficient against insect pests. Flotation sulfur and calcium sulfide coni- 

 bined with lead arsenate controlled scab as well as or better than the 

 lead arsenate — lime-sulfur spray and showed somewhat better control of 

 insect pests. The record on Baldwins showed sin\ilar results excejit that 

 scab was practically absent in all the sprayed plots. 



Control of Onion Thrips. (A. I. Bourne). The dry, hot weather early 

 in the season interfered somewhat with the growth of both set and seed 

 onions and tiireatened an early and heavy infestation of thrips. Subse- 

 quent rains during June and July allowed the plants to make rapid re- 

 covery and tended to retard the development of the insects. As a result, 

 thrips were but moderately abundant and caused less injury than in 1929 

 except in some fields of seed onions adjoining sets. 



The seasonal development and activity of thrips were normal and oc- 

 curred at the usual periods. This insect did not reflect the tendency ofi 

 the season to be somewhat earlier than usual, which was very noticeable 

 in many crops as well as insects. 



Observations, through the growing season, of a field of seed onions at 

 a distance from sets showed the infestation of thrips to be negligible up 

 to Jul.v 7, from July 21 to 28 it averaged 25 to 40 thrips per plant, and 

 reached its peak during the week of July 28 to August 4 with an average 

 of 40 to 42 thrips per plant. This coincided very nearly with the point 

 where the plants had reached maximum height. Beyond this point the 

 numbers of thrips fell rapidly. In this field the plants showed little scar- 

 ring and matured a good crop. 



In contrast to this, a field similar to the above but subject to infestation 

 from an adjoining field of set onions was found to be infested early in 

 the season, and by July 7 the number of thrips had reached an average 

 of 35 per plant. By July 14 noticeable injury^ was taking place. The peak 

 of abundance was reached on July 28 with an average of more than 80 

 thrips per plant. Plants in this field were not making satisfactory growth 

 and were badly scarred by the insects. Two applications of the nicotine- 

 soap spray reduced the average infestation from 80 to 10. These plants 

 revived somewhat and made new growth but matured a small and rather 

 inferior crop. 



Several species of insects predacious on thrips were collected in onion 

 fields. Their numbers were insufficient, however, to make any significant 

 inipression upon the infestation. 



Four applications of nicotine soap spray were necessary to protect seed 

 onions growing alongside fields of sets. Due to the transferrence of thrips 

 in large numbers from the sets and consequent early colonization of the 

 small, tender plants of seed onions, two of these applications were made 

 earlier than would be necessary on fields not so exposed. 



In connection with the study on l)last in cooperation with the Botany 

 Department, spraying and dusting experiments were conducted with Bor- 

 deaux mixture, commercial copper fungicides and with milk of lime, 

 alone and in combination with nicotine. The weather conditions prevailing 

 during the summer were unfavorable for the develojiment of blast. Mildew 

 was also absent. In the absence of disease, no appreciable increase or de- 



