22 MASS. EXPERIMENT STATION BULLETIN 2L3. 



RoGurNG WITHOUT Resettixg. 



When only a few plants in a field are diseased, it is probably best to 

 remove them from the field and leave empty the places from which they 

 were taken. This was tried with success by three growers in North 

 Hadley whose fields were under the writers' observation during the present 

 season. Other growers have told the writers that they kept wildfire in 

 check by this method. 



Experiment 16. — In a plot at the Windsor Station, where five plants were 

 found to be diseased ten days after setting, they were all removed and the places 

 not filled. The surrounding plants were inspected regularly and in two cases they 

 became infected later. 



In a later experiment, where the plants were about I5 feet high, the diseased ones 

 were removed and not replaced. Before harvesting, however, wildfire had ap- 

 peared on the adjacent plants and had spread through four to six plants to the wind- 

 ward and along the row. 



It is reasonable to believe that bacteria which came into the soil from 

 the original diseased plant would have less opportunity for further in- 

 fection if no plant replaced the diseased one which was removed. Cer- 

 tainly the danger of surrounding plants becoming infected is diminished 

 by removal of infected ones from the field. On the whole, there is no 

 question but that this practice of roguing will help to a great extent where 

 there is only a light infection in the field, especially if the plants are pulled 

 when small. After plants are half -grown, however, under favorable 

 conditions the disease may spread in its customary manner, and it may be 

 necessary to remove plants or infected leaves from plants for some distance 

 around the original point of infection. 



Picking off Diseased Leaves. 



If the plants are large and infection is light, a certain amount of benefit 

 may be derived from removing all diseased leaves and carrying them 

 from the field. The principle of this measure is the elimination of as 

 many as possible of the centers of spread. Then when the rains come the 

 number of bacteria splashed to the healthy leaves will be greatly reduced. 

 This method was tried by Anderson on a 4-acre field in Whately. 



Experiment 17. — Infection in this field started from about six to eight rows near 

 the east side, which had been planted from a diseased bed. At the time when the 

 experiment was started a majority of the plants in these rows were diseased, and it 

 had spread more or less to plants on adjacent rows. There was practically no in- 

 fection on the west half. On June 30 all diseased leaves were picked from the east 

 half (forty-eight rows). No attention was paid to the west half. On the badly in- 

 fected rows mentioned above a large basketful of leaves was taken from each row, 

 some of the plants being left almost without leaves. It was picked again four days 

 later, the weather having been very rainy during the last month. Probably as 

 many leaves were removed the second time as during the first picking. It was 

 picked over at short intervals five times afterward, and with each picking the num- 

 ber of diseased leaves decreased, until on July 26 hardly a diseased leaf could be 

 found. After the heavy rains of the last few days of July and the first of August, 



