284 TWENTY-FIRST REPORT. 



LEAF ROLL. 



This trouble was observed as a trace only in Oakland, Schoolcraft, Luce 

 and VanBuren counties. As two of these counties are located in the upper 

 peninsula, and two in the lower peninsula, it is e\ident that it is not limited to 

 any one particular section of the state. The small amount of leaf roll in the 

 state was not cutting down the yield to any appreciable extent. 



MOSAIC. 



This disease was not observed to any extent over the lower peninsula, l)ut 

 was (juite general in the upper peninsula. Of the 30 counties visited, only 

 six showed the disease; five of these, i. e., Delta, Schoolcraft, Baraga, Mar- 

 quette and Ontonagon counties being in the upper peninsula. 



The average pei'centage of infection for the diseased fields was 11%. 

 Of the counties visited, Marquette showed every field infected, while none of 

 the other counties showed over 28% of the observed fields infected. The 

 highest percentage of infection for the various varieties was as follows: 

 Triumph 75%, Green Mountains 46%, Mayflower 40%, Russet Rural trace. 

 On the variety Triumph, the disease appeared to stunt the plants quite mark- 

 edly, whereas in the other varieties the affected plants in many cases had a 

 normal spread of foliage with the characteristic mosaic leaves. Investigation 

 .showed that the disea.se was cutting down the yield only to a slight extent in 

 those sections where it had been occurring iiimnally. 



CURLY DWARF. 



This disease was found in only three of Ww '■>() counties visited, Eighteen 

 fields in ('heboygaii comity .showed a trace in three fields; 1.'") fields in Char- 

 levoix county, a trace in one field ; and 7 fields in Mecosta county, a trace in 

 one field. The susceptit)le variety in each case was Russet Rural. The above 

 facts go to show that (-urly Dwarf was a nuuor factor in cutting down 

 the crop. 



LIGHTNING INJURY. 



Four cases were observed in the state during the summer. All these were 

 fniMid in (lie lower peninsula and in .separate covuities. The affected spot in 

 each did not exceed two rods in diameter, and was circular in form. There 

 was no indication that the electricity had followed the rows. Evidence seemed 

 to show that the injury radiated from a common center, even though there 

 was no central spot where the soil had been disturbwl by the bolt. In some 

 cases practically all the plants had been killed, while in others some of the 

 plants remained alive. The injury came so suddenly that the killed plants 

 wilted down immediately without their tissues becoming browned. The stems 

 usually were dry and blackened where the electric current had pas.sed. The 

 stem below the ground appeared to Immediately undergo a dry rot. The new 



