-3- 

 WEEDS 



CANADA THISTLES 



Various types of Canada thistles respond differently to herbicides , according to a 

 study by ARS researchers in Montana. The researchers have defined ten different 

 Canada thistle ecotypes and have determined that the ecotypes vary in the amount and 

 kinds of hydrocarbons , waxes , fatty acids , and alcohols present on the leaf surfaces 

 (the materials that make up the waxy coat and cuticle); also, in the ratio of epider- 

 mal cells to stomata. The differences were consistent for the ecotypes grown under 

 three different altitude and rain- fall environments in Montana and Idaho and help to 

 explain the different responses to herbicides. 



READ THE LABEL AND FOLLOW ALL PRECAUTIONS 



This weekly report was prepared as follows : 



INSECTS: H.B. Petty, Steve Moore, Roscoe Randell , Don Kuhlman, and Tim Coo ley , Col- 

 lege of Agriculture , University of Illinois at Urbana-Champaign and the Illinois Na- 

 tural History Survey. 



WEEDS: Ellery Knake and Marshal McGlamery , Department of Agronomy, and A.J. Turgeon, 

 Department of Horticulture . 



PLANT DISEASES: M.C. Shurtleff and Tim Bowyer, Department of Plant Pathology . 



AG COMMUNICATIONS : Ray Woodis. 



AG ENGINEERING: John C. Siemens. 



The information for this report was gathered by these people, staff members, county 

 Extension advisers , and others, in cooperation with the USDA Animal and Plant Health 

 Inspection service. 



