MONTANA INSECT PESTS, 1953-1954 9 



tmhealthy appearance of the plant. Investigation showed that the mite, 

 Aceria tiilipae, was carrying a virus known as wheat streak mosaic. We 

 know that this disease has been in Montana for a number of years. How- 

 ever, the combination of weather conditions and the cultural practices 

 generally followed dining the summer and fall of 1953 were probably the 

 cause of the large buildup in these mites and the resulting outbreak of 

 wheat streak mosaic. The mites, which transmit the virus from one plant 

 to the other, must live on and be transferred from one green plant to an- 

 other. They do not live on ripened or dead plant tissue. The spring of 

 1953 was comparatively wet. Consequently, many farmers did not get 

 their spring wheat planted until late in the year. This resulted in green, 

 immature fields being present well into the fall. In addition, winter wheat 

 was generally planted earlier than usual in the fall of 1953. Therefore, the 

 small number of mites, which were present in the spring wheat, were able 

 to transfer into adjacent fields of green winter wheat. The population of 

 mites, thus uninhibited, reached tremendous numbers and resulted in the 

 outbreak of wheat streak mosaic, which was experienced in the snring of 

 1954. In some cases, this damage was very severe and infested fields were 

 total losses. In all cases where this occurred, it was found that winter 

 wheat had been seeded early and was up before adioining fields of spring 

 wheat had ripened. At the present time, there is no known cure for wheat 

 streak mosaic. Therefore, cultural practices are the best and most effective 

 methods of control. Winter wheat should not be sown next to a field 

 of spring wheat until the spring wheat is ripened or harvested. Likewise, 

 the elimination of volunteer wheat plants is important so that virus-bearing 

 mites cannot be transmitted from one crop to the next. 



ENGLISH GRAIN APHID (Macrosiphum granarium) 



Economic infestations were more widespread in 1953 than in 1954. 

 Ravalli and Lake counties suffered considerable damage in 1953. Light 

 infestations occurred in Daniels, Libert\^ Roosevelt, Richland, Sheridan, 

 Teton, and Toole counties. These aphids were present in light noneconomie 

 infestations in the same general areas in 1954. 



SAY'S PLANT BUG (Chlorochroa sayi^ 



Severe but localized infestations occurred in Chouteau County in winter 

 wheat in 1953. In 1954 one local, severe infestation occurred in McCone 

 County. 



WHEAT JOINTWORM (Harmolita trittci) 



Widely scattered light to moderate infestations occurred in Sweet Grass 

 and Stillwater counties in 1953. Light infestations occurred in Stillwater 

 and Fergus counties in 1954. This pest has never been a serious enemy of 

 wheat in Montana, with infestations rarely exceeding one percent. How- 

 ever, due to the nature of the injury, it is rather outstanding in the field. 



