PPFS-AG-SG-4



	<H1><CENTER>WHEAT SPINDLE STREAK MOSAIC (WSSM)</CENTER></H1><BR>




	<H3>Don Hershman and Paul Bachi</H3>					(Revised 7-94)<BR>




	Wheat spindle streak mosaic is a virus disease transmitted to plants by a non-pathogenic fungus (Polymyxa graminis) present in a large number of agricultural soils in Kentucky. Infection takes place primarily in the fall, but symptoms do not develop until the following spring.<BR>
 



<B>SYMPTOMS</B><BR>


	Symptoms include the formation of short yellow streaks in leaves starting as early as plant green-up in the spring. Severely diseased plants will be slow to grow during early plant development and may be stunted and thin throughout the season. Some varieties have a more severe reaction to WSSMV than is "typical" of susceptible varieties. For instance, McNair 1003 develops lesions with necrotic (dead) areas resembling lesions caused by Septoria or bacterial streak. The variety Saluda develops an extreme yellow leaf reaction which is usually noted in the crop throughout the season.<BR>




<B>DISEASE DEVELOPMENT</B><BR>


	Infected plants are usually uniform in a field because of the uniform distribution of the transmitting fungus, P. graminis. Symptoms are most severe in springs following a consistently cold winter. Symptoms are less intense following winters and early springs where numerous mild days were experienced at regular intervals. In most years, infections become symptomless as temperatures warm in the spring. In these cases, yield reductions associated with WSSMV infection will be minimal. However, when symptoms continue to be visible as the plants move into the boot stage or later, yield reductions of up to 25% may be experienced.<BR>
 



<B>CONTROL</B><BR>


	Once plants are infected in the fall, nothing can be done to moderate the effects of the disease the following spring; fungicides will not control it! The only way to control WSSM is to plant resistant varieties and delay planting until mid October or later. Delayed planting means that wheat seedlings will be emerging in cooler soils which are less favorable to activity of P. graminis and, thus, infection by WSSMV.