I assume your concerned with head scab??  If so, Prosaro or Caramba.  I used Prosaro at 6.5oz/ac with 5 gallon/acre water.  If your applicator won't do 5 gal, consider upping the Prosaro rate to around 8 oz, I believe it was.  But I'd lean into them to use more water because head coverage is more important than using a real high rate of product.