More rain is in the forecast for later this week as wheat fields in the northern half of the state go through the flowering growth stage. Fields flowering today (May 30) are at low risk for scab in the northwestern corner of the state, but the risk will increase progressively later in the week as tropical storm Alberto comes through (see maps for May 30 through June 1 below). Fields in the southern third of the state are now at much less susceptible growth stages for infection by the scab fungus.
Treating fields with an effective triazole fungicide (also called DMI) such as Caramba or Prosaro at flowering will reduce scab and vomitoxin by about 50%. On the other hand, treating fields with a strobilurin fungicide (also called QoIs) such as pyraclostrobin, azoxystrobin, fluoxastrobin, of trifloxystrobin when conditions are favorable for head scab will increase vomitoxin in the grain. On average, strobilurin fungicides increase vomitoxin by about 15% when applied at boot and about 17% when applied at heading.
Premixes of strobilurin and triazole fungicides (QoI+DMI) such as pyraclostrobin + metconazole, azoxystrobin + propiconazole and trifloxystrobin + prothioconazole are much less effective than Caramba or Prosaro against scab, and some combination products may even increase vomitoxin contamination of the grain by as much as 15%.