By Nathan Kleczewski Ph.D
Extension Specialist- Plant Pathology
Wheat season is winding down and the window to see scab in fields started last week in many fields. Overall we are looking at very low levels of scab in the majority of fields in Delaware. However, the striking symptoms associated with Fusarium head scab can make it appear worse than it is. Assessing scab in a field is important as it provides you with information about the current years management practices and environment, and it also gives you an idea of if you have issues that may require additional intervention.
To scout a field for scab you want to look at the field 18-21 days after flower. A little sooner and you may miss symptoms, later and the heads may start to dry down, making it impossible to assess scab.
1) Select a minimum of 10 sites per field. Choose sites at random-do not scout only field edges or along the road. You want to ensure that the entire area is covered.
2) Take a gallon paper or plastic bag with you. At each site keep your head up, and every 5 steps reach down, pick a head (don’t look down) and place it in the bag. Do this 10-20 times per site. You should end up with a bag of at least 100 heads, chosen at random.
3) Assess the incidence, or number of heads with any scab. This is a simple number to obtain. Simply count the number of heads with scab. Then use the following formula to determine the incidence:
% Incidence = ((# heads with scab symptoms)/ total # heads collected)) x 100
In most fields this season we have observed 0-2% incidence, with most under 1%. In 2013 we observed between 40-85%.
If you have a significant level of scab can attempt to minimize scabby kernels (tombstones) by increasing the fan speed on your combine. The majority of vomitoxin is found in tombstones and chaff, so the idea here is to remove as much of this from the bin as possible.