Local producers: Watch your wheat for head scab infection

The weather was beau­ti­ful this past week for bal­ing hay, and looks like the crops are almost all in around Delaware County. I’ve been out scout­ing the wheat fields this past week, and I’ve seen head scab in a few fields and I’ve seen sur­pris­ing good wheat. The wet and humid spring has made it favor­able for head scab. All areas around the state are report­ing of head scab in fields. The sever­ity has var­ied around the state. The reports of affected fields range from indi­vid­ual bleached heads scat­tered through­out the field to huge sec­tions of fields or entire fields with the bleached heads. The affected fields in Delaware County have just scat­tered affected wheat heads. Most of our fields missed the worst of it.

We start to see the devel­op­ment of these symp­toms in one to three weeks after flow­er­ing. Bleached heads can con­tain no seeds or have just have some blank pods in the head. There has been con­fu­sion among pro­duc­ers as to whether they are deal­ing with head scab or some other prob­lem stem­ming from this wide vari­ety of pat­terns and symp­toms. Scab does indeed cause bleached heads, but it is not the only cause of this type of head dis­or­der. Accord­ing to Pierce Paul, OSU Exten­sion Spe­cial­ist in Plant Pathol­ogy, the fol­low­ing infor­ma­tion can help you deter­mine whether you are deal­ing with scab: 1) the weather con­di­tion shortly before and dur­ing flow­er­ing, 2) the tim­ing of symp­tom devel­op­ment after flow­er­ing, 3) the bleach­ing pat­tern on the head and the plant and 4) the dis­tri­b­u­tion of affected heads in the field.

Infec­tion by the scab fun­gus occurs at flow­er­ing and early grain fill, result­ing in symp­tom devel­op­ment between 18 and 21 days after flowering.

How­ever, under wet, humid con­di­tions, symp­toms may develop ear­lier. Scab symp­toms appear as par­tially, one or a few spikelets or com­pletely bleached heads, usu­ally borne on green, healthy stems. With flood dam­age, wheat stem mag­got injury or take-all dis­ease, com­pletely bleached heads are usu­ally borne on bleached stems, as a result of pre­ma­ture death of the entire plant, not just the head. With scab, symp­toms are usu­ally seen scat­tered through­out the fields, with par­tially or com­pletely bleached heads inter­min­gled with healthy-looking heads. This is con­trary to what is usu­ally seen with dam­age caused by flood­ing or take-all, where all heads in cer­tain sec­tions of the field or even the entire field may be affected. Paul says that although scab may cause heads to be par­tially or com­pletely blank, scab infected heads nor­mally pro­duce grain, how­ever, these are usu­ally small and light­weight, with a pinkish-white dis­col­oration. Com­pletely blank heads are very com­mon with frost and flood­ing injuries.

“Adding to the con­fu­sion is the fact that some of the bleached heads are show­ing up in fields that were treated with a fungi­cide for head scab con­trol, lead­ing some pro­duc­ers to believe that they should not be see­ing scab after hav­ing their fields treated,” said Paul. Remem­ber, even the best fungi­cides, applied at the right time will not pro­vide 100 per­cent scab con­trol. Fungi­cides are about 50 per­cent effec­tive against scab. Think about this in a very sim­ple way: A field that would have had 50 per­cent of the spikes infected with­out a fungi­cide treat­ment will end up hav­ing about 25 per­cent of the spike infected after fungi­cide appli­ca­tion, not 0 percent.

It is impor­tant to be able to tell scab apart from other prob­lems, since scab infec­tion is usu­ally asso­ci­ated with vom­i­toxin con­t­a­m­i­na­tion of grain, which does not occur with dam­age caused by take-all, hail, frost, flood­ing or insects. Paul says that sep­a­rate grain han­dling, pro­cess­ing, stor­age and feed­ing guide­lines need to be fol­lowed when deal­ing with vom­i­toxin con­t­a­m­i­nated grain.

Rob Leeds is an OSU Exten­sion Edu­ca­tor for Agriculture/NR.

Posted by Rob Leeds on Jun 18 2011. You can follow any responses to this entry through the RSS Feed. Comments can be made below.