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Monday, August 18, 2014

Sorghum Midge 2014

Sorghum Midge
                Much of our later planted sorghum will be coming into bloom this week.  This means that the long anticipated sorghum midge season is starting.  Today, August 18, 2014, I was in a southwestern Swisher County sorghum field that was at boot to bloom stage.  Only about 5 % of the heads had blooms yet, but every head with blooms also had a midge.  This is not a treatable level of midge… yet.  As the field progresses farther into bloom I would expect to find additional midge infesting an economic level of heads.
Midge are tiny Dipterans, or flies, that feed exclusively on sorghum type plants.  The adult midge only lives less than one day, just long enough to lay eggs into blooming sorghum.  The tiny resulting maggot feasts on a single developing grain from within consuming it fully only to emerge as an adult a short time later (usually about 2 weeks) as an adult to start the process over.  Midge cannot overwinter in our area and must migrate from the south every growing season, usually hopping generationally from blooming sorghum field to blooming sorghum field.  Johnson grass can also harbor the midge life cycle.  Sorghum fields blooming early in the growing season are normally immune to midge damage, as the midge typically do not arrive in force until an average date of August 4th. 
We have been finding midge at sub-economic levels in sorghum since late July.  So far we have not had any fields reach ET (economic threshold) for midge but I really think that is about to change.  The midge population has been gradually growing on our early planted sorghum and the abundant Johnson grass population that our early summer rains have fired.  As sorghum fields enter bloom, I recommend scouting daily, and if your later sorghum planted sorghum is near a healthy Johnson grass population or an earlier planted field I recommend extra caution. 
                When scouting for midge, I prefer to make use of beat buckets or jugs by placing the bucket over the blooming head, tiling downward and shaking vigorously.  Midge should be shaken loose and counted.  A minimum of thirty plants per field should be checked, but total number needed to be checked will vary depending upon field size.  Another good method for use on windy days involves enveloping the blooming head in clear plastic, disturbing the head and counting midge trying to escape.  While in bloom, sorghum should be checked daily for midge starting about 11AM, temperature depending.
                The ET for sorghum midge at the current market level for grain sorghum should be near 1 midge per head during bloom stage.  This ET level should be slightly lower for seed milo, contracted grain value depending. 

Please call or come by with any questions,
Blayne Reed