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Texas Plains Sorghum: Sugarcane Aphid Confounds and Confuses

Debra Ferguson
By Blayne Reed, EA - IPM Hale, Swisher, and Floyd County - Texas AgriLife August 12, 2016

Texas Plains Sorghum: Sugarcane Aphid Confounds and Confuses

Sugarcane aphid nymphs and an adult on a grain sorghum leaf. (Texas A&M AgriLife Extension Service photo by Dr. Pat Porter)

It seems this rascally invasive insect loves to keep us confounded and confused.  In 2014 they discovered late in the growing season we do raise quite a bit of sorghum in West Texas, which made the fall and period right before harvest interesting to say the least.  In 2015 they hit the area sorghum fairly early with a massive population invasion that felt like a full speed locomotive that smashed sorghum fields and bank accounts alike as we struggled to learn about the pest while using control tools designed for another region.   Then they successfully overwintered in Hale County and made their intimidating presence known in Lubbock and Swisher Counties early in the spring only to fall completely off the radar without a trace of the pest to be seen.  Meanwhile, their 2015 impact and spring intimidation was enough to impact planting intentions and / or force a full IPM plan in sorghum devoted to managing this one pest.  Now they are back for 2016 and their behavior and impact is a puzzling as ever.

 

 

We certainly have sorghum fields in Hale, Swisher, & Floyd replay this insect’s incredible reproductive capacity that we have seen over the past two seasons.  In these fields, we witnessed a mere three weeks or so time frame from detection to treatment level.  Our producers and entomologists for the most part seem to have taken the threat very seriously and implemented our new Texas High Plains Sugarcane Aphid Threshold to some substantial effects at holding and cleaning this aphid from those troubled fields.  While there are some escapes and fields with less than ideal control levels, it is nothing like last year.  But then again, the aphid is not behaving as badly as last year either.

The sugarcane aphid is very far flung in its 2016 invasive march through the ‘northern’ sorghum territory of Texas but this march does not seem to be the rolling fog of devastating aphids that the 2015 movement was.  Meaning to say that applied entomologists are detecting establishing sugarcane aphids in sorghum fields well into Kansas, the western counties of the Texas Panhandle (if not New Mexico) and northeast into Virginia already but not every field between detection sites was infested and / or devastated along the way.  We can say the same thing in micro across my three counties of responsibility.  There are fields in southeastern Floyd, which had the aphid first, and fields in northwestern Hale and southwestern Swisher that needed to be treated for economic populations of sugarcane aphids alike.  However, in between these two opposite sections of adjoining counties are plenty of healthy sorghum fields without any detectable sugarcane aphids.  By the way, this also includes our research plot trials still awaiting the arrival of the aphid so that we can gain better knowledge on understanding the aphid and how to best control it economically.

There are a lot of unanswered questions here. 

Why were these fields passed over?  Is the aphid population just so low today that they can be choosy about which fields they infest?  If so, why are they choosing certain fields?  Is it variety related?  We have resistant lines but this feels larger than the known “slight resistance” factor.  Are they just following some geographical feature to skip over fields, say the draws that cross the area?  Is it wind and weather patterns that carry them in what appears to be random patterns?  Or are we just getting better about finding the lighter populations before the aphid really gets rolling?  Could the aphid’s choice in fields be plant stage related?  Is the aphid population smaller due to less sorghum in the area?  Is this more of a typical behavior patter for the aphid?  Will the aphid fill in and eventually attack the passed over fields?  And the really big question might be, will another wave of aphids invade the area and be as heavy as we know the aphid can be?

A lot of us have hypothesis to these questions, but with only one true year of research on this aphid few of us on the Texas High Plains have definitive answers for this aphid’s many questions at this time.  What we can state with certainty is what is before us.  Based upon the current distribution of the sugarcane aphid in Hale, Swisher, & Floyd Counties, every sorghum field is at risk for sugarcane aphid damage and will remain at risk until the grain is in the bin.  Only about half of our program fields currently have aphids in them.  I do not expect all sorghum fields to need treatment this year based upon what I am seeing today.  We all know this can change rapidly so we must remain vigilant.  Honestly, we have no idea when or why aphids are choosing some fields and not others, but we must identify the aphid infested fields as early as possible.  I believe the least likely fields to require treatment are early planted fields already going into hard dough stage right now. These fields have a smaller window of damage opportunity from the aphid now.  Conversely, late planted fields still in the whorl have a wide window of damage opportunity today.

Of the fields that are infested, there are no guarantees that they will need to be treated as the predators are having a big impact on the aphids, but most earlier infested fields have already needed treatment and that happened typically about three weeks post detection.  If a field reaches our new High Plains Sugarcane aphid Threshold, we need to act quickly.  Not only do we need to act quickly in making treatment, we need to make that treatment with one of the two proven to work and labeled products Sivanto or Transform and we need to be very particular in terms of getting good coverage that reaches to the very bottom of the canopy with solid rates.  The gallons of mix per acre for these treatments must be minimum 15 gallons per acre via ground and 5 gallons per acre via air, but higher rates, almost without limits, practicality aside, are very advisable.

While I feel the SCA pressure is much litter this year, they still demand respect.  The bottom line in treatments is this; if we are forced into treating, we must make this one treatment count and last.  We cannot give the aphids a day or two to see if they continue increasing as the population will become too large for one treatment to contain.  We cannot try a cheaper, predator harsher product that is not likely to work as we will not clean the aphids out, if we impact them at all, and we will take out all predators and have a larger more expensive mess on our hands than if we had done nothing at all.  We cannot fudge on our GPA for convenience, or we will not get good treatment coverage on the lower leaves and the aphids will re-infest the upper portions of the plants in a matter of days.  Our two 2015 High Plains SCA research efficacy trials on the High Plains (Hale Center & Bushland) proved these trends are very likely.

So far, by following the High Plains SCA Threshold, acting quickly and using the recommended products in the best recommended manor, we have had some really good success in controlling this aphid when needed.  Behind a “good” SCA treatment, we are not seeing aphids.

Debra Ferguson
By Blayne Reed, EA - IPM Hale, Swisher, and Floyd County - Texas AgriLife August 12, 2016