SCA Efficacy Trial 21 DAT Counts & SCA 2nd Treatment Decision Options

SCA Efficacy Trial 21 DAT Counts & SCA 2^nd Treatment Decision Options

                Before we started our counts today, we discussed the validity of these 21 DAT counts.  We knew that the untreated check would have fewer aphids due to the overall plant health and predation (although the predators are so far outpaced by the sugarcane aphids that this is not a control option alone).  We also suspected that most treatments would be losing control altogether this far out past treatment.  If both of those factors are true, these results would be skewed with heavier aphid numbers on treated plots.  We also knew that we did not get good control on the lower leaves in this trial.  To counter this potential affect, we are including a plant damage rating.  These were collected at 15 DAT and again today at 21 DAT.  This rating system is based on a 0-10 scale where 0 = no aphid damage and 10 = dead plants.  All graphs and statistics are shared below.  This rating system is new for the SCA and is only ready to evaluate damage and cannot be utilized as a threshold marker… yet.

                The take home message from the researchers involved in this trial today and gathering from our field experience these past few weeks is this: If you got good control with your first SCA treatment, you MIGHT be able to hold off on the next treatment until 17-21 DAT for the next (assuming aphids are still an issue; I have seen no field where they were not).  If you did not get good control, it is VERY LIKELY your next treatment needs to fall 10-14 DAT.  If and when a second, or even third treatments become necessary, remember we need to rotate chemistry between Tranform and Sivanto to prevent resistance from this aphid.

                I feel the majority of treatments in this trial fall into the second category.  If these plots were in a field situation, they would have required a second treatment 5 – 7 days ago.  Neither of these situations are what we want but that looks like what the situation is with even more aphids moving in to re-infest and / or populations recovering.  Both of these situations need to fall into considerations about how far out harvest is.  We would certainly prefer the next treatment, likely the third treatment if needed, would be the one that cleans the aphids for the combine in conjunction with a sorghum harvest aid.  We are so far out from a freeze at this point and these SCA still have a ballooning population that can stay in-field until and after harvest, I do not envision the possibility of being able to wait for a freeze to finish these aphids off so we can harvest.   

Blayne Reed

Sugarcane Aphid Update & 2015 Sugarcane Aphid Efficacy Trial – 14 DAT Counts

Sugarcane Aphid Update &

2015 Sugarcane Aphid Efficacy Trial – 14 DAT Counts

                The sugarcane aphid (SCA) is still having a heavy handed impact on the region.  In the field it does seem we are performing better in terms of knockdown and control with our treatments with several factors playing key roles.  The adjusted action threshold seems to me a better fit for the High Plains and hits these prolific aphids before they get their population built up too high.  Producers, consultants, and applicators seem to have a better understanding of the coverage needed via air or ground (air - 5 GPA minimum, 10 GPA preferred / ground – 15 GPA minimum, 20 GPA preferred) and the change of adjuvants to something heavier, such as an MSO or silicone based product, to better pull the treatment down lower into the canopy for control on the lower portion of the plant.

                On August 19, 2015 we gathered our 14 DAT counts from our SCA Efficacy Trial.  I have just now had the time to get the data analyzed and this information released. This trial is an RBD and has 4 replications.  Due to noted differences in control between the upper leaves and lower leaves, we have calculated differences in aphid numbers in terms of upper and lower leaves in addition to total aphids averaged per leaf.  Despite using 16.5 GPA, a standard rate of 0.25% NIS was utilized as an adjuvant, a standard practice for all treatments applied in this area and what was recommended for this research protocol.  We did not get good control on the lower leaves and no differences were found on those leaves.   This is one of the factors that lead us to recommend an adjuvant change with company agreement for all commercial applications.  For this trial, continuing to count the lower leaves was proving pointless and quite time consuming.  As a result we opted to only count the upper leaf for the 14 DAT counts.  This upper leaf is actually the second leaf below the flag leaf.

Questions about rainfastness

                Questions about the rainfastness of these two leading products Transform and Sivanto are common this season.  All I can speak of is this trial and what appears on the company label, which might not be mentioned specifically.  In addition, there are questions about Transform’s performance in this trial. 

                Applications for this trial were made on August 5, 2015.  Treatments began with the low rate of Sivanto at 9 am and continued down the treatment list until Lorsban was applied at 11 am.  We then gathered our pretreatment aphid counts in the untreated border rows from each plot.  Almost immediately following our leaving this trial location, a heavy 0.75 inch rain began at 4:15 pm. 

                Dr. Mike Lovelace, Dow, toured this trial with us as we made our 14 DAT counts.  Quoting from our discussion with Dr. Lovelace, “This is a good trial and I can see the differences it is showing…  This is the first instance with Transform I have seen that control that was not a premium and I feel we have a stronger product than this…  The rates are off due to the mistake in calibration, but all treatments are off the same… There must be some outside reason for Transform’s lackluster performance here…  The trial methodology is strong and there is no research bias here but right now I am looking at the rainfall that occurred after treatment on these plots as the culprit.”

Blayne Reed

Sugarcane Aphid Threshold Lowered for the Texas High Plains

After a few weeks of dealing with the new pest to the region, the sugarcane aphid, at threshold levels, we have learned quite a bit.  Many regional professional entomologist agree that the action threshold for sugarcane aphid treatment set farther south along the Gulf Coast and in the Lower Rio Grande Valley simply is to high for the Texas High Plains and allows this pest's population to get too firmly established before initiating treatment.  Wishfully, we would have much preferred to have had this information ahead of the aphid's arrival this season rather than getting the expensive experience first hand, but this area was among the first on the Texas High Plains to reach treatable levels.

The following was written by Dr. Pat Porter, district 2 entomologist, and represents a consensus opinion of our region's Texas A&M AgriLife IPM working group:

Sugarcane Aphid Threshold Lowered for the Texas High Plains

Now that we have had a few weeks of experience with field-scale sugarcane aphid control in the southern High Plains, it appears that we need to move to a more conservative treatment threshold than the one currently in use. What we are finding in commercial fields and our insecticide trial is that our insecticides do not seem to be working quite as well as they do in more southern locations with higher humidity and less intense sunlight. Whether our environment affects the insects, plants and/or insecticides differently is unknown, and what we are seeing could be a combination of all three factors – or two or one or none, we just don’t know. Insecticide coverage issues may also be in play. We could be experiencing insecticide interception by excessive honeydew such that some of the insecticide never gets to the leaf surface.  We also do not know the importance of reduction in coverage and canopy penetration attributable to aerial application rather than ground application with higher volumes of water. Additionally, we also have reports of narrow row fields (less than 36 inches) having reduced insecticide efficacy, and this of course is a coverage issue.

The preceding paragraph is basically to say that we are not sure what is causing reduced control. We want to make it absolutely clear that there is no reason to think this is a resistance issue. However, with regard to application timing the prudent thing to do is to initiate insecticide applications sooner, before the aphids reach 50-125 aphids per leaf. For that reason we are recommending the action thresholds in use in Mississippi.

The threshold for soft dough stage sorghum is when 30% of the plants are infested and there are localized areas of heavy honeydew and established aphid colonies. This threshold would trigger significantly earlier insecticide applications than our Texas threshold of an average of 50–125 aphids per leaf. The full explanation of the Mississippi threshold can be found here: http://www.mississippi-crops.com/2015/02/24/management-guidelines-for-sugarcane-aphids-in-ms-grain-sorghum-2015/ . Note that this document estimates a 21% yield loss if fields at soft dough stage are left untreated after reaching the threshold. Missing an application at the boot stage threshold of 20% of plants infested with localized heavy honeydew and established aphid colonies would cause a 67% reduction in yield.

Of course another prudent step would be to increase the insecticide rate if possible. Bayer CropScience has some good recommendations for tank additives on the High Plains. Insecticide applications made at relatively low to normal numbers of aphids can be tank mixed with MSO/silicone blends. For heavier infestations they are recommending that Crop Oil Concentrate or High Surfactant Crop Oil be added at the recommended rates. The thought here is do drive the insecticide deeper in to the canopy. 

Posted by Pat Porter 

Thanks Pat and the whole working group!  It has been an ‘interesting’ few days. 

Good luck out there folks!

Blayne