Sugarcane Aphids and Sorghum Midge: MS Grain Sorghum

Over the last 7-10 days reports of sugarcane aphids in grain sorghum are becoming more frequent across the state. To date, I am not aware of any applications going out yet but numbers within some fields are definitely increasing. So far I have had about 10 reports of findings from the Delta region ranging from Cleveland to south of Inverness. The only find that I have heard of so far in the Hill region is from Starkville in test plots. I suspect if things progress like last year we will be starting sprays maybe as early as late next week. My limited experience with SCA has shown a lag time of 10-21 days from initial finds of small colonies to very high populations.

Currently we have grain sorghum from the soft dough stage to just emerging around the state. The earliest planted struggled early on with cool temps but will very likely miss the extremely high SCA numbers later in the year. I am starting to get calls about midge applications. I fully understand that midge can be an extremely damaging pest if not controlled but our early planted Milo generally escapes midge pressure so automatic applications should be avoided if no midge are present because you can quickly flare SCA populations. Midge are very easy to scout for. I prefer visual scouting. Simply observe the flowering portions (yellow anthers) for small red gnats. If midge are present it is not difficult to see them fluttering around. You may want to also thump the neck of the stalk to get them moving. Grain sorghum will flower from the top down and will generally flower at a rate of 20-25% per day so individual heads will flower out in 4 to 5 days. Midge applications should start at 25-30% flowering. If numbers are low and fields are heading uniformly, you can often get away with one application. If numbers are high or there is non uniform head emergence it may take multiple applications. We mainly see this on the later planted Milo. If you see orange anthers it is too late. Midge are laying eggs in the yellow anthers. This is important. I saw many fields last year where midge sprays were not timed correctly and simply was a waste of money. The picture below shows a head that is blooming down the plant. The first picture is about 30% bloom (note yellow anthers), the second picture is about 60% bloom. Again, note where the yellow anthers are and the ones above it are now orange. The last picture on right is the 100% flowering out. Thresholds for midge is 1/midge per plant. There have been some questions about products for control of midge. Pyrethroids at low rates have been very consistent over the years. Some have asked about Dimethoate or Lorsban because they may not flare SCA’s as bad. This may or may not be true, however, there midge efficacy has been inconsistent. Bottom line: spray midge as needed and use products that have proven track records. Click on this link for more information about Sorghum Midge

When trying to detect SCA’s before populations get high, there are a couple very easy techniques. It is important to find them early so you can begin to monitor closely and tighten your scouting intervals. The first is simply walk fast and look for honeydew. If you choose this method, it will have to be later in the day since this does not work if the canopy is wet. I prefer to get a sweep net handle and lift a couple foot of row of the lowest leaves an quickly scan for aphids. Once you have determined that aphids are in the field then you can refine your searches.

Once aphids are found colonizing you should try and scout twice weekly. Remember they simmer for a little while with slow increase, but once they get going, populations can explode rapidly. As far as thresholds go, all the states are generally on the same page with recommendations of treatment around 20-30% infestations depending on timing. Most states with the exception of MS recommend some percent infestation level with at least 50 aphids per leaf. We do not disagree with their thresholds but we simply word it in a way we felt was more “scout friendly” by not putting a number per leaf but adding the caveat that includes “areas of heavy honeydew and established aphid colonies”. When we see this we are generally at around at least 50 aphids per leaf also. This will continue to be refined as we gain more experience.

Product choices: For 2015 we have Transform available through a Section 18 Emergency Exemption at use rates of .75-1.5 oz/acre with the most common rate being 1 oz./acre. Also, this year there is a full section 3 label for Sivanto by Bayer CropScience at use rates of 4-7 oz/acre. As far as mixing Pyrethroids with SCA products, I do not have a problem with this at all…If you have a reason. Don’t do it just to do it. There are numerous early planted fields out there right now with no aphids in them. You would not benefit from adding SCA material in any way if aphids are not present. Remember, try and maximize coverage with tips and GPA. We saw much better control last year when we were able to get the GPA up to 15-20 by ground and minimum of 5 by air.

One final thought: with all the issues around honeybees out there, try and hold your midge sprays to late in the afternoon. Our research indicates that foraging honeybees are much less likely to become exposed to insecticides if they are applied within 3 hours of sunset. Honeybees are highly attracted to flowering sorghum so take every precaution you can to avoid bee exposure. Middle of the day would be the worst time to apply a pesticide that is toxic to bees. This is when  foraging activity peaks.