Sorghum: Who’s Afraid of the Big Bad Sugarcane Aphid?

    With prices good for grain sorghum (compared to other crops) there is a lot of interest in growing the crop this year. We can’t begin to tell you how many calls we’ve had with growers about growing some grain sorghum this year. Many of the calls revolve around the concern about sugarcane aphid. There are evidently a lot of rumors and outright misconceptions out there about just how bad the pest can be. 

    One grower called today and asked me if it really cost $30 an application to control sugarcane aphid in milo–it doesn’t. Also, there have been a lot of questions about tolerant varieties. Evidently, a lot of seed companies are trying to sell varieties that claim to be tolerant to sugarcane aphid; so, let’s try to get to the bottom of this situation and figure out whether grain sorghum is a viable option for your operation this year.

    Background on sugarcane aphid

     Last year was our first year to deal with sugarcane aphid to any great degree. In 2013, it jumped hosts from sugarcane in Louisiana and Texas to grain sorghum and moved north just to the border of Arkansas. It may have gotten into some grain sorghum in SE Arkansas but we didn’t find it.

    In 2014, we found it in June in the southeast part of the state in Ashley and Chicot Counties. By the end of the summer it had spread throughout the milo growing region of the state and into the bootheel of MO and west TN. Obviously it is extremely mobile. It has tremendous reproductive potential and once it hits a field can build to damaging levels in a short period of time. We saw fields that were not treated that were devastated by this pest, but we also learned a lot about managing it.

    Can you grow grain sorghum with sugarcane aphids?

    If you minimize your potential for sugarcane aphid problems you should be able to grow grain sorghum and be profitable. Here are our suggestions for growing grain sorghum in 2015:

    Plant early – By planting early and getting off to an early start we may be able to avoid much of the aphid problem before they build up to large populations across the state. Our experience with sugarcane aphids is that the younger the grain sorghum is when they hit a field the bigger potential is for reducing yields. The hardest hit fields last year were ones that were pre-boot or boot stage grain sorghum. Fields infested after heading can still experience yield loss, but it is not nearly as severe. Also, and just as important, by planting early we may be able to avoid midge and headworms (fall armyworm and corn earworm).

    Pyrethroid applications for sorghum midge will cause aphid populations to flare up. Sorghum midge can be a serious pest and in recent years many growers have made applications for this pest without scouting. That has to change. We need to scout and treat for midge if, and only if, we have a problem. Since midge are only a problem during the bloom period, the grain sorghum will need to be scouted very closely at this time to make sure midge is not a problem. However, if midge is found you will have to treat accordingly. Usually early planted grain sorghum will miss midge and, in most cases, headworms too. So what’s early? Planting in April. Early April in SE, mid- to late-April in the rest of the state.

    Use an insecticide seed treatment – Studies in other states where aphids hit milo in the early vegetative stages of development show that the insecticide seed treatments provide suppression of sugarcane aphid. They also provide protection from many other important pests of milo. All of the insecticide seed treatments will work.

    Scout early and often – If you have a scout or consultant this will help you greatly, as they will be able to watch the field and keep you from getting into a problem with aphids. Sugarcane aphids are usually easy to scout. Look on the undersides of leaves on the edge of the field for small clusters of the aphids. Once they get going you will look for the shiny spots on the edge of the field made from the honeydew they excrete on the leaves. Because of the tremendous reproductive potential we mentioned earlier, if your consultant comes only once a week, it would be a good idea for you to ease around the field yourself between visits to make sure they don’t sneak in on you.

    Remember, treat for midge, headworms and aphids only if you hit established thresholds which are: Midge- one per head; Headworms- one per head; and, sugarcane aphid- 25% of the leaves infested with 50+ aphids per leaf. That may sound like a lot of aphids but it’s really not.

    Don’t try to outrun aphids – Remember aphids are a problem late season and can cause issues with harvest if not controlled. Many growers experienced problems with harvest when they decided to not spray and honeydew built up on upper leaves and the head, causing clogging of the header. The preharvest period for Transform is 14 days and Sivanto is 21 days.

    Beware of planting late! Late planted fields would be fields planted in late-May, June or even later. These are the fields that get hit hardest by sugarcane aphid as well as midge and headworms. Spraying once or twice for midge, once for headworms and twice for aphids leaves little room for profit.

    What about Tolerant Hybrids?

    We’ve been receiving a lot of calls and questions concerning varieties that are touted to be tolerant to sugarcane aphid. So what does it mean if a variety is “tolerant” to sugarcane aphid? Tolerant implies that although aphids get on the plant the plant is not impacted and does not respond as poorly to infestation as a susceptible variety. So they may get just as many aphids as a non-tolerant hybrid but plants are not impacted as much compared to a susceptible variety. They may have honeydew issues similar to a non-tolerant hybrid even if they are tolerant. There may still be some symptomology and even yield loss, but not to the same degree.

    The problem that could occur with these tolerant hybrids is that they might not perform as well as conventional hybrids that are adapted to our region, and in a head-to-head test would not yield as well as a conventional hybrid when aphids are not an issue. If a well-adapted hybrid with no tolerance will yield 10 bu/ A better than a tolerant hybrid if no aphids or low aphid levels occur, you may be a lot better off sticking with the hybrid that yields well and spray for control if needed for aphids. Also, remember that a tolerant hybrid doesn’t mean you won’t get yield reduction, it just means it wouldn’t be as bad as a non-tolerant hybrid.

    There are no crystal balls, and we don’t know what kinds of issues we will have with aphids this year. But, we do know that in many cases one application was needed last year and in some cases two applications were needed for control. You can spray a couple of times and maintain yield with a hybrid that has a good yield history here in Arkansas. One application of one of the aphid insecticides currently available, such as Transform or Sivanto will cost about $10 per acre. In the example above a 10 bu/ A difference will more than cover the cost of one or even two applications for aphid.

    If the tolerant hybrids have a place here in Arkansas we think, at least for this year, it would be in late planted situations and not on grain sorghum planted early. We plan to screen as many varieties this year as we can that are touted to be tolerant and hopefully we will be able to see their fit for production in the years to come. Hopefully, at least some tolerant or resistant hybrid will be a good agronomic fit and provide another tool for sugarcane aphid management.

    Growers have enough issues to deal with this growing season without worrying about sugarcane aphid. If grain sorghum looks like a profitable situation for your operation don’t let sugarcane aphid get in the way. Plant on time, scout closely, spray when needed and you should be successful.

    Aphids that are circled are the common Yellow sugarcane aphids, they are brighter in color. The Sugarcane aphid however is in much greater numbers all around and is a bit lighter in color.

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