There have been many articles written on sugarcane aphids (SCA) and grain sorghum, but very few on SCA and forage sorghums. In grain sorghum we have come a long way in developing sound management practices for dealing with SCA; however, forage sorghum in many ways is a completely different crop.

The downward trend of having to apply an insecticide to control SCA continued in 2020. Where hot spots occurred, growers acted quickly to protect their crop. In most cases, a single insecticide application was sufficient to provide season-long control. The exception was in silage sorghum where, in a few fields, a second application was required. These outbreaks were typically in fields where a particularly susceptible hybrid was planted.

In grain sorghum, planting a tolerant hybrid in regions where SCA are a potential annual problem is often the first step many growers take to manage the aphid. Most seed companies now have several SCA-tolerant grain sorghum hybrid options, and these hybrids are getting better all the time.

Unfortunately, with forage sorghum, there are only a few hybrids with a significant tolerance that have been identified. With the exception of these few, at best, all we can say is that certain hybrids are less susceptible than others. On a positive note, companies have been working to incorporate SCA tolerance into their forage sorghum, particularly those used for silage. It is expected that SCA-tolerant silage sorghum hybrids will be introduced to the market over the next couple of years.

In sorghum silage, Texas A&M University research has shown yield can be reduced as much as 40 percent prior to sorghum flowering if a high infestation of SCA occurs and is left uncontrolled.(1) Additionally, quality of the silage is reduced, primarily because of a reduction in starch. Both yield and quality are affected much less if the SCA infestation occurs after  the grain milk stage. However, late infestations can produce honey dew in sufficient quantities that could interfere with harvest.

The insecticides labeled and most recommended for use in forage sorghum are the same as those used in grain sorghum. These are Corteva’s Transform and Bayer’s Sivanto Prime, and its soon-to-be replacement, Sivanto HL. The label for Sivanto HL includes soil applied application. This is new and will be especially useful in forage sorghum. A third product, Sefina from BASF, recently received a federal label for sorghum with state labels expected soon.

Management Practices to Avoid or Minimize SCA Damage

Sorghum Silage

• Plant early with an early maturing hybrid. Hope to harvest prior to SCA infesting the field.
• Avoid planting in narrow rows. Use at least a 30-inch row, which allows better coverage if an insecticide application is needed.
• Insecticide coverage is critical. If SCA populations are beginning to increase prior to canopy closure, consider making an insecticide application even if levels have not yet reached an economic threshold.
• Consider applying by chemigation (labeled for Sivanto) when possible for improved insecticide coverage.
• In regions where SCA infestations are a regular occurrence, consider applying Sivanto HL in the seed furrow at planting or other soil application methods as stated on the label.

Sorghum Sudangrass Hay

• In regions where early season SCA infestation may occur, consider using an insecticide seed treatment such as Cruiser, Poncho or Gaucho, which will provide early season control, normally for 40-45 days. This is especially important if the planting date is delayed.
• If SCA infestation occurs and canopy closure is such that good insecticide application coverage cannot be achieved, consider harvesting early and monitoring regrowth forage for SCA. Apply an insecticide as needed prior to canopy closure.

Grazing

• Using good management grazing practices will go a long way in managing SCA. This means turning cattle out to graze sorghum that is no taller than 40 inches or approximately 40 days after emergence. Rotational grazing should also be an effective management tool.
• If SCA infestation levels begin to build, consider treating as soon as possible to achieve good insecticide coverage. High levels of SCA will result in moldy leaves and cattle will avoid grazing these areas leading to wasted forage.
• There is a seven-day grazing restriction following a Transform or Sivanto application.

Reference:

(1) Ed Bynum and Jourdan Bell. 2019. Sugarcane Aphid Damage to Forage Sorghum Silage Yield and Quality induced by different Infestation Levels for the Texas High Plains. TGSP Final Report. https://www.sorghumcheckoff.com/for-farmers/forage-production/.

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This story originally appeared in the Fall 2020 Issue of Sorghum Grower magazine the From the Field department.