Be on guard against these developing forage insect pests in Missouri

  • Published: Thursday, March 5, 2020

Agricultural insect pests seem to develop when we least expect them according to Tim Schnakenberg, a field specialist in agronomy with University of Missouri Extension.

“There are the perennial pests like alfalfa weevils and armyworms,” said Schnakenberg. “But, there are a few new ones that have the potential to become regular invaders of our pastures.”

Being on guard for pests is more important than ever.  Insect invasions used to be more gradual because the transportation system across America was much slower. Today, pests can hop onto an airplane shipment and be at our doorsteps in short order.
    
According to Schnakenberg, there are several insects that producers should be on guard against in 2020.  

Schnakenberg started noticing significant sugar cane aphid populations in late season sudangrass and forage sorghums in 2016, specifically around Stone and Christian counties.  

“The aphid populations would be so intense that late-season harvests of forage sorghum fields would be severely reduced or destroyed.  Sometimes the problem would be minimal 20 miles away,” said Schankenberg.

Sugar cane aphids are yellow. They congregate on the stems and leaves of individual plants by the hundreds, sucking life out of the plant. These insects have moved in from the southern states.

Traditional insecticides are not effective for control.  Transform WG and Silvanto 200SL are the only products that seem to work. These are generally legal for grain sorghum and can be used in a forage situation. 

“The most practical way to deal with this pest is to convert acreage to one of the millets, which do not appear to be affected by the aphid.  Many growers I have worked with have made this switch,” said Schnakenberg.

The bermudagrass stem maggot is new to the area and impacts bermudagrass growers.

“I first saw it in Barry County in 2019.  Other southern Missouri agronomists have been finding it as well for a couple of years.  Gulf states bermudagrass growers have dealt with it for several years,” said Schankenberg.

Like sugar cane aphid, the stem maggot seems to be an issue with mid-late season growth and can cause yields to taper off quickly.  The first sign of infestation appears when the upper terminal leaves look like they have been frosted and die.  

Closer examination inside the stem reveals a small white maggot feeding.  This maggot originated from a fly that laid eggs on the plant a few weeks before.  

The standard threshold for control used in the southern states is to spray with an insecticide 7-10 days following the previous hay harvest or grazing.  Fortunately, inexpensive pyrethroid insecticides can be effective on this insect if applied at the right time.   

“Routine insecticide use in bermudagrass stands is not a desirable practice by most producers,” said Schnakenberg.

Two other pests have the potential to have a negative impact in southwest Missouri shortly according to Schankenberg.

The Brown Marmorated Stinkbug feeds on many plants, including alfalfa.  It is moving in from the northeast states and is now found in seven counties in Missouri, including Greene County.  

The spotted lanternfly, which can have a devasting effect on vineyard owners and walnut growers, also deserves our attention.

“Lanternflies are in the northeastern states but they have been known to lay eggs on metal surfaces like trains and truck trailers which means they could arrive quicker than expected into Missouri,” said Schankenberg.
 
Invasive insect species are nothing new.  If you see something that is questionable or new in your forage or row crop, please contact any MU Extension field specialist in agronomy or an entomologist with the Missouri Department of Agriculture.

For more information, contact any of these MU Extension agronomy specialists in southwest Missouri: Tim Schnakenberg in Stone County, (417) 357-6812; Jill Scheidt in Barton County, (417) 682-3579 and Sarah Kenyon in Howell County, (417) 256-2391. 
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Writer: David Burton

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