Sugarcane Beetle Reported in Sweetpotato.

This week marked the first reported appearances of sugarcane beetles in sweetpotato fields in Mississippi for the 2013 growing season.  The sugarcane beetle is a relatively new pest of sweetpotato in Mississippi.  However, in recent years, heavy sugarcane beetle populations have caused significant losses for some growers in Louisiana, as roots with sugarcane beetle damage are unmarketable.  Unfortunately, compared to other insect pests of sweetpotato, relatively little is known about the sugarcane beetle.  Here is what we do know:

Identification:  Adult sugarcane beetles are stout, dull black, and approximately ½â€ long (Figure 1).  Their well-developed forelegs are designed to enable the insect to burrow into the soil.

Life Cycle:  Adult beetles overwinter, emerge in the spring, and mate/lay eggs in the soil in early summer.  Larvae develop in the soil over a period of about two months and feed on decaying plant matter.  The beetles transition from larvae to pupae and remain in the pupal stage for approximately two weeks.  Pupae become adults, and the adults emerge late August through September.

Crop Hosts:  Sugarcane beetles are documented to be a pest of sweetpotato, rice, sugarcane, corn, strawberry, and turf.

Damage:  The sugarcane beetle differs from most sweetpotato pests in that the adult insects, not the larvae, are the predominant injury-causing life stage.  Adult beetles feed on enlarged storage roots and create “ragged holes” and channels, rendering affected roots unmarketable (Figure 2).

Management:  Control options for sugarcane beetle are limited.  There is some evidence suggesting that incidence of sugarcane beetle injury are greater in sweetpotato fields near hay fields or pasture.  Ensuring that sweetpotatoes are not planted  adjacently to hay fields and pasture may be helpful.  However, sugarcane beetles are mobile and research has not determined how far the insects may travel.  If fields have experienced sugarcane beetle injury in previous growing seasons, growers may opt to plant those fields first- doing so can allow for an earlier harvest and will remove the storage roots from the field before adults emerge and begin feeding.

The current best recommendation for chemical control of sugarcane beetle is 12 oz of Belay preplant-incorporated.  Foliar insecticide applications late in the season or near harvest have not been affective.  The beetles can burrow into the soil quickly and avoid contact with the applied insecticide.  While sugarcane beetles appear to be susceptible to pyrethroid insecticides, there is currently no proven method of ensuring that the beetles actually come in contact with the insecticide.  Given what we presently know, there is no benefit of a late-season insecticide application for sugarcane beetle control.

Finally, it is advisable to be diligent in keeping sugarcane beetles out of the bin boxes as beetles will continue to feed on roots in the bin.

Now What?:  Researchers at land-grant universities in sweetpotato growing states as well and USDA have on-going research to learn more about the sugarcane beetle and the best means of controlling it.  If you suspect that you have a commercial sweetpotato field in Mississippi with sugarcane beetle, please contact Stephen Meyers (smeyers@ext.msstate.edu or 662-489-4621).  Sugarcane beetles congregate near light sources at night making night an ideal time to scout for the pest.  For those growers with sugarcane beetle injury, sharing the answers to the following questions will help researchers develop an improved management strategy moving forward:

What was the previous crop?

What is immediately adjacent to the damaged field (ditch banks, pasture land, hardwood or pine forest, agronomic crops)?

What insecticides were applied and when, how, and at what rate were they applied?

What weeds are present in the field?

For more information about sugarcane beetle in sweetpotatoes, visit the LSU-AgCenter Sweetpotato page at: http://www.lsuagcenter.com/en/our_offices/research_stations/Sweetpotato/Features/publications/

Photos courtesy of Tara Smith, LSU-AgCenter.