The spread of guava root-knot nematode and black rot on sweet potato seed roots has moved both of these problems to locations where they had not been before. In response, the LSU AgCenter plant pathologist Chris Clark has worked to find resistance to each disease. So far, the lines screened for black rot are mostly susceptible, though there are small differences in degree of susceptibility. Screening for guava root-knot nematode resistance began in late 2018 in confinement in a greenhouse and was repeated in early 2019. This has confirmed that the currently grown orange-fleshed cultivars (Bayou Belle, Beauregard, Bellevue, Bonita, Covington, Evangeline and Orleans) are all very susceptible to this nematode even though some are highly resistant to the southern root-knot nematode. Several LSU AgCenter breeding lines that are susceptible to southern root-knot nematode were resistant to guava root-knot nematode, including orange-fleshed 14-117w and 14-123, and purple-fleshed 14-15p and 14-41p. One orange-fleshed line, 14-31, was resistant to both southern root-knot nematode and guava root-knot nematode. Should guava root-knot nematode become established in Louisiana, we have lines that would appear to provide a good stop-gap control, providing the resistance holds up as well in the field as in the greenhouse tests.

A clear objective of the breeding program is to identify lines with the potential to be harvested early. An extra week or two means a grower can extend the harvest season just a bit more and move the new crop to market and processing into french fries, according to Don La Bonte, LSU AgCenter sweet potato breeder. This year is a good example as stockpiles are diminished and prices are robust, so the new crop is in demand. The plot at the field day is about 85 days after planting. Normally we look at 100-110 days as a typical harvest date. One of the intriguing prospects is LA 14-31, a red-skin, slightly round sweet potato line. It has a consistent shape, and so far in plots harvested early has had a nice yield. It also has resistance to southern root-knot nematode and guava root-knot nematode – an emerging concern. The plot has a number of other prospects, one of which might be the next best variety.

Louisiana sweet potato producers have another option for weed management beginning in 2019, according to Donnie Miller, LSU AgCenter weed scientist. Reflex (fomesafen) herbicide received a Section 24(c) Special Local Needs Label for the 2019 growing season. Producers must agree to Syngenta conditions and disclaimers associated with labeling. The application rate is 1 pint per acre with only one pre-transplant application allowed per season. At this rate, Reflex will provide control of a number of small seeded broadleaves including pigweeds and groundcherry. The herbicide will provide partial control of yellow nutsedge. It is to be used as part of an integrated weed management program including herbicides applied post-transplant such as Command and Dual Magnum. Reflex and Valor herbicide cannot be used in the same field in a given season, and because both have similar modes of action, offer little benefit from a resistance management standpoint. Producers are cautioned that tolerance to all varieties has not been evaluated so application to small areas may be best initially. At the time of Reflex application, producers must have in possession of a copy of the label. This can be obtained by visiting the Syngenta website found here.

The discovery of guava root knot nematode infestation on a farm in Morehouse Parish has led to an aggressive response by state regulatory agencies, AgCenter research and extension faculty and growers across the state. Because the soil borne pest is extremely aggressive and can pose a threat to many crops, including sweet potatoes, soybean, cotton and some vegetables, several steps are underway to avoid any spread of the pest. Josielle Rezende with the LSU AgCenter Nematode Laboratory is conducting a survey to collect soil samples from cooperating growers for testing. The guava root knot nematode and common southern root knot nematode species look the same under the microscope, so more extensive DNA testing is required to identify the species and determine its presence. “We want to make sure we don’t have this nematode here. We are hoping we don’t find it; but if we do, this will help us to take steps to avoid the spread and develop management strategies that can be used if this nematode develops into a problem in our future,” Rezende said.

Despite early setbacks, sweet potato growers can expect a timely harvest, said AgCenter extension associate Myrl Sistrunk. Like most Louisiana producers, growers dealt with delayed planting due to wet conditions in the Spring, and subsequent cool nights created slow growing conditions among some varieties. Insect disease and weeds have been manageable throughout the growing season but more chemistries are needed. Beauregard, Orleans and Bayou Belle continue to be the mainstay varieties for Louisiana growers with the largest percentage of the state’s harvest headed to the processing industry. “While some fields did not get harvested last year due to wet conditions, we saw a bump in the average yield of about 100 bushels across the state and it looks like we could be setting up to have another great harvest this year despite the delays,” Sistrunk said. Sweet potato acreage has been on the decline over recent years, largely due to cost of production. The response to the discovery of guava root knot nematode in Louisiana has been aggressive, he said.

Electrical conductivity is widely used in precision agriculture applications in many crop production systems. AgCenter associate professor Luciano Shiratsuchi is conducting experiments using soil electrical conductivity to understand potato yield. Electrical conductivity has been well correlated with grain yield, but little information is available regarding potato yield. Porosity, water content and organic matter are among many parameters that can affect electrical conductivity in the soil. The sweet potato is an additional element in the soil that soil sensors pick up as electrical currents pass through. Shiratsuchi is using numerous methods to collect digital data with a variety of soil sensor technologies to try to predict potato yield.

Several soil insects can be damaging to sweet potatoes. Cucumber beetles or rootworms have been the most prolific and damaging insect pest in recent years, said entomologist and AgCenter Sweet Potato Research Station coordinator Tara Smith. One of the goals of the AgCenter’s sweet potato insect research program is to evaluate various management options in an effort to maximize crop quality. The trial highlighted at Black Gold during the field day evaluates labeled preplant insecticides in conjunction with the producers’ on-farm foliar insecticide management program. In addition, evaluation of advanced lines in the sweet potato breeding program is ongoing to determine inherent levels of resistance to certain insects affecting sweet potato, namely cucumber beetles and the sweetpotato weevil.