[dropcap]I[/dropcap]n 2016, losses to tomato spotted wilt across the peanut production region of the Southeastern United States increased slightly compared to losses from 2015. Losses associated with spotted wilt were approximately 3 percent in 2015 and 3.5 percent in 2016, though tomato spotted wilt was more severe in some fields than in others. Also, tomato spotted wilt was less severe in Mississippi and the panhandle of Florida and more severe in South Carolina and parts of Georgia.
Growers can successfully manage this disease, and other important diseases, using Peanut Rx. This disease risk index can help growers better understand how careful selection of production practices can reduce the risk to disease losses.
Peanut Rx allows growers to assess their risk to tomato spotted wilt, leaf spot diseases and white mold. It also notes which varieties have some resistance or increased susceptibility to the peanut root-knot nematode (Meloidogyne arenaria), Cylindrocladium black rot (CBR) and Rhizoctonia limb rot. The 2017 version of Peanut Rx has been fully reviewed and updated by the authors based upon data and observations from the 2016 field season.
Updates For 2017
Most of the updates to Peanut Rx 2016 from the 2015 version can be found in the cultivar/variety section. Also, risk points have been adjusted for leaf spot under the “planting date” category to better reflect our better understanding of the relationship between later planting dates and increased risk to leaf spot. The planting date ranges have been adjusted slightly.
With additional data, risk points for spotted wilt assigned to variety TUFRunner™ ‘297’ have been reduced from 15 to 10.
Two new varieties have been added to the 2017 version of Peanut Rx; both have high oleic chemistries. These varieties include runner-type FloRun™ ‘157’ and Virginia-type Sullivan.
Varieties Georgia Greener and TUFRunner™ ‘727’ have been removed from the index for 2017 because seed is generally no longer commercially available for these varieties.
As in the previous versions of the Disease Index, growers will note that attention to variety selection, planting date, plant population, good crop rotation, tillage and other factors, has a tremendous impact on the potential for diseases in a field.
Plant Population Change
In the 2017 version of Peanut Rx, peanut varieties with a risk of TSWV at 25 points or less have a reduced risk (10 points) when planted at 3 to 4 seeds per foot than do varieties with a risk of 30 points or greater (15 points). This is based upon recent research conducted at the University of Georgia by Dr. Scott Tubbs.
Plant population has less effect on fungal diseases than on spotted wilt. However, it is now known that the severity of white mold increases when the space between the crowns of individual plants decreases. This is because the shorter spacing allows for greater spread of the white mold fungus, Sclerotium rolfsii.
Note On Planting Date
Plant peanuts only in conditions conducive to rapid, uniform emergence. Less than optimum conditions at planting can result in poor stands or delayed, staggered emergence, both of which can contribute to increased spotted wilt.
Because of the reduction of tomato spotted wilt in recent years, the increased resistance in new varieties and the need for timely harvest of the peanut crop, growers may consider planting a portion of their crop in April, assuming the risk to tomato spitted wilt is appropriately managed. Growers who plant the more resistant peanut varieties in the latter part of April should not be at a significant risk to losses from tomato spotted wilt in the 2017 season.
To read the complete 2017 Peanut Rx and for other information on minimizing disease in peanuts, visit www.ugapeanuts.com or contact your state Extension plant pathologist or local Extension agent.
Severity of white mold increases when the space between the crowns of individual plants decreases, which allows for greater spread of the fungus.
In a year in which the dry weather should have been an environment resulting in less disease presence, many producers experienced problematic leaf spot and underground white mold. Factors contributing to this unexpected result include poor peanut field rotations, a response to low commodity prices, and a possible decline in efficacy to fungicides. Varietal changes may also be a factor.