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Peanut production acreage has increased substantially in southwest Alabama in the past several years. Since prevailing weather conditions in this newer production area are conducive to peanut diseases, primarily due to frequent rainfall during summer months, a 2-week calendar fungicide treatment schedule is considered essential to controlling leaf spot diseases and rust in order to optimize yields. In 2003, 2004, and 2005, extended calendar application intervals and the AU-Pnuts leaf spot advisory were compared with the recommended 2week calendar schedule for peanut disease control on partially disease-resistant peanut cultivars (DP-1 in 2003 and Florida C99R in 2004 and 2005). Fungicide programs included recommended rates of azoxystrobin, chlorothalonil, and tebuconazole. Numbers of fungicide applications for the 2-, 3-, and 4-week calendar schedule treatments were 7, 5, and 4, respectively in each year. Fungicide applications made according to AU-Pnuts are based on rain events and resulted in 5 sprays in 2003 and 7 sprays in 2004 and 2005. Fungicide application schedule had a significant impact on leaf spots, rust, southern stem rot and yield in at least two of the three study years. Results indicate that recommendations for the 2-week fungicide application schedule should be maintained in this area. Fungicide program also had a consistent effect on measured variables, with the azoxystrobin program providing better disease control and higher yields. Introduction Over the past decade, peanut (Arachis hypogaea) production has expanded into southwest Alabama. This newer production area is approximately 200 mi west of the western edge of the historically important southeastern US peanut production region encompassing southeast Alabama, southwest Georgia, and northwest Florida. Southwest Alabama differs from peanut-production areas to the east in that it is warmer with greater rainfall (24). From May through September, average daily ambient temperature in southwest Alabama is 78.6°F, which is 1°F warmer than southeast Alabama. In addition, rainfall is an almost daily occurrence due to convection thundershowers. 10 November 2006 Plant Health Progress In southwest Alabama, late leaf spot (caused by Cercosporidium personatum) is more common and damaging than early leaf spot (caused by Cercospora arachidicola), although both diseases are damaging (11). Rust (caused by Puccinia arachidis) is also a common disease found on peanut in southwest Alabama (Fig. 1), but is rarely found to the east. In contrast, southern stem rot (SSR; caused by Sclerotium rofsii) does not appear at as high incidence here as the disease does in Alabama’s traditional peanut production counties (2), probably due to cropping history. When not controlled, early and late leaf spot diseases can defoliate peanut and reduce anticipated yield by as much as 50% (27). Peanut rust can also contribute to plant defoliation and pod yield reduction. In the arid tropics and subtropics, rust-related yield losses have been found to be in excess of 50% when no fungicides have been applied to the peanut crop (29). With almost daily afternoon thunderstorms and the occasional tropical storm, an intensive fungicide program is considered essential to protecting peanut in southwest Alabama from damaging outbreaks of late leaf spot, early leaf spot, and rust in order to optimize pod yields. To effectively control these diseases, fungicide applications, which should be initiated 30 to 40 days after planting, must be repeated at 10to 14-day intervals until 2 weeks before the anticipated digging date (30). Depending on rainfall patterns and cultivar selection, often eight fungicide applications are made to a peanut crop. The recommended calendar fungicide program for controlling foliar, stem, and pod diseases can account for nearly 25% of the variable costs in a peanut production budget (1). With the availability of peanut cultivars with partial resistance to early and late leaf spot (3,7,10,12,13,14), reduction of fungicide inputs by lengthening application intervals may be an option for peanut producers. However, lengthening application intervals for chlorothalonil at 1.12 lb a.i./acre from 2to 3-weeks on the partially late leaf spot-resistant peanut cultivar Southern Runner resulted in a significant increase in disease severity (4). In addition, a sizable reduction in yield was seen in one of three years on several partially leaf spot-resistant peanut cultivars when application intervals for chlorothalonil were extended from 2to 3-weeks (4,13). Heavier leaf spot damage was noted on the peanut cultivars Florida C99R, MDR-98, and Georgia Green when they were treated at extended intervals, regardless of fungicide. However, yields were similar with 2and 3-week application intervals when the fungicides used were tebuconazole or azoxystrobin (22). The AU-Pnuts leaf spot advisory can be used for timing fungicide applications, and is an alternative to extending fungicide application intervals in order to reduce fungicide sprays. AU-Pnuts triggers a fungicide application based on the number of accumulated rain events, each with 0.10 inch of rain or irrigation within a 24-hour period, and the 5-day average rainfall forecast (18). Rain events are recorded for this advisory starting at true ground cracking when seedlings first emerge. Regardless of the 5-day average rainfall forecast, the first fungicide application must be made no later than the sixth rain event. Beginning 10 days after that, and for each subsequent fungicide application, additional applications are triggered: (a) after three rain events, (b) when the 5-day average rainfall forecast is ≥ 50%, or (c) when one or two rain events have been recorded and chance of rain in the 5-day forecast is ≥ 40% or ≥ 20%, respectively (18). Studies with the susceptible cultivar Florunner demonstrated that an average of 1.25 applications of chlorothanil per year were saved with AU-Pnuts scheduling compared to 2-week application intervals (18). Thresholds for fungicide application were adjusted for the partially leaf spot-resistant cultivar Southern Runner, and up to 2.5 applications were saved (17). Brenneman and Culbreath (4) noted a reduction of two fungicide applications in two of three years Fig. 1. Section of row in peanut plot showing damage from peanut rust. 10 November 2006 Plant Health Progress using AU-Pnuts compared to the standard 2-week calendar schedule. A similar reduction in fungicide applications was observed with scheduling azoxystrobin applications using AU-Pnuts by Hagan et al. (12), but there was an increased risk of inadequate control of early leaf spot and yield loss. These previous studies with AU-Pnuts were conducted in southwest Georgia and southeast Alabama. The objective of this study was to compare the effectiveness of 2-, 3-, and 4week calendar application schedules to the AU-Pnuts leaf spot advisory in the newer production area of southwest Alabama. The study also evaluates three fungicide programs that include azoxystrobin, tebuconazole, and chlorothalonil for control of leaf spots and rust. These studies were conducted using partially disease-resistant peanut cultivars. Production Methods Peanuts (Arachis hypogaea L.) were planted on 28 May 2003, 13 May 2004, and 12 May 2005 at the rate of 6 seed/ft of row in a field at the Gulf Coast Research and Extension Center, Fairhope, Baldwin County, AL. The latematuring (maturity group 5) runner peanut cultivar DP-1, which was planted in 2003, was replaced with the late-maturing (maturity group 5) cultivar Florida C99R in 2004 and 2005. Both of these cultivars are partially resistant to early and late leaf spot, as well as southern stem rot (7,10,15). The test sites are maintained in a cotton-cotton-peanut rotation. The soil type is a Malbis fine sandy loam (fine-loamy, siliceous, thermic Plinthic Paleudults) with less than 1% organic matter. The test site was prepared for planting with a disk harrow and ripper/hipper. Optimal soil fertility and pH were maintained according to the results of a soil fertility assay conducted by the Soil Testing Laboratory at Auburn University (16). Broadleaf and grass weeds were controlled by lightly incorporating a preemergence application of pendimethalin (Prowl 3.3, BASF, Research Triangle, NC) at 0.82 lb a.i./acre with a disk harrow. Newly emerged weeds were controlled with an application of paraquat (Gramoxone Maxx 3.0, Syngenta Crop Protection, Greensboro NC) at 0.11 lb a.i./acre of + bentazone at 0.33 lb a.i./acre + aciflurofen (Storm 4L, United Phosphorus Inc., Trenton, NJ] at 0.16 lb a.i./acre + Activate (Agriliance LLC, St. Paul, MN) non-ionic surfactant at 0.23 oz/gal of spray volume about 5 to 7 days after ground cracking. In 2005, 2,4 DB (Butyrac 200, Agri Star Inc., Ankey, IA) at 0.24 lb a.i./acre + paraquat 0.11 lb a.i./acre + a premix of bentazone (0.33 lb a.i./acre) + aciflurofen (0.16 lb a.i./acre) + Induce wetter/spread adjuvant (Helena Chemical Company, Collierville, TN) at 0.76 oz/gal of spray volume was applied. Sethoxydim (Poast Plus 1EC, BASF, Research Triangle, NC) at 0.17 lb a.i./acre + Prime Oil at 0.12 gal/acre was applied to control escape grass weeds on 25 June 2003. Imazapic (Cadre 70DG, BASF, Research Triangle, NC) at 0.06 lb a.i./acre + Activate surfactant at 0.20 oz/gal of spray volume was made on 11 July 2003 for broadleaf and nutsedge control. On 27 June 2005, imazapic at 0.04 lb a.i./acre + diclosulam (Strongarm 84WDG, Dow AgroSciences, Indianapolis, IN) at 0.14 lb a.i./acre at 0.3 oz/acre + Induce wetter/spreader adjuvant at 0.8 oz/gal of spray volume was broadcast to control escaped broadleaf weeds. In addition, escape weeds were pulled by hand. Aldicarb (Temik 15G, Bayer CropScience, Kansas City, MO) at 1 lb a.i./acre was applied in-furrow at planting to control thrips. The test sites were not irrigated. Plots were inverted on 18 October 2003, 18 October 2004, and 10 October 2005. Wind

Calendar and AU-Pnuts Advisory Programs Compared for Leaf Spot Diseases and Rust Control on Peanut in Southwest Alabama