Evaluation of a Weather-Based Spray Advisory for Management of Early Leaf Spot of Peanut in Oklahoma1

Abstract

A simplified version of the weather-based advisory program developed by Pawin, Smith, and Crosby (PSC) for scheduling fungicide sprays for management of early l e d spot (Cercospora arachidicoh Hori) of peanut (Arachis hypogea L.) was evaluated under various productions systems in Oklahoma from 1990-1992. Over eight trials with spanish cultivars, the number of sprays per season averaged 5.7 for the 14-d schedule and 4.0 for the advisory program. Final disease incidence (symptomatic and defoliated leaflets) with the fungicide chlorothalonil (1.26 k@a) averaged 15% for the 14-d schedule, 34% for the advisoryprogram, and 77% for the control. However, disease incidence (75%) and defoliation (!jO%) approached unacceptable levels on the Spanish cultivars in some trials. In six trials with runner cultivars, the number of sprays averaged 6.7 for the 14-d schedule and 4.7 for the advisory program. Final disease incidence with chlorothalonil on the runner cultivars averaged 5% for the 14-d schedule, 14% for the advisory program, and 68% in the control. Yields did not differ in any of the 14 trials between the advisory and 14-d programs using chlorothalonil. Yields averaged 3015,3003, and2303 kg/ha for Spanish cultivars and 4108, 3855, and 3066 kg/ha for runner cultivars with the 14-d schedule, advisory program, and control, respectively. The advisory program was effective in irrigated trials where weather stations were deployed either under or outside the influence of irrigation. The fungicides tebuconazole at 0.14 k@a and propiconazole at 0.13 kg/ ha generally provided better leaf spot control with the advisory program than chlorothalonil. The post-infection activity of these fungicides was observed in one trial and probably accounts for their improved performance. Yields were reduced and leafspot incidence was high where tank mixes of benomyl(O.28 kg/ha) or thiophanatemethyl (0.38 k@a) plus mancozeb (1.68 kg/ha) were used with the advisory program. Area under the disease progress curve, leaf spot incidence, and defoliation in the controls were lower for runner than for Spanish cultivars at sites where both market types were planted in adjacent trials. Fungicides applied according to the advisory program provided better leaf spot control on the runner cultivars. Results showed the need for a weather-based advisory which allows greater levels of leafspot control on Spanish cultivars than the PSC advisory.'Approved for publication by the Director, Oklahoma Agric. Exp. Stn. This study was funded in part by Hatch project

Weather-based Pest Forecasting for Efficient Crop Protection

“…In addition to temperature and precipitation, relative humidity is another weather variable that has been shown in many studies to be related to the development of fungal pathogens (Damicone et al, 1994;Boyle, 1965, 1966;Jewell, 1987;Olatinwo et al, 2008Olatinwo et al, , 2009Olatinwo et al, , 2011Shew et al, 1988;Wu et al, 1999). In monitoring the likelihood of infection initiation through sporulation of fungal spores, the available moisture on a leaf surface can be estimated using relative humidity, since it correlates with wetness of a leaf surface within a canopy.…”

“…Examples of internetbased interactive systems include the potato late blight in Michigan (http://www.lateblight. org/forecasting.php) described by Wharton et al (2008); the AWIS Weather Services, Inc (http://awis.com); the Oklahoma mesonet peanut leaf spot advisor (http://www.mesonet.org/index.php/agriculture/category/ crop/peanut/leaf_spot_advisor) based on a model described by Damicone et al (1994); North American Plant Disease Forecast Center, North Carolina State University (http://cdm. ipmpipe.org/); HortPlus (http://www.hortplus.com/Brochure/MetWatch/MWSoftware.…”

“…Jewell (1987) identified a strong correlation between early leaf spot incidence and cumulative hours of relative humidity (RH ≥ 95). The Oklahoma peanut leaf spot model described by Damicone et al (1994) calculates the daily 'infection hours' based on 24 h of temperature, and leaf wetness or relative humidity. According to Grichar et al (2005), other systems have used a similar combination of relative humidity/leaf wetness and temperature to forecast favourable conditions for disease development and scheduling of fungicide applications.…”

Predicting favorable conditions for early leaf spot of peanut using output from the Weather Research and Forecasting (WRF) model

“…Use of weather information in most models is typically obtained from several sources, including the National Weather Service or observational weather networks such as the Automated Environmental Monitoring Network (AEMN; www.georgiaweather.net), which is the largest automated weather station network in the southeastern USA (Hoogenboom 2000(Hoogenboom , 2001Hoogenboom et al 2003). Weather observations from similar regional networks have been used in disease prediction models, as documented in many studies including for potato light blight in Michigan (Wharton et al 2008), peanut leaf spot in Oklahoma (Damicone et al 1994), and as a web-based tool for risk assessment of Fusarium head blight (http:// www.wheatscab.psu.edu).…”

“…The study also confirmed a correlation between leaf spot and a weatherdependent infection index previously described by Jensen and Boyle (1966). Some disease models including the Oklahoma peanut leaf spot model developed by Damicone et al (1994) were based in part on the earlier work of Jensen and Boyle (1966). The Oklahoma peanut leaf spot model calculates the daily "infection hours" based on 24 h of temperature, and leaf wetness or relative humidity.…”