Field trials were conducted in Texas during 2001 at Pearsall and 2002 at Yoakum to determine cultivar responses to certain foliar and soilborne diseases in single row (91 cm) vs. twin-row (rows spaced 18 cm on 91-cm centers) patterns and sprayed four times with tebuconazole at 0.23 kg ai/ha or twice with azoxystrobin at 0.34 kg ai/ha. Azoxystrobin and tebuconazole controlled southern stem rot similarly. Tebuconazole controlled rust more effectively than azoxystrobin. In 2002, early leaf spot severity was high and disease control was less than desirable with both fungicides, but still better than the nontreated plots. Both fungicides reduced early leaf spot severity in the single and twin-row patterns when compared to nontreated plots. Early leaf spot severity in the nontreated plots was greater in the twin-row pattern compared to the single row pattern. Tamrun 96 yielded better than any of the other cultivars in the study and showed less southern stem rot than all other cultivars when averaged across fungicide treatments and row spacing. Tebuconazole and azoxystrobin increased yield compared to nontreated control. No significant differences in yield occurred between fungicide treatments. The twin-row pattern showed a yield increase compared to the single row pattern when averaged across cultivar and fungicide treatments.
Foliar and soilborne diseases can severely affect yield and quality of peanut.
Control of early leaf spot includes the use of fungicides and cultural practices. Until recently, south Texas growers relied on the use of chlorathalonil for control of early leaf spot. Chlorothalonil does not control soilborne pathogens, resulting in the need for additional fungicides to control southern stem rot (caused by
Much like early leaf spot, rust (caused by
Southern stem rot is a soilborne disease that south Texas growers have to manage every growing season. Southern stem rot is greatly influenced by moisture (
The development of peanut fungicides over the last 5 to 10 yr has given growers additional options in controlling early leaf spot, rust, and southern stem rot. In Georgia, tebuconazole controlled southern stem rot when applied multiple times as a foliar spray (
Azoxystrobin controls leaf spot and southern stem rot similar to tebuconazole (
Little research documents the effects of a twin-row planting pattern on the development of foliar and soilborne diseases in conjunction with fungicides. Growers in south Texas have been slow to adopt twin-rows because of concerns that a quicker canopy closure may increase the risk of damage by soil and foliar diseases from favorable microclimate conditions.
The objective of this study was to evaluate the response of four runner-type cultivars to disease development (southern stem rot, early leaf spot, and rust), pod yield, and quality when sprayed with azoxystrobin and tebuconazole and planted in single and twin-row planting patterns. To exclusively determine season-long disease control with these two fungicides, chlorothalonil was not applied to test areas. However, alternate use of fungicides with different modes of action should be used commercially to minimize risk of disease tolerance to azoxystrobin or tebuconazole.
Field studies were conducted in Texas during 2001 near Pearsall and 2002 at the Texas Agric. Exp. Sta. near Yoakum. Soil at the Pearsall location was a Duval very fine sand (fine-loamy, mixed, hyperthermic Aridic Haplustalfs) with less than 1% organic matter. Soil at Yoakum was a Straber loamy sand (fine mixed thermic Aquic Palenstalfs) with less than 1% organic matter. The test site in Pearsall was in a 2-yr crop rotation with corn and grain sorghum while the Yoakum site was in continuous peanut for more than 5 yr. Both sites had a known history of leaf spot and southern stem rot disease incidence. The runner-type cultivars AT 1-1, Flavor Runner 458, Georgia Green, and Tamrun 96 were planted on 30 May 2001 and 3 Jun 2002. Seed of each cultivar was planted with a Monosem precision vacuum planter (Monosem ATI, Inc., Lenoxa, KS). Number of seeds per meter on a bed were held constant for both the single and twin-row patterns to achieve approximately 87 and 120,000 plants/ha, respectively. The experimental design was a split-split plot arrangement with three replications. Whole plots consisted of cultivars, fungicide treatments represented the split-plot, and row patterns represented split-split plots. Plot size was two rows × 7.6 m long.
Azoxystrobin (Syngenta, Greensboro, NC) at 0.34 kg/ha was applied 62 and 90 DAP in 2001 and 59 and 87 DAP in 2002. Tebuconazole (Bayer Crop Sciences, Research Triangle Park, NC) at 0.23 kg/ha was applied 62, 76, 90, and 105 DAP in 2001 and 59, 73, 87, and 102 DAP in 2002. Fungicides were applied with a CO2-pressurized backpack sprayer with D3-13 hollowcone nozzles delivering 187 L/ha. Rust only developed in 2001 at Pearsall and was evaluated using the Intl. Crops Res. Inst. for the Semi-Arid Tropics (ICRISAT) scale of 1 to 9 (where 1 = no disease and 9 = plants severely affected) and 50 to 100% of the leaves are withering (
Peanuts were dug on 19 Oct. 2001 and 15 Oct. 2002, allowed to field dry 5 to 7 d, and then harvested using a power-take-off driven combine. Plot weights were taken after all foreign matter was removed. Analysis of variance (ANOVA) was performed on southern stem rot disease incidence and peanut yield to test the effect of year, row pattern, fungicide treatments and all possible interactions. All main effects and possible interactions were analyzed for rust and early leaf spot for the year when these diseases occurred. Mean separation was then calculated using Fisher's Protected LSD test (P ≤ 0.05).
Data for southern stem rot and yield were combined over years due to lack of year × treatment interaction (
Southern stem rot incidence was lower when azoxystrobin and tebuconazole were applied regardless of row pattern or cultivar compared with the nontreated control (
Azoxystrobin and tebuconazole reduced rust when compared to the nontreated control (
Early leaf spot severity was extremely high in 2002 when fungicides were not applied (
Each cultivar displayed a high level of early leaf spot incidence (
When averaged across row patterns and cultivar, pod yields were higher when azoxystrobin and tebuconazole were applied when compared with the nontreated peanut (
Row pattern effects on yield revealed that the twin-row pattern was significantly higher in yield then the single row pattern (
This study revealed that azoxystrobin and tebuconazole effectively controlled both southern stem rot and rust but was not as effective for control of early leaf spot. Azoxystrobin and tebuconazole were applied two and four times, respectively, throughout the growing season. Because leaf spot severity was high, additional fungicide applications would be required for better control. This study also revealed that Tamrun 96 was lower in southern stem rot incidence than AT 1–1, Flavor Runner 458, and Georgia Green. Therefore, growers who have fields with a history of southern stem rot may benefit by planting this cultivar. Peanuts planted in a twin-row pattern had higher yields than peanuts planted in a single row pattern when averaged across cultivar and fungicides. Based on these findings, there may be an advantage to planting twin-rows to increase yield.
The authors would like to express their appreciation to Kevin Brewer, Bill Klesel, and Dwayne Drozd for their assistant in data collection and plot harvesting. We would also like to thank the Texas Peanut Producers Board for their partial support of this research.
1 Sr. Res. Assoc., Res. Scien., and Sr. Res. Assoc., Texas Agric. Exp. Sta., Yoakum, TX 77995.
2 Prof., Dept. Plant Path. and Microbiology; Assoc. Prof. and Prof., Dept. Soil and Crop Sci., Texas A&M Univ., College Station, TX 77843.