No‐Till Seeding of Grazing‐Tolerant Alfalfa as Influenced by Grass Suppression, Fungicide, and Insecticide

Abstract

No‐till planting of grazing‐tolerant alfalfa ( Medicago sativa L.) offers an opportunity to improve the nutritive quality and seasonal production of endophyte‐infected tall fescue ( Festuca arundinacea Schreb.) but grass competition and pest problems reduce dependable alfalfa establishment in the southeastern USA. The objectives of this research were to study the following effects on no‐till establishment and yield of ‘Alfagraze’ alfalfa: (i) grass suppression and insecticide and fungicide application with September‐planted alfalfa, and (ii) fungicide application date for September and March plantings. Sixteen field experiments were conducted in the limestone valley area near Calhoun, GA, and in the mountains at Blairsville, GA, over 3 yr. Alfagraze alfalfa was no‐till planted in September and paraquat (used as a herbicide) grass suppressant, vinclozolin [3‐(3,5‐dichlorophenyl)‐5‐ethenyl‐5‐methyl‐2,4‐oxazolidinedione] fungicide, and chlorpyrifos [O,O‐diethyl O‐(3,5,6‐trichloro‐2‐pyridinyl) phosphorothioate] insecticide were applied alone and in all combinations to compare alfalfa stand and yield with that of a nontreated check. The effect of fungicide application dates on alfalfa forage yield and stand when planted in September or in March were determined in additional experiments. Sod suppression in September was necessary to obtain good alfalfa stands. Insecticide application had little effect on yield. In 2 out of 3 yr at both locations, there was a significant ( P < 0.05) response to suppressant and fungicide. For September‐planted alfalfa, monthly fungicide application improved forage yield, indicating substantial control of fungal diseases, primarily crown and stem rot caused by Sclerotinia trifoliorum Eriks. In 2 out of 3 yr at two locations, alfalfa yields increased from 48 to 89% with monthly fungicide application on September plantings. March no‐till planting resulted in poorer stands and lower alfalfa yields than September planting. Grass suppression was beneficial in no‐till planting of alfalfa in northern Georgia. Autumn was superior to winter plant‐ing despite potential disease losses in no‐till planted alfalfa. Research Question No‐till seeding of alfalfa into grass sods is generally less dependable than planting in prepared seedbeds, probably because of grass competition and greater pest problems. The present study evaluated the effects on establishment and yield of no‐till seeded Alfagraze alfalfa at two north Georgia locations of: (i) grass suppression, insecticide, and fungicide application on September‐planted alfalfa, and (ii) fungicide application date on alfalfa establishment and yield from September and March plantings. Literature Summary No‐till seeding of alfalfa in grass sods in the upper South and lower Midwest of the USA is generally more successful when carried out in late winter or spring than late summer or autumn because of less disease loss, primarily crown and stem rot. The impact of crown and stem rot on stand and forage yield of alfalfa no‐till seeded in autumn vs. late winter has not been determined in the lower Southeastern USA. Grass suppression has been especially helpful in no‐till seeding of alfalfa but insecticide application has given only small improvement. Study Description Sixteen field experiments were conducted over 3 yr at Blairsville (2300 ft elevation) and Calhoun (640 ft) in northern Georgia. Alfagraze alfalfa was no‐till planted in September and paraquat grass suppressant, vinclozolin fungicide, and chlorpyrifos insecticide were applied alone and in all combinations to compare alfalfa stand and yield with that of an untreated check. Another set of experiments studied the effect of fungicide application dates on alfalfa stand and yield when planted in September and March. Applied Questions How did grass suppression affect no‐till planted alfalfa? As in previous studies, grass suppression with a herbicide was important in getting good alfalfa stands and forage yields. Disease control with a fungicide was effective only where the grass was suppressed, possibly because nonsuppressed grass continued to grow and provide a more favorable environment for fungal development and, in the case of crown and stem rot, also may have prevented direct contact of the fungicide with the sclerotia. How did insecticide affect no‐till planted alfalfa? Insecticide applications had little effect on stands or yield, indicating that insects were a minor factor. How did fungicide application affect alfalfa? Monthly fungicide application was used to assess the impact of disease on establishment and yield of alfalfa. We assumed that the major effect of the fungicide was on limiting crown and stem rot development so the yields of untreated sod may indicate the losses incurred from this disease. In 2 out of 3 yr at two locations, alfalfa yield losses ranged from 28% in a drought year to 89% in a more normal rainfall year. The lack of response to fungicide application during 1 yr at both locations indicates that weather and the sclerotia reservoir in the soil greatly affect development of crown and stem rot. What was the effect of September vs. March planting dates? September plantings were superior. The lower yields from March planting at Calhoun may be a result of hot, dry late spring and summer weather which often occurs, making it difficult for alfalfa seedlings to compete with tall fescue. In contrast, the cooler temperature and higher rainfall of the mountain location should have been more favorable but excessive competition from volunteer weeds resulted in no advantage for March planting. Recommendation Risk is inherent in no‐till establishment of alfalfa. In areas with a history of fungal diseases in legumes, it may be necessary to plant alfalfa in late winter. However, autumn planting offers the potential of better stands and substantially higher first year forage yields. This appears to be especially true at lower elevations in the lower southeastern USA where hot and dry late spring and summer conditions often reduce late winter planted alfalfa stands and forage yields.

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