Influence of postdormancy development on herbicide scheduling for control of dandelion in turf
Abstract
Early spring control of dandelion (Taraxacum officinale Weber) in turf has been inconsistent among years when postemergence herbicide applications are scheduled by calendar date. Mobilization of taproot reserves to support early postdormancy shoot growth increases acropetal phloem transport and may inhibit basipetal transport of herbicide in toxic amounts. The objectives of this research were to identify a growing degree-day (GDD) threshold that would provide consistent, acceptable ($\ge$80%) control of dandelion, test the relationship between assimilate transport and herbicide efficacy, and improve herbicide scheduling using GDD. The dimethylamine salt or the butoxyethyl ester of 2,4-D + 2,4-DP was applied postemergence to dandelions in field and growth chamber studies at 2.07 kg ae ha$\sp{-1}$ in 786 L water ha$\sp{-1}$ at predetermined thresholds between 25 and 185 GDD, base 10$\sp0$C (GDD$\sb{10}$ ($\sp0$C)). The fluorescent, phloem-mobile tracer 5(6) carboxyfluorescein (CF) was monitored in phloem of crown, petiole, and taproot at 6, 12, 24, 48, and 96 h after introduction of its acylated precursor into dandelion leaves at 35, 65, 95, 125, 155, or 185 GDD$\sb{10}$ ($\sp0$C) in 1996. Thresholds for $\ge$80% dandelion control in field studies were identified at 81 (27 April), 55 (8 April), and 68 (18 March) GDD$\sb{10}$ ($\sp0$C) in 1993, 1994, and 1995, respectively, using 2,4-D + 2,4-DP ester. Efficacy with 2,4-D + 2,4-DP amine was not consistent, compared to 2,4-D + 2,4-DP ester, and GDD$\sb{10}$ ($\sp0$C) thresholds were not similar among years. Carboxyfluorescein was observed in the phloem of the petiole of dandelion at all GDD$\sb{10}$ ($\sp0$C) treatments, but no CF was detected in the lower taproot from the 35 GDD$\sb{10}$ ($\sp0$C) treatment. Relative fluorescence (RF) for the 35 GDD$\sb{10}$ ($\sp0$C) treatment was significantly less than the other GDD$\sb{10}$ ($\sp0$C) treatments at all harvest comparisons. Dandelions not treated with CF in 1996 were controlled 100% with treatments of 2,4-D + 2,4-DP ester applied at $\ge$95 GDD$\sb{10}$ ($\sp0$C), 87% at 65 GDD$\sb{10}$ ($\sp0$C), but only 43% from treatments applied at 35 GDD$\sb{10}$ ($\sp0$C). Turf managers scheduling applications of 2,4-D + 2,4-DP ester after 81 GDD$\sb{10}$ ($\sp0$C) should expect consistent, acceptable control of dandelion.
Degree
Ph.D.
Advisors
Throssell, Purdue University.
Subject Area
Agronomy|Botany|Botany
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