The effects of different external nitrate concentrations on growth of Avena sativa cv. Amuri treated with diclofop‐methyl

Abstract

Avena sativa cv. Amuri fed either low or high nitrate was sprayed with diclofopmethyl ( 1 kg a.i. ha-I) at the three leaf stage. The short term effects of the herbicide on chlorophyll concentration of leaves (laminae) and short and long term effects on d.wt of the component plant parts were determined by comparison with unsprayed plants.For unsprayed and sprayed plants, total leaf d.wt approximately doubled during the first twelve days after commencing treatments. Growth was substantially greater at high nitrate than low nitrate. For unsprayed plants, the increase in total leaf d.wt was due primarily to growth of leaf 3 but for sprayed plants it was due to growth of leaves 1 and 2. Twelve days after commencing treatments, d.wt of leaves 1 and 2 was substantially greater for sprayed plants than for unsprayed plants given similar nitrate, while chlorophyll concentration was substantially less. Leaf 3 d.wt and chlorophyll concentration were substantially greater in unsprayed plants than in sprayed plants given similar nitrate. For unsprayed plants, values were greater at high nitrate than low nitrate, for sprayed plants the converse was the case.Forty nine days after commencing treatments, unsprayed plants had a greater total plant d.wt than sprayed plants given similar nitrate. Total plant d.wt for unsprayed plants was greater at high nitrate than low nitrate, the opposite was the case for sprayed plants. Unsprayed plants a t both nitrate levels and sprayed plants given low nitrate produced seed heads but sprayed plants given high nitrate did not. Diclofop-methyl at a rate of 0.3 kg a.i. ha-' stopped seed head production at high nitrate. Retention and uptake of diclofop-methyl were not significantly different at low and high nitrate. At 1 kg a.i. ha-l diclofop-methyl, plants switched from low to high nitrate at spraying showed damage similar to that shown by plants given high nitrate throughout. Addition of 200 vg GA into the leaf sheaths two days prior to spraying increased the efficacy of diclofop-methyl at low nitrate.It is proposed that increased efficiency of diclofop-methyl at high nitrate is due to increased leaf damage caused by a greater rate of leaf expansion.

Influence of Nitrogen Rate, Seeding Rate, and Weed Removal Timing on Weed Interference in Barley and Effect of Nitrogen on Weed Response to Herbicides

“…Dickson et al (1990) found that fluazifop (0.25 kg ha −1 ) and glyphosate (0.18 kg ha −1 ) were more effective in preventing seed head formation of oats grown under 200 (high) vs. 0 (low) kg added N ha −1 . Similarly, the efficacy of diclofop-methyl on oats was greater at the high compared with the low N soil (Andrews et al 1989). Cathcart et al (2004) reported that the amount of nicosulfuron required for 50% shoot dry weight reduction of green foxtail was 6-fold greater at low (0.7 mM) compared with high (7.7 mM) N rate in a growth chamber study.…”

Effect of Water Stress, Nitrogen, and Gibberellic Acid on Fluazifop and Glyphosate Activity on Oats (Avena sativa)

“…Stressed plants were maintained at wilting point for 9 days after spraying, then the soil moisture content was returned to field capacity by the addition of nutrient solution. Field capacity was maintained until harvest, 17 days after spraying, at which time shoot dry weight and chlorophyll concentrations in the individual laminae were measured as described previously (7). The long-term experi ment was similar to the short-term experiment except that soil moisture was maintained at field capacity until 32 days after spraying, at which time shoot dry weight was determined.…”

“…Application of abscisic acid (ABA) 3 at time of spraying can protect against diclofop without affecting uptake and translo cation of the herbicide (24,26). Recently, diclofop has been shown to be less effective against plants growing in low external NO3 concentrations (7). Diclofop causes membrane disruption in annual grasses (23).…”

“…The mode of action of diclofop and other PCA herbicides is inhibition of the enzyme acetyl-coenzyme A carboxylase, a key enzyme in the biosynthesis of fatty acids which are necessary for membrane production (12,42,46). It has been proposed that increased plant tolerance to diclofop at low external NO3 concentra tions, high soil moisture deficits, and with ABA treatments is due to a reduced rate of leaf expansion (7). This results in less demand for membrane synthesis and decreased strain on cell membranes damaged by the herbicide, and consequently less cellular disruption occurs (6,7).…”

“…It has been proposed that increased plant tolerance to diclofop at low external NO3 concentra tions, high soil moisture deficits, and with ABA treatments is due to a reduced rate of leaf expansion (7). This results in less demand for membrane synthesis and decreased strain on cell membranes damaged by the herbicide, and consequently less cellular disruption occurs (6,7). Gibberellic acid (GA) 3 enhancement of diclofop activity in oat at low external NO3 may be due to an increased rate of tissue (primarily stem/leaf sheath) expansion (7).…”