Italian ryegrass (Lolium multiflorum) Control in Imidazolinone-tolerant Wheat (Triticum aestivum). Under the direction of Dr. Alan York

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Title: Italian ryegrass (Lolium multiflorum) Control in Imidazolinone-tolerant Wheat (Triticum aestivum). Under the direction of Dr. Alan York
Author: Clemmer, Kevin Christman
Advisors: Dr. Ron Heiniger, Committee Member
Dr. J. R. Bradley, Committee Member
Dr. Alan York, Committee Chair
Abstract: Italian ryegrass is the most problematic weed of small grains in North Carolina. This weed has traditionally been controlled in wheat with diclofop. However, after many years of continuous use, much of the Italian ryegrass in the state is now resistant to diclofop. A field experiment was conducted at three locations to determine control of Italian ryegrass and response of imidazolinone-tolerant wheat to imazamox and other herbicides. Imazamox ammonium salt applied POST in the fall to 3- to 4-leaf Italian ryegrass at 35 to 53 g ae/ha controlled Italian ryegrass 90 to 100% 10 weeks after treatment. Late-season control ranged from 83 to 98% at two locations and 24 to 55% at the third location. Late-season control from spring-applied imazamox on 1- to 3-tiller ryegrass ranged from 53 to 58% at one location and 7 to 16% at the other locations. Split application of imazamox at 27 g/ha in the fall and 27 g/ha in the spring was less effective than fall-applied imazamox at 53 g/ha at two of three locations. However, split application was more effective than spring application. Fall-applied imazamox was less effective than fall-applied diclofop on diclofop-susceptible Italian ryegrass but more effective on mixed populations of diclofop-resistant and -susceptible biotypes. Pendimethalin applied PRE at 1120 g ai/ha increased late-season control 10 to 33 percentage points when used in combination with fall-applied imazamox at 35 g/ha. Imazethapyr ammonium salt at 70 g ae/ha was less effective than imazamox, while imazethapyr at 47 g/ha plus imazapyr isopropylamine salt at 16 g ae/ha and imazamox were similarly effective. Imazapic ammonium salt at 70 g ae/ha and imazamox at 53 g/ha were similarly effective at two locations, while imazapic was more effective at the third location. Imidazolinone herbicides caused only minor, temporary chlorosis on the wheat. In greenhouse experiments, a diclofop-susceptible biotype of Italian ryegrass was more sensitive to imazamox than a diclofop-resistant biotype. Imazamox controls Italian ryegrass in imidazolinone-tolerant wheat but is only marginally effective on some broadleaf species. A fallow-area field experiment was conducted at three locations in North Carolina to determine control of Italian ryegrass by imazamox as affected by imazamox rate, weed size at application, and mixtures with the broadleaf herbicides 2,4-D, dicamba, and thifensulfuron plus tribenuron. Interactions of imazamox rate, weed size, and broadleaf herbicides were not observed. Italian ryegrass control 56 days after treatment increased as imazamox rate increased. Pooled over weed sizes at application and mixtures, imazamox at 27, 35, and 44 g/ha controlled Italian ryegrass 44, 53, and 67%, respectively, at two locations and 83, 86, and 91% at the third location. Control decreased as weed size at time of application increased. Pooled over imazamox rates and mixtures, Italian ryegrass was controlled 86, 54, and 24% at two locations when herbicides were applied to 2-leaf, 4-leaf, and 2-tiller weeds, respectively. At the third location, Italian ryegrass was controlled 95, 94, and 71% when treated at the 2-leaf, 4-leaf, and 2-tiller stages, respectively. Small increases in control were sometimes noted with mixtures of imazamox and 2,4-D dimethylamine salt at 530 g ae/ha or thifensulfuron plus tribenuron at 18 plus 9 g ai/ha, while minor decreases were sometimes noted with mixtures of imazamox and dicamba diglycolamine salt at 140 g ae/ha. In a greenhouse experiment, mixing 2,4-D with imazamox did not affect Italian ryegrass control. Dicamba reduced control, while thifensulfuron plus tribenuron increased control.
Date: 2002-05-06
Degree: MS
Discipline: Crop Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/2761


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