Vol. 54—2000 - NorthEastern Weed Science Society

TIMING OF GL VPHOSATE, SULFOSATE AND IMAZETHAPYR APPLICATION FOR
IVYLEAF MORNINGGLORY CONTROL
A.D. Ayeni and BA. Majek l
ABSTRACT
IvyJeaf momingglory (Ipomoea hederacea) is a common weed of glyphosate-tolerant
soybean (OTS) not readily controlled with POST applications of glyphosate. Studies were
conducted at Rutgers Agricultural Research and Extension Center under greenhouse
conditions (75 to 90°F day, 60 to 70'l' night. 16 h light) to compare the effectiveness on
ivyleaf morningglory of glyphosate (0.75 Ib/A), sulfosate (l.l Ib/A), imazethapyr (0.056
Ib/A), glyphosate + imazethapyr (0.75 + 0.056 Ib/A), and sulfosate + imazethapyr (l.l +
0.056 Ib/A) applied at 15, 20, 25, and 30 d after planting (DAP). Ammonium sulfate (1%
w/v) was added to glyphosate and glyphosate + imazethapyr solutions, and a non-ionic
surfactant (2%) to sulfosate and sulfosate + imazethapyr solutions. Untreated ivyleaf
momingglory/GTS mixture and sole GTS were included as checks. Ivyleaf momingglory
(seed source: Valley Seed Service, Fresno, CAl and GTS (Roundup Ready Soybean, Lot
9134 from UAP Seed, Greeley, CO) were raised together in 2-801 plastic pots tilled with
regular mix (2:1 v/v peat moss:vennicullite mix plus lime, fertilizers and micronutrients).
Three stands of ivyleaf momingglory and two of GTS were maintained per pot. A calibrated
greenhouse sprayer, fitted with 8002VS-nozzle tip and operated at 30 psi and 68 gpa, was
used for herbicide application. Experiments were set up in four randomized complete blocks
and herbicides were evaluated basedon ivyleaf momingglory control and soybean injury.
Glyphosate alone applied 15 to 25 DAP reduced ivyleafmomingglory biomass 90 to 93%.
8 WAF. Application at 30 DAP reduced biomass 71%. Limited regrowth (= new growth)
occurred after initial injury at all stages of herbicide application. Sulfosate alone caused
biomass reduction that ranged from 35 to76%. The herbicide was ineffective due to rapid
recovery of ivyleaf momingglory from initial phytotoxicity. Imazethapyr caused 97, 80, 76.
and 41% reduction in biomass when applied at IS, 20, 25 and 30 DAP, respectively; and
prevented regrowth in ivyleafmomingglory for the duration of the experiment. Glyphosate +
imazethapyr and sulfosate + imazethapyr caused 84 to 99% biomass reduction in ivyleaf
momingglory when applied 15 to 25 DAP. The effectiveness of both mixtures declined to 73
and 52%, respectively, when applied 30 DAP. The mixtures also prevented regrowth as
observed with imazethapyr treatments.
Glyphosate and sulfosate were safe on GTS, but imazethapyr and its mixture with glyphosate
or sulfosate were phytotoxic (50 to 95% injury rating) at all stages of application. Recovery
of GTS from herbicide injury was fast when application was at 15 DAP, but relatively slow
with subsequent applications. The highest soybean total dry weight was obtained with
glyphosate alone applied 15 and 20 DAP followed by glyphosate + imazethapyr at 15 DAP
and imazethapyr alone at 20 DAF. Other treatments resulted in low dry weight due to
herbicide injury or ivyleaf momingglory interference or a combination of both factors.
I Research. Associate in Weed Scienceand Professorof weed Science, Rutgers Agric. Res. & Ext. Ctr.,
Bridgeton, NJ 08302
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