Evaluation of a 'Caliente' Mustard Cover Crop, S-metolachlor, Imazosulfuron, and Thifensulfuron-methyl for Weed Control in Bell Pepper

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Title: Evaluation of a 'Caliente' Mustard Cover Crop, S-metolachlor, Imazosulfuron, and Thifensulfuron-methyl for Weed Control in Bell Pepper
Author: Pekarek, Ryan Andrew
Advisors: David W. Monks, Committee Chair
Abstract: Bell pepper production has relied on pre-plant fumigation with methyl bromide under polyethylene mulch for weed control. With the pending loss of methyl bromide under the Montreal Protocol and the lack of registered herbicides to control yellow nutsedge and broadleaf weeds, new weed management strategies for bell pepper are needed. Studies were conducted near Clinton, NC, in 2007 and 2008 to evaluate effects of a ‘Caliente’ mustard cover crop in four vegetable cultural systems on weed and nematode populations. Cultural systems included a flat seed bed (TILL), a raised bed with no mulch (RAISED), low density polyethylene mulch (LDPE), and virtually impermeable film (VIF) mulch. The ‘Caliente’ mustard cover crop did not reduce weed populations. The mulched treatments (LDPE and VIF) reduced yellow nutsedge populations compared to the non-mulched (RAISED and TILL). No differences between the two polyethylene mulches were detected. More large crabgrass, goosegrass, and smooth pigweed were present in the RAISED compared to the TILL treatments. The ‘Caliente’ mustard cover crop generally had no effect on nematode populations, but ring and bacterivore nematode populations increased compared to bareground. The polyethylene mulches generally did not affect nematode populations. However, polyethylene mulched treatments increased ring nematode populations compared to non-mulched treatments. Omnivore, root-knot, and spiral nematode populations were unaffected by treatments. Greenhouse and field studies were conducted to evaluate bell pepper tolerance imazosulfuron and thifensulfuron-methyl. Imazosulfuron was applied postemergence-over-the-top (POST-OTT) at 56, 112, 224, 336, or 448 g ai/ha. Thifensulfuron-methyl was applied POST-OTT at 2.6, 5.3, 10.5, 21.0, or 31.6 g ai/ha. In the greenhouse over 2 years, bell pepper injury from imazosulfuron POST-OTT ranged from 12 to 27%. Reductions in plant height were generally minor. Injury due to thifensulfuron-methyl POST-OTT ranged from 41 to 61% in the greenhouse. Similar trends were observed for leaf chlorosis and distortion. Thifensulfuron-methyl tended to decrease numbers of buds, flowers, and fruits in the greenhouse. In the field at 3 locations, bell pepper injury from imazosulfuron applied postemergence-directed (POST-DIR) was less than 10% at all ratings. Height and yield were not reduced. Total and marketable yield averaged 40,300 and 35,810 kg/ha, respectively, across locations. Bell pepper injury from thifensulfuron-methyl applied POST-DIR in the field was less than 20% with all rates and below 10% when rates below 10.6 g ai/ha thifensulfuron-methyl were applied. Thifensulfuron-methyl did not reduce stand or height. Thifensulfuron-methyl did not affect total bell pepper yield (39,310 kg/ha across locations), however, reductions in Fancy yield were observed. No. 1 and cull yield grades tended to increase with increasing thifensulfuron-methyl, apparently compensating for lost Fancy grade yield. Studies were also conducted at 4 site-years in North Carolina in 2007 and 2008 to evaluate the effects of ‘Caliente’ mustard cover crops, bareground, S-metolachlor preemergence (PRE), and imazosulfuron POST-DIR on weed control, bell pepper height, injury, stand, and yield. S-metolachlor injury to bell pepper was generally less than 15% at all sites except 3 WAT at HRCS 2007. S-metolachlor provided greater than 88% control of fall panicum, goosegrass, and large crabgrass. Control of carpetweed, common and pink purslanes, and hairy galinsoga ranged from 42 to >90%. Yellow nutsedge control with S-metolachlor and imazosulfuron ranged from 15 to 63% and 76 to 84%, respectively. Imazosulfuron did not injure pepper. S-metolachlor at 1.6 kg ai/ha reduced yield of bell pepper in some instances, although, overall yield reductions were minor. ‘Caliente’ mustard did not routinely increase weed control and only increased Fancy grade yield at HCRS 2007. ‘Caliente’ mustard reduced Fancy grade bell pepper yield at the MHCRS site compared to a bareground check. Benefits of the ‘Caliente’ mustard cover crop were transient to non-existent.
Date: 2009-04-23
Degree: MS
Discipline: Horticultural Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/2968

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