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ARS Home » Southeast Area » Dawson, Georgia » National Peanut Research Laboratory » Research » Publications at this Location » Publication #177124
Title: BROADCAST APPLICATIONS OF GLYPHOSATE TO GLYPHOSATE RESISTANT COTTON DURING LATE BLOOM PERIOD

Author
item HAMM, GARY - NC STATE
item Nuti, Russell
item CASTEEL, SHAUN - NC STATE
item LANIER, JAMES - NC STATE
item COLLINS, GUY - NC STATE
item EDMISTEN, KEITH - NC STATE

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/5/2005
Publication Date: 3/1/2005
Citation: vol. 76.

Interpretive Summary: None required.

Technical Abstract: Late season applications of glyphosate to glyphosate resistant cotton is a practice that farmers commonly use in their cotton management programs due to adverse weather and higher than normal weed pressure. Depending upon the severity of the weed pressure, farmers are sometimes forced to make an application of glyphosate to their crop that may not coincide with label restrictions. The current Monsanto label for Round-up Weathermax states that no broadcast application over the top should be applied after the 4-leaf stage until twenty percent boll crack in cotton. Experiments were conducted to determine if there is a safe time period in late season reproductive growth of glyphosate cotton that a broadcast application of Glyphosate can be made before twenty percent cracked boll? Field experiments were conducted in 2002 at Cherry Farms Research Station, Goldsboro, NC, 2003 at Central Crops Research Station, Clayton, NC, and 2004 at Upper Coastal Plains Research Station, Rocky Mount, NC. In 2002, 'Suregrow 125RR' was planted and in 2003 and 2004 'Stoneville 4892BR' was planted. Treatments consisted of three broadcast applications of 0.75lb ae/A of glyphosate delivered at 15 GPA along with an untreated check (UTC). The first treatment was made at seven nodes above white flower (7 NAWF). Two additional treatments were made at two weeks after initial treatment (2 WAIT) and 4 weeks after initial treatment (4 WAIT). Treatments were arranged in a randomized complete block design and replicated four times. Ten uniform plants were tagged at each treatment application to be box mapped prior to harvest. The purpose of box mapping was to group bolls into node zones 3-5, 6-10, 11-15, and 16-20 by position with all boll weights recorded as grams of seed cotton to examine differences in boll weights by position. The two middle rows of the four row plots were spindle picked and seed cotton samples were taken and ginned for lint turnout and fiber quality will be determined by high volume instrument analysis. Data were analyzed with the general linear model in SAS and means will be separated according to Fisher's Protected LSD at '=0.05. Data were reported separately due to a location by year interaction. In 2002, the UTC produced 167 pounds more lint than the 4 WAIT treatment and in 2003 there were no differences between the treatments and the UTC. In 2004, there was a 262 pound yield reduction in the 7 NAWF treatment and the UTC. In 2003, the UTC average boll weight was 3.7 g/boll and the glyphosate treatment boll weights did not weigh as much as the UTC. This trend was the same in 2002 as well. There were some micronaire differences also in 2002 and 2003, in which treatments were less than the UTC for both years and 2004 there were no difference found between treatments. The 2 WAIT micronaire was greater than the premium of 4.2 in 2003 and in 2002 showed no significant difference between treatments but all were above the premium level. Also in 2004, the percent open boll counts at harvest showed that the 7 NAWF treatment was 72 % percent open while all other treatments were 95 % open. There were variable environmental differences in 2002, 2003, and 2004 allowing for possible differences in year-to-year data and results. In 2002, the cotton was under a drought stress when treatments were applied. In 2003, the cotton was under optimal growing conditions promoting rapid growth. In 2004, the cotton has been under a variety of environmental conditions ranging from drought stress to abnormally wet conditions. Late season applications of glyphosate on glyphosate resistant cotton should be carefully examined when making a pre harvest decision due to the unpredictable results of such applications causing crop loss and economic loss.