No description available.

Two varieties of sideoats grama (Vaughn and NM-28) were planted in late summer of 1980. The seedlings were treated with a variety of broadleaf weed control treatments at 1-, 3-, 5-leaf, and tillering stages of grass seedling growth to determine the effectiveness of these treatments for controlling weeds and the appropriate stages of grass seedling growth to apply them and consequently on grass establishment, density, forage production and plant height. Four months after seeding, NM-28 stands were more dense, produced more forage and the plants were taller than Vaughn. Treatments of dicamba at 0.28 and 0.56 kg/ha were the most effective herbicidal treatments in controlling weeds and resulted in highest stand densities and yields when applied at the 1- and 3-leaf seedling growth. Both treatments gave over 90% control of weeds at the earlier stages but control decreased at later stages of treatment. Lower control resulted when 2,4-D at 0.56 and 1.12 kg/ha were applied. Even though hand weeding treatment resulted weed-free plots during the first four months of seedling development, it resulted in less stand densities and yields when compared to herbicidal treatments. One year after treatment, Vaughn established into taller stands and produced higher yields than NM-28. Dicamba 0.28 kg/ha and 2,4-D 0.56 kg/ha effectively aided in better stand density and yield. Treatments applied at earlier stages of growth resulted in better establishment of both varieties. Dicamba at 0.28 kg/ha was the most effective herbicidal treatment for both varieties. However, hand weeding evaluated one year after seeding, effectively increased both accessions' yield and was the most effective treatment. Greenhouse and laboratory experiments were conducted to determine the uptake and distribution of ('14)C-2,4-D in both sideoats grama accessions and palmer amaranth seedling plant parts at 1, 4, 8 and 24h after treatment. Over all harvest times, 25.3, 2.8 and 3.1% activity were recovered in Vaughn treated leaf, tillers and crown, respectively. That was compared to 33.9, .68 and 6.8% in the same NM-28 plant parts, respectively. Higher percentages of activity were recovered in palmer amaranth plant parts; 50.5% in treated leaf, 8.5% above treated leaf and 5.4% below.

A field demonstration was conducted in Mohave Valley to compare cotton morningglory control programs that combined the use of over the top herbicides Roundup Ultra on Roundup Ready cotton (Deltapine 436 RR) or Staple on non-transgenic cotton (SureGrow 125) with and without precision cultivation.

In the fall of 1999 an experiment was conducted to measure the effect of CGA- 362622, halosulfuron (Permit), glyphosate (Roundup Ultra) and Pyrithiobac (Staple) on purple nutsedge. Five rates of Permit (0.25, 0.375, 0.495, 0.75 and 1.0 oz a.i./A), three rates of CGA-362622 (3.035, 4.047, and 6.07 g a.i./A), and a single rate each of Roundup Ultra (0.75 lb a.e./A), Staple (1.5 oz a.i./A), Staple + Bueno 6 (2 lb a.i./A), and Staple + Fusilade (0.25 lb a.i./A) were applied either once or twice to field populations of purple nutsedge. Efficacy of each treatment was measured in three ways: phytotoxicity (stunting, chlorosis and/or necrosis) ratings were assigned to each plot (0 being no injury and 10 indicating death), the number of green leaves were counted on 3 large ($8 leaves) and 3 small (≤4 leaves) plants per plot at various times after treatment, and the amount of regrowth after the herbicide treatments was assessed. All of the herbicide treatments caused stunting, induced chlorosis and necrosis, and were fairly effective in controlling nutsedge plants treated at or before the 4-leaf growth stage. Only Permit and CGA-362622 effectively controlled plants treated at the 8-leaf growth stage after one application. The other four herbicides required two applications to obtain effective control. For the regrowth parameter parameters, Permit, CGA-362622 and Roundup Ultra effectively controlled regrowth, but the Staple, Staple + Bueno 6 and the Staple + Fusilade treatments did not control regrowth. Two applications of Permit at the .495 oz a.i./A or greater rates, Roundup Ultra (0.75 lb a.e./A) and 1 or 2 applications of the 6.070 g a.i./A rate of CGA-362622 controlled nutsedge with respect to all measured regrowth parameters and may be the best choices for controlling purple nutsedge.

Johnsongrass control with BAS 620 was 60% and 67% for the 0.124 and 0.248 lb ai/A rates respectively, 14 d after initial application. Control was comparable to Select at the corresponding rates. Control 28 d after the second application of graminicides ranged from 60% to 88%. Both rates of BAS 620 and Select as well as Fusilade DX provided the most effective control. Seed cotton yields ranged from 1347 to 3134 lbs/A and all herbicide treatments yielded significantly greater than the nontreated check.

Experiments were conducted at the University of Arizona Safford and Maricopa Agricultural Centers during the 2001 cotton season to compare the effectiveness of 0.5 and 1.0 lb a.i./A topical applications of Buctril (bromoxynil) on annual morningglory species. At Safford, the percent control of annual morningglory was statistically greater following 1.0 lb a.i./A Buctril applications at 97 percent control compared to 83 percent control resulting from 0.5 lb a.i./A Buctril applications. Both the 0.5 and 1.0 lb a.i./A Buctril rates, had similar initial effects on morningglory seedlings. Initial leaf symptoms included a dark-green “water soaked” appearance that progressed into leaf necrosis. At both rates, all morninglory leaf tissue was destroyed leaving green stems which sometimes remained viable and produced new leaves rather than turning chlorotic and dying. The number of escapes in the center two rows of four-row plots was significantly greater after 0.5 lb a.i./A Buctril applications at 12.4 escapes compared to 1.5 escapes following 1.0 lb a.i./A Buctril applications. An average of 12 escapes in an area 40 ft by two cotton rows is sufficient to cause substantial yield losses in the absence of other control methods. At Maricopa, there was no statistically significant difference in the phytotoxicity caused by 0.5 and 1.0 lb a.i./A Buctril rates when applied to 1, 2, or 3 true-leaf exposed morningglory seedlings (i.e., not partially covered or shaded by other plants) that were thoroughly contacted by the herbicide sprays. Both experiments found that morningglory control was significantly greater following two sequential 0.5 lb a.i./A Buctril applications compared to a single 1.0 lb a.i./A application due to continued emergence of seedlings. Growers with morningglory infested fields that make a 1.0 lb a.i./A application should be prepared to make an early season post-direct application using other herbicides to control later emerging morningglory plants.

Conservation or reduced tillage practices in cotton-based crop rotation systems were studied in field experiments initiated at Marana, Coolidge and Goodyear by planting barley cover and grain crops in the fall of 2001. In the 2002 cotton season, conservation tillage practices reduced the number of cultural operations required to grow a cotton crop. Adequate cotton weed control was achieved in conservation tillage systems using only postemergence herbicides; weedsensing, intermittent spray technology reduced the amount of herbicide spray volume used for weed control. Cotton yields in conservation tillage systems were similar to the yields in conventional tillage systems at two sites and greater at one site.

The tolerance of Roundup Ready (RR) Flex cotton to topical Roundup Weathermax (glyphosate) applications and weed management programs in RR Flex cotton were studied in 2002 and 2003 at the University of Arizona Maricopa Agricultural Center. RR Flex cotton demonstrated excellent tolerance to glyphosate as measured by flower pollen shed and lint yield when sprayed topically with glyphosate at 2.25 lb ae/A four times (at the 3 leaf, 6 node, 10 node and 14 node growth stages). Line 1445 containing the current commercial RR genetic construct had a flower sterility/pollen shed rating of 4.6 (1 equals full pollen shed and 5 equals no pollen shed) on 28 June 2003 compared to ratings of 1.1 to 1.9 in lines containing the RR Flex genetic construct. Cotton yields followed a similar pattern with 1145 yielding 386 lb seed cotton/A compared to 1477 to 1894 lb seed cotton/A for the best lines containing the RR Flex genetic construct (yields were generally low because all lines had a Cocker genetic background that is not adapted to hot desert production conditions.) The presence of the RR gene did not affect the yield of genotype pairs that were identical except for the presence or absence of the RR Flex genetic construct. In the weed management study, delaying the first topical glyphosate application resulted in larger, more difficult to control weeds and reduced cotton yield by allowing greater early season competition between weeds and cotton. The best weed control programs included early (1 to 2 leaf growth stage) topical applications at rates greater than 0.75 lb ae/A and a second Roundup application after the first post-planting irrigation (10 node growth stage). The data also suggested that there may be significant value in making a layby, directed-broadcast application that includes a residual herbicide such as prometryn at layby.

The tillage operations conducted in a barley and cotton double-crop rotation were reduced by eliminating tillage prior to planting cotton, eliminating cultivations for weed control in cotton, and especially by eliminating tillage following cotton prior to planting barley. Data collected in 2002 and 2003 in Coolidge and Marana showed that a weed sensing, automatic spot-spray system reduced the amount of spray volume and herbicide used by 50 to 60%. Data from Maricopa in 2003 indicated that the savings can be much greater (e.g., in a treatment with thick Solum barley cover crop residues) or much less if volunteer grain germinates after grain harvest. Similar weed control was obtained with the weed sensing, automated spot-spray system compared to conventional continuous spray systems for most weed species. At Coolidge in 2002, the minimum tillage treatment with a barley cover crop produced 24% more lint than the conventional tillage system (1089 versus 880 lb/A) because more water was applied in that treatment. In 2003, the minimum tillage treatment yielded 24% less than the conventional tillage treatment (1178 versus 1539 lb/A) due to herbicide injury. There were no differences in cotton yields among the tillage systems at Goodyear in 2002 and 2003. In Marana (2002 and 2003) and Maricopa (2003), there were yield differences between treatments related to planting date, with late-planted cotton yielding less than early-planted cotton. At Marana, the cotton yields of the minimum-till and conventionally tilled treatments were not statistically different. At Maricopa, the early-planted minimum-till cotton yielded less than the early-planted conventionally tilled cotton (956 versus 1141 lb/A). The yield comparisons between conservation tillage and conventional tillage cotton production systems are not yet definitive and more research needs to be conducted. Economic comparisons between productions systems indicated an advantage for conservation/minimum tillage treatments if cotton yields were comparable.

The tillage operations required to grow an annual barley and cotton crop rotation were reduced by eliminating tillage prior to planting cotton, eliminating cultivations for weed control in cotton, and especially by eliminating tillage following cotton. A light activated, weed sensing automatic spot-spray system reduced the amount of spray volume and herbicide used by 40% to 60% at Marana and 36% to 56% at Maricopa in 2004. At Maricopa, a large number of volunteer cotton plants in the furrows of early planted no-till cotton reduced the spray volume savings from using the weed sensing automatic spot-spray system. Weed control was similar with the weed sensing, automatic spot-spray system compared to the conventional continuous spray system for most weed species but weeds with narrow leaf, upright leaf canopies such as sprangletop, barley and skeleton weed were more difficult to detect and control. In both Marana and Maricopa, there were yield differences between treatments related to planting date, with late-planted cotton yielding less than early-planted cotton. At Marana, the early-planted conventional tillage cotton out-yielded the barley cover crop, early-planted no-till cotton treatment. At Maricopa, there were no yield differences between the two early planted cotton treatments; however, the late-planted conventionally tilled cotton yielded 28% more than the late-planted no-till cotton. Although the yield comparisons are not yet definitive, it appears that in some situations no-till cotton may yield less than conventionally tilled cotton. At Maricopa, the height of cereal crop stubble did not affect subsequent cotton establishment, field populations, plant height or lint production (2003 and 2004) and the position or node of the first fruiting branch and the first retained boll were similarly unaffected in 2004.