Studies were conducted on the campuses of Texas A&M University in College Station, TX, and New Mexico State in Las Cruces, NM, to determine the spray droplet size spectra produced by quinclorac and 2,4-D as the liquid, dry, and emulsion formulations during application with various nozzle sizes using a laser spectrometer. Quinclorac and 2,4-D formulations were also sprayed through three different nozzle sizes in a drift chamber and allowed to settle on glass slides placed downwind. The amounts of each herbicide deposited on the slides were quantified using high-performance liquid chromatography/photodiode array (HPLC/PDA) analysis to assess spray deposition of each formulation at different wind velocities. Data from the laser spectrometer suggested that formulations of 2,4-D affected droplet size, particularly when the 380 ml/min flat-fan nozzle was used. Quinclorac droplet sizes were similar to water regardless of nozzle size. Liquid and dry-formulated 2,4-D tended to be deposited downwind in greater quantities than the emulsion formulation when using the 380 and 760 ml/min spray nozzles with wind velocity of 15 km/h.

Field studies were conducted in 1997 and 1998 to evaluate the efficacy of imidazolinone weed management systems and crop tolerance of imidazolinone-tolerant (IT) corn to imazapic. Imazapic (36 and 72 g/ha) was evaluated when applied PRE; early postemergence (EPOST), when corn was at the two- to three-leaf stage; and late postemergence (LPOST), when corn was at the six- to eight-leaf stage. Imazapyr + imazethapyr EPOST and metolachlor + atrazine followed by (fb) primisulfuron LPOST were evaluated as commercial standards. Imazapic at 36 g/ha EPOST controlled johnsongrass, Texas panicum, smellmelon, and ivyleaf and entireleaf morningglory at least 93% when adequate rainfall occurred. Devil's claw was controlled at least 85% with imazapic EPOST or LPOST at either rate. Imazapic at 36 g/ha EPOST and LPOST controlled eclipta 88 and 91%, respectively. Yellow nutsedge was controlled >91% with imazapic LPOST, which was superior to imazapic applied EPOST. Broadleaf signalgrass was controlled 94% with imazapic at 72 g/ha LPOST, which was significantly higher than other herbicide treatments. Imazapic at 36 and 72 g/ha applied PRE under moisture stress resulted in reduced weed control; but when adequate rainfall occurred, weed control was generally similar to that of EPOST and LPOST applications. Imazapic crop response at 72, 105, 140, and 211 g/ha applied at EPOST and LPOST was evaluated in two IT corn hybrids. Crop response varied with soil and environmental conditions and application timings. Imazapic at 72, 105, and 140 g/ha EPOST resulted in crop injury 33 to 55% at 6 wk after planting (WAP) in a coarse soil; however, crop injury decreased to <20% at 12 WAP. Low crop injury (<9%) was observed at 12 WAP in a clay soil. Imazapic applied LPOST resulted in lower crop injury than EPOST application. Corn plant height and yield were not affected by any imazapic treatment.

Field trials were conducted in 2000, 2001, and 2002 at Tifton, GA, and Plains, GA, to evaluate the effects of simulated imazapic residues on cotton growth and yield. Preemergence applications of imazapic at 1, 2, 5, 9, 18, and 36 g ai/ha were made to four different cotton varieties (two at each location) and included a nontreated control. There were no differences in cotton variety response to imazapic. Each cotton variety responded to imazapic in a similar manner. Analysis of cotton yield as a percentage relative to the nontreated control indicated no difference in variety for location, so data for varieties were combined. At Tifton, cotton injury was exponentially related to imazapic rate with a maximum injury of 44% for 35 g/ha. Seed cotton yields at this location were reduced 0, 6, 6, 14, 16, 34, and 61% at 1, 2, 5, 9, 18, and 36 g/ha, respectively. For Plains, cotton exhibited extreme sensitivity with injury exceeding 70% for imazapic at 5 g/ha and greater than 95% for 18 g/ha. Seed cotton yields at this location were reduced 60% or more from imazapic rates of 5 g/ha and greater. These results indicated that soil type is a key factor in the response of cotton to imazapic.

Few herbicides are used in carrot production in the United States, and none suppress volunteer potato, a serious weed where the two crops are grown in rotation. Hand-weeding is the primary method of controlling emerged volunteer potato within carrot. The objective of this work was to evaluate carrot tolerance and volunteer potato control with single or sequential applications of prometryn, prometryn plus fluroxypyr, and ethofumesate. The treatment with fluroxypyr resulted in malformed carrots with numerous root hairs and reduced carrot yield. Treatments with prometryn, either as single or sequential POST applications at 2.23 kg ai/ha, were safe on carrot and frequently controlled volunteer potato similar to the hand-weeded treatment. Ethofumesate applied as single or sequential PRE or POST at 2.2 kg ai/ha proved safe on carrot, but higher rates reduced yield. Ethofumesate applied POST or PRE followed by POST consistently reduced volunteer potato tuber mass. If registered for use in carrot, prometryn and ethofumesate would help modernize weed management in carrot and reduce or eliminate the need for hand-weeding volunteer potato.

Field studies were conducted in 2000 and 2001 to evaluate corn yield-loss predictions generated by WeedSOFT, a computerized weed management decision aid. Conventional tillage practices were used to produce corn in 76-cm rows in Illinois, Indiana, Kansas, Michigan, Missouri, Nebraska, and Wisconsin. A total of 21 site-years from these seven states were evaluated in this study. At 4 wk after planting, weed densities and size, crop-growth stage, estimated weed-free yield, and environmental conditions at the time of application were entered into WeedSOFT to generate POST treatments ranked by percent maximum yield (PMY). POST treatments were chosen with yield losses ranging from 0 to 20%. Data were subjected to linear regression analysis by state and pooled over all states to determine the relationship between actual and predicted yield loss. A slope value equal to one implies perfect agreement between actual and predicted yield loss. Slope value estimates for Illinois and Missouri were equal to one. Actual yield losses were higher than the software predicted in Kansas and lower than predicted in Michigan, Nebraska, and Wisconsin. Slope value estimate from a data set containing all site years was equal to one. This research demonstrated that variability in yield-loss predictions occurred at sites that contained a high density of a single weed specie (>100/m2) regardless of its competitive index (CI); at sites with a predominant broadleaf weed with a CI greater than five, such as Palmer amaranth, giant ragweed, common sunflower, and common cocklebur; and at sites that experience moderate to severe drought stress.

Corn and soybean farmers across Indiana were surveyed in 2003 to determine the perceived importance of weeds at the state and district levels. Weeds were considered the primary crop pest by 69 to 84% of farmers, depending on district. Diseases or insects were ranked first by no more than 14% of farmers and nematodes were ranked first by no more than 11%. Giant ragweed, Canada thistle, common lambsquarters, common cocklebur, and velvetleaf were considered the most problematic summer annual and perennial weeds statewide. Chickweed, horseweed, dandelion, and henbit were considered the most problematic winter annual weeds statewide. However, no weed species was listed by more than 41% of farmers statewide suggesting that relatively unique weed management problems may exist on many farms. Also, the perceived importance of most weed species varied substantially among Indiana's nine districts. For example, velvetleaf was not listed as a problematic weed by any farmers in three districts. Burcucumber was not considered a statewide problem but was listed among the top three weeds by 14 and 16% of farmers in two southern districts. This survey supports the idea that educational programs focused on weed management should be tailored to geographic regions within Indiana.