Agrichemical interactions between propanil; the herbicides HOE 30374, pendimethalin, piperophos, quinclorac, and thiobencarb; and the insecticide carbaryl were evaluated under field conditions to find synergistic or additive interactions useful to control a barnyardgrass biotype resistant to propanil (R-BYG) without injuring rice. Propanil and each compound were evaluated at four rates for a total of 16 rate combinations for each additive. Averaged over all experiments, 2- to 3-leaf R-BYG control with propanil alone at 0.83, 1.65, 3.3, and 6.6 kg ai/ha was 33, 53, 62, and 81% at 7 d after treatment (DAT). Propanil-susceptible barnyardgrass (S-BYG) response to propanil alone at similar rates was 52, 73, 88, and 94% control. HOE 30374, carbaryl, piperophos, or pendimethalin in combination with propanil produced synergistic effects on R-BYG. For each compound tested, at least one rate combination with propanil controlled R-BYG > 80% with minimal rice injury (< 20%) at 7 DAT. Use of these combinations of compounds could provide more effective control of this resistant biotype and help prevent its spread.

A decision criterion is presented for postemergence johnsongrass control in soybeans. Models derived from actual data describing the relationship between johnsongrass density (X) and soybean yield loss are used to develop the decision criterion for soybeans planted in 0.25- and 1-m row spacings. The yield loss equations are L1 = 424–424 exp (-0.023X2) for 0.25-m row spacing and L2 = 643-643 exp (−0.004X2) for 1-m row spacing. When combined with the cost of control (Px) and the expected price of soybeans (Py), these equations can be used to find the density thresholds where johnsongrass control becomes profitable. For the 0.25-m row spacing, this relationship was Px = Py [424–424 exp (−0.023X2) or more simply Px = Py L1, which equates the cost of control to the value of the soybean yield increase from control. The johnsongrass density (X) that satisfies this equality is the threshold (X*) above which control is profitable.

Studies were conducted in 2003 and 2004 to determine the effect of application timing and halosulfuron rate on sweetpotato yield and quality. Halosulfuron was applied 1, 2, and 4 wks after transplanting (WAP) sweetpotato in 2003, and 2, 3, and 4 WAP in 2004. Treatments within each timing included halosulfuron at 13, 26, 39, 52, and 65 g ai/ha plus a weed-free control. Combined over year, site, cultivar and rate, halosulfuron applied at 1, 2, 3, and 4 WAP stunted sweetpotato 32, 15, 11, and 14%, respectively, rated 2 wks after treatment. The stunting observed with the 1 and 2 WAP timings caused a 17 and 10% reduction in yield of No. 1 roots, respectively, compared with the weed-free control. The 3 and 4 WAP timings of halosulfuron did not reduce yield of No. 1 roots. Total yield was reduced approximately 11% at the 1, 2, and 3 WAP application timings. Halosulfuron at 4 WAP did not reduce total yield. Combined over year, site, and cultivar, halosulfuron applied at 39 g/ha did not reduce the weight of No. 1 roots or total crop yield and thus could be an effective POST option for weed control in sweetpotato.

A semi- and high-density apple and peach orchard was established at Blacksburg, VA. Starting 1 yr after transplanting, tree rows were treated with paraquat, 2,4-D, or amitrole plus simazine for 4 yr. Thereafter, diuron, simazine, or terbacil was applied in conjunction with paraquat or glyphosate. During the 12th growing season, young trees planted between existing trees failed to make proper growth. Oat bioassay of soils collected from treated rows revealed that the tree row topsoil (0 to 7.5 cm) produced less oat biomass than did deeper row soils (to 30 cm) or soils of corresponding depths from adjacent non-treated tall fescue sod alleyways. Poor growth of trees may have been related to other factors (competition from older trees, drought conditions, etc.) since herbicide residues in the upper 7.5 cm would have little effect on tree roots below this depth. After 3 yr the trees developed normally. Tree rows became heavily infested with weeds 1 yr following cessation of 23 yr of consecutive herbicide treatments.

An experiment was conducted to evaluate the translocation pattern of 14C-glyphosate and 14C-quizalofop in five quackgrass biotypes at two stages of growth. Whole plant translocation differed between stages for each herbicide. The percentage of 14C-glyphosate and 14C-quizalofop in the leafwash and in the treated leaf did not differ among biotypes, but differences occurred for the translocation to the underground parts. The partitioning of the 14C-glyphosate and 14C-quizalofop in the treated crown, other crowns, propagating rhizomes, and other rhizomes differed among biotypes. On a disintegration per minute (DPM) mg-1 basis, differences among biotypes were found with 14C-glyphosate but much less with 14C-quizalofop. Metabolism of 14C-quizalofop in the treated leaf was similar in the two biotypes tested except for the percentage of polar metabolites 1 d after treatment. The percentage of 14C-quizalofop available for translocation was the same in both biotypes.

Field and greenhouse experiments were conducted to determine the effect of selected insecticides on cotton when applied in combination with pyrithiobac. In the field, acephate, azinphos-methyl, bifenthrin, chlorpyrifos, dicrotophos, esfenvalerate, malathion, methomyl, or oxamyl was applied foliarly with the sodium salt of pyrithiobac at 70 g ae/ha. Pyrithiobac plus malathion resulted in greatest injury when compared with other treatments. There were no differences observed in fruiting characteristics of cotton. Cotton yield was lower with oxamyl, methomyl, and chlorpyrifos when applied in combination with pyrithiobac in one of three experiments. In greenhouse experiments, injury due to pyrithiobac was greater in a cool (21 C day, 13 C night) temperature than in a warm temperature (30 C day, 21 C night), but differences were less than 15%. Pyrithiobac plus malathion in the cool environment injured cotton more severely 7 DAT than either pesticide alone. Adding insecticides to pyrithiobac did not influence injury in the warm environment.

The ARS Pesticide Properties Database (PPD) is a compendium of chemical and physical properties of a collection of widely used pesticides. At present, there are 92 compounds in the database and we have focused on 19 of the most important properties impacting on groundwater and atmospheric quality. The PPD relies upon experimentally determined data points. With the help of the National Agricultural Chemicals Association (NACA) we have been communicating directly with manufacturers to obtain the original experimental data with which they characterize pesticide properties and fulfill requirements for federal and state regulations. This provides the basis for the PPD which is augmented with data from the scientific literature. Features of the PPD are: 1. 19 parameters are provided for each pesticide. 2. References are given for all data. 3. When there are several values for a given property, all are cited. 4. All data have been verified and provide the latest, most reliable figures available.

In recent years considerable research in the private and public sectors has been directed toward introducing herbicide tolerance into normally susceptible crop species (9). Interest in developing herbicide-tolerant crop cultivars, clones, or hybrids (HTCs)3 has been spurred by the reduction in the rate of discovery of new herbicidal compounds, the rising expense of developing new herbicides, and new tools of biotechnology that greatly increased our ability to develop HTC genotypes. Potential benefits of developing HTCs include: a) an increased margin of safety with which herbicides can be used with subsequent reduced crop losses due to herbicide injury, b) reduced risk of crop damage from residual herbicides from rotational crops, and c) introduction of new herbicides for use on normally susceptible crops. The last objective can be considered to be similar to breeding for resistance to diseases or insects. The most serious weed problems for a crop can be solved by developing crop tolerance to herbicides that control the weeds. This approach is particularly promising for minor crops for which new herbicide development is essentially lacking. However, the reluctance of herbicide manufacturers to register their products for minor crops may impede this approach. By developing tolerance to nontoxic, nonpolluting herbicides that are suitable for conservation tillage, the negative environmental effects of weed control can be reduced.

The effect of season-long interference by bands of weeds growing only between rows (BR) on field corn yields has not been reported before or compared with weedy and weed-free (i.e., weeded) plots or bands of weeds growing only in row (IR). The null hypothesis of this research was that field corn yields would be ranked as weed-free > BR weedy only > IR weedy only > weedy (IR + BR weedy) in response to season-long weed interference by these four treatments. Weeds growing as bands closest to field corn were expected to reduce field corn yields more than those growing as bands further away between field corn rows. Field corn yield response to these four weed interference treatments was studied in Missouri for 4 yr. In late summer, most weed ground cover consisted of giant foxtail, the chief weed present, and common waterhemp, a lesser weed. Observed field corn yields averaged for 4 yr were ranked as weed-free > IR weedy only > BR weedy only > weedy. Field corn yields of the IR weedy only, BR weedy only, and weedy treatments averaged 76, 63, and 41%, respectively, of the weed-free treatment (=7,820 kg/ha). In two of the 4 yr, field corn yield of the IR weedy treatment exceeded that of the BR weedy treatment, whereas these treatments could not be statistically distinguished from one another in the other 2 yr. These research results refute the null hypothesis and demonstrate that it may be more critical to control BR than IR weeds, although controlling both BR and IR weeds maximized field corn yields.

Research was conducted in 2006 and 2007 to evaluate nicosulfuron tank-mixes for field sandbur control and crop injury to ‘Tifton 85’ and ‘Jiggs’ bermudagrass. In 2006, sequential applications of nicosulfuron + metsulfuron controlled field sandbur 86 to 90% 30 d after treatment (DAT) and 77 to 85% 90 DAT. Single applications of nicosulfuron provided less than 63% control 90 DAT. In 2007, sequential applications of nicosulfuron + metsulfuron controlled field sandbur 84 to 95% 42 DAT. Injury data showed Jiggs bermudagrass was generally more sensitive to herbicide treatment than Tifton 85. Injury to Tifton 85 bermudagrass ranged from 0 to 15%, whereas injury to Jiggs was 7 to 29% 22 DAT. Forage yield data for Jiggs showed significant reductions at the first and second harvests but no differences by the third harvest. No yield reduction was noted for Tifton 85 bermudagrass from any herbicide treatment. Results of these studies indicate that nicosulfuron + metsulfuron combinations are a viable option for field sandbur control in bermudagrass pastures.

Cold stress and field studies were conducted to determine the effects of alachlor, metolachlor, butylate plus dichlormid, and EPTC plus dichlormid on germination and seedling vigor of 30 sweet corn cultivars with three commercially important endosperm mutants (su, se, and sh2). Seedling emergence from cool soils was best when treated with EPTC plus dichlormid and alachlor and was decreased 11% by metolachlor and butylate plus dichlormid. The se and sh2 endosperm mutants were injured the most by the herbicides. Plant size was reduced by the thiocarbamate herbicides but not by the chloracetamides.

The optimum weeding regime for thorny mimosa control in cassava established at 10,000 plants/ha was studied at Ibadan, Nigeria (7°22½′N, 3°50½′ E), a humid tropical environment. The study compared six weeding regimes, each comprising manual removal of thorny mimosa three times at different intervals within 13 wk after planting (WAP). Cassava vegetative growth recovered from thorny mimosa interference when the first weeding occurred within 5 WAP, but interference for more than 5 WAP reduced storage root yield. Allowing thorny mimosa infestation after 11 WAP had no effect on cassava growth or root yield. Manual removal of thorny mimosa at 4, 7, and 11 WAP consistently gave the highest cassava root yield.

Two field studies were conducted to compare bentazon tolerance in “Bohemian Chili” (BCH) and “Keystone Resistant Giant” (KRG) with other pepper cultivars and plant introductions (PIs). In the first study, BCH, KRG, “Santaka” (SA), and “Sweet Banana” (SB) were treated with five rates of bentazon from 1.1 to 9.0 kg ai/ha. Based on foliar injury, the cultivars ranked BCH = SA < KRG < SB; based on yield tolerance to bentazon, they ranked KRG ≤ SB < SA ≤ BCH. In the second study, the response of BCH, KRG, SA, SB, and five PIs to 4.5 kg/ha bentazon showed that 3 PIs (127445, 163187, 246123) tolerated bentazon similarly to BCH and SA.

Studies were conducted to determine whether glufosinate treatments to glufosinate-resistant cotton caused changes in floral morphology, pollen viability, and seed set. Four glufosinate treatments were included: (1) glufosinate applied postemergence over the top (POST) at the four-leaf stage, (2) glufosinate applied POST at the eight-leaf stage, (3) the first two treatments sequentially, and (4) a POST application at the four-leaf stage followed by (fb) a postemergence-directed stem application (PDS) at the eight-leaf stage. Glufosinate was consistently applied at 0.49 kg ai/ha. A nontreated control was included. Glufosinate treatments did not affect stigma height, length of the staminal column, or pollen viability. However, the distance from the top anther to the tip of the stigma was less in plants treated with an eight-leaf POST treatment than in nontreated plants, although this difference is not likely to influence pollen deposition because in both cases anthers reached above the stigma tip. Plants receiving four-leaf POST fb eight-leaf PDS treatment with glufosinate had eight seeds per boll less than nontreated plants; however, the more rigorous four-leaf POST fb eight-leaf POST treatment did not differ from the nontreated in seeds per boll.

The difficulty of monitoring growth parameters of climbing invasive plants subjected to different control options can be overcome by using standardized support structures (trellises). The utility of such support structures on aboveground biomass accumulation and fruit production was demonstrated using the invasive climber, bridal creeper in three invaded nature reserves near Perth in Western Australia. Mean above-ground plant biomass for plots provided with trellises ranged from 204 ± 38 g/m2 to 336 ± 31 g/m2, whereas it ranged from 66 ± 10 g/m2 to 118 ± 10 g/m2 in plots with no trellises. The mean number of fruits/m2 produced on shoots in plots provided with trellises ranged from 424 ± 159 to 3,787 ± 873 and was up to almost four orders of magnitude greater than the number of fruits produced on plants in plots with no trellis (ranging from 0 to 5.25 ± 7.9). The use of standardized trellises also showed that fruit volume and fruit seed number can vary significantly between sites. Standardized trellises have been installed at sites across Australia to assess the long-term impact of biological control agents introduced to manage bridal creeper.

Field studies were conducted at Dekalb, Urbana, and Brownstown, IL, in 1996 and 1997 to evaluate corn (Zea mays) injury and weed control from preemergence applications of RPA 201772 alone and tank-mixed with metolachlor, atrazine, or both. No significant corn injury from RPA 201772 was observed at any time for all experiments. Giant foxtail (Setaria faberi) control at 60 days after treatment (DAT) was variable and ranged from 47 to 93% for RPA 201772 applied alone at 105 g ai/ ha. Giant foxtail control of at least 90% was observed by applying metolachlor at 1,120 g ai/ha with 105 g/ha RPA 201772. The addition of atrazine at either 1,120 or 1,680 g ai/ha improved control of giant foxtail compared with RPA 201772 applied alone at 105 g/ha in two of the six studies. RPA 201772 applied at 105 g/ha controlled at least 88% of velvetleaf (Abutilon theophrasti), Pennsylvania smartweed (Polygonum pensylvanicum), and smooth pigweed (Amaranthus hybridus). RPA 201772 controlled 88% or less of common waterhemp (Amaranthus rudis), common ragweed (Ambrosia artemisiifolia), and common cocklebur (Xanthium strumarium). Control of these three species was 92% or greater with RPA 201772 plus atrazine. Control of common lambsquarters (Chenopodium album) was at least 96% with RPA 201772 applied alone at any rate in four of the six studies. However, common lambsquarters control was 68 and 77% for RPA 201772 applied alone at 105 g/ha at Urbana and Brownstown in 1997, respectively, where high common lambsquarters densities were prevalent. Under these conditions, the addition of atrazine to RPA 201772 at 105 g/ha improved control of common lambsquarters. RPA 201772 has excellent potential to provide consistent control of velvetleaf compared with atrazine. In contrast, these studies indicate RPA 201772 may provide inconsistent control of certain weed species in different environments. In order to achieve consistent control of a broad spectrum of weed species, RPA 201772 must be combined with other herbicides.

Research trials conducted at two locations in the spring of 2004 evaluated the effect of soil temperature as an indicator for application timings of certain sulfonylurea herbicides for perennial ryegrass control while maintaining acceptable turfgrass quality during bermudagrass spring transition. Herbicide application timings began when soil temperatures reached 17 C (April 14, 2004). Greater perennial ryegrass control 4 wk after initial treatment (WAIT) was achieved when sulfonylurea herbicides were applied at 26 C soil temperature compared to 17 or 21 C. Bermudagrass density 6 WAIT increased with treatments applied at 26 C soil temperature compared to cooler soil temperatures. There was a decrease in overall turfgrass quality 2 WAIT when treatments were applied at 17 C. However, by 4 WAIT all application timings provided overall turfgrass quality comparable to the untreated control. Acceptable turfgrass quality and maximum perennial ryegrass control was achieved by delaying transition-aid herbicide applications until soil temperatures reached 26 C and growing conditions were more conducive to bermudagrass growth.

Pathogens were not seriously considered as biological control agents for aquatic plants in the United States until the Chesapeake Bay Eurasian watermilfoil decline occurred in the 1960s. The decline and suggestion that it was induced by pathogens spawned interest in the use of pathogens as biological control agents for nuisance aquatic species. In the years that followed, emphasis was placed on finding pathogen agents for some of the most problematic aquatic weeds, including waterhyacinth, Eurasian watermilfoil, and hydrilla. The scientist that has contributed the most to our knowledge of pathogen biological control in aquatic plants has been Dr. Raghavan Charudattan (University of Florida, Gainesville, FL). For the past 40 yr, he has authored or coauthored more than 50 manuscripts devoted to the subject in peer-reviewed journals, books, and proceedings.

Selected herbicide treatments from 25 winter annual broadleaf weed control experiments conducted across Oklahoma from 1979 to 1993 were examined for winter wheat yield response to weed control. All experiments contained one or two of the same three weeds (henbit, bushy wallflower, or cutleaf eveningprimrose) as the primary target(s). Herbicide treatments included chlorsulfuron at 8.8 or 17.6 g ai/ha, and/or 2,4-D at 420 g ae/ha, all broadcast POST to wheat. Most herbicide treatments controlled the weeds, but increased wheat grain yield at only one site, wherein bushy wallflower density was 830/m2. Correlation analysis found no relationship between weed densities and wheat yield when chlorsulfuron at 8.8 g/ha was applied for henbit or moderate levels of bushy wallflower or cutleaf eveningprimrose. There was a significant positive relationship favoring spraying of bushy wallflower when the correlation analysis included data from one site with a density of 830 plants/m2.

Centipedegrass is tolerant of both atrazine and mesotrione when applied separately to established turf. However, no information is available regarding the use of mesotrione or the synergistic mixture of atrazine plus mesotrione applied to centipedegrass during seeded establishment. Research was conducted to evaluate centipedegrass tolerance to various rates and combinations of atrazine plus mesotrione when applied 14 d after emergence (DAE). Experiment 1 evaluated centipedegrass tolerance to atrazine and mesotrione in a broad rate-range screen in a greenhouse environment. Variations were observed between greenhouse trial runs with respect to injury and biomass with less injury and decrease in biomass observed in run 2. Overall, atrazine alone and atrazine plus mesotrione were more injurious for a greater time period and decreased biomass more than mesotrione alone. In fact, although mesotrione alone initially reduced centipedegrass photosystem II efficiency, an overall increase in efficiency was observed 28 d after treatment (DAT). Based on experiment 1, atrazine at 0.28 kg ai/ha was the maximum rate that could be applied to seedling centipedegrass when tank mixed with mesotrione. Experiment 2 evaluated atrazine at 0.28 kg/ha plus mesotrione at 0.03 to 0.28 kg/ha on centipedegrass field establishment. Although all atrazine plus mesotrione treatments reduced centipedegrass ground cover 28 DAT; no treatment reduced centipedegrass ground cover 49 DAT.