A mixture of diquat [6,7-dihydrodipyrido(1,2-α: 2′,1′-c) pyrazinediium ion] and copper sulfate pentahydrate was applied to artificial chinook salmon (Onchorhynchus tshawytscha Wal.) spawning channels to reduce excessive growths of algae [Cladophora glomerata (L.) Kutz]. Juvenile salmon were not harmed by the applications. A concentration of 100 ppb w/w diquat plus 150 ppb copper-ion was maintained for 3 hr. The alga was controlled satisfactorily for distances up to 0.5 km per treatment. Each treatment consisted of one to three applications, each made on consecutive days. Water temperature was 11.2 C during three winter applications and 15.5 C during a spring application. Diquat was rapidly sorbed out of the treated water to 3.8 ppb at 1.6 km. Copper-ion residues dissipated to 60 ppb at 1.6 km.

The tolerance of wheat (Triticum aestivum L. ‘Waldron’) and wild oat (Avena fatua L.) to various rates of flufenprop-methyl {methyl-2-[benzoyl(3-chloro-4-fluorophenyl)amino]propanoate} applied weekly after wheat and wild oat emergence was determined under field conditions. Wild oat control increased at all growth stages as flufenprop-methyl rate increased. Wild oat control was greater than 80% with flufenprop-methyl at all rates when applied up to 6 weeks after wild oat emergence: (anthesis stage), but decreased when application was delayed further. Wheat was most susceptible to flufenprop-methyl during anthesis. Flufenprop-methyl at 0.56 kg/ha injured weed-free wheat only at the boot and anthesis stages. Injury intensity and the number of weeks that injury remained evident increased as flufenprop-methyl rate increased. Flufenprop-methyl injury to wheat was expressed as reduced plant height, grain yield, and kernels per spike and increased grain protein. Plant height reductions were attributed to reduced cell elongation. Grain yield reductions resulted from reduced kernels per spike.

Bermudagrass growing in a creeping bentgrass green is a severe problem where both grasses are grown. An experiment was conducted to determine the effects of multiple flurprimidol-herbicide applications on tolerance of bentgrass and on suppression of three bermudagrass cultivars in bentgrass. Application of 1.4 kg ai ha–1 flurprimidol on April 15 and 0.8 kg ha–1 repeated on June 1 injured creeping bentgrass 44% in 1988 and 22% in 1989. Bermudagrass was suppressed from the two flurprimidol applications until mid-June in 1988. Growth in 1989 was not influenced by number of applications since bermudagrass was suppressed only until late May. Application of 0.8 + 54 kg ai ha–1 flurprimidol plus siduron on April 15 and 0.4 + 27 kg ha–1 on June 1 injured creeping bentgrass 23 to 28% and suppressed bermudagrass until mid-July in 1988 and mid-June in 1989. Application of 0.8 + 1.7 kg ha–1 flurprimidol plus ethofumesate on April 15 and 0.4 + 0.8 kg ha–1 on June 1 injured creeping bentgrass 25 to 28% and effectively suppressed bermudagrass until late August in 1988 and late June in 1989. Application of 0.8 + 54 kg ha–1 flurprimidol plus siduron or 0.8 + 1.7 kg ha–1 flurprimidol plus ethofumesate applied in June or June and July to plots treated in April did not improve bermudagrass suppression. In most instances there was an inverse relationship between bermudagrass suppression and number of bermudagrass stolons. There were interactions between flurprimidol-herbicide treatments on bermudagrass cultivars on number of stolons but not on suppression.

Our objective was to determine if the chlorsulfuron-induced reduction in assimilate export from leaves can be attributed to a shortage of carbohydrates. Treated canola leaves showed no reduction in carbon fixation or carbohydrate production during the first 24 h, but they exuded only 17 to 27% of the amount of sucrose exuded by corresponding control leaves. Exposure of the leaves to higher concentrations of CO2 (500 vs. 350 μl L−1) resulted in greater net carbon exchange and higher starch content, but failed to overcome the reduction in sucrose export, presumably because of increased carbon allocation to starch.

Thirteen prominent species decreased 40% or more after applications of (2,4-dichlorophenoxy)acetic acid (2,4-D) at 2.2 kg/ha. Four of the “most-susceptible” species [gumweed (Grindelia squarrosa (Pursh) Dunal), fringed sagebrush (Artemisia frigida Willd.), drummond milk vetch (Astragalus drummondii Dougl. in Hook.), and hairy goldaster (Chrysopsis villosa (Pursh) Nutt.)] are considered undesirable and two of them [bluebells (Mertensia lanceolata (Pursh) A. DC.) and evening-primrose (Oenothera coronopifolia Torr. & Gray)] desirable. The other seven species of this group are quite unimportant for cattle. Therefore, spraying mixed-grass prairie with 2,4-D improves range condition and increases forage production.

I am grateful for the opportunity to share with you some thoughts on the benefits of agricultural chemicals. I want to invite you to help examine some important aspects of this complex subject.

Environmental control chamber experiments showed that cotton (Gossypium hirsutum L. ‘Stoneville 213′) and soybean [Glycine max (L.) Merr. ‘Bragg’] root and shoot growth were reduced when treated with increasing rates of dinitramine (N4,N4-diethyl-α,α,α-tri-fluoro-3,5-dinitrotoluene-2,4-diamine), profluralin [N-(cyclopropylmethyl)-α,αα-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α-trifluoro-2,6-dintrio-N,N-dipropyl-p-toluidine). Viusal root ratings, dry root weights, and fresh and dry herbage weights were used to evaluate plant response to herbicide treatments in environmental chambers. The order of increasing GR50 values for cotton on two soils and with all response measurements, except dry root weights on one soil, was trifluralin, dinitramine, and profluralin. The order of increasing GR50 values for soybeans on two soils and with all response measurements was dinitramine, trifluralin, and profluralin.

Phytochrome was assayed in vivo in the rhizomes of 12 to 14-week old johnsongrass [Sorghum halapense (L.) Pers.] plants. The phytochrome levels decreased basipetally from the apex through the eighth node. The decrease was logarithmic on a dry weight basis, but less rapid on a per segment basis. On a dry weight basis, higher phytochrome measurements were obtained with samples from the interior of the rhizome than from the external regions. The far-red absorbing form of phytochrome (Pfr) was shown to be very labile at 25 C in johnsongrass rhizomes. These results provide a basis for examining photomorphogenic responses of rhizomes to light and for correlating these responses to phytochrome photophysiology.

Field and laboratory studies were conducted to examine effects of prior butylate use on biodegradation of subsequent applications of butylate and four other carbamothioate herbicides. Bioassays were used to demonstrate reductions of butylate and EPTC activity in four soils preconditioned by annual butylate applications. Combining these herbicides with dietholate, an enzyme inhibitor, prolonged persistence and restored normal herbicidal activity. Expected herbicidal efficacy occurred in adjacent plots with no history of carbamothioate use. Prior applications of butylate resulted in cross-adapted degradation of EPTC but not vernolate, pebulate, or cycloate. When samples of Cecil soil were treated in the laboratory with 14C-butylate, evolution of 14CO2 was significantly higher from soils that had received repeated field applications of butylate. The use of 14C-herbkides could be used to predict problem soils and potential herbicide failure.

When applied at 0.1 or 0.3 kg/ha, acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} did not reduce rough rice (Oryza sativa L. ‘Labelle’) yield, milling yield, seed weight, seed germination, or plant height, regardless of growth stage. Application of 0.6 kg/ha to rice in the boot, late boot, or panicle filling stage reduced yields, but had no effect on plant height, seed germination, or whole milling yield.

Use of R-25788 (N,N-diallyl-2,2-dichloroacetamide) eliminated early-season corn (Zea mays L. '501D′) injury, stand loss, and yield reduction caused by EPTC (S-ethyl dipropylthiocarbamate) at 3.4, 6.7, and 13.4 kg/ha. R-25788 also eliminated early-season corn injury from butylate (S-ethyl diisobutylthiocarbamate) at 9.0 kg/ha. R-25788 did not consistently prevent corn yield reduction from 2,4-D [(2,4-dichlorophenoxy)acetic acid] or EPTC + 2,4-D. R-25788 had no effect on weed control from any of the herbicides evaluated nor any effect by itself on corn injury or corn yield. No corn injury or yield reductions occurred from vernolate (S-propyl dipropylthiocarbamate) at rates up to 6.7 kg/ha or alachlor [2-chloro-2′, 6′-diethyl-N-(methoxymethyl)acetanilide] at rates up to 13.4 kg/ha. Early-season corn injury frequently did not result in reduced corn yield.

Screening studies initiated in 1969 to determine the effectiveness and selectivity of herbicides for herbaceous weed control during the first growing season in American sycamore (Plantanus occidentalis L.) plantations indicated that simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], atrazine [2-chloro-4-(ethylamino)-6- (isopropylamino)-s-triazine], and dalapon (2,2-dichloropropionic acid) had the desired properties at economically feasible use rates. To further evaluate these herbicides and ametryne [2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine], permanent plots were established in a sycamore plantation in 1970. Weed control obtained from a single herbicide application in the spring after planting seedlings in the winter has resulted in increased height, diameter, and volume growth of the sycamore for at least three growing seasons. No serious phytotoxicity on the crop species was noted with application rates from 4.5 to 9.0 kg/ha of the s-triazines alone or from 5.6 kg/ha of dalapon in combination with the lower rate of simazine and atrazine.

Experiments conducted for two consecutive years indicated measurable interference of barnyardgrass, large crabgrass, and giant foxtail with container-grown Bailey's redosier dogwood as early as 21 days after transplanting of grass seedlings into the containers. Few differences in interference were seen among the three grass weeds. Grass weed densities ranging from one to six weeds per container reduced the dogwood growth. By the termination of the studies, dogwood shoot dry weight, averaged over all grass weeds, was decreased as much as 72% by five weeds per container. Eight weeks after recommended rates of fenoxaprop, haloxyfop, and ethyl ester of quizalofop were applied to dogwood, no phytotoxicity was apparent. These compounds exhibited selectivity for postemergence use in Bailey's redosier dogwood.

Our purpose was to investigate the influence of growth reserves of perennial range grasses on their tolerance to applications of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Competing annual grasses were removed with atrazine treatment at 1.1 kg/ha. The carbohydrate reserves of the perennial grasses were reduced by mowing the previous season. Crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult.] plants with reduced carbohydrate reserves, as indicated by reduced etiolated growth, were less tolerant to atrazine than their nonmowed counterparts. Without reduced carbohydrate reserves, squirreltail [Sitanion hystrix (Nutt.) J. G. Smith] was much more susceptible to atrazine than crested wheatgrass. Thus, the weed control treatment did not necessarily increase the density of desirable perennial grasses.

Paraquat is known to affect all green plants and other eukaryotic organisms including mammalian cells. The aim of this study was to improve the understanding of paraquat toxicity in nonphotosynthetic plant cells using dark-grown kidney bean cells in tissue culture. It is shown that uptake of paraquat is an active process, and that paraquat inhibits cell growth, reduces DNA synthesis, and inhibits the activity of hydroxypyruvate reductase while enhancing the activity of glutathione reductase which is involved in cellular defense against oxidant stress. Additionally, it is demonstrated that iron ions are involved in paraquat toxicity. We conclude that uptake of paraquat into cells is via polyamine channels and that the deleterious effects of paraquat on these nonphotosynthetic cells are mediated by iron.

The tolerance of four legume species to nitrofen (2,4-dichloro-phenyl-p-nitrophenyl ether), fluorodifen (p-nitrophenyl α,α,α-trifluoro-2-nitro-p-tolyl ether), and oxyfluorofen [2-chloro-1-(3-ethoxy-4-nitro-phenoxy)-4-(trifluoro-methyl)benzene] was investigated both pre- and postemergence in the greenhouse. Seedlings of species that emerged most rapidly seemed to be most tolerant to preemergence herbicide applications. There was no direct relationship between preemergence and postemergence tolerance. Oxyfluorfen was found to be at least 10 times as active as the other two herbicides both pre- and postemergence. Field experiments were conducted at two locations in Indiana to test the effect of method of application on the activity and selectivity of fluorodifen and oxyfluorfen on soybean [Glycine max (L.) Merr. ‘Wayne’] and greenbean (Phaseolus vulgaris L. ‘Spartan Arrow’). Crop injury and grass weed control were reduced by incorporation of the herbicides 8 cm deep in a silt loam. Method of application did not affect the activity of the herbicides on a sandy soil low in organic matter. Soybean was more tolerant than greenbean to both herbicides when applied preemergence but oxyfluorfen was far more active than fluorodifen on both crops.

This paper reports on a microtitre plate version of the 2,6-dichlorophenol-indophenol (DCPIP) reduction assay. DCPIP reduction rates of alfalfa thylakoid membranes were determined by measuring absorbance at 600 nm before and after a 1 min illumination period. The membranes were near light-saturated at intensities above 600 μE m–2 s–1. Saturation of thylakoid membranes with DCPIP occurred above 120 μM. DCPIP reduction rates increased linearly with chlorophyll concentrations from 0.25 to 2 μg. The rate of DCPIP reduction was linear throughout a 2 min illumination period (R2 = 0.99). The assay was sensitive enough to terbacil to differentiate between a 20% change in the I50 concentration. DCPIP reduction rates were sensitive to concentrations of terbacil as low as 100 nM. It only takes 13 minutes to load and read 96 samples using the microtitre plate assay compared to 5.5 h using the conventional procedure.

Fomesafen is a protoporphyrinogen oxidase (PROTOX) inhibitor that has the potential to be used as an alternative mechanism of action for PRE nutsedge and broadleaf weed control in Florida production of small fruit and vegetables. Fumigation in the raised-bed plasticulture system may increase herbicide persistence. Fomesafen persistence could dissuade Florida growers from using the herbicide for fear of injury to subsequent susceptible crops. Field experiments were conducted in Balm, FL, in 2015 and 2016 to investigate the effect of fumigation on fomesafen dissipation, eggplant tolerance, and purple nutsedge control. Treatments included fomesafen at 0.42 kg ai ha−1, S-metolachlor at 1.06 kg ai ha−1, and a nontreated control in either a fumigated bed injected with a combination of 39% 1,3-dichloropropene and 59.6% chloropicrin at 336 kg ha−1 or no fumigant. Fomesafen concentration in the soil decreased by 83% and 96% from application to harvest in 2015 and 2016, respectively. Fumigation did not affect fomesafen dissipation in either year. At 2 wk after transplant (WATr), fomesafen caused 14% eggplant injury. Injury decreased to less than 5% at 6 WATr. Fomesafen and S-metolachlor treatments did not reduce eggplant height or yields compared with the nontreated control. Fumigation and fomesafen did not decrease purple nutsedge density; however, S-metolachlor applications resulted in a 48% reduction. Further research is needed to assess efficacy on broadleaf and grass weeds.

Annual application of AC-94377 at 3.4 kg ha−1 in the field reduced survival of shallowly buried (1.25 cm deep), undisturbed wild mustard seed compared to untreated check seed in two 4-yr-long trials. By the second fall, greater than twofold more untreated check seed survived as did AC-94377-treated seed. Moreover, no AC-94377-treated seed survived beyond year three following treatment in fall alone or fall plus spring in each of 3 yr. In contrast, 25% of untreated check seed survived into the fall of year four. AC-94377 applied in spring alone, fall alone, or both spring and fall for each of 4 yr progressively reduced seed survival. Seed survival expressed as a percent of the initial number of seed buried was best modeled as a negative exponential function of time in years. In the greenhouse, more wild mustard seed on the soil surface established after AC-94377 treatment at 3.4 kg ha−1 when enclosed in large seed packets (5 by 12 cm), like those used in the field, than when in small seed packets (5 by 6.25 cm), whether or not the packets contained soil. When soil was added to either sized seed packet, fewer seed survived compared to seed not in seed packets or seed in packets without soil. Thus, it is likely that the field seed survival study underestimated effectiveness of AC-94377 to reduce wild mustard seed survival.

Field experiments were conducted to determine density-dependent effects of eastern black nightshade season-long interference on tomato-yield loss when growing in-row with staked plasticulture tomato. Eastern black nightshade was transplanted at densities of zero, one, two, three, four, or five plants per crop plant hole in the plastic. Eastern black nightshade densities of one to five reduced the number and weight of larger fruit grades (threes, extra larges, jumbos, marketables, totals) similarly but did not reduce yields of smaller fruit grades (culls, mediums, and larges) from the weed-free. Eastern black nightshade reduced percent yield loss of jumbo grade, the premium grade, which could be predicted by a rectangular hyperbola model. The value ($ ha−1) of jumbo fruit and the value of the sum of large, extra large, and jumbo grade was reduced at densities of eastern black nightshade as low as one plant per hole.