The effect of the herbicide buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} on photosynthesis, respiration, anthocyanin formation and leaf ultrastructure of corn (Zea mays L. ‘Pioneer 3780’) was studied following pre- or postemergence applications. Total photosynthesis and dark respiration were measured with an infrared CO2 analyzer in an open air flow system 12, 18, and 24 days after preemergence treatment with 0, 0.56, 1.12, and 2.24 kg/ha of buthidazole. The 0.56 and 1.12 kg/ha preemergence treatments had no effect on total corn photosynthesis even 24 days after treatment, whereas buthidazole at 2.24 kg/ha inhibited photosynthesis as early as 12 days. Total photosynthesis and dark respiration were also measured in whole plants, 30 cm tall, before herbicide application and 4, 24, 48, and 96 h after postemergence treatment with buthidazole at 0, 0.28, 0.56, 0.84, and 1.12 kg/ha. Following postemergence treatment, buthidazole inhibited total corn photosynthesis at any rate examined as early as 4 h after treatment. Neither pre- or postemergence buthidazole applications influenced respiration with the exception of a transitory increase caused by 0.56 kg/ha 12 days after preemergence treatment and by 0.84 and 1.12 kg/ha 4 h after postemergence treatment. Transmission electron micrographs revealed that buthidazole applied postemergence at 0.28 and 1.12 kg/ha reduced or prevented the accumulation of starch in bundle sheath chloroplasts as early as 24 h after treatment. Ultrastructural disruptions in some mesophyll chloroplasts of treated corn plants were also evident. Preemergence application of buthidazole at rates of 0.28, 0.42, 0.56, and 1.12 kg/ha inhibited anthocyanin formation indicating an alteration in corn metabolism.

Field studies and laboratory analyses were conducted to examine factors affecting degradation of 14C-atrazine [2-chloro-4-(ethylamine)-6-(isopropylamino)-s-triazine] under field conditions. The effects of these factors on weed control under no-tillage and conventional tillage systems were also examined. The amount of radioactivity which was unextractable in 90% methanol increased with time following treatment with 14C-atrazine. The rate of formation of unextractable 14C compounds was greater under no-tillage and increased with decreasing pH. After 14 to 18 days, a greater amount of extractable atrazine was present in areas receiving lime. The degradation of atrazine occurred more rapidly when surface pH was less than 5.0 compared with a pH greater than 6.5. The effect of lime on the amount of parent atrazine present in the soil was directly correlated to its effect on soil pH. Extractable atrazine in the soil 45 days after treatment was significantly correlated with weed control with the greatest effect under no-tillage.

Rates of loss of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], and pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] from soil surfaces were evaluated in a series of field sampling studies. Herbicides were sprayed onto soil enclosed in rings with nylon mesh bottoms, exposed to field conditions, and analyzed periodically by gas chromatography. The herbicides were lost rapidly in the first 3 to 5 days from Bosket silt loam and Sharkey clay, although the initial rate of loss was less rapid in the clay. Trifluralin and fluchloralin were lost more rapidly than pendimethalin. Half-life values for the first 3 to 5 days for trifluralin, fluchloralin, and pendimethalin, respectively, were 2, 1.5, and 4 days on silt loam and 2, 4, and 6 days on clay. Rates of loss were much lower for the remainder of the 7- or 12-day sampling periods. Rainfall on the first day of the sampling period resulted in increased initial loss of all herbicides. Shading from direct sunlight greatly reduced the loss of fluchloralin and pendimethalin as compared to exposure to full sunlight, although trifluralin loss remained fairly rapid under shaded conditions. Simulated rainfall on the first day resulted in significantly increased dissipation of fluchloralin and pendimethalin.

Six ecotypes of saltcedar (Tamarix pentandra Pall.), an introduced competitive phreatophyte, were collected from Wyoming to Texas and grown at Los Lunas, New Mexico. Cladophyll epicuticular alkane and fatty acid contents were analyzed by gas-liquid chromatography. Fatty acid and alkane contents varied among the six morphologically-indistinguishable ecotypes. Alkane content patterns varied on the basis or absence of C39 and other constituents. Fatty acid contents of the C16 to C22 were different among the ecotypes. Variation was not explicable on the basis of latitude, light intensity, temperature, nutrition, or water status. Thus, the chemical taxonomy hypothesis of uniform epicuticular alkane quality within a species is not substantiated in saltcedar, and a portion of the ecotypic resistance to postemergence herbicide sprays may be due to differences in epicuticular wax quantity and quality.

Absorption and translocation of 14C-glyphosate [N-(phosphonomethyl)glycine] in johnsongrass [Sorghum halepense (L.) Pers.] and soybeans [Glycine max (L.) Merr. ‘Lee 68’] were evaluated under various environmental conditions. The toxicity of unlabeled glyphosate applied similarly was determined in soybeans under similar conditions. In johnsongrass, absorption of 14C-glyphosate nearly doubled and translocation increased as air temperature increased from 24 to 35 C. Translocation in johnsongrass and soybeans was often greater at a relative humidity (RH) of 100% than at 45% and at a soil moisture level of 20% (field capacity) than at 12% (near the wilting point). In soybeans, absorption of 14C-glyphosate increased about 100%, translocation increased between 100 and 1200%, and glyphosate toxicity increased more than 200% as temperature decreased from 35 to 24 C. At 35 C, translocation in soybeans was often greater at 20% than 12% soil moisture. Absorption of 14C-glyphosate in soybeans was greater when the herbicide was applied to mature rather than immature leaves and stems, but the age of the treated tissue had less effect on 14C translocation. The addition of surfactant plus KH2PO4 to the treatment solution increased glyphosate absorption and translocation in soybeans, but addition of surfactant alone reduced translocation and addition of KH2PO4 alone increased translocation. Injury to six soybean cultivars from application of unlabeled glyphosate at 0.4 kg/ha ranged from 37% to 95% while total absorption of 14C-glyphosate into treated leaves of the same six cultivars ranged from 23% to 74% of the amount applied.

Based on an herbarium survey, clover broomrape (Orobanche minor J. E. Smith) was found to have an 116 yr history in the United States. It has been collected 98 times in a total of 32 counties in 12 states and the District of Columbia, and it appears to have become established in seaports and along railroads. It most commonly parasitizes red and white clover, but also burley tobacco, carrots, and several species of ornamental shrubs and herbs. Distribution of clover broomrape indicates either a pattern of repeated introductions from foreign sources, or a persistence in areas where the parasite has become established. While not presently a significant threat, the potential for damage to crops of economic importance cannot be ruled out. The flowers are autogamous.

Viability of enzymatically isolated and purified oat (Avena sativa L. ‘Markton’) mesophyll protoplasts was established by their ability to photosynthetically fix CO2 and to accumulate neutral red. When protoplasts were treated with 10-3 M alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], barban (4-chloro-2-butynyl m-chlorocarbanilate), dalapon (2,2-dichloropropionic acid), dicamba (3,6-dichloro-o-anisic acid), glyphosate [N-(phosphonomethyl)glycine], oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), picloram (4-amino-3,5,6-trichloropicolinic acid), or trifluralin [α,α,α-trifluroro-2,6-dinitro-N,N-dipropyl-p-toluidine), only alachlor and barban caused significant leakage of 14C-labeled material from the protoplasts as compared to controls. An abrupt increase in leakage occurred when protoplasts were treated with Tween 20 (polyoxyethylene 20 sorbitan monolaurate) at concentrations above 0.01% (v/v). The amount of leakage from protoplasts treated with dalapon or paraquat in combination with Tween 20 appears to be equivalent to the sum of the individual treatments. Treatment of the plasma membrane ATPase with the above named herbicides during the assay period shows that alachlor, barban, and dicamba reduces enzyme activity whereas glyphosate increases the activity. Pretreatment of the membrane ATPase with the herbicides in assay buffer [36mM Tris [tris-(hydroxymethyl)-aminomethane]-MES [2-(N-morpholino)ethanesulfonic acid], 3mM MgSO4, 50mM KC1] did not inhibit the enzyme activity during the assay period. Pretreatment with dicamba, glyphosate, and picloram in gradient buffer [1mM Tris-MES, 1mM MgSO4, 1mM dithiothreitol] did inhibit enzyme acitivty during the assay period. However, these herbicides cause the pH of the gradient buffer to be acidic.