Field and greenhouse experiments in 1981 and 1982 determined the potential interactions of three preemergence and three postemergence herbicides with four granular insecticides in soybeans [Glycine max (L.) Merr.]. Generally, metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] increased soybean injury and lowered yields when applied to plots treated with an organophosphate insecticide at planting. Soybean injury from these treatments and from aldicarb [2-methyl-2-(methylthio)-propionaldehyde-o-(methylcarbamoyl)oxime] plus metribuzin applied in the field was greater in 1982 than 1981 due to excessive rainfall immediately after planting. Oryzalin (3,5-dinitro-N4,N4 -dipropylsulfanilamide) plus several of the in-furrow insecticide treatments in the greenhouse increased injury to soybeans. Other than this, the method of insecticide application, banded or in-furrow, had no effect on that caused by each pesticide combination.

Rosering gaillardia (Gaillardia pulchella Foug. # GAIPU) and other herbaceous broadleaf plants were effectively controlled for one season by sprays of 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 1.1 kg ae/ha or glyphosate [N-(phosphonomethyl)glycine] at 1.1 kg ai/ha, or a 4:1 combination of 2,4-D and picloram (4-amino-3,5,6-trichloropicolinic acid) at 0.7 kg ae/ha applied in late March in the southern Rolling Plains of Texas. Production of perennial warm-season grasses increased 428, 480, 728, and 1440 kg/ha on a clay site 7 months after spraying with 2,4-D, 2,4-D plus picloram (4:1), atrazine [2-chloro-4-(ethylamino)-6-isopropylamino-s-triazine], and glyphosate, respectively. Application of 4.4 kg ae/ha of dalapon (2,2-dichloropropionic acid) severely damaged perennial warm-season grasses. Annual cool-season grasses were effectively controlled with sprays of atrazine or glyphosate at 1.1 kg ai/ha or dalapon at 4.4 kg ae/ha. Texas wintergrass (Stipa leucotricha Trin. & Rupr.) production was greatest on rangeland treated with 2,4-D or 2,4-D plus picloram (4:1).

Major differences in above- ground biomass and tuber production of yellow nutsedge (Cyperus esculentus L. # CYPES) were not observed when corn (Zea mays L. “CO-OP S265”) was seeded on different dates (1st, 2nd, 3rd and 4th week of May; and 1st week of June). The final seedbed was prepared just prior to each seeding date and this cultivation stimulated dormant tubers to sprout. As a result, a large population of yellow nutsedge emerged with the corn at all seeding dates. Because fertilizer was banded near the corn row, yellow nutsedge biomass, tuber dry weight and number of tubers were higher within corn rows than between rows. Tuber size was affected by seeding date and shifted toward smaller tubers within corn rows and larger tubers between the rows as the corn was sown late. The optimum seeding date of corn was in the 3rd week of May when the highest corn yield was obtained and yellow nutsedge growth was generally reduced.

Nine soil-applied herbicides were evaluated in the field in cotton (Gossypium hirsutum L.) and soybeans [Glycine max (L.) Merr.] and in the greenhouse without crops to determine their effects on the control, regrowth, and tuber production of yellow nutsedge (Cyperus esculentus L.). Fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl) phenyl]-4(1H)-pyridinone} and norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] provided the best (100%) control in the greenhouse. Tubers exposed to herbicide-treated soil in the greenhouse for 4 or 8 weeks produced fewer new tubers when transplanted into nontreated soil than nontreated tubers did. Yellow nutsedge shoot and tuber populations in the field were significantly reduced by all herbicides, except for alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], after 2 yr of treatment in cotton and soybeans.

Simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] inhibited photosynthesis 50% at concentrations of 1.1 μM for Spirogyra jurgensii (Kutz), 3.0 μM for Pithophora oedogonia (Mont.) Wittr., and 3.8 μM for Cladophora glomerata (L.) Kutz. Photosynthesis of Ankistrodesmus braunii (Brun.), a nonfilamentous species, was inhibited the same amount by 4.7 μM simazine. The filamentous algal species had significant reductions in growth but no other phytotoxic symptoms when exposed to 5 μM simazine at light intensities of 100 μE·m–2·s–1 and below. Algicidal effects did occur at a light intensity of 400 μE·m–2·s–1 and were most severe in Spirogyra. The relationship between light intensity and simazine toxicity indicates algicidal effectiveness on these filamentous algae will be limited in habitats where light is reduced by turbidity, depth, or self-shading.

Field studies were conducted in 1979 and 1980 to determine yield losses caused by perennial sowthistle (Sonchus arvensis L. # SONAR) in rapeseed (Brassica napus L., B. campestris L.) fields in Saskatchewan and Manitoba. The relationship between percentage yield loss and density of perennial sowthistle was expressed by the linear regression equation y = −3.81 + 13.76 rdx. Weed survey data indicated that perennial sowthistle occurred in 39% of the rapeseed fields but infested only 7% of the hectares surveyed. Using both the survey data and the yield loss equation, the average annual loss in rapeseed yield was estimated to be 9.4 million kg in Saskatchewan and 6.1 million kg in Manitoba, with a value of 2.6 million and 1.7 million dollars (Cdn.), respectively. Perennial sowthistle occurs with a similar frequency and density in other crops so that the total loss from this weed would be much greater.

Field sudies on the persistence of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] showed less persistence under coulter than chisel or conventional plow tillage in the year of application. The residue on the coulter system from the previous corn (Zea mays L.) crop initially prevented as much as 30% of the atrazine from reaching the soil surface. After five annual applications, the atrazine residue was generally higher in the coulter than the chisel or conventional tillage systems, but below levels considered to be biologically active.

The adsorption of naphthalene by a Bosket loam soil was studied at 6.5, 15, 25, and 37C. Because the solubility and vapor pressure of naphthalene are precisely known over this temperature range, a complete thermodynamic description of the differences between standard vapor, crystal, solution, and soil-adsorbed states is possible. The results indicate that enthalpies and entropies of the solution and surface standard states are quite similar (though very different from the vapor state) resulting in a near-zero standard enthalpy difference and a small standard entropy increase for adsorption from solution. Considering naphthalene as a model for herbicides and as a probe into the nature of the soil surface, the results emphasize the importance of the unique structured nature of water acting as a solvent, and the competition of water for adsorption sites.

Effects of temperature, sunlight, soil incorporation and surface irrigation on the phytotoxicity of oryzalin (3,5-dinitro-N4,N4 -dipropylsulfanilamide) were studied. The activity of oryzalin applied 4 to 6 weeks prior to planting was enhanced by covering the soil with plastic as measured by the inhibition of grain sorghum [Sorghum bicolor (L.) Moench. 'Sexauer G-701′] root growth. Growth chamber studies demonstrated that oryzalin phytotoxicity to grain sorghum was greater at 20 and 25 C than at 30C. The control of foxtail millet [Setaria italica (L.) Beauv. #5 SETIT] bristly foxtail [Setaria verticillata (L.) Beauv. # SETVE], redroot pigweed (Amaranthus retroflexus L. # AMARE), and smooth pigweed (Amarantbus hybridus L.), and injury to grain sorghum increased as the thoroughness of mechanical incorporation of oryzalin into soil increased. The phytotoxicity of surface-applied oryzalin increased with increasing amounts of irrigation water until it equaled the level of a preplant-incorporated treatment.