The phytotoxicity of terbacil (3-tert-butyl-5-chloro-6-methyluracil) is not closely correlated with the amount applied, the amount in available soil solution, or the concentration in available soil solution since soil type has a pronounced effect on the levels necessary for phytotoxicity. About 19 times more terbacil was needed in a Chalmers silty clay loam (24% organic matter) than in a Bloomfield fine sand (0.3% organic matter) to cause a 30% control of sorghum (Sorghum biclor (L.) Moench ‘R.S. 610’). However, the Bloomfield fine sand required twice as great a concentration of terbacil in the soil solution as the Chalmers silty clay loam (0.314 μg/ml versus 0.157 μg/ml). The total adsorption of terbacil in the latter soil decreased 4.5 fold when the water: soil ratio was increased from 0.6:1 (approximately field capacity) to 32:1, but the ratio of the concentration adsorbed: concentration in the soil solution did not vary appreciably.

The 14C-labelled insecticide, 2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate (carbofuran), supplied to the roots of barley (Hordeum vulgare L. ‘Larker’) and corn (Zea mays L. ‘Mich 400’) seedlings was readily taken up and transported to the shoots. Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] did not inhibit carbofuran metabolism in barley or corn. Butylate (S-ethyl diisobutylthiocarbamate) slightly inhibited carbofuran metabolism in corn roots. Chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea] inhibited carbofuran metabolism by decreasing the concentration of 14C found in the acetone-insoluble residue and the methanol-soluble fraction in barley shoots. Chlorbromuron increased the carbofuran content and decreased the 2,3-dihydro-3-hydroxy-2,2-dimethyl-7-benzofuranyl methylcarbamate (3-hydroxycarbofuran) content of the chloroform-soluble fraction in both barley shoots and roots. Chlorbromuron did not affect carbofuran metabolism in corn.

Effects of herbicide combinations on aquatic invertebrates were evaluated in Inglis Reservoir, which is located in west coastal Florida. The addition of 6,7-dihydrodipyrido [1,2-a: 2′1′-c]pyrazinediium ion (diquat) plus the triethanolamine complex of copper sulfate (TAC) and diquat plus copper sulfate pentahydrate (CSP) for control of hydrilla (Hydrilla verticillata Casp.) decreased the number of invertebrates inhabiting the treated areas. The diquat plus CSP combination exerted the greatest effect upon invertebrate numbers. Both herbicide combinations, however, did alter significantly the number of taxonomic groups in the areas. Invertebrate declines were due more generally to resultant habitat changes (i.e., loss of hydrilla) than to direct herbicide toxicity. The response of fish to the effects of the herbicide treatments on invertebrates could be ascribed to dietary changes, decreased growth rates, and possible mortality.

Weed control trials were conducted on loblolly pine (Pinus taeda L.) or slash pine (Pinus elliottii Engelm.) seedbeds at 12 locations in the southeastern United States. Good weed control was obtained from 2,4-bis-(isopropylamino)-6-(methylthio)-s-triazine (prometryne) at 2.2 and 4.5 kg/ha; N,N-dimethyl-2,2-diphenylacetamide (diphenamid) at 4.5 and 9 kg/ha; α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) at 1.1 and 2.2 kg/ha; and 2-ethylthio-4,6-bis-isopropylamino-s-triazine (GS-16068) at 2.2 and 4.5 kg/ha as preemergence applications immediately followed by irrigation. Diphenamid and trifluralin treatments were not injurious to either pine species at either rate. GS-16068 was only slightly injurious at the high rate at one location. Prometryne was injurious at two locations at the high rate and at one location at the low rate.

Several herbicides and growth substances were applied singly and in combination at varying concentrations to soybean [Glycine max (L.) Merr. ‘Lee’]. This was an attempt to compare the growth inhibition obtained with that previously measured in the single-celled organism Chlorella pyrenoidosa Chick, and to investigate the plant pathways and sites by which inhibition occurs. Inhibition induced by paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), and 2,4-D [(2,4-dichlorophenoxy)acetic acid] satisfactorily supported the hypothesis inherent in a kinetic analysis of such results, whereas, that induced by atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and chloramben (3-amino-2,5-dichlorobenzoic acid) did not. A probit analysis of the atrazine and chloramben results indicated variability in the type of toxicity. Soybean was considerably more susceptible to 2,4-D than Chlorella pyrenoidosa but there was little difference in the type of growth inhibition response produced. Both were equally susceptible to atrazine. High concentrations of the growth regulator IAA (indoleacetic acid) were antagonistic to the growth inhibition induced by 2,4-D, while competitive inhibition occurred at the low concentration of IAA. The 2,4-D had only a slight effect on the inhibitory effect of paraquat and antagonistically interfered with that induced by atrazine.

Thirteen soil-incorporated herbicides, mainly of the dinitroaniline and carbamate groups, were evaluated in the greenhouse for selective control of hemp broomrape (Orobanche ramosa L.) in tomato (Lycopersicon esculentum Mill. ‘Rutgers’). Hemp broomrape readily parasitized tomato roots and competed vigorously with the host. Shoots of the parasite emerged within 6 weeks after inoculation. Herbicides at 0.1 to 10.0 ppmw, with one exception, significantly reduced shoot dry weight of tomato measured at 10 weeks after treatment, in comparison with untreated, noninoculated controls. Generally, the degree of inhibition of establishment of the parasite was correlated with herbicidal injury to tomato. None of the treatments prevented the establishment of the parasite without causing severe crop injury. However, N-n-propyl-N-tetrahydrofurfuryl-4-trifluoromethyl-2,6-dinitroaniline (CGA-14397, ER-9063) at 3.3 and 6.6 ppmw exhibited some degree of selectivity as indicated by relative shoot dry weights of the host and parasite. Activated charcoal applied as a root dip on tomato or in soil admixtures prior to transplanting had no effect on parasitism and growth of hemp broomrape.

The effects of seven s-triazines on the opening of the hypocotyl hook of cotton (Gossypium hirsutum L. ‘DPL Smooth Leaf’) and the germination of lettuce seed (Lactuca sativa L. ‘Grand Rapids’) were investigated. The s-triazines used were ametryne [2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine], atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], cyprazine [2-chloro-4-(cyclopropylamino)-6-(isopropylamino)-s-triazine], prometone [2,4-bis (isopropylamino)-6-methoxy-s-triazine], prometryne [2,4-bis (isopropylamino)-6-(methylthio)-s-triazine], propazine [2-chloro-4,6-bis(isopropylamino)-s-triazine], and simazine [2-chloro-4,6-bis(ethylamino)-s-triazine]. All triazines except cyprazine stimulated germination of lettuce seed given 4 min of dim red light but none were stimulatory in the dark. Maximum stimulation occurred with 1 X 10-8 to 1 X 10-12 M s-triazine. All triazines except atrazine and cyprazine stimulated the opening of cotton hypocotyl hooks given 2 hr of dim red light of the s-triazines tested. Prometryne and ametryne were the most stimulatory to hook opening in the light and the most inhibitory in the dark. Their effects paralleled those of kinetin.

Fall-applied 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) satisfactorily controlled annual and biennial weeds in tall bearded iris (Iris germanica L.). Increased application rates improved control of semitolerant weeds. Trifluralin controlled grass weeds better than simazine. Simazine caused leaf tip and root necrosis, and trifluralin prevented root growth of iris plants when incorporated in the root zone at high rates of application.

Proso millet (Panicum miliaceum L. ‘Turghai’, ‘M28’, and ‘Panhandle’) was planted at three or four dates from late April to late June in 1970, 1971, and 1972 on silt loam soil and in 1972 on sandy soil. A single spray application of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) at 2.24 kg/ha on half of each date plot was preemergence to the first date and preplanting to the last two or three dates of planting. Proso millet was not injured by atrazine. At each date, weed control was better on sprayed than on untreated plots. Foxtails (Setaria spp.) were the only weeds present after all plots on silt loam soil were sprayed postemergence with (2,4 dichlorophenoxy)acetic acid (2,4-D). Millet planted early produced higher yields than millet sown at normal planting dates if foxtail competition was not serious. Use of selective herbicides and spring planting offer a potential major gain in the profitability of millet production in areas where annual weed problems now relegate millet to summer planting.

Enhanced foliar injury was obtained with sprays containing the herbicide linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] and the insecticide carbaryl (napthyl-N-methylcarbamate) in tolerant carrot (Daucus carota L. ‘Chantenay’). Synergism occurred when the compounds were applied as tank mixes or applied at 1 day intervals. The photosynthetic rate of parsnip (Pastinacea sativa L. ‘Hollow Crown’) leaf discs exposed to both chemicals was greatly reduced when compared to tissues receiving linuron or carbaryl alone. Carbaryl enhanced the penetration of 14C-linuron into intact carrot leaves and parsnip leaf discs. The rate of linuron metabolism was also decreased in the presence of carbaryl. Both of these factors may contribute to the enhanced toxicity obtained with this combination of pesticides.

Vapor losses of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-p-toluidine), and nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] were studied under controlled laboratory conditions using a Florisil vapor trap. No nitralin vapor losses were detected at 50 C from a Lakeland loamy sand at field capacity with an air flow rate of 0.04 m3/hr for 3 hr; whereas, 24.5% and 12.5% of trifluralin and benefin, respectively, were lost as vapors. Volatility of trifluralin and benefin increased with increasing temperatures of 30, 40, and 50 C and increasing soil moisture from air dryness to field capacity. Vapor losses from granular benefin were similar to the spray applications at 30 and 40 C. Volatilization of granular trifluralin was reduced when compared to the spray application at 40 C and 30 C but was similar for both formulations for benefin. No significant losses from photodecomposition were noted for trifluralin, benefin, or nitralin when comparing radiated and unradiated soil surface treated samples.

Preemergence flame weeding followed by postemergence herbicide treatment was the best procedure found for controlling weeds in field plantings of two Dioscorea species. Of eight herbicides tested in one or more of five experiments, norea [3-(hexahydro-4,7-methanoindan-5-yl)-1,1-dimethylurea] gave the best weed control without crop injury. Two applications of norea (3.8 kg/ha each) controlled most weeds for one growing season. Better control resulted when plots were flamed one or two times before crop emergence and treated one or two times subsequently with norea. Although new growth developed in most cases when emerged Dioscorea shoots were destroyed by flaming, yields from plots so treated were low.

Johnsongrass [Sorghum halepense (L.) Pers.] control in corn (Zea mays L.) was studied from 1970 to 1972 using consecutive annual applications of alachlor (2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide) at 3.4 kg/ha, butylate (S-ethyi diisobutylthiocarbamate) at 4.5, 9.0, and 13.4 kg/ha, and EPTC (S-ethyl dipropylthiocarbamate) at 3.4, 6.7, and 13.4 kg/ha. In 1970, control was less than 60% for all herbicides, and there was no significant rate response. In 1971 butylate and EPTC at all rates provided 79 to 93% control. Alachlor gave 49% control. In 1972 control was similar to 1971. Control with one cultivation was additive to these herbicidal effects. Seed treatment with 0.5% 1,8-naphthalic anhydride adequately protected the corn from herbicide injury. Corn yields were closely correlated with johnsongrass control.