Canada Thistle Control by Atrazine

In greenhouse studies, atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine killed Canada thistle [Cirsium arvense(L.) Scop.] when applied as preemergence or postemergence treatments. Postemergence atrazine applications caused more rapid kill when allowed to cover the ground as well as the foliage compared to only foliar atrazine applications. In three field experiments conducted in 1967, 1968, and 1969, Canada thistle was controlled with atrazine and amitrole (3-amino-s-triazole) + NH4SCN. Control resulting from atrazine was as good or superior to amitrole + NH4SCN when both were applied to foliage prior to plowing. Control from 2.2 kg/ha of atrazine applied prior to plowing was 78% for the 3-year average. Atrazine applied preemergence at 2.2 kg/ha resulted in inferior control, whereas postemergence atrazine applications resulted in thistle control similar to treatments applied prior to plowing.</jats:p

Soil Organic Matter Effect on Activity of Acetanilides, CDAA, and Atrazine

Field and greenhouse studies were conducted to determine the influence of soil organic matter on herbicidal activity using four Pocomoke soils with organic matter contents of 4.8, 7.0, 11.9, and 17.0%. In field experiments, control of giant green foxtail [Setaria viridisvar.major(Gaud.) Posp.] was greater than 75% from all treatments of 2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide (alachlor), 2-chloro-N-isopropylacetanilide (propachlor), andN,N-diallyl-2-chloroacetamide (CDAA) with no statistical differences between chemicals, rates, or organic matter levels. Control was statistically lower from all 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) treatments except 2.6 kg/ha at 7% organic matter and 4.4 kg/ha at 7 and 17% organic matter. Under greenhouse conditions, giant foxtail (Setaria faberiHermm.) was used to establish GR50values on soils or soil mixtures containing 0.8, 1.9, 3.9, 6.4, 11.0, and 18.7% organic matter for the herbicides used in the field study and for 2-chloro-N-(1-methyl-2-propynyl)acetanilide (prynachlor). Generally as organic matter levels increased, the GR50values for herbicides increased; the rate of GR50increase varied with herbicides. A ranking of herbicides from most toxic to least toxic is: propachlor&gt;alachlor&gt;prynachlor&gt;CDAA. Atrazine GR50values varied from a low similar to propachlor at 0.8% organic matter to 20 times greater than propachlor at 17% organic matter.</jats:p

BEHAVIOR OF POTASSIUM AZIDE AND TWO CARBAMITE HERBICIDES IN THE SOIL

Abstract not availabl

Yellow Nutsedge, Giant Green Foxtail, and Fall Panicum Control in Corn

In a 3-year field study in corn (Zea maysL.), several herbicides and combinations were studied for the control of yellow nutsedge (Cyperus esculentusL.), giant green foxtail [Setaria viridisvar.major(Gaud.) Posp.], and fall panicum (Panicum dichotomiflorumMichx.). Best yellow nutsedge control (87 to 88%) resulted from applications of 4.48 kg/ha of either alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] preplant incorporated or atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] preplant incorporated plus atrazine postemergence with a phytobland oil. Between 72 to 83% control of yellow nutsedge resulted from applications of 2.24 kg/ha of alachlor, 4.48 kg/ha of butylate (S-ethyl diisobutylthiocarbamate), and combinations of atrazine plus butylate. Greater than 90% control of giant green foxtail and fall panicum resulted from butylate plus atrazine or alachlor; postemergence applications of atrazine resulted in significantly less control of fall panicum or giant green foxtail.</jats:p

Johnsongrass Control in Soybeans with Dalapon and Preemergence Herbicides

Treatments were applied to heavily infested johnsongrass [Sorghum halepense(L.) Pers.] in the field for 3 years. Half of each treated plot was cultivated 5 weeks after planting soybeans [Glycine max(L.) Merr.]. Dalapon (2,2-dichloropropionic acid) applied to johnsongrass foliage 7 to 10 days before plowing plus either of the following three preplant incorporated herbicides, trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], or vernolate (S-propyl dipropylthiocarbamate), gave 85, 68, and 82% johnsongrass control, respectively, at the end of a 3 year study. The preemergence incorporated herbicides applied following plowing and two diskings resulted in poor (35 to 50%) johnsongrass control with significant yield reductions in 2 of the 3 years. When the preemergence incorporated herbicides were applied following two diskings and eight rototillings, johnsongrass control was 62% after 3 years which was significantly less than the 79% control resulting from dalapon plus preemergence herbicides. Cultivation 5 weeks after planting soybeans increased johnsongrass control 22, 35, and 36% and soybean yields 439, 370, and 320 kg/ha in 1969, 1970, and 1971, respectively, over comparable plots without cultivation.</jats:p

Volatility and Photodecomposition of Trifluralin, Benefin, and Nitralin

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.</jats:p