Application of 112 to 336 kg/ha N as ammonium nitrate [NH4(NO−3)] failed to affect population numbers of common lambsquarters(Chenopodium albumL.), giant foxtail(Setaria faberiHerrm.), velvetleaf(Abutilon theophrastiMedic.), jimsonweed(Datura stramoniumL.), or redroot pigweed(Amaranthus retroflexusL.). Common lambsquarters seeds harvested from NO−3-treated plots were less dormant than control seeds. Seed germination in the laboratory increased from 3.0% for control seeds to 34.0% for seeds harvested from plots treated with 280 kg/ha N as NH4(NO−3). Nitrate concentration in common lambsquarters seeds increased as nitrogen fertilization increased. Seeds from nonfertilized plots contained 18.7 μg/g NO−3, while seeds from plots fertilized with 280 kg/ha N contained 126.3 μg/g. Adding exogenous NO−3to the germination medium brought the germination of most seed lots to a similar level, except for control seeds which germinated at a lower rate. In contrast to common lambsquarters, nitrogen fertilization did not greatly affect dormancy or NO−3accumulation in velvetleaf seeds. Exogenous NO−3failed to stimulate velvetleaf germination because dormant velvetleaf seeds did not imbibe.

2,4-D [(2,4-dichlorophenoxy)acetie acid] and dalapon (2,2-dichloropropionic acid) were applied to a natural stand of annual weeds at a time near flowering to determine effects on seed production and the dormancy and viability of seeds produced. At rates of 0.6 and 1.1 kg/ha, 2,4-D reduced, respectively the seed production of common lambsquarters(Chenopodium albumL.) 99 and 99%, redroot pigweed(Amaranthus retroflexusL.) 77 and 84%, and jimsonweed(Datura stramoniumL.) 64 and 100%, while giant foxtail(Setaria faberiHerrm) seed production was increased to 307 and 381% of the control, respectively. Dalapon at rates of 2.2 and 4.5 kg/ha reduced respectively seed production of giant foxtail 100 and 100%, and jimsonweed 100 and 91%. Before and after overwinter burial in the soil, common lambsquarters seeds from plants treated with 4.5 kg/ha dalapon were less dormant than control seeds. After overwintering, redroot pigweed seeds from dalapon-treated plants were less dormant than controls, and more seeds survived the winter burial. Common lambsquarters and redroot pigweed seeds from plants treated with 1.1 kg/ha 2,4-D were more dormant than control seeds before overwintering,’ while giant foxtail seeds from 2,4-D treated plants were less dormant than controls after overwintering. Viability of seeds produced by herbicide-treated plants, as determined by germination in KCN, was not greatly different from control seeds. Treatment with 2,4-D or dalapon resulted in the production of common lambsquarters seeds which produced seedlings about half as vigorous as controls. Jimsonweed seedlings grown from seeds from 2,4-D-treated plants showed phenoxy herbicide injury symptoms.

Establishment of alfalfa (Medicago sativa L.) alone rather than with an oat (Avena sativa L.) companion crop usually results in a reduction in dry matter production. Use of herbicides for weed control during alfalfa seedling establishment also reduces yield since weeds are harvested along with the alfalfa and contribute to forage yield. Thus, if there are benefits from seeding alfalfa alone using herbicides for weed control they would only be expressed in terms of animal consumption, nutritional value, digestability, and finally animal growth or milk production. Consequently, a study was conducted to determine the benefits of annual weed control during alfalfa establishment. Alfalfa was sown into field test plots (Plano silt loam, 3.5 to 4% organic matter, Typic Argindoll, fine, silty, mixed mesic) in April 1976 with an oat companion crop and alone with and without herbicide treatments. Herbicide treatments included were S‐ethyl dipropylthiocarbamate (EPTG) + 4‐(2,4‐dichlorophenoxy) butyric acid (2,4‐DB), and Nbutyl‐N‐ethyl‐α,α,α‐trifluoro‐2,6‐dinitro‐p‐toluidine (benefin). Weeds were also allowed to grow in the absence of an alfalfa or oat seeding. The oat companion crop was harvested at the early dough stage and the alfalfa treatments at first flower, all as chopped hay. The stand of weeds was harvested at the same time as the alfalfa. The oat hay, weeds, and alfalfa established with and without herbicides, were analyzed in laboratory studies for in vitro digestible dry matter (IVDDM), neutraldetergent fiber (NDF), aciddetergent fiber (ADF), crude protein, and nitrate. A sheep feedingdigestion trial was used to determine the palatability, digestible dry matter (DDM), digestible crude protein (DCP), digestible neutraldetergent fiber (DNDF) and digestible aciddetergent fiber (DADF) of the forages, and N balances of the sheep fed the forages. The four forages were ranked as follows in order of increasing quality as measured by animal intake and digestible dry matter: oat, hay, weed forage, untreated alfalfa, herbicide‐treated alfalfa. The lower quality of the untreated alfalfa in comparison with the herbicide treated alfalfa was attributed to the fact that weeds constituted 50% of the dry weight of the untreated alfalfa stituted 50% of the dry weight of the untreated alfalfa forage. Chemical analysis of the weeds indicated that the Pennsylvania smartweed (Polygonum pensylvanicum L.), shepherds‐purse (Capsella bursa‐pastoris (L.) Medic), and yellow foxtail (Setaria lutescens (Weigel) Hubb.) had the greatest influence in lowering the forage quality. These three weeds, which composed 25% of the untreated alfalfa forage, had the lowest % crude protein and IVDDM and the highest % CWC and ADF. The digestion trial also showed the annual weeds, as a whole, to be the lowest in DCP, DNDF, and DADF. These results confirm that seeding alfalfa alone using herbicides for weed control is beneficial, and that feeding forage thus produced will improve livestock performance.

Preferential flow has been shown to be an important mechanism affecting water and solute movement in some soils. The movement of agricultural chemicals to groundwater is of special concern. Soil columns containing an artificial macropore were used to study alachlor [2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl)acetamide], cyanazine [2‐{[4‐chloro‐6‐(ethylamino)‐1,3,5‐triazin‐2‐yl]amino}‐2‐methyl‐propanenitrile], pendimethalin [N‐(1‐ethylpropyl)‐3,4 dimethyl‐2,6 dinitrobenzenamine], and chloride movement. Packed columns were modified by removing a 6‐mm diam. core from the center. Herbicides and chloride were applied to the soil surface and columns were irrigated with 63 mm of a 0.0075 M calcium sulfate solution. Initial chloride breakthrough occurred much sooner in columns with a continuous macropore than in columns with either a partial or no macropore. Total chloride loss in column drainage, however, was less in columns containing a continuous macropore than in those without a continuous macropore. In contrast, alachlor, cyanazine, and pendimethalin were only detected in drainage from columns with a continuous macropore. Because herbicides were not detected in column drainage unless a continuous macropore was present, leaching studies using packed soil columns may significantly underestimate the extent of herbicide movement through a structured soil. Pesticide leaching experiments using soil columns with an artificial macropore may provide estimates that are more representative of field behavior and could be used to supplement current pesticide mobility studies required by the USEPA to support product registration.

Research conducted since 1979 in the north central United States and southern Canada demonstrated that after repeated annual applications of the same thiocarbamate herbicide to the same field, control of some difficult-to-control weed species was reduced. Laboratory studies of herbicide degradation in soils from these fields indicated that these performance failures were due to more rapid or “enhanced” biodegradation of the thiocarbamate herbicides after repeated use with a shorter period during which effective herbicide levels remained in the soils. Weeds such as wild proso millet [Panicum miliaceumL. spp.ruderale(Kitagawa) Tzevelev. #3PANMI] and shattercane [Sorghum bicolor(L.) Moench. # SORVU] which germinate over long time periods were most likely to escape these herbicides after repeated use. Adding dietholate (O,O-diethylO-phenyl phosphorothioate) to EPTC (S-ethyl dipropyl carbamothioate) reduced problems caused by enhanced EPTC biodegradation in soils treated previously with EPTC alone but not in soils previously treated with EPTC plus dietholate. While previous use of other thiocarbamate herbicides frequently enhanced biodegradation of EPTC or butylate [S-ethyl bis(2-methylpropyl)carbamothioate], previous use of other classes of herbicides or the insecticide carbofuran (2,3 -dihydro-2,2 -dimethyl-7-benzofuranyl methylcarbamate) did not. Enhanced biodegradation of herbicides other than the thiocarbamates was not observed.