Velvetleaf is difficult to control in corn and soybean and the seed can persist in soil for many years. Seven cultural and tillage practices were established in 1974 on a site heavily infested with velvetleaf to determine the time required to eradicate velvetleaf seed from the soil. A rapid decline in velvetleaf seed population in the top 23 cm of soil occurred during the first 5 yr of this study. In the fifth year, the chemical fallow and continuous alfalfa treatments had 37 and 56% of the original velvetleaf seed population remaining, respectively. In the 17th year, soils in these treatments that had received no tillage since study initiation still contained 15 and 25% of the original velvetleaf seed population, respectively. Systems involving moldboard plowing with continuous-tillage fallow, continuous cropping of corn or oat, or an annual corn and soybean rotation had a more rapid decline in the velvetleaf seed population in soil compared to the chemical fallow and continuous alfalfa treatment. After 17 yr, soil in any system that had received at least one moldboard plowing per year still contained 1 to 3 million velvetleaf seed ha−1, which is only 0.8 to 2.5% of the initial viable seed population. Nearly 100% of the seed remaining in the soil in the 17th year for all treatments was still viable.

In the greenhouse, postemergence treatments of 1.12 kg/ha of HOE 22870 [4-(4′-chlorophenoxy)-phenoxy-α-propionic-isobutylester] or HOE 23408 methyl 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate were applied to three perennial weeds (two grasses and one sedge) and to 27 species or varieties of annual grasses (crops and weeds). The perennials were resistant to both compounds, but control of the seedling grasses ranged from 0 to 100%, indicating the potential of controlling certain grass weeds in certain grass crops, as well as in broadleaf crops. Generally, the response of a given species was similar for both compounds. However, on some grasses one compound was considerably more effective than the other. Seven species or varieties of foxtail (Setaria spp.) were treated with various rates of either compound. Differential responses were observed, but it appeared that all the foxtail species or varieties studied should probably be controllable with HOE 23408. All but yellow foxtail [Setaria lutescens (Weigel) Hubb.], should probably be controllable with HOE 22870.

When grown without soybean [Glycine max (L.) Merr.] interference, eastern black nightshade (Solanum ptycanthum Dun.) planted in May produced as many as 7000 berries and 800000 seeds per plant. Eastern black nightshade planted in mid-July produced as many as 100 berries, but those planted in mid-August failed to produce berries. Eastern black nightshade produced less than 85 berries per plant when planted with soybeans in May, 0 to 3 berries per plant when planted into soybeans in June, and no berries when planted into soybeans in July. However, when soybeans were defoliated in July to simulate hail injury, eastern black nightshade that had been planted with soybeans in May produced up to 1600 berries per plant, and those planted into the defoliated soybeans in July produced up to 58 berries per plant. We suggest, therefore, that in vigorously growing soybeans, control of eastern black nightshade emerging in the row would only be required through June to prevent berry production. If, however, the soybean canopy were disturbed by hail or other factors, eastern black nightshade seedlings emerging in late July or early August might produce berries by soybean harvest.

An annual weed, found in Minnesota in the summer of 1984, was identified as Polygonum bungeanum Turcz. This species is not included in floras of North America and may have been introduced from Asia as long ago as 25 yr. Because the stems of this weed are prickly, we propose “prickly smartweed” as a common name for this species. Currently, we know the weed to occur in six counties in southern Minnesota and one county in northern Iowa. Field observations suggest that this species may be at least as competitive as other annual smartweeds.

Two wild oat (Avena fatua L.) biotypes and two barley (Hordeum vulgare L.) varieties known to have intraspecific differential response to foliarly-applied 4-chloro-2-butynyl m-chlorocarbanilate (barban) were studied. When barban was applied to the roots, the intraspecific differential response (measured by shoot retardation) was maintained in both species but to a much lesser extent than previously observed with foliar application. Wild oat maintained a greater differential response than barley. Therefore, the factors causing the differential response to foliarly-applied barban may reside primarily in the leaves of both species but to some extent elsewhere (perhaps at the plant apex) in the wild oat biotypes and to a lesser extent elsewhere in the barley varieties. Differential response to foliar applications was not caused by differential uptake, but may be caused primarily by the susceptible biotype or variety's reduced ability to degrade barban beyond 3-chloroaniline. This might cause the greater build-up of compound X (a water-soluble 3-chloroaniline-containing metabolite of barban) observed in the susceptible biotype or variety. Compound X appeared to be nonphytotoxic. The build-up of compound X in turn may reduce the rate of metabolism of barban resulting in the greater amount of free barban found in the treated leaf of the susceptible biotype or variety 12 to 24 hr after treatment. This greater amount of free barban in the leaf of the susceptible biotype or variety may be responsible for the differential response to foliar applications of barban. Evidence for this partial explanation of the differential response was better for barley than for wild oat.

In field studies, HOE 22870 [4-(4′-chlorophenoxy)-phenoxy-α-propionic-isobutylester] and HOE 23408 methyl 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate at 0.84 to 3.36 kg/ha were sprayed over the top of soybeans [Glycine max (L.) Merr.], corn (Zea mays L.), and giant foxtail (Setaria faberi Herrm.). Rates of 0.84 or 1.68 kg/ha of either herbicide controlled corn and giant foxtail. Soybeans tolerated 3.36 kg/ha (the highest rate used) of either herbicide. Both herbicides performed quite similarly, but HOE 22870 was generally more effective on giant foxtail and less effective on corn than was HOE 23408. The optimum time of application, in terms of soybean development, was the first trifoliolate stage. At this stage, corn had four to five leaves and giant foxtail had three to five leaves. HOE 23408 was applied to 32 inbred lines of corn in a greenhouse study. Several inbreds had considerable tolerance. When HOE 23408 at 0.56 kg/ha was applied to these 32 inbreds in a field study, control ranged from 100% for the most susceptible inbred to 22% for the most resistant inbred. At 1.12 kg/ha, control of corn ranged from 100% to 42%.

Velvetleaf, eastern black nightshade, wild mustard, common cocklebur, green foxtail, and yellow foxtail, grown for 4 weeks in nonaerated nutrient solution, developed satisfactorily compared to plants grown in soil. For experiments involving certain weed species grown in nutrient solution, aeration may be unnecessary.

In a 2-yr field study with preplanting-soil-incorporated treatments of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], tolerance of soybeans [Glycine max (L.) Merr.] to these herbicides, as measured by seed yield, was increased by increasing the seeding rate one-and-one-half or two times that normally recommended. These results agree with suggestions in the literature that plants can compete for herbicide in the soil, and suggest that increased seeding rates of soybeans can partially reduce the adverse effects of atrazine carryover or excessive metribuzin application.

A field experiment involving seven cultural practices was begun in 1974 in an area heavily infested with velvetleaf (Abutilon theophrasti Medic.) seed. Our objective was to determine the time required to eradicate velvetleaf seed from the soil. This paper reports the results of the first 4 yr of a long-term study. A cultural practice is repeated on the same plot year after year. Since the experiment was begun, no velvetleaf plants have been allowed to produce seed in any plots. The number of viable velvetleaf seeds is monitored by yearly soil sampling. In 1978, after 4 yr of a fallow treatment involving intensive tillage (two plowings per yr plus monthly tillage throughout the growing season), only 10% of the original seed population remained. However, that 10% was 1,300 viable seeds per m2 (to a depth of 23 cm). Four other practices that involved tillage gave generally similar results. Under undisturbed, continuous alfalfa, 56% of the original seed population remained after 4 yr, and under undisturbed, continuous chemical fallow, 37% remained. The results thus far demonstrate the extreme difficulty of eradicating velvetleaf seeds from the soil, and generally agree with reports in the literature, which primarily include studies conducted under more artificial conditions than we used. Our results also suggest that, in soil, velvetleaf seeds that have become water permeable (nonhard) may later again become water impermeable (hard).

We evaluated 214 lines of wild oat (Avena fatua L.) for response to S-2,3-dichloroallyl N,N-diisopropylthiolcarbamate (diallate), S-2,3,3-trichloroaHyl N,N-diisopropylthiolcarbamate (triallate), and 4-chloro-2-butynl m-chlorocarbanilate (barban). We found large differences among the lines in response to these herbicides and some lines that might not be controlled by recommended rates of these herbicides. Frequency distributions of response to herbicides suggest that reaction to these three herbicides is quantitatively inherited. We were unable to establish a relationship between morphological characteristics and plant response to these herbicides.

We compared diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}, as an early over-the-top spray treatment, and glyphosate [N-(phosphonomethyl)glycine], applied twice in repeated applications with a rope-wick applicator, for control of simulated volunteer corn (Zea mays L.) planted in clumps at various intervals in rows of soybeans [Glycine max (L.) Merr.]. Uncontrolled corn at the lowest density (clumps 2.4m apart in the row) reduced soybean yields an average of 31%. Both herbicides were highly effective in controlling corn, but when corn densities were high, diclofop treatments often resulted in greater soybean yields than did glyphosate treatments — presumably because corn interfered with the soybeans for a longer time before glyphosate was applied.

Simulated rainfall less than 8 hr after postemergence application of bentazon (3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2, 2-dioxide) reduced its activity on velvetleaf (Abutilon theophrasti Medic.) and common cocklebur (Xanthium pensylvanicum Wallr.) in greenhouse studies. In field studies, simulated rainfall less than 24 hr after application reduced bentazon's activity on velvetleaf. on common cocklebur, bentazon's activity was reduced even if simulated rainfall was delayed for more than 24 hr after application. In greenhouse studies, spray adjuvants (vegetable or petroleum oil) were helpful in overcoming the detrimental effects of simulated rainfall. Greenhouse and field studies indicated that soybeans [Glycine max (L.) Merr.] could tolerate bentazon-oil adjuvant combinations.

Two species of annual nightshades were commonly found as agronomic weeds in Minnesota. Eastern black nightshade (Solanum ptycanthum Dun.), the most common species, was found throughout the southern half of the state. Hairy nightshade (Solanum sarrachoides Sendt. ♯3 SOLSA) was found only in a few scattered locations. Eastern black nightshade seedling emergence began in mid-April or early May, and more than 80% of the total yearly emergence occurred before June. Hairy nightshade emergence began in May, but less than 70% of its total yearly emergence occurred before June. Eastern black nightshade berries first contained viable seeds 4 to 5 weeks after flowering of the plants and a week or more before the berries began to turn black. Hairy nightshade generally required a week longer than eastern black nightshade for viable seed production after flowering.

The fungus Colletotrichum coccodes (Wallr.) Hughes was isolated from diseased plants of eastern black nightshade (Solanum ptycanthum Dun. ♯ SOLPT) growing in the field. In greenhouse experiments, the isolate was highly pathogenic to eastern black nightshade and less so to seven other weedy species within the Solanaceae. No disease symptoms were observed on seedlings of tomato (Lycopersicon esculentum Mill.), potato (Solanum tuberosum L.), or 10 other species inoculated with the isolate. Dew periods of 16 h or longer were required for maximum disease development. This requirement could limit the practical use of this pathogen as a my coherbicide.

Bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2, 2-dioxide] was applied postemergence to common cocklebur (Xanthium pensylvanicum Wallr.) and velvetleaf (Abutilon theophrasti Medic.) at various times of the day in growth chamber and field studies and to soybeans [Glycine max (L.) Merr.] in field studies. Soybeans were tolerant of bentazon regardless of time of day when treated. Results with common cocklebur and velvetleaf suggest that the time of day when bentazon is applied can be of practical importance. Poor control might occur following application in late evening, night, or early morning.

Postemergence treatments with 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea [chloroxuron], for broadleaf weed control in soybeans [Glycine max (L.) Merr.] often partially defoliate, and temporarily stunt the crop. Chloroxuron was applied at 3 lb/A and at 1, 1½, and 3 lb/A with surfactant over the tops of weed-free soybeans in the cotyledon, unifoliate, and first trifoliolate stages of growth in 1967, 1968, and 1969. Relatively small but statistically significant yield reductions, particularly from treatments in the unifoliate stage, resulted in 1967. No significant yield reductions resulted in 1968 or 1969. These studies demonstrated the ability of soybeans to withstand initial injury from early postemergence treatments with chloroxuron without serious reductions in yield.

Corn (Zea mays L.) in soybeans [Glycine max (L.) Merr.] currently can be controlled with either glyphosate [N-(phosphonomethyl)glycine] applied to corn that is taller than soybeans, or diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} sprayed over-the-top of both corn and soybeans. We found a wide range in tolerance to over-the-top spray applications of glyphosate among 240 F2 hybrids of corn. Glyphosate was then applied with a rope-wick to one tolerant and one susceptible F2 corn hybrid growing in soybeans. In only two instances out of six (three stages of growth times 2 yr), the susceptible corn was controlled better than the tolerant corn; but, in these two instances, the better control was not reflected in greater soybean yields. In another experiment, one F2 corn hybrid identified (in a previous study) as tolerant of diclofop and one identified as susceptible were sprayed in soybeans with over-the-top diclofop treatments. In 11 instances out of 12 (two stages of growth times three rates times 2 yr), the susceptible corn was controlled better than the tolerant corn, and in nine of these instances, the better control was reflected in greater soybean yields. Corn parentage could be important in determining the degree of control obtained with either herbicide, but this is more likely with diclofop than with glyphosate.

Burs of common cocklebur (Xanthium strumarium L.) obtained from Stoneville, Mississippi; Urbana, Illinois; and Lamberton, Minnesota, were used in greenhouse and growth chamber studies. The Mississippi and the Illinois strains were both classified as being in the “strumarium” complex of X. strumarium, whereas, the Minnesota strain was classified as being in the “hybrid” complex. The Minnesota common cocklebur developed branch leaves in the leaf axils of the main stem to a much greater extent than did the Mississippi and Illinois common cocklebur. The Mississippi common cocklebur was frequently more tolerant of postemergence applications of bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] than were the Illinois and Minnesota common cockebur. The Mississippi and Illinois common cocklebur developed leaf necrosis when sprayed with an insecticide formulation containing malathion (o, o-dimethyl phosphorodithioate of mercaptosuccinate) and petroleum solvents; the Minnesota common cocklebur did not.

The general appearance of plants was similar for 14 accessions of velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH) obtained from Stoneville, MS (33° 25’ N), Rosemount, MN (44° 43’ N), and various locations in between. All accessions were equally susceptible to bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. Variation in maturity characteristics was found among the accessions in the field at Rosemount; southern accessions began seed capsule production later and continued it longer than did northern accessions. Velvetleaf accessions from Stoneville and Rosemount both produced seeds in the field at Weslaco, TX (26° 09’ N), but at Fairbanks, AK (64° 49’ N), neither accession produced seeds before being killed by frost.

An applicator is described that uses the principle of the cone seeder to obtain uniform distribution of granules along the length of the plot and conventional, commercially manufactured, granular spreaders for distribution across the width of the treated area. If plot size is held constant, no calibration or adjustment is necessary when rates of application are varied or when different formulations of granules are used.