Shifts toward herbicide resistant weed populations in row crop agriculture is a widespread epidemic. Sequential applications of EPSPS synthase-inhibitors, acetolactate synthase-inhibitors, and other herbicide site-of-action groups, have led to the selection and spread of herbicide-resistant weed biotypes (Powles, 2008; Tranel and Wright, 2002). New soybean systems with resistance to auxin herbicides, along with proprietary herbicide formulations, have been developed to control these herbicide-resistant weeds in soybean production. These new technologies will be compared in both conventional- and no-till with technologies which have been available for several years, in the aspects of weed control, yield, and economic return on investment (EROI). In both 2016 and 2017, when using preemergence (PRE) followed by postemergence (POST) herbicide programs, there were few differences in weed control between the six soybean systems. Adequate grain yield was provided by all soybean systems when proper herbicide programs were used. EROI was the highest when optimum yields were achieved, regardless of treatment cost.

Johnsongrass (Sorghum halepense) is one of the most troublesome weeds in the southeastern United States. -everal herbicides have been developed to combat johnsongrass, and many new experimental herbicides with high johnsongrass control potential are presently being tested. Two of these new experimental herbicides for johnsongrass control in soybeans (Glycine max) are sethoxydim and MBR 22359. Field experiments were conducted in 1981 and 1982 to evaluate the effectiveness of MBR 22359 preemergence and postemergence, sethoxydim in single and split applications, trifluralin in combination with mefluidide, or with glyphosate or sethoxydim in the wick, and alachior in combination with glyphosate or sethoxydim in the wick for rhizome johnsongrass control in soybeans. In 1982 fluchioraiin was also tested for rhizome johnsongrass control in soybeans. In both years MBR 22359 was applied at 2.2, 3.4, and 4.5 kg/ha preemergence, and at 1.1 and 2.2 kg/ha postemergence. In 1981 sethoxydim was applied in single applications at 0.3, 0.4, and 0.7 kg/ha early postemergence, 0.7 kg/ha late postemergence, and in split applications early postemergence and late postemergence respectively at 0.2 plus 0.2, 0.3 plus O.', 0.4 plus 0.4, and 0.4 plus 0.2 kg/ha. In 1982 sethoxydim was applied in single applications at 0.2, 0.3, 0.4, and 0.6 kg/ha early postemergence, and in split applications early postemergence and late postemergence respectively at 0.2 plus 0.1, 0.2 plus 0.2, 0.3 plus 0.1, 0.3 plus 0.2, and 0.4 plus 0.2 kg/ha. In 1981 and 1982 trifluralin at 1.1 kg/ha was applied in combination with mefluidide at 0.3 kg/ha early postemergence, mefluidide at 0.3 kg/ha early postemergence plus mefluidide at 0.3 kg/ha late postemergence, mefluidide at 0.3 kg/ha early postemergence in combination with glyphosate plus water (1:2, v/v) directed postemergence, sethoxydim plus oil plus water (2:1:3, v/v) directed postemergence, or with glyphosate plus water (1:2, v/v) directed postemergence in the rope wick applicator. Alachlor was applied at 3.4 kg/ha in combination with sethoxydim plus oil plus water (2:1:3, v/v) or with glyphosate plus water (1:2, v/v) directed postemergence in the rope wick applicator. In 1982 fluchloralin was applied at the rate of 2.2 kg/ha. Sethoxydim single and split application treatments at all rates employed excellent rhizome johnsongrass control in 1981 and 1982. No soybean injury was noted and good yields were obtained where sethoxydim was applied. MBR 22359 preemergence treatments provided good to excellent rhizome johnsongrass control. soybean injury and yield reductions were noted with the MBR 22359 postemergence and the 4.5 kg/ha preemergence treatments in 1981. No significant differences in yields were found between any of the herbicide treatments in 1982. Trifluralin combinations and alachlor combinations provided poor to fair rhizome johnsongrass control in both years. Soybean injury was noted for the trifluralin combination treatments that contained mefluidide. Yields were generally not as high for the trifluralin combinations and alachlor combinations as they were for the sethoxydim, and the lower rate MBR 22359 preemergence treatments in 1981. Fluchloralin provided extremely poor rhizome johnsongrass control in 1982.

Preemergence (PRE) herbicides are used to control weeds and reduce pressure on postemergence (POST) herbicides. However, knowledge of length of control each herbicide provides, as well as the amount of activation rainfall required for adequate weed control, is unknown in Mississippi soybean production. Twenty-one PRE applied soybean herbicides were evaluated for their duration of residual control for five weeks over twelve site years on three weed species from 2021-2022. Some differences in control following herbicide application used on certain weed species were observed at different times. However, most PRE herbicides resulted in adequate (greater than or equal to 90%) control of weed species evaluated up to 35 days after emergence. Also, four PRE herbicides were evaluated in the greenhouse to quantify the amount of rainfall needed for activation when applied to three different soil textures. These data suggest that rainfall recommendations vary by herbicide and soil texture, and some herbicides were effective at controlling weed species at low rainfall amounts (less than 12.7mm).

Sandea at 0.05 lb ai/A tank-mixed with Matrix at 0.02 lb ai/A and applied POST following Prefar applied preemergence on cantaloupes gave very good control of pigweeds, lambsquarters, purple nutsedge, and junglerice. Melon injury was just acceptable at 15%. The tank-mix treatment applied POST was similarly effective on the pigweeds, lambsquarters, and nutsedge but grass weed control decreased slightly and melon injury increased when following preemergence herbicide treatments of Dual Magnum, Outlook, or Chateau. Single or multiple POST applications of Sandea alone were not effective against pigweeds.

Spinach exhibited progressively increased injury and crop stand reduction with increasing rates of s-metolachlor and dimethenamid-p. At the lowest rate applied, s-metolachlor at 0.38 lb ai/A caused minimal injury at 10% and slight stand reduction compared to the untreated check. Dimethenamid-p injured spinach 25% at the lowest rate applied and significant stand reduction was observed at 0.5 lb ai/A or greater. At equivalent rates, dimethenamid-p was more injurious to spinach than s-metolachlor.

Carduus nutans L., commonly called nodding thistle or musk thistle, has been in the United States for over 50 years; however, it was not until the early 1940's that it was identified in Kentucky. It was first identified in Kentucky in Warren County, and by 1970 had spread to 88 of the 120 counties in Kentucky. The thistle is present in all regions of the state, but most of the counties not having the thistle are located in the mountainous region of Eastern Kentucky. The thistle plant has a fleshy tap-root which is characteristically hollow near the soil surface. Flowering is determinate and the flowers vary in color from a deep pink at opening to near white at maturity. The plant is a prolific seed producer and may grow to a height of over eight feet in favorable growing conditions. In Central Kentucky, nodding thistle seeds are disseminated from June through August. The seeds are about three millimeters long and vary in color from gray to straw-brown at maturity. There appears to be a minimum eight-week dormancy period before the seeds will germinate. Ninety percent germination was obtained using one-year-old seeds. After emergence, plants enter the rosette stage in which they over-winter. Rosettes may reach four feet in diameter prior to bolting. Bolting occurs between March and August, and flowering begins in mid-May and continues through August. Nodding thistle plants in the study produced up to 561 heads per plant, and up to 1200 seeds per head. Individual plants produced from 200 to over 160,000 seeds. Nodding thistle plants in Central Kentucky may act as summer annuals, winter annuals, or biennials.

Johnsongrass (Sorghum halepense) competition in soybeans (Glycine max) has adverse effects on soybean yields. Profitable soybean production in Kentucky and the Southeastern United States has depended upon good, cost effective johnsongrass control. Several herbicides have been developed to control johnsongrass in soybeans. Four of these recently developed compounds were imazaquin (2-[4,5-dihydro-4-methy1-4- (1-methyl-ethyl)-5-oxo-1H-imidazo1-2-y1]-3-quino1inecarboxy1ic acid), imazethapyr (+/-)-2-C4,5-dihydro-4-methy1-4-(1-methy. lethyl)-5-oxo-IH-imidazol-2-y1)-5-ethy1-3-pyridinecarboxylic acid, quizalofop 2-[4-[(6-chloro-2-quinoxalinyl) oxylphenoxyjpropaonic acid,ethyl ester, and analog of quizalofop (DPX Y6202-31). Field experiments were conducted in 1986 to evaluate (a) the effectiveness of imazaquin and imazethapyr preplant incorporated, postemergence, or in combination with pendimethalin [N-(1-ethylpropy1)-3,4-dimethy1-2.6-dinitrobenzenamine], and (b) herbicide antagonism with fluazifop[butyl(R)-2-(4-[(5- trifluoromethy 1 ) - 2-pyridinl] oxy] phenoxy] propanoate], quizalofop, sethoxydim [2-[1-(ethoxyimino)butyl] -5-(2- (rthylthio)propy1]-3-hydroxy-2-cyclohexen-l-one, fenoxaprop [(+/-)-2-[4-((6-chloro-2-benzoxa-zoly) oxy]phenoxy]propanoic acid], and DPX-Y6202-31, in combination with imazaquin, bentazon [3-(1-methylethyl)-(ih)-2,1,3, benzothiadiazin- 4(3h)-one 2,2-dioxide], acifluorfen [5-[2-chloro-4(trifluoromethyl) phenoxy]-2-nitrobenzoic acid], and chlorimuron [3-(3,4-dichloropheny1)-1-methoxy-1-methylurea and Ethyl 2--[[[[(4-chloro-6-methoxy-pyrimidin-2-yl)amino)-carbonyl] amino]sulfonyl]binzoate], for johnsongrass control in soybeans. Imazaquin was applied preplant incorporated, tankmixed with pendimethalin and imazethapyr. Imazethapyr was applied preplant incorporated and postemergence with surfactant at equal rates. DPX-Y6202-31 was applied postemergence at four different rates, and in tankmix combinations with chlorimuron, acifluorfen, bentazon, and imazaquin, with surfactant or crop oil contrate. Quizalofop was applied postemergence at tour use rates.

Investigations were conducted to determine the effects of the herbicide glyphosate and its time of application on the control of johnsongrass. Johnsongrass plots were divided into areas designated undisturbed, spring plowed, and clipped. These areas were compared to determine differences in control of johnsongrass when using glyphosate with different management procedures. Glyphosate was applied at weekly intervals and treatment effects were statistically analyzed. There were three replications of each treatment. It appears from the results that: Glyphosate kills approximately 100% of the johnsongrass topgrowth regardless of the application date. Height of the johnsongrass plant at the time of glyphosate application had little influence on the ability of the herbicide to kill the rhizomes. Rhizomes from plants that had received an application of glyphosate produced a significantly lower number of plants than did rhizomes from untreated plants. The management procedures (spring plowed, clipped, undisturbed) had no effect on the ability of glyphosate to kill the rhizomes. As glyphosate applications were applied later in the growing season, johnsongrass control increased. In 1975 glyphosate utilized with spring plowing produced better total johnsongrass control than either clipped or undisturbed plots which had utilized glyphosate. In 1976 there was no significant difference in the control given by the three methods.

Alachlor [2'-chloro-2',6'-diethyl-N-(methoxymethyl) acetanilide] in combination with linuron [3-(3,4-dichlorphenyl)-1 methoxy-1-methylurea (n'-(3,4-dichlorophenyl)-N-methoxy-Nmehtylures)] and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one 4-amino-6-(1,1-dimethy-ethyl)-3-(methylthio)-1,2,3-triazin-5(4 H)-one] was evaluated for its control of broadleaf and annual grasses in Mitchell soybeans (Glycine max L.) under four different tillage conditions. The experiment was conducted in the summers of 1978 and 1979. The tillage treatments evaluated were conventional tillage, double disking, single disking, and no-tillage. Alachlor at 2.2, 2.8, and 3.4 kg/ha was used alone and in combination with metribuzin at 0.4, 0.6, and 0.8 kg/ha and linuron at 0.6, 0.8, and 1.2 kg/ha. All treatments were compared with a check which received no residual herbicide application. All plots received an application of glyphosate [N,N-bis(phosphonmethyl) glycine] at 2.2 kg/ha to control emerged vegetation. The results of the experiment showed no interaction between tillage conditions and herbicide applications. There were no significant differences in broadleaf weed control or yields in the tillage plots for either 1978 or 1979. Significant differences were found in yields as affected by herbicide treatments in 1978, but none were found in 1979. Differences did not follow any logical pattern and were not consistent between years.

Cover crops are typically sown between cash crops and can suppress weed emergence and growth. If cover crops are sown after cash crop harvest the system is left susceptible to weed emergence while they establish. Interseeding cover crops into a standing cash crop may limit this bare period by allowing cover crops to become established, go into dormancy, and then revive around cash crop senescence. Studies were conducted in Princeton and Lexington, KY, to determine (i) which corn pre-emergent herbicides and mixtures of herbicide active ingredients commonly used by Kentucky growers would impact interseeded cover crop density and biomass, (ii) which grass entries that are adapted to Kentucky would be best to interseed in corn, and (iii) if interseeded cover crops would suppress weeds similar to a cover crop planted after cash crop harvest. There were few reductions in interseeded cover crop density and biomass from the pre-emergent herbicides tested. Among the entries interseeded in four site-years, the tall fescue pre-cultivars generally performed the best but none were consistently able to survive the summer when interseeded into corn. Compared to a cereal rye cover crop seeded after corn harvest, interseeded cover crops produced less biomass and therefore suppressed fewer weeds.