Economically solvent fresh-market potato production is predominantly dependent on the ability to efficiently produce consistent tuber quality and high yield, and the ability to meet first-to-market demand with early-season potatoes. Unfortunately, these two qualifiers often work against each other in terms of production management. In response, we studied integrated potato vine management programs that support timely early-season potato harvest. Vine management with a flail chopper, roller, and flame burner used alone or followed by diquat was evaluated when initiated 21 or 14 d prior to harvest in 2015 and 2016. Potato varieties included ‘Yukon Gold’ and ‘Dark Red Norland’. Potato leaf and stem management, as well as tuber skinning, stolon separation, grade, and yield were quantified. Among mechanical methods, potato leaf and stem management were poor when vines were rolled or mowed but better when flail chopped. In general, vine management and tuber skin set was better when treatments were initiated 21 d prior to harvest as opposed to 14 d. Vine management, tuber skin set, and yield were comparable when potato vines were flail chopped followed by flame burning and where diquat was applied twice, offering a viable program for smaller scale or organic production.

Weed management is a major constraint in organic cropping systems. In 2004, the Cornell Organic Vegetable Cropping Systems Experiment was established in central New York state using a split-plot randomized complete block design with two crop rotation entry points (split-plot factor). Four organic vegetable cropping systems that varied in cropping intensity and tillage (main plot factor) were compared: (1) intensive, (2) intermediate, (3) bio-extensive, and (4) ridge tillage. The basic crop rotation was cabbage, lettuce, potato, and winter squash, with additional short-season crops in the intensive system and with cover crops and fallow substituted for cabbage and potato in the bio-extensive system. In 2014, two uniformity trials were conducted in which oat and then a mixture of sorghum-sudangrass plus Japanese millet were grown uniformly over the entire experiment. Prior to sowing oat, soil samples were collected from each plot and an emergence bioassay was conducted to assess the soil weed seedbank. Crop biomass, weed density, and weed biomass were sampled in the uniformity crops. Soil weed seedbank density was three to four times greater in the intensive, intermediate, and ridge-tillage systems than in the bio-extensive system. The bio-extensive system also had lower weed density and weed biomass in the oat uniformity trial compared with the other three systems. Oat biomass did not differ between the cropping systems. Weed density and biomass in oat were also affected by the crop rotation entry point. Cropping system legacy effects on weed abundance and community composition were greater in the oat than in the sorghum-sudangrass plus Japanese millet uniformity trial. Our results illustrate the effects of different organic vegetable production practices on weed community structure and highlight the value of tilled fallow periods, cover crops, and prevention of weed seed rain for reducing weed populations.

Chlorsulfuron was applied to wheat at rates of 0, 10, 20, and 40 g ai ha-1 in three locations at Lethbridge and Brooks between 1980 and 1984. The soil pH and organic matter contents at Lethbridge and Brooks were 8.0 and 2.1% and 7.4 and 3.0%, respectively. Rotational crops were seeded for up to 7 yr after chlorsulfuron application. The criteria used to indicate when susceptible crops will grow safely were no significant yield loss at the 40 g ha-1 rate and the magnitude of the upper confidence limit for this difference. The following times after application before crop yields were not affected were required at Lethbridge: barley, 2 yr; canola, 3 yr; peas, beans, 4 yr; flax and potatoes, 5 yr; alfalfa and sugarbeets, 6 yr; and lentils at least 7 yr. The effect of chlorsulfuron residues in the soil on rotational crops appeared to be similar at Brooks and at Lethbridge. Estimated chlorsulfuron concentrations were related to the tolerance of rotational crops.

Field mint is widespread on Prince Edward Island and has become a problem in the production of cereal grains, potatoes, and other crops. Studies were conducted to determine if deep burial of the rhizome could be used as a control method. Rhizome pieces measuring 2.5, 5.0, or 10.0 cm in length were hand-buried in soil at depths of 2.5, 5.0, 10.0, or 20.0 cm in the spring. As planting depth increased, shoot emergence was delayed and fewer shoots emerged throughout the season. The smallest rhizome of 2.5 cm produced the fewest shoots during the season, but larger rhizomes (5.0 or 10.0 cm long) produced greater amounts of shoot and rhizome dry weights than smaller rhizomes. Deep burial of field mint to 20.0 cm by inversion plowing could be used as a means of field mint control, especially in early planted competitive crops that close canopy quickly.

Quinclorac was registered for weed control in wheat (Triticum spp.) for western Canada in 1997. Residues from quinclorac may persist in the soil and may damage following crops; therefore, field and growth chamber experiments were conducted to determine the tolerance of several following rotational crops. Cereals and bromegrass (Bromus biebersteinii) were sufficiently tolerant that they could be seeded within 16 d of quinclorac application without risk of injury. At the other extreme, marketable and total potato (Solanum tuberosum) yields were reduced by quinclorac on irrigated land 1 yr after application. Growth chamber experiments were used to rank crops in order of their tolerance of quinclorac residues and to compare the tolerance of crops that were grown in the field with additional crops. Quinclorac injured several legume and oilseed crops when the crops were seeded immediately after application, but quinclorac did not reduce the dry matter yield of two of the most sensitive legumes, faba bean (Vicia faba) and alfalfa (Medicago sativa), 1 yr after application on irrigated land. However, based on a previous study, one can conclude that injury to these crops may occur in the field under drought conditions in rain-fed agricultural systems.

Linuron, metribuzin, oryzalin, and metolachlor were applied at recommended (1X) and two-thirds (0.67X) rates to evaluate control of redroot pigweed and common lambsquarters in conventional and rye-stubble reduced-tillage potato production systems. Regardless of tillage, common lambsquarters control was satisfactory during both seasons at both rates of linuron, metribuzin, and oryzalin. Redroot pigweed control by these three herbicides, although excellent in 1988, was poor in RT plots during 1987. Yields did not differ between tillage systems. Reduced weed control with metolachlor during both seasons, and possible crop injury with linuron in 1987 resulted in significant yield reductions.

Spent spearmint hay from mint that had been treated with clopyralid in the fall or spring injured ‘Russet Burbank’ potato planted into loamy sand soil amended with 50 g hay/kg soil. Lowering the ratio of mint hay to soil from 50 to 3.1 g/kg reduced, but did not eliminate, the injury to potato. Potato was inured by clopyralid at concentrations as low as 3 ppbw in soil.

Field research was conducted at Fargo, Langdon, and Prosper, ND to determine carryover of clopyralid applied at 70 to 560 g ae ha-1 in soil as indicated by response of crops planted 1 yr after application. Flax, potato, and safflower growth at Fargo were not affected by clopyralid residues. At Fargo, soybean height, stand, and yield were reduced by residues from clopyralid at 560 g ha-1, and sunflower heads ha-1 and yield were reduced by residues from clopyralid at 280 and 560 g ha-1 and 560 g ha-1, respectively. Potato and sunflower at Langdon and Prosper and lentil at Langdon were not affected by clopyralid residues. Soybean yield at Prosper was not affected by clopyralid residues, but plant height was reduced by residues from clopyralid at 280 and 560 g ha-1. These results indicate that residues from clopyralid applied at labeled cropland rates, of 280 g ha-1 or less, in silty clay, clay loam, and silty clay loam soils in North Dakota probably will not adversely affect the dicot crops tested in these experiments planted 11 mo or more after application.

AC 222,293, a postemergence herbicide for wild oat control in wheat, barley, and sunflower, was applied at five rates at three locations in Montana in the spring of 1985. Twelve and 11 crops were seeded into treated soil in 1985 and 1986, respectively. Sugarbeet, lentil, and rape were injured by residual levels of AC 222,293 14 months after application. Injury was significantly greater at one location, indicating herbicide bioavailability varied by location. Soil pH was correlated negatively with crop injury, indicating the herbicide persists longer on lower pH soils.

A triazine-resistant (TR) biotype of Powell amaranth was discovered in 1989 in a potato field treated with metribuzin. A survey of all agricultural counties in Idaho showed that the TR Powell amaranth infestation was localized in the southeastern corner of Gooding county in southern Idaho. To determine the mechanism of triazine resistance, I50 values for inhibition of photosystem II were determined for atrazine, metribuzin, and diuron using thylakoids isolated from TR and triazine-susceptible (TS) biotypes. TR/TS ratios based on I50 values were 134 for atrazine, 62 for metribuzin, and 1.9 for diuron. Results of binding studies with atrazine and metribuzin were consistent with the I50 studies, indicating that resistance was due to reduced binding of triazines to the thylakoid membrane D1 protein. Sequencing the chloroplast psbA gene from TR and TS biotypes revealed a serine 264 to glycine change in the TR biotype. The mutation presumably resulted in reduced hydrogen bonding between triazine herbicides and the Dl protein.

Field investigations were conducted for 2 yr to characterize the responses of wheat, kidney bean, field corn, squash, okra, potato, and banana to soil-applied hexazinone, imazapyr, tebuthiuron, and triclopyr at rates used for control of woody perennial plants. Test species were planted at seven selected intervals through the first and second years after herbicide applications to assess residual herbicide activity. Tebuthiuron treatments of 2.2 kg ai ha−1 were not tolerated by any bioassay species planted 436 d after application (DAA). Only potato was tolerant of residual hexazinone 436 DAA. All species except banana generally tolerated residual imazapyr and triclopyr by the second growing season. Indigenous plants repopulated all herbicide-treated areas, except those treated with tebuthiuron, by the third growing season. Plots treated with tebuthiuron were 90% free of indigenous plants 40 mo after herbicide application.

Ten herbicide treatments were evaluated for early season control of three broadleaf weeds and effects on marketable potato yields in low-organic, coarse-textured soil. All treatments controlled prostrate pigweed 100%. Trifluralin with metolachlor or with EPTC did not control kochia well. Pendimethalin alone or with EPTC controlled Russian thistle poorly, and produced the lowest marketable tuber yields. Fluorochloridone at 0.6 kg ai/ha caused chlorosis and reduced potato yield 11%. Treatments with metribuzin tended to have high potato yields.

The effect of soil residues of flumetsulam plus clopyralid on several vegetable crops grown in rotation with field corn was investigated over 2 yr. The effect of soil residues of flumetsulam plus clopyralid on sweet corn cultivars of varying sensitivity to acetolactate synthase (ALS)-inhibiting herbicide was also investigated. Flumetsulam plus clopyralid was applied preemergence (PRE) to field corn at 0, 50 + 135, and 100 + 270 g ai/ha, respectively, in 1993 and 1994. Cucumber, tomato, cabbage, potato, pepper, pea, and sweet corn were planted each spring, both 1 and 2 yr following the herbicide application. Cabbage was very sensitive and showed visible injury symptoms and yield reductions both years following flumetsulam plus clopyralid application. Pepper showed a yield reduction only in 1995. All other crops showed no injury or yield reductions. Flumetsulam plus clopyralid was applied PRE and postemergence (POST) to six sweet corn cultivars in 1995. These six sweet corn cultivars were replanted into the same site 1 yr later. Flumetsulam plus clopyralid severely injured three of six sweet corn cultivars in 1995, the year of application. Soil residues 1 yr later, however, did not injure or reduce yield of any sweet corn cultivars, including cultivars sensitive to ALS-inhibiting herbicides.

Five sulfonylurea herbicides were applied to Typic Boroll soil with pH 8.0 and 2% organic matter in the field and growth chamber to assess their residual effects on following crops. Under irrigated conditions, triasulfuron at 22 g/ha reduced the growth of alfalfa, canola, corn, lentil, pea, potato, and sugarbeet the year after application but caused no injury after two years. Alfalfa GR50 (rate required to reduce growth by 50%) values immediately after application of chlorsulfuron, triasulfuron, and metsulfuron were < 2.2 g/ha and similar in the growth chamber and field. Alfalfa and canola GR50 values immediately after thifensulfuron application in the growth chamber were ≥ 90 g/ha. Alfalfa, canola, flax, and sugarbeet GR50 for tribenuron in the growth chamber were < 4 g/ha. Crop response curves developed by growth chamber experiments could replace many of the multiple site and crop field experiments now required to develop recropping guidelines for residual herbicides.

Phoma herbarum was evaluated as a potential biological control agent for dandelion (Taraxacum officinale) in turf. A preliminary controlled environment study identified selected adjuvants that enhanced disease severity by P. herbarum. Subsequently, these adjuvants were evaluated for disease enhancement under field conditions. Adjuvants evaluated included gluten flour, liposome, guar gum from ground guar (Cyamopsis tetragonoloba), durum (Triticum durum), and pectin. Regression analysis revealed a significant (P = 0.05) increase in disease severity by P. herbarum when formulated with gluten Hour, guar gum, or durum semolina compared to treatment with 20% mycelium in potato (Solanum tuberosum) dextrose broth (PDB) alone. No phytotoxicity to dandelion was observed among the adjuvant controls.

Winter rape (Brassica napus L.) green manures have shown potential for erosion control and suppression of weeds and other pests in potato cropping systems. However, little information on residue cover, biomass production, glucosinolate concentration, and glucosinolate production with winter rape grown as a green manure is available. In field trials in southern Idaho, ‘Aspen,’ ‘Bridger,’ ‘Cascade,’ ‘Dwarf Essex,’ and ‘Humus’ winter rape were planted in mid-August and incorporated the following spring in late April or early May. All five cultivars provided > 80% fall, winter, and early spring residue cover. Winter rape dry weight just before incorporation was 2,880 to 4,462 kg/ha in 1994 and 5,438 to 7,837 kg/ha in 1995. The major glucosinolate in roots of all five cultivars was phenylethyl glucosinolate; the major glucosinolates in shoots were 4-pentenyl, 2-hydroxybutenyl, 3-butenyl, and 2-hydroxypentenyl glucosinolate. Glucosinolate concentrations varied between years, but concentrations were higher in Dwarf Essex and Humus than in Aspen both years. Glucosinolate production per hectare also was highest in Dwarf Essex and Humus and lowest in Aspen. Dwarf Essex and Humus produced higher amounts of isothiocyanate (ITC) and oxazolidinethione (OZT)-producing glucosinolates than Aspen, Bridger, or Cascade, and therefore may be better biofumigants.

In greenhouse replacement series experiments, ‘Atlantic’ and ‘Russet Burbank’ potatoes and barnyardgrass were more competitive than redroot pigweed as measured by relative competitive ability. In additive design field studies, four redroot pigweed or barnyardgrass per meter of row did not reduce Atlantic tuber yield when planted between the row following hilling (6 to 7 weeks after planting). However, as few as one barnyardgrass or redroot pigweed per meter of row reduced marketable tuber yield 19 to 33% when seeded in the row at the time of potato planting. Redroot pigweed reduced tuber yield more than barnyardgrass did in 1 yr of research. The correlation coefficients were similar for both weed density and weed biomass regressed on tuber yield. Aboveground potato biomass was not consistent in predicting total tuber yield. Furthermore, variability in aboveground potato biomass was not due to increasing weed weight or density. Neither specific gravity nor tuber quality was altered by the presence of any density of either weed species.

Field experiments were conducted from 1989 to 1992 in Balcarce, Tandil, and San Cayetano, all in Buenos Aires province (Argentina), to evaluate clethodim, fenoxaprop-P-ethyl, fluazifop-P, haloxyfop, propaquizafop, and quizalofop-P-ethyl for bermudagrass control in sunflower, soybean, and potato. The highest levels of bermudagrass control 60 days after treatment (DAT) were generally obtained with fenoxaprop-P-ethyl, haloxyfop, propaquizafop, and quizalofop-P-ethyl. Late season bermudagrass control, based on biomass of stolons and rhizomes, suggested that the most consistent treatments in potato and sunflower were haloxyfop at 180 g ai/ha and quizalofop-P-ethyl at 54 g ai/ha. In soybean, clethodim at 336 g ai/ha, haloxyfop at 180 g/ha, propaquizafop at 100 g ai/ha, and quizalofop-P-ethyl at 54 g/ha provided the greatest reductions in bermudagrass biomass. All of the postemergence (POST) graminicide treatments increased crop yields when compared to a nontreated check. However, little or no difference in yield was obtained when herbicide rate was increased.

The effects of metribuzin herbicide and phorate insecticide were studied on summer harvest chipping-potatoes at Muscatine, IA, from 1989 to 1991. Phorate at 1.5 kg/ha increased total and ‘A’-size tuber yield and tuber specific gravity. Metribuzin applied at 0.56 kg/ha postemergence decreased total and ‘A’-size tuber yield. Metribuzin applied at 0.56 kg/ha preemergence and 0.28 kg/ha postemergence did not reduce Atlantic cultivar yield. Metribuzin did not affect ‘B’-size tuber yield or specific gravity. Phorate in combination with metribuzin did not increase plant injury or reduce tuber yield.

About 15 years ago, I heard several speakers saying that our crop yields were “leveling off.” This stimulated me to assemble data on the subject. The result is shown in Table 1, which gives the U.S. average yields for 10-yr periods during this century for nine crops. The increases are spectacular, varying from two- to sevenfold. Factors contributing to these increases differ from crop to crop. To obtain information on this subject, several experts on each crop were consulted, and their conclusions are summarized in the following text. Only those factors contributing to increased yields are covered. However, great improvements in efficiency of production, product quality, and reduction in soil erosion also have occurred as cultivars and production practices have changed. For most of the crops, increases in yields started in the 1940s and have increased dramatically during the rest of the century. We have not attempted to predict the future at this time, but the rate at which yields are increasing does not appear to be slowing.