The effects of arbuscular mycorrhizal fungi and chitosan sprays on yield and late blight resistance in potato crops from microplants

The established microplants, mycorrhized and non-mycorrhized controls, were planted in the field and unsprayed (controls), sprayed with a conventional fungicide (Ridomil), with Ridomil alternating with N,O-carboxymethyl chitosan (NOCC — a soluble chitosan) or sprayed only with NOCC. The effects of the treatments on late blight progression in the crop were monitored throughout the season and yield measured. In a preliminary study on the inoculation of detached leaves from unsprayed plants and plants sprayed with Ridomil and NOCC, respectively, NOCC was shown to delay disease development. In the field, late blight development was most rapid in the unsprayed controls, delayed in the Ridomil-treated plants and disease progression was slowed in the other treatments (AMF-inoculation, AMF-NOCC sprayed, NOCC-sprayed and Ridomil-NOCC sprayed). It was shown that plant chitinase activity increased in the AMF, AMF-NOCC and NOCC treatments. At harvest, yields for the Ridomil-NOCC, NOCC and AMF-NOCC treatments were significantly higher than the un-sprayed, non-mycorrhizal control and were not significantly different to the Ridomil-sprayed control. The results are discussed in relation to the production of seed potatoes for organic (ecological) growers.     

Interactions of crop density of field beans, abundance of Aphis fabae Scop., virus incidence and aphid control by chemicals

The number of Aphis fabae Scop. per plant and per acre developing on field beans (Vicia faba L.) was inversely related to seeding rate (i.e. plant density) except sometimes at very low rates; with equal numbers of plants per acre, fewer aphids developed on plants in rows 11 in. than 22 in. apart. Plots sown in mid-March with more than about 150,000 plants per acre were more attractive than less dense stands to colonizing alate A. fabae, but established colonies multiplied most on the sparsest and least on the densest plots. The number of plants per acre infected by pea leaf-roll virus was inversely related to planting density. There were more virus-infected plants on II in. than on 22 in. spaced rows-in contrast to the numbers of A. fabae. A single spray with demeton-methyl, timed to control A. fabae, did not significantly decrease virus incidence. Grain yields of sprayed plots were little altered by increasing the seed rate above a critical minimum, except in one year when the densest crops lodged. Increased yields from spraying were closely related to the numbers of A. fabae on unsprayed plots. Dense planting (more than 400,000 plants per acre) prevented or greatly decreased losses caused by A. fabae in unsprayed plots except in one year when the aphids were exceptionally abundant.     

Yield loss of faba bean (Vicia faba) due to chocolate spot (Botrytis fabae) in sole and mixed cropping systems in Ethiopia

Two field experiments were conducted during 2004 and 2005 cropping seasons at Adet Agricultural Research Center, Ethiopia to assess yield losses caused by chocolate spot(Botrytis fabae) of faba bean in sole and mixed cropping systems using two cultivars. Cropping systems were sole faba bean (FB), faba bean mixed with field pea (FB: FP), barley (FB: BA) and maize (FB: MA). Mancozeb was sprayed at the rate of 2.5 kg a.i/ha at 7-, 14- and 21-day interval to generate different levels of chocolate spot disease in all the four cropping systems, and unsprayed control was also included. The treatments were arranged in a randomised complete block design (RCBD) with four replications. FB: MA mixed cropping significantly reduced disease severity and the area under disease progress curve (AUDPC) and increased faba bean grain yield. The highest faba bean grain yield among the three mixed croppings under different spray schedules was obtained from FB: MA mixed cropping in both 2004 and 2005 (2.56 and 3.74 t/ha, respectively) cropping seasons. There were highly significant yield differences (P < 0.05) among the spray intervals of mancozeb in both seasons. The highest grain yield (4.9 t/h) was recorded from the 7-day spray interval in 2005. The unsprayed faba bean had a lower grain yield (1.9 t/ha in 2004 and 2.3 t/ha in 2005) compared to the sprayed plots. The highest relative yield loss (67.5%) was calculated in 2005 from FB: FP mixed cropping in unsprayed plots. The relative yield losses in the unsprayed plots were in the range of 35.8–41.5% in 2004 and 52.6–67.5% in the 2005 cropping season. Severity and AUDPC were inversely correlated with faba bean grain yield. Significant differences were recorded in the 100-seed weight and days to maturity (DM). The unsprayed plots had shorter DM ranging from 126 to 128.5 day (except FB: MA mixed cropping) in 2004 and 122–123.9 days in 2005. In the sprayed plots DM was relatively longer than the unsprayed plots. A higher seed weight was recorded in the sole FB (56 g) and FB: MA (55 g) mixed cropping, and the lowest value of 100-seed weight was recorded from FB: FP (53 g) mixed cropping. The productivity of the mixed cropping evaluated by land equivalent ratio (LER) exceeded that of sole cropping. Faba bean grain yield was highly influenced by the severity of chocolate spot. The disease affects the DM, forcing early maturing of the plants.     

EFFECTS OF CULTURAL TREATMENTS ON WHEAT AND ON THE INCIDENCE OF EYESPOT, LODGING, TAKE-ALL AND WEEDS. Field Experiments 1945–8

An experiment was made on the fourth, fifth and sixth successive crops of winter wheat to determine the effects of various treatments on the troubles which result from close cereal cropping. Eyespot and lodging were prevalent in the first year (1946); weeds in the second; eyespot, lodging, take-all and weeds in the third.
Spraying with H₂SO₄ reduced the incidence of eyespot, lodging and weeds, and increased yield of grain on plots which received sulphate of ammonia (by 2.7, 2.2 and 10.0 cwt./acre in successive years).
Sulphate of ammonia increased the incidence at harvest of eyespot and lodging, reduced take-all and consistently increased yield of straw. Eyespot and lodging reduced the effect of the fertilizer on yield of grain, take-all increased it.
Increase in seed rate increased the incidence of severe eyespot and of take-all; it increased lodging except when plants were dwarfed by take-all.
Weight of straw and percentage straws with severe eyespot lesions independently affected lodging, together accounting for 51% of the variance in percentage area lodged at harvest and 64 % of that lodged 33 days earlier.
Mean yields of grain on untreated plots sown with 3.3 1/2 bushels seed/acre fell from 26.0 to 22.5 to 11.7 cwt./acre in successive years, whereas yields of 28.4, 29.9 and 29.1 cwt./acre were obtained on sprayed plots sown with 1 1/2.2 bushels seed/acre which received 4 cwt./acre sulphate of ammonia, showing that high yields were maintained when eyespot, lodging, take-all and weeds were controlled.
By 1948 yields of grain on unsprayed plots had fallen to the level of those on similarly manured plots on the continuous wheat experiment on Broadbalk field. Spraying increased grain by amounts similar to those resulting from one year's fallow on Broadbalk; but fallow had its greatest effects on plots with low nitrogen, spraying on those with high nitrogen.     

The effects of different external nitrate concentrations on growth of Avena sativa cv. Amuri treated with diclofop-methyl

Avena sativa cv. Amuri fed either low or high nitrate was sprayed with diclofop-methyl (1 kg a.i. ha^-1) at the three leaf stage. The short term effects of the herbicide on chlorophyll concentration of leaves (laminae) and short and long term effects on d.wt of the component plant parts were determined by comparison with unsprayed plants. For unsprayed and sprayed plants, total leaf d.wt approximately doubled during the first twelve days after commencing treatments. Growth was substantially greater at high nitrate than low nitrate. For unsprayed plants, the increase in total leaf d.wt was due primarily to growth of leaf 3 but for sprayed plants it was due to growth of leaves 1 and 2. Twelve days after commencing treatments, d.wt of leaves 1 and 2 was substantially greater for sprayed plants than for unsprayed plants given similar nitrate, while chlorophyll concentration was substantially less. Leaf 3 d.wt and chlorophyll concentration were substantially greater in unsprayed plants than in sprayed plants given similar nitrate. For unsprayed plants, values were greater at high nitrate than low nitrate, for sprayed plants the converse was the case. Forty nine days after commencing treatments, unsprayed plants had a greater total plant d.wt than sprayed plants given similar nitrate. Total plant d.wt for unsprayed plants was greater at high nitrate than low nitrate, the opposite was the case for sprayed plants. Unsprayed plants at both nitrate levels and sprayed plants given low nitrate produced seed heads but sprayed plants given high nitrate did not. Diclofop-methyl at a rate of 0.3 kg a.i. ha^-' stopped seed head production at high nitrate. Retention and uptake of diclofop-methyl were not significantly different at low and high nitrate. At 1 kg a.i. ha-^l diclofop-methyl, plants switched from low to high nitrate at spraying showed damage similar to that shown by plants given high nitrate throughout. Addition of 200 μg GA into the leaf sheaths two days prior to spraying increased the efficacy of diclofop-methyl at low nitrate. It is proposed that increased efficiency of diclofop-methyl at high nitrate is due to increased leaf damage caused by a greater rate of leaf expansion.     

EXPERIMENTS ON THE CONTROL OF BEET YELLOWS VIRUS IN SUGAR-BEET SEED CROPS BY INSECTICIDAL SPRAYS

Field experiments made in eastern England between 1943 and 1951 showed that Myzus persicae lived on the stecklings throughout some winters, and that most plants with yellows in transplanted seed crops were from infections that occurred in the steckling bed. A larger proportion of stecklings sown at the end of July or in early August became infected than of those sown about a month later. The incidence of yellows was reduced by nicotine sprays which cleared the stecklings of aphids after autumn migrations had ceased, thus preventing spread of the disease during the winter. A greater reduction was obtained with persistent and systemic organo-phosphorous insecticides; in one experiment three applications of E 605 reduced incidence to one-ninth that in unsprayed plots. However, in years when stecklings were exposed to large migrations of aphids, even plots sprayed three times had 78% of the plants with yellows. Although spraying often greatly reduces the incidence of yellows, it is unlikely to give adequate control in years and districts in which many viruliferous aphids move in the autumn. Spraying in September and October was usually more effective than in August.     

The effects of sowing date and choice of insecticide on cereal aphids and barley yellow dwarf virus epidemiology in northern England

During the mid-1980s, Sitobion avenae became recognised as an important vector of barley yellow dwarf virus (BYDV) in the Vale of York. A field trial at the University of Leeds Farm, North Yorkshire, was carried out during the autumn/winter of 1984-85 to evaluate different control procedures against S. avenae-transmitted BYDV and to investigate its epidemiology. Winter barley was sown on three dates in September, and plots were sprayed with either deltamethrin, demeton-S-methyl or pirimicarb on one of three dates between mid-October and mid-November, making a factorial design. Rhopalosiphum padi, the main vector of BYDV in southern England, were rarely found during the experiment, but the numbers of S. avenae were much higher, reaching a peak of 21% of plants infested in the unsprayed plots of the first sowing date. Single applications of each insecticide reduced populations of S. avenae to zero. Some treatments, particularly in the early sown plots and those treated with pirimicarb, however, did allow some recolonisation, and thus led to increased virus incidence and decreased yields. Sprays applied before the end of the migration of S. avenae were more efficient at controlling BYDV if the insecticide was persistent, otherwise a spray after this period, in November, was more effective. Virus incidence, although reduced by sprays, was generally low in plots sown on 18 and 27 September. In contrast, about 11% of plants were infected in unsprayed plots sown on 6 September and a small yield benefit was obtained with insecticidal treatments. Enzyme-linked immunosorbent assay (ELISA) of plants taken from the plots indicated that MAV- and PAV-like strains were present, and were most likely to have been transmitted by S. avenae.     

The effects of a paclobutrazol-based growth regulator on the yield, quality and ease of management of oilseed rape

A mixture of paclobutrazol and chlormequat chloride plant growth regulators (JF10405, Parlay C) was tested on field crops of two ‘double zero’ oilseed rape cultivars in two seasons. Application rate and timing of JF10405 were varied. Very large plots enabled the use of commercial farm equipment to treat and harvest the experiments. Untreated plots showed considerable lodging at harvest in all experiments. Treatment with JF10405 had only small effects on the height of mature plants but, generally, reduced lodging substantially even at the lowest rate tested. All JF10405 treatments increased seed yields, several significantly so, particularly a 2.50 litre/ha rate, although the optimum timing varied between experiments. Seed oil contents were little affected, but levels of glucosinolates were significantly decreased in some instances. Treatments giving good control of lodging also took less time to harvest, especially when cutting against the direction of the lodging. The results-are discussed in relation to the means by which these improvements in seed yield and quality were achieved, and crop management facilitated.     

Temporal Dynamics of Powdery Mildew (Oidium neolycopersici) and its Effects on the Host Growth Dynamics of Tomato

Controlled glasshouse experiments were conducted to investigate the temporal progress of powdery mildew and its effects on host dynamics of tomato, without and with one fungicide application. Healthy tomato transplants (5‐ to 6‐week old) were artificially inoculated with powdery mildew, and disease progress as well as host growth were monitored in both fungicide sprayed and unsprayed treatments and compared with non‐inoculated plants. Actual disease severity on a plant basis increased in unsprayed plants reaching maximum severity in the proportionate range of 0.53–0.83. One fungicide spray significantly reduced the maximum disease severity by two‐ to fourfolds. Despite adjustments for defoliation, declines in the proportion of disease severity between successive assessments were evident. Whereas the estimated growth rates of diseased plants were significantly lower than that of healthy plants, no significant differences were observed in the maximum leaf area formed of inoculated and non‐inoculated plants. A considerable effect of the powdery mildew epidemics was manifested through hastened shrivelling and defoliation of diseased leaves within the tomato canopy. An average of 18–29% and 40–52% of leaves had abscised from the plant canopy at the last date of assessment in sprayed and non‐sprayed plants, respectively. Accordingly, defoliation accounted for 14–33.3% and 58.3–63.1% losses in leaf area of sprayed and non‐sprayed plants, respectively. Duration of healthy leaf area and yield of inoculated plants were also significantly reduced by powdery mildew epidemics.     

RESPONSES OF POPULATIONS OF SOLIDAGO SEMPERVIRENS (COMPOSITAE) TO SALT SPRAY ACROSS A BARRIER BEACH

The responses of four populations of Solidago sempervirens to salt spray at Island Beach State Park, a barrier beach in Ocean County, New Jersey, were examined under both field and greenhouse conditions. At increasing distances from the ocean, these populations were Primary Dune (PD), Dune Hollow (DH), Intermediate (INT), and Bayshore (BAY). Salt deposition on cheesecloth traps was found to drop significantly from PD to BAY. Population responses to the salt spray gradient were monitored by examining leaf stomatal and trichome densities, leaf thickness, and the salt spray tolerance of genotypes established in the greenhouse. No significant differences in either stomatal or trichome density were found among populations in the field. Leaf thickness of field plants at the PD site was significantly greater than the DH, INT, or BAY plants: however, unsprayed plants of these populations in the greenhouse did not vary significantly in leaf thickness, and for sprayed plants, leaf thickness varied only in relation to intensity of salt application. Thus, the differences in leaf thickness of field populations were not genetically based. Both nonexpanded and fully expanded leaves of BAY plants consistently showed the greatest percentage leaf damage following both low- and high-intensity artificial salt spray, indicating possible selection for population differences in salt spray tolerance.     

Effect of ascochyta blight (Mycosphaerella pinodes) on yield components of single pea (Pisum sativum) plants under field conditions

Field studies were made in 1992 and 1993 to examine the yield components of pea inoculated with Mycosphaerella pinodes and those of healthy pea (sprayed with a mixture of flutriafol + chlorothalonil), in a split-plot design with the cv. Solara sown at different plant densities. Ascochyta blight was severe on leaves and on internodes of the basal part of the plants; pods had few lesions. The number and length of stems per plant were the same for diseased and healthy plants. The number of reproductive nodes and pods per stem were affected by disease only in 1993. In 1992 and 1993 respectively, disease caused reductions in the number of seeds per stem of 18% and 25%, and in seed size of 13.5% and 16.7%, compared with healthy plants. The harvest index and total biomass were lower in diseased than in healthy plants and seed yield was reduced by 40% in diseased plots. These results show a high relationship between the disease parameters (disease mean on stipules/nodes 8–18/ and on internodes/nodes 5–15/, percentages of stipules or internodes with a disease score 4, and percentage of stems encircled by lesions), plant density and yield reduction.     

GROUNDNUT ROSETTE DISEASE IN TANGANYIKA

Rosette disease of groundnuts in Tanganyika is brought into the crop by infective alatae of Aphis craccivora : spread within the crop is by apterae and alatae. During the dry season the aphids maintain themselves on self-set groundnuts and on two genera of Leguminosae: Vigna and Millettia or Lonchocarpus. No native source of the virus causing rosette disease has been discovered, but self-set groundnuts carry over the virus from one cropping season to the next. Syrphid larvae and other predators are important in controlling the vector. Preliminary spraying trials with 0.5% schradan gave promising results in controlling the aphids on groundnut crops and consequently checking the spread of rosette disease. Selections of the variety Mwitunde showed the lowest incidence of rosette infection and gave the highest yields in trials in 1952.     

Effects of eyespot on the yield of winter wheat

In two experiments, on Julia and Zephyr spring barley, evidence was obtained that the development of powdery mildew in sprayed plots depended very much on their proximity to unsprayed crop. The effective period of control achieved with one spray was greater where plots were well separated from unsprayed crop than where they were surrounded by or very close to unsprayed crop. There is probably a risk that small plot experiments may not only underestimate the potential effectiveness of fungicides in agricultural practice, but also give misleading information on optimal spray timing.     

Accumulation and persistence of a nuclear polyhedrosis virus of the cabbage looper in the field

A nuclear polyhedrosis virus of the cabbage looper, Trichoplusia ni, was applied to foliage of Fall-planted broccoli and cabbage plants. Soil bioassays demonstrated that appreciable quantities of active virus accumulated in the upper 1 cm of the soil of plots sprayed with 10, 20, and 100 larval equivalents (LE)/acre as well as in unsprayed plots. After completion of the spray program, soil from plots treated with 8 foliar applications of 10 LE/acre contained only slightly more virus than the soil from unsprayed plots, but considerably more virus accumulated in plots treated with 20 and 100 LE/acre. The accumulation of virus continued after the completion of spraying and considerable quantities of active virus persisted through the winter.     

The relationship between leaf blotch caused by Rhynchosporium secalis and losses in grain yield of spring barley

Two methods were used to investigate the loss in grain yield associated with specific levels of leaf blotch. Yields from plots sprayed with fungicide were compared with those from unsprayed plots and yields of varieties of different susceptibility to the disease were compared with one another. A disease assessment key is presented, which was used to assess the percentage laminar area of the top two leaves affected by the disease. A linear relationship between disease on the upper two leaves and yield was established. Results from nine trials showed a consistent relationship between the disease level, at growth stage 11·1 (Feekes scale), and loss in yield. The loss in yield expressed as a percentage of the yield of an uninfected crop was equivalent to approximately two-thirds of the percentage of the flag-leaf area visibly infected, or one-half of the infected area on the second leaf. The predicted loss in yield is the average of these two estimates.     

The survival of gamebird (Galliformes) chicks in relation to pesticide use on cereals

Field experiments were carried out to test the effects of cereal pesticides (herbicides, fungicides and insecticides) on chick survival of Grey Partridge Perdix perdix , Red-legged Partridge Alectoris rufa and Pheasant Phasianus colchicus. On fields in experimental plots the outer 6 m of cereal (the headland) were not sprayed with pesticides from 1 January 1984, whereas control plots were fully sprayed. Gamebird brood counts were carried out after the cereal harvest. In addition, nine Grey Partridge broods were radio-tracked for 21 days after hatching (four in sprayed plots and five in unsprayed plots) to determine their movements, home range size and survival in relation to pesticide spraying.
The mean brood size of Grey Partridge and Pheasant was significantly higher on plots where field edges were unsprayed than on fully sprayed control plots. Data for Red-legged Partridge were inconclusive. The survival of individually marked Grey Partridge broods was negatively related to the distance moved between successive nocturnal roost sites. Survival was significantly higher, the distance moved between roost sites significantly shorter and the proportion of home range including headland significantly greater for broods feeding in spring barley fields with unsprayed field edges compared with broods feeding in fully sprayed fields.     

Virus infection stimulates phyto-oestrogen production in pasture legume plants growing in grazed swards

Four field experiments were sown with AMV‐infected or healthy seed of burr medic (Medicago polymorpha) and grazed by sheep; two were sown with cv. Circle Valley and two with cv. Santiago. Seed‐infected plants acted as primary sources for virus spread by naturally occurring aphids. Insecticides and admixture with annual ryegrass (Lolium rigidum), a non‐host of AMV, suppressed virus spread to different extents in the plots sown with infected seed. Effects of the different amounts of virus spread obtained on overall concentration of the oestrogenic compound coumestrol (dihydroxycoumestan) in dry stems and pods, and on seed production were measured in the medic. With cv. Santiago, stem and pod coumestrol concentration values for plots sown with healthy seed were significantly smaller than those for all plots sown with infected seed regardless of whether they were sprayed. With cv. Circle Valley, the coumestrol values for stems from plots sown with healthy seed were significantly smaller than those for unsprayed plots sown with infected seed but not than those for sprayed plots or ones with grass admixtures, and there were no significant differences with pods. There was always a significant positive relationship between concentration of coumestrol in medic stems and percentage AMV infection of swards; this was also so with pods in two experiments. A linear model best fitted this relationship with cv. Circle Valley but a logarithmic model did so with cv Santiago. In glasshouse grown plants, the coumestrol content of dried medic shoots was increased 11 (cv. Circle Valley) and five (cv. Santiago) times by AMV infection. AMV increased mean coumestrol concentrations up to 256 ppm (field) and 237 ppm (glasshouse) in stems and 223 ppm in pods (field). Sowing healthy seed in new pasture swards was an effective strategy for minimising coumestrol accumulation in burr medic swards. Two, but not single, applications of a newer generation pyrethroid insecticide to swards in which AMV was spreading significantly diminished coumestrol accumulation but applying organophosphorus insecticide twice and carbamate insecticide repeatedly did not. Medic seed yields and individual seed weights were sometimes significantly increased by the treatments, suppression of AMV spread by regular carbamate sprays being sufficient to increase seed yield by 55%.     

Some factors influencing the performance of spray programmes for the control of coffee berry disease

In 1968 in a field trial at Kamundu, Kenya, early-season (Jan.-Mar.) sprays of copper, captafol and Tuzet failed to control coffee berry disease (CBD), in the late (main) crop of cultivars S.L.28 and S.L.34. Copper and captafol caused some delay in disease development but eventually infection reached over 50 % in all treatments and final yields of sprayed plots were below those from unsprayed plots. In a similar trial in 1969 at Yara on the cultivar French Mission a similar spray programme achieved significant benefits: copper and captafol kept the level of disease below 20% and gave improved yields compared with unsprayed plots. A continuation of the sprays until June increased yields still further. In a second trial in 1968 at Kiamara on the cultivar French Mission substantial quantities of early crop were present and disease in this was effectively controlled by early-season sprays of captafol, although the late crop on the same trees became severely affected. Removal of this overlapping early crop in January caused only a limited delay in disease development in the late crop, despite the fact that with some treatments this stripping resulted in the removal of a large source of potential inoculum from the tree. The results are considered in relation to differences between seasons and fungicides and it is concluded that further evidence has been provided for the importance of the protective role of fungicides against CBD. It is considered that stripping of the early crop is never likely to be a necessary management practice.     

Invasion of a West Everglades wetland by Melaleuca quinquenervia countered by classical biological control

The population dynamics of Melaleuca quinquenervia were monitored over a 5-year period in a cypress-pine wetland while subjected to two levels of herbivory. The trees had been recruited during 1998–1999 after a destructive crown fire. Half of 26 experimental plots were sprayed every 4–6 weeks with an insecticide to reduce herbivory by the biological control agents Oxyops vitiosa and Boreioglycaspis melaleucae. After only 1-year melaleuca density increased by 26% in sprayed plots and by 7% in unsprayed plots. However, over the entire 5-year period melaleuca density increased in sprayed plots by 0.1% while decreasing by 47.9% in unsprayed plots when compared to initial densities. Annual mortality of melaleuca never exceeded 6% in any year in sprayed plots but ranged from 11% to 25% in unsprayed plots. There was a significant year by treatment interaction indicating the importance of the environment on tree mortality. Limited seed production occurred on sprayed trees but never on unsprayed trees. Mean tree height increased by 19.6% in sprayed plots while declining by 30.6% in unsprayed plots. Coverage by native vegetation did not increase with decreasing melaleuca density. This is the first study with controls that quantifies the population level regulation of melaleuca by introduced biological control agents and corroborates other correlative studies that documented significant changes in melaleuca communities after the introduction and establishment of biological control agents.     

Effect of soil potassium availability on soybean aphid (Hemiptera: Aphididae) population dynamics and soybean yield

Studies were conducted to examine the effect of potassium (K) on soybean aphid, Aphis glycines Matsumura, population growth. A laboratory feeding assay examined the effect of K-deficient foliage on life table parameters of soybean aphids, and field experiments were designed to determine the effect of three soil K treatment levels on aphid populations and their impact on soybean yields. The feeding assay found that life table parameters differed between aphids feeding on the K-deficient and nondeficient soybean leaves. Soybean aphids in the K-deficient treatment exhibited significantly greater intrinsic rate of increase (r(m)), finite rate of increase (lambda), and net reproductive rate (Ro) relative to aphids feeding on nondeficient leaves. No significant difference was observed in mean generation time (T) between the two treatments. However, the field experiment repeated over 2 yr showed no effect of K on soybean aphid populations. Soybean aphid populations were high in unsprayed plots and feeding resulted in significant yield losses in 2002 at all three K treatment levels: when averaged across 2001 and 2002, unsprayed treatments yielded 22, 18, and 19.5% less than the sprayed plots in the low, medium, and high K treatments, respectively. No significant interaction was observed between aphid abundance and K level on soybean yields in either year. This study therefore suggests that although aphids can perform better on K-deficient plants, aphid abundance in the field may be dependent on additional factors, such as dispersal, that may affect final densities within plots.