Soil-applied Insecticides Research Articles

Field Trial Performance of Herculex XTRA (Cry34Ab1/Cry35Ab1) and SmartStax (Cry34Ab1/Cry35Ab1 + Cry3Bb1) Hybrids and Soil Insecticides Against Western and Northern Corn Rootworms (Coleoptera: Chrysomelidae).

Western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), and northern corn rootworm, Diabrotica barberi Smith and Lawrence (Coleoptera: Chrysomelidae), are important insect pests in corn, Zea mays L. For more than a decade, growers have been using transgenic plants expressing proteins from the bacterium Bacillus thuringiensis (Bt) to protect corn roots from feeding. In 2011, western corn rootworm populations were reported to have developed resistance to Bt hybrids expressing Cry3Bb1 and later found to be cross-resistant to hybrids expressing mCry3A and eCry3.1Ab. The identification of resistance to Cry3 (Cry3Bb1, mCry3A, and eCry3.1Ab) hybrids led to concerns about durability and efficacy of products with single traits and of products containing a pyramid of a Cry3 protein and the binary Bt proteins Cry34Ab1 and Cry35Ab1. From 2012 to 2014, 43 field trials were conducted across the central United States to estimate root protection provided by plants expressing Cry34Ab1/Cry35Ab1 alone (Herculex RW) or pyramided with Cry3Bb1 (SmartStax). These technologies were evaluated with and without soil-applied insecticides to determine if additional management measures provided benefit where Cry3 performance was reduced. Trials were categorized for analysis based on rootworm damage levels on Cry3-expressing hybrids and rootworm feeding pressure within each trial. Across scenarios, Cry34Ab1/Cry35Ab1 hybrids provided excellent root protection. Pyramided traits provided greater root and yield protection than non-Bt plus a soil-applied insecticide, and only in trials where larval feeding pressure exceeded two nodes of damage did Cry34Ab1/Cry35Ab1 single-trait hybrids and pyramided hybrids show greater root protection from the addition of soil-applied insecticides.

Effects of foliar and systemic insecticides on whitefly transmission and incidence of Cucurbit yellow stunting disorder virus.

Cucurbit yellow stunting disorder virus (CYSDV) is a cosmopolitan viral disease transmitted by Bemisia tabaci that infects cucurbit crops. Cantaloupe production in the southwestern USA has been confronted by epidemics of CYSDV since 2006 when it was first identified in Arizona and California. As a phloem-limited virus that is vectored in a semi-persistent manner by B. tabaci, CYSDV has transmission characteristics that may be suppressed by select insecticide applications. Eight active ingredients formulated as foliar and/or soil-applied insecticides were tested to determine the suppressive effect on transmission and incidence of CYSDV in greenhouse and field studies. Many compounds limited virus transmission to <10% infected plants even when challenged by 30 viruliferous whiteflies. Foliar formulations had greater knockdown activity than their soil-applied analogs and resulted in lower virus transmission. Insecticides that had the greatest effect on reducing virus transmission in the greenhouse also showed the lowest incidence of CYSDV in field trials. Select insecticides can significantly reduce transmission of CYSDV. However, insecticide management of CYSDV incidence in cantaloupes has limitations in chronically high infestation areas such as the southwestern USA, and is often only able to delay disease onset rather than prevent its occurrence. © 2016 Society of Chemical Industry.

Using bioassays with the green peach aphid (Myzus persicae) to determine residual activity of two systemically soil-applied neonicotinoid insecticides in field-grown tobacco

ABSTRACTDuration of systemic pesticide activity under field conditions has wide implications for pest management. Our aim was to determine the duration of activity of systemic insecticides commonly used in cultivated tobacco (Nicotiana tabacum) by measuring the levels of insect infestations on field plots and effects on reproduction and survival of the green peach aphid (Myzus persicae) in controlled bioassays using field grown leaves. Plants were treated with different concentrations of two systemic neonicotinoid pesticides, imidacloprid and thiamethoxam, and grown in small field plots. Our results show that these materials are effective under field conditions against aphids for at least 13 weeks after transplant. Pesticides also affected aphid reproduction and nymph survival in bioassays, although some aphids survived on pesticide-treated leaves. We also observed that leaf age affected aphid survival. We showed that neonicotinoids were very effective against M. persicae, aphids are a useful organism to assess pesticide efficacy early in the growing season, but plant characteristics are more important than pesticide concentration in the second half of the growing season.

Control of western corn rootworm damage by application of soil insecticides at different maize planting times

The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) (WCR), is one of the most damaging maize crop pests. Damage to maize is primarily caused by the larvae feeding on roots, which results in a reduction of water and nutrient uptake and may cause lodging as well as a substantial reduction in grain yield.The effects of soil insecticides, applied at different planting times, on controlling WCR damage were investigated in 76 naturally infested fields in Northern Italy over a 4-year period. Without furrow insecticides, plant density was reduced at all of the considered planting times (−5%). Insecticide application led to a significant reduction in the WCR larval density (−43%). As a consequence, the root injury measured by node injury scale, was reduced (−65%) as was the incidence of plants with “gooseneck” symptoms (−76%). Furthermore, the soil-applied insecticide plots showed a significant increase in plant biomass yield at the dough stage (+6%) and in grain yield at physiological maturity (+8%). The application of soil insecticides showed a positive yield increase in 95% of the compared production situations. The yield increase was higher than 5% in 70% of considered cases. The effect of the soil-applied insecticides on root and plant damage symptoms, and the consequent biomass and grain advantage were steady over the different intervals between planting time and WCR egg hatching.The results of this study have underlined that the application of a soil insecticide to the furrows at planting leads to a clear control of injuries from insects and a consequent maize yield advantage.

Effects of Field History on Corn Root Injury and Adult Abundance of Northern and Western Corn Rootworm (Coleoptera: Chrysomelidae).

Western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), and northern corn rootworm, Diabrotica barberi Smith & Lawrence, are major pests of corn (Zea mays L.). Corn producing Bacillus thuringiensis (Bt) toxins are widely used to manage Diabrotica spp.; however, Bt resistance by D. v. virgifera has led to high levels of feeding injury in the field. We tested whether field history affected root injury and abundance of adult Diabrotica spp. In 2013 and 2014, four types of cornfields were sampled: 1) recently rotated fields, 2) continuous cornfields, 3) fields with a history of injury to Bt corn (past problem fields), and 4) fields with greater than one node of injury to Bt corn at the time of sampling (current problem fields). Data were collected on field history, root injury, and the abundance of adult Diabrotica spp. from each field. Root injury and the abundance of D. v. virgifera were significantly greater in current problem fields compared to the other field types, while D. barberi were significantly more abundant in recently rotated fields. Root injury and the abundance of D. v. virgifera did not differ among recently rotated fields, continuous cornfields, and past problem fields. Analysis of field history showed that recently rotated fields were characterized by significantly less Bt corn, soil-applied insecticides, and years planted to corn continuously. These results suggest that greater cropping practice diversity can reduce management inputs for Diabrotica spp.; however, its effects on resistance evolution remain undetermined.

Field-Based Assessment of Resistance to Bt Corn by Western Corn Rootworm (Coleoptera: Chrysomelidae).

Western corn rootworm, Diabrotica virgifera virgifera LeConte, is a serious pest of corn and is managed with corn that produces insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt). Beginning in 2009, resistance to Cry3Bb1 corn, and severe injury to Cry3Bb1 corn in the field, was observed in Iowa. However, few data exist on how Cry3Bb1-resistant western corn rootworm interact with various management practices in the field. Using a field experiment, we measured adult emergence and feeding injury to corn roots for both Cry3Bb1-resistant and Cry3Bb1-susceptible populations of western corn rootworm when tested against various Bt corn hybrids and a soil-applied insecticide. Between 2012 and 2013, we evaluated five fields that were associated with greater than one node of feeding injury to Cry3Bb1 corn by western corn rootworm (i.e., problem-field populations), and a laboratory strain that had never been exposed to Bt corn (i.e., control population). Adult emergence for western corn rootworm and root injury to corn were significantly higher in problem-field populations than control populations for both Cry3Bb1 corn and mCry3A corn. By contrast, corn with Cry34/35Ab1, either alone or pyramided with Cry3Bb1, significantly reduced adult emergence and root injury in both problem fields and control fields. In problem fields, application of the soil-applied insecticide to Cry3Bb1 corn significantly reduced root injury, but not adult emergence. Our results are discussed in terms of developing strategies for managing western corn rootworm with resistance to Cry3Bb1 and mCry3A, and delaying the additional evolution of Bt resistance by this pest.

IPM Use With the Deployment of a Non-High Dose Bt Pyramid and Mitigation of Resistance for Western Corn Rootworm (Diabrotica virgifera virgifera).

Recent detection of western corn rootworm resistance to Bt (Bacillus thuringiensis) corn prompted recommendations for the use of integrated pest management (IPM) with planting refuges to prolong the durability of Bt technologies. We conducted a simulation experiment exploring the effectiveness of various IPM tools at extending durability of pyramided Bt traits. Results indicate that some IPM practices have greater merits than others. Crop rotation was the most effective strategy, followed by increasing the non-Bt refuge size from 5 to 20%. Soil-applied insecticide use for Bt corn did not increase the durability compared with planting Bt with refuges alone, and both projected lower durabilities. When IPM participation with randomly selected management tools was increased at the time of Bt commercialization, durability of pyramided traits increased as well. When non-corn rootworm expressing corn was incorporated as an IPM option, the durability further increased. For corn rootworm, a local resistance phenomenon appeared immediately surrounding the resistant field (hotspot) and spread throughout the local neighborhood in six generations in absence of mitigation. Hotspot mitigation with random selection of strategies was ineffective at slowing resistance, unless crop rotation occurred immediately; regional mitigation was superior to random mitigation in the hotspot and reduced observed resistance allele frequencies in the neighborhood. As resistance alleles of mobile pests can escape hotspots, the scope of mitigation should extend beyond resistant sites. In the case of widespread resistance, regional mitigation was less effective at prolonging the life of the pyramid than IPM with Bt deployment at the time of commercialization.

Efficacy of Soil-Applied Systemic Insecticides Against Tobacco Pests, 2014

Efficacy of several soil-applied insecticides (Table 1) was tested against key tobacco pests: TFB, TBW, GPA, and tobacco/tomato hornworms (HW). Two identical experiments were conducted at the Upper Coastal Plain Research Station (UCPRS) in Rocky Mount, NC, and the Lower Coastal Plain Research Station (LCPRS) in Kinston, NC. In each experiment, four replicates of the six treatments, including an untreated check, were arranged an RCB design. Each 0.018-acre plot consisted of four, ca. 25 plant, rows. At LCPRS, pre-transplant greenhouse tray drench (GTD) insecticide applications were made on 7 May 2014 in 1 L water using a CO2-pressurized sprayer fitted a single flat-fan nozzle. Twice the application volume was used to wash the material into the root zone immediately following treatment. GTD treatments were applied as above at UCPRS on 28 Apr. The plants were transplanted on 5 May at UCPRS and 8 May at LCPRS, and in-furrow transplant water (TPW) treatments were applied in ca. 160 gal/A of water using four 5-gal mini-tanks affixed to the planter. Plants received no additional insecticide treatments for the …

Control of Corn Rootworm Larvae with Soil-Applied Insecticides and Bt Hybrids, 2014

We established one trial at the Northwestern Illinois Agricultural Research and Development Center near Monmouth, IL, to evaluate the efficacy of soil-applied insecticides and Bt hybrids to control corn rootworm (CRW) larvae. The experimental design was a RCB with four replications. The plot size for each treatment was 10 ft (four rows) × 40 ft. The previous crop was a trap-crop (late-planted corn and pumpkins). Corn was planted on 7 May using a four-row, vacuum-style planter (SRES, South Hutchinson, KS) at a rate of 36,600 seeds/acre in 30-inch rows at an approximate depth of 1.75 inches. Hybrid information is provided in Table 1. Granular insecticides were applied through modified Noble metering units or through modified SmartBox metering …

Soil-applied Insecticidal Control ofScirtothrips dorsalis(Thysanoptera: Thripidae) in Pepper, 2011

The objective of this study was to evaluate the efficacy of several conventional and novel soil-applied insecticides against a new invasive thrips pest, chilli thrips (CT), Scirtothrips dorsalis (Hood), in pepper under greenhouse condition. The trial was conducted at Tropical Research and Education Center in Homestead, FL, to find an alternative to standard effective chemistries used in thrips control. The peppers were grown in Fafard 2 Mix (Canadian Formula; Conrad Fafard, Inc., Agawam, MA 01001-2907) from seed in seedling trays and transplanted in 1 gal plastic pot when seedlings were 7-wk …

Control of Corn Rootworm Larvae with Soil-Applied Insecticides, 2014: Table 1

We established one trial at the Northern Illinois Agronomy Research Center near DeKalb, IL, to evaluate the efficacy of soil-applied insecticides to control CRW larvae. The experimental design was a RCB with four replications. The plot size for each treatment was 10 ft (four rows) by 40 ft. The previous crop was a trap-crop (late-planted corn and pumpkins). The trial was planted on 8 May using a four-row, vacuum-style planter (SRES, South Hutchinson, KS). Seeds were planted at a rate of 38,500 seeds/acre in …

Soil-applied imidacloprid translocates to ornamental flowers and reduces survival of adult Coleomegilla maculata, Harmonia axyridis, and Hippodamia convergens lady beetles, and larval Danaus plexippus and Vanessa cardui butterflies.

Integrated Pest Management (IPM) is a decision making process used to manage pests that relies on many tactics, including cultural and biological control, which are practices that conserve beneficial insects and mites, and when needed, the use of conventional insecticides. However, systemic, soil-applied neonicotinoid insecticides are translocated to pollen and nectar of flowers, often for months, and may reduce survival of flower-feeding beneficial insects. Imidacloprid seed-treated crops (0.05 mg AI (active ingredient) /canola seed and 1.2 mg AI/corn seed) translocate less than 10 ppb to pollen and nectar. However, higher rates of soil-applied imidacloprid are used in nurseries and urban landscapes, such as 300 mg AI/10 L (3 gallon) pot and 69 g AI applied to the soil under a 61 (24 in) cm diam. tree. Translocation of imidacloprid from soil (300 mg AI) to flowers of Asclepias curassavica resulted in 6,030 ppb in 1X and 10,400 ppb in 2X treatments, which are similar to imidacloprid residues found in another plant species we studied. A second imidacloprid soil application 7 months later resulted in 21,000 ppb in 1X and 45,000 ppb in 2X treatments. Consequently, greenhouse/nursery use of imidacloprid applied to flowering plants can result in 793 to 1,368 times higher concentration compared to an imidacloprid seed treatment (7.6 ppb pollen in seed- treated canola), where most research has focused. These higher imidacloprid levels caused significant mortality in both 1X and 2X treatments in 3 lady beetle species, Coleomegilla maculata, Harmonia axyridis, and Hippodamia convergens, but not a fourth species, Coccinella septempunctata. Adult survival were not reduced for monarch, Danaus plexippus and painted lady, Vanessa cardui, butterflies, but larval survival was significantly reduced. The use of the neonicotinoid imidacloprid at greenhouse/nursery rates reduced survival of beneficial insects feeding on pollen and nectar and is incompatible with the principles of IPM.

A multi-year field study to evaluate the environmental fate and agronomic effects of insecticide mixtures

A mixture of insecticides used in corn production was monitored over a three-year period in a field study to determine how long each persists in the environment, where each insecticide travels within the corn field, and the efficacy of using soil-applied insecticides with genetically modified corn. The genetically modified corn contained the insecticidal Cry1Ab and Cry3Bb1 proteins (Bt corn) and the Cry1Ab protein was found to persist only during the corn growing season in soil, runoff water, and runoff sediment with highest concentrations measured during pollination. Very low concentrations of Cry1Ab proteins were measured in soil collected in the non-Bt corn field, and no Cry1Ab proteins were detected in shallow groundwater or soil pore water. Clothianidin, a neonicotinoid insecticide used as a seed coating, was detected in all matrices and remained persistent throughout the year in soil pore water. Tefluthrin, a pyrethroid insecticide applied at planting to control corn rootworm larvae (Diabrotica spp., Coleoptera: Chrysomelidae) populations, was consistently detected in soil, runoff water, and runoff sediment during the corn growing season, but was not detected in groundwater or soil pore water. Tefluthrin did not have an effect on root damage from corn rootworm larvae feeding to Bt corn, but did prevent damage to non-Bt corn. A slight reduction in grain yield was observed in the non-Bt, no tefluthrin treatment when compared to all other treatments, but no significant difference in grain yield was observed among Bt corn treatments regardless of soil insecticide application. In the current study, the use of tefluthrin on Bt corn did not significantly affect crop damage or yield, and tefluthrin may travel off-site in runoff water and sediment.

Environmental fate of soil applied neonicotinoid insecticides in an irrigated potato agroecosystem.

Since 1995, neonicotinoid insecticides have been a critical component of arthropod management in potato, Solanum tuberosum L. Recent detections of neonicotinoids in groundwater have generated questions about the sources of these contaminants and the relative contribution from commodities in U.S. agriculture. Delivery of neonicotinoids to crops typically occurs as a seed or in-furrow treatment to manage early season insect herbivores. Applied in this way, these insecticides become systemically mobile in the plant and provide control of key pest species. An outcome of this project links these soil insecticide application strategies in crop plants with neonicotinoid contamination of water leaching from the application zone. In 2011 and 2012, our objectives were to document the temporal patterns of neonicotinoid leachate below the planting furrow following common insecticide delivery methods in potato. Leaching loss of thiamethoxam from potato was measured using pan lysimeters from three at-plant treatments and one foliar application treatment. Insecticide concentration in leachate was assessed for six consecutive months using liquid chromatography-tandem mass spectrometry. Findings from this study suggest leaching of neonicotinoids from potato may be greater following crop harvest in comparison to other times during the growing season. Furthermore, this study documented recycling of neonicotinoid insecticides from contaminated groundwater back onto the crop via high capacity irrigation wells. These results document interactions between cultivated potato, different neonicotinoid delivery methods, and the potential for subsurface water contamination via leaching.

Variable concentration of soil‐applied insecticides in potato over time: implications for management of Leptinotarsa decemlineata

Select populations of Colorado potato beetle, Leptinotarsa decemlineata, in Wisconsin have recently become resistant to soil-applied neonicotinoids in potato. Sublethal insecticide concentrations persisting in foliage through the growing season may select for resistance over successive years of use. Over the 2 years of this study, the aim was to document the in-plant insecticide concentrations over time that result from four different types of soil-applied insecticide delivery for thiamethoxam and imidacloprid in potato, and to measure the impact upon L. decemlineata populations following treatments. After plant emergence, insect life stages were counted and plant tissue was assayed weekly for nine consecutive weeks using ELISA. Peak concentration of both imidacloprid and thiamethoxam occurred in the first sample week following plant emergence. The average concentration of both insecticides dissipated sharply over time as the plant canopy expanded 50 days after planting in all delivery treatments. Both insecticides were detected at low levels during the later weeks of the study. Among-plant concentrations of both neonicotinoids were highly variable throughout the season. Populations of L. decemlineata continued to develop and reproduce throughout the period of declining insecticide concentrations. Sublethal, chronic exposure to soil-applied systemic insecticides resulting from these delivery methods may accelerate selection for resistant insects in potato.

Probing Behaviors of Adult Asian Citrus Psyllid (Hemiptera: Liviidae) are Not Appreciably Affected by Soil Application of Field-Rate Aldicarb to Citrus

In 2005, Huanglongbing disease (HLB), also known as citrus greening, was discovered in Florida. The presumptive causal agent of this disease is the phloem-limited bacterium ‘Candidatus Liberibacter asiaticus’ (Las) which is spread by the Asian citrus psyllid (Diaphorina citri Kuwayama). Following the discovery of HLB, insecticide use for control of the vector has increased dramatically. One such insecticide is aldicarb, a soil-applied systemic carbamate insecticide that has been used in Florida citrus since the 1970's for both control of insect and mite pests and for its potential plant growth promoting benefits. The objective of this study was to determine the effects of soil-applications of aldicarb to citrus on the feeding behavior of D. citri, including whether this systemic insecticide disrupts feeding behaviors responsible for Las transmission. To achieve this goal, an electrical penetration graph monitor was used to examine D. citri feeding behavior when given a feeding access period of 12 h on aldicarb-treated and untreated citrus plants. Results showed no reduction in D. citri probing behaviors between treatments, and no insects died during recordings. Unexpectedly, at the cohort level, both phloem salivation and phloem ingestion were significantly longer on aldicarb-treated compared with untreated plants, suggesting that aldicarb application may increase the likelihood of Las transmission. Although registration of aldicarb for use in the U.S. has been discontinued for the last year, it has been reregistered for use in certain crops that may include citrus in the future. Thus, there is renewed importance in understanding the effects of aldicarb and other insecticides applied to suppress insect-transmitted diseases.

Integration of soil applied neonicotinoid insecticides and acibenzolar-S-methyl for systemic acquired resistance (SAR) control of citrus canker on young citrus trees

Soil application of systemic neonicotinoid insecticides for control of psyllid vectors of Huanglongbing disease on young citrus trees also produces season-long SAR control of citrus canker caused by Xanthomonas citri subsp. citri Schaad et al. The neonicotinoids imidacloprid (IMID) and thiamethoxam (THIA) were compared with soil or sprinkler applications of the commercial SAR inducer acibenzolar-S-methyl (ASM) and foliar sprays of copper hydroxide (CH) and/or streptomycin (STREP) to evaluate their effects on the percentage of canker-infected leaves on 2-yr-old ‘Vernia’ orange and 3-yr-old ‘Ray Ruby’ grapefruit trees in Southeast Florida. All treatments significantly reduced the incidence of foliar canker compared to the untreated check. Soil drenches of ASM and season long rotations with IMID and THIA were highly effective for suppressing foliar canker on young grapefruit and orange trees under weather conditions absent of high intensity rains or tropical storms. Sprinkler application of ASM was less effective than soil drench. The level of control for SAR treatments was comparable to eleven 21-day interval sprays of CH and/or STREP. SAR induced by soil-applied insecticides provides substantial benefits for canker disease management on young citrus trees that may be augmented with ASM.

Effect of Bt Maize and Soil Insecticides on Yield, Injury, and Rootworm Survival: Implications for Resistance Management

A 2-yr field experiment was conducted to determine the effects on Diabrotica spp. (Coleoptera: Chrysomelidae) of an insecticidal seed treatment (Poncho 1250, (AI)/clothianidin) and a granular insecticide (Aztec 2.1G, (AI)/tebupirimphos and cyfluthrin) alone and in combination with maize producing the insectidical toxin Cry3Bb1 derived from the bacterium Bacillus thuringiensis (Bt). Yields for Bt maize plots were significantly greater than for non-Bt maize; however, insecticides did not significantly affect yield. Insecticides significantly decreased root injury in non-Bt maize plots, but there were no significant differences in root injury between Bt maize with or without either insecticide. Maize producing the Bt toxin Cry3Bb1 and the soil-applied insecticide Aztec significantly decreased survival of western corn rootworm (Diabrotica virgifera virgifera LeConte), while only Bt maize significantly decreased survival of the northern corn rootworm (Diabrotica barberi Smith & Lawrence). For both species, Bt maize and each of the insecticides delayed emergence. In the absence of density-dependent mortality, Bt maize imposed 71 and 80% reduction in survival on the western corn rootworm and the northern corn rootworm, respectively. The data from this study do not support combining insecticide with Bt maize because the addition of insecticide did not increase yield or reduce root injury for Bt maize, and the level of rootworm mortality achieved with conventional insecticide was likely too low to delay the evolution of Bt resistance. In addition, delays in emergence from Bt maize combined with insecticides could promote assortative mating among Bt-selected individuals, which may hasten resistance evolution.

Efficacy of Soil Applied Neonicotinoid Insecticides Against the Azalea Lace Bug,Stephanitis pyrioides, in the Landscape

Azalea lace bugs (Heteroptera: Tingidae) are common pests of azaleas in the landscape and in plant production. Adults and nymphs feed on foliage causing stippling damage, which persists for multiple seasons. This study was conducted to determine the speed of translocation and residual longevity of various soil-applied neonicotinoid insecticides for control of azalea lace bugs in the landscape. Mass plantings of azaleas were treated with different formulations and application rates of clothianidin, dinotefuran, imidacloprid, and thiamethoxam. Treatments were evaluated at intervals of 3, 7, 14, 30 d, and 1 yr using a laboratory assay with excised shoots and field-collected adult lace bugs. A sample of field populations was taken 2 mo after the initial treatment. Plant health was determined by rating the severity of leaf injury and percent of damaged leaves per shoot. Dinotefuran and thiamethoxam provided the best control after 3 and 7 d in lab assays. A greater application rate improved efficacy of granular dinotefuran and thiamethoxam formulations in the 3–14 d evaluations. After 2 mo, azalea lace bug populations, primarily composed of nymphs, were lower than the controls. A laboratory choice test indicated that adult lace bugs do not avoid treated plants as has been shown for other sucking pests. After 12 mo, survival of lace bugs across all treatments averaged 61% and at least 1 product containing dinotefuran, thiamethoxam, and imidacloprid was significantly different from untreated controls. Plant appearance was also improved relative to untreated controls with fewer damaged leaves per plant on all treated plants after 1 yr.

Dynamic plant uptake model applied for drip irrigation of an insecticide to pepper fruit plants

Drip application of insecticides is an effective way to deliver the chemical to the plant that avoids off-site movement via spray drift and minimizes applicator exposure. The aim of this paper is to present a cascade model for the uptake of pesticide into plants following drip irrigation, its application for a soil-applied insecticide and a sensitivity analysis of the model parameters. The model predicted the measured increase and decline of residues following two soil applications of an insecticide to peppers, with an absolute error between model and measurement ranging from 0.002 to 0.034 mg kg fw(-1). Maximum measured concentrations in pepper fruit were approximately 0.22 mg kg fw(-1). Temperature was the most sensitive component for predicting the peak and final concentration in pepper fruit, through its influence on soil and plant degradation rates. Repeated simulations of pulse inputs with the cascade model adequately describe soil pesticide applications to an actual cropped system and reasonably mimic it. The model has the potential to be used for the optimization of practical features, such as application rates and waiting times between applications and before harvest, through the integrated accounting of soil, plant and environmental influences.