Tomato Spotted Wilt Incidence Research Articles

Comparison of Field Performance of Georgia-16HO and Florunner Cultivars in the Presence of Tomato Spotted Wilt

Field experiments were conducted at Tifton, Georgia from 2019 to 2020 to compare the effects of new peanut (Arachis hypogaea L.) cultivar ‘Georgia-16HO’ with the former industry standard cultivar ‘Florunner’, and in-furrow applications of phorate or imidacloprid insecticides on severity of tomato spotted wilt (TSW) caused by Tomato spotted wilt virus (TSWV), resultant yield, and crop value. Incidence of TSW was much lower for Georgia-16HO than for Florunner in both years, with differences more obvious in 2019 when the virus pressure was higher. Yield was greater for Georgia-16HO than Florunner in both years with greater differences when disease pressure was higher. Across all treatments, adjusted crop value for Georgia-16HO was ~$1450 /ha greater than for Florunner in 2019 and ~$839 /ha greater in 2020.

Performance of Imidacloprid or Phorate Co-Applied In-Furrow with Superabsorbent Polymer and Evaluation of Aldicarb

Management decisions mitigating thrips injury and tomato spotted wilt infection are primarily limited to being enacted at the beginning of the growing season. Previous work explored corresponding potential management contribution of concurrent insecticide application with a superabsorbent polymer in-furrow but reported effects to be marginal or variable across experiments. To more thoroughly probe this potential, data from a collection of 40 experiments conducted from 2009 through 2022 was analyzed to examine the efficacy of insecticides (aldicarb, imidacloprid, imidacloprid plus fluopyram, and phorate, in addition to a nontreated check) applied in-furrow at planting for peanut production. In addition to treatments applied individually, experiments included imidacloprid (n = 11) or phorate (n = 18) applied in the presence of 2.2 kg/ha superabsorbent polymer. Results indicated that neither imidacloprid nor phorate alone significantly varied with regard to stand count (P > 0.35), thrips injury (P > 0.27), tomato spotted wilt incidence (P > 0.08), or yield (P > 0.37) when compared to their co-application with the polymer. These results were consistent across variety susceptibility levels to tomato spotted wilt. The fitted models were determined to be robust to the treatment composition of screened studies (P > 0.089). Where there were differences in projected returns above the nontreated check, phorate or aldicarb were the most consistently profitable treatments.

General Tomato Spotted Wilt Virus Field Resistance among Spanish and Valencia Market Type Peanut Cultivars.

During 2016 through 2020, field tests were conducted to determine general Tomato spotted wilt virus (TSWV) resistance among seven spanish and seven valencia-type peanut (Arachis hypogaea L.) cultivars. These tests were planted early in April each year to enhance tomato spotted wilt (TSW) disease pressure at the University of Georgia, Coastal Plain Experiment Station, Tifton, GA. TSW disease incidence was first assessed at about midseason (60 DAP), and total disease (TD) incidence which was primarily TSW was again assessed prior to digging. The five-year average results showed significant differences (P≤0.05) among the spanish-type cultivars. The lowest TSW and TD incidence was found with the TSWV-resistant spanish cultivar, ‘Georgia-17SP’. This cultivar also produced the highest pod yield, total sound mature kernel (TSMK) grade, and gross dollar value returns per hectare. The five-year average results among the valencia-type cultivars also showed significant differences. The lowest TSW and TD incidence was found with the moderately TSWV-resistant valencia cultivar ‘Georgia-Val/HO’. This cultivar also produced the highest pod yield, TSMK grade, and dollar value return. These new Georgia cultivars are not the traditional spanish and valencia-types; however, pod and seed traits meet or exceed the criteria for each market type, respectively.

Relative Tomato Spotted Wilt Incidence and Field Performance among Peanut Cultivars as Influenced by Different Input Production Practices in Georgia.

ABSTRACT During 2017-19, 30 replicated yield trials were conducted to determine relative tomato spotted wilt (TSW) incidence and general field performance among 19 runner and virginia market type peanut (Arachis hypogaea L.) cultivars. Four different input production practices were compared across three Georgia locations (Tifton, Plains, and Midville). Two early-planted (April) field tests were conducted at Tifton and Plains each year. One early-planted trial involved maximum-input practices of recommended pesticides with irrigation, and the other early-planted field trial did not receive any fungicides, insecticides, or irrigation. Early-planted maximum-input production practices with irrigation resulted in the highest percentage of mid-season TSW and late-season total disease incidences while also producing the highest pod yields and dollar values. Two other optimum-planted (May) maximum-input field tests were conducted at Tifton, Plains, and Midville, GA as part of the official statewide variety trials (OVT). These OVT utilized maximum-input production practices of pesticides both with and without irrigation. In the OVT, midseason TSW incidence showed no difference between irrigated and non-irrigated; however, the end-of-season total disease percentages which were predominantly TSW did show significantly higher disease percentage, produced the highest pod yields and dollar values within the irrigated field tests compared to the non-irrigated tests. In the overall four tests comparison, disease results showed significantly lower TSW incidence in the early-planted tests without fungicides and insecticides input production practices and no-irrigation; whereas, both optimum planted OVT(s) had the lowest total disease incidence. Overall average field performance for pod yields and dollar values were significantly highest in the optimum-planted tests with maximum-inputs including irrigation. Significant differences were also found among the 19 peanut cultivars. ‘Georgia-06G', ‘Georgia-12Y', and ‘Georgia-18RU' had the lowest relative TSW incidence compared to the other runner-type cultivars. ‘Georgia-19HP' had the lowest TSW incidence and total disease incidence among the virginia-type cultivars. Among the runner cultivars, Georgia-12Y had the lowest total disease incidence at the end of the season. The highest pod yields were found with Georgia-06G and ‘Georgia-16HO'; whereas, Georgia-18RU and Georgia-06G had the highest dollar values among the runner-type peanut cultivars. Georgia-19HP had the highest pod yield and dollar value among the virginia-type cultivars.

Effect of thiamethoxam seed treatment in peanut

AbstractTobacco thrips (Frankliniella fusca) and tomato spotted wilt (TSW) orthotospovirus (family Tospoviridae, genus Orthotospovirus) can reduce peanut (Arachis hypogaea L.) yield. Systemic insecticides are applied in the seed furrow at planting and to peanut foliage to reduce injury from tobacco thrips and decrease incidence of TSW. Research was conducted in Georgia, North Carolina, South Carolina, and Virginia in 2013 and 2014 to compare the effect of the following treatments on tobacco thrips feeding injury and expression of TSW in peanut: thiamethoxam seed treatment, thiamethoxam seed treatment followed by acephate 3 weeks after planting, phorate applied in the seed furrow at planting, and a nontreated check. Tobacco thrips feeding injury and TSW incidence were significantly higher in thiamethoxam and thiamethoxam followed by acephate‐treated peanut than peanut treated with phorate. Thiamethoxan seed treatment followed by acephate resulted in significantly lower tobacco thrips feeding injury compared to thiamethoxam seed treatment alone. Yield of Virginia market type cultivars was greater when thiamethoxam was followed by acephate applied to peanut foliage or when phorate was applied compared with nontreated peanut or the seed treatment alone. Runner market type cultivars yielded higher when phorate was applied compared with nontreated peanut while peanut treated with thiamethoxam with or with acephate yielded similar to both of these treatments.

Efficacy and Profitability of Insecticide Treatments for Tomato Spotted Wilt Management on Peanut in South Carolina.

Tomato spotted wilt (TSW) is a common and serious disease of peanut (Arachis hypogaea L.) caused by Tomato spotted wilt virus (TSWV; family Tospoviridae, genus Orthotospovirus). Management frequently uses an integrated approach, with cultivar resistance and application of in-furrow insecticide as two critical components. In-furrow insecticides help suppress thrips, which can injure and stunt young growing plants and transmit TSWV, with postemergent application of acephate capable of providing additional thrips control. To examine effects of systemic insecticides (imidacloprid, imidacloprid plus fluopyram, phorate, and acephate) on TSW management, yield, and economic return across cultivar susceptibilities (susceptible, moderately susceptible, and resistant) in South Carolina, a meta-analysis was used to synthesize results from 32 studies conducted between 2009 and 2018. Although efficacy and magnitude of individual treatments varied with susceptibility, imidacloprid increased, whereas phorate generally decreased TSW incidence relative to nontreated controls. In-furrow treatments followed by acephate further reduced TSW incidence and increased profitability. All examined treatments improved yield compared with untreated peanuts except for susceptible cultivars treated with imidacloprid. Imidacloprid plus fluopyram increased yield more than imidacloprid alone for the susceptible group, although there was little difference between these treatments in association with moderately susceptible cultivars. When comparing individual applications, phorate was overall the most profitable option across susceptibilities, although imidacloprid plus fluopyram exhibited analogous profitability for susceptible cultivars. Results from this study can be used to assist producer selection of management options for TSW in peanut.

Effects of new field resistant cultivars and in-furrow applications of phorate insecticide on tomato spotted wilt of peanut

Field experiments were conducted at Tifton, Georgia from 2008 to 2014 to determine the effects of new peanut (Arachis hypogaea) cultivars and in-furrow applications of phorate insecticide on severity of tomato spotted wilt (TSW) caused by Tomato spotted wilt virus. Several cultivars, including Florida-07, Georgia-06G, Georgia-07W, Georgia Greener, and Tifguard, had final incidence of TSW that were less than that of Georgia Green. In-furrow applications of phorate insecticide reduced incidence of TSW in Georgia Green in three experiments in which that cultivar was included. In-furrow application of phorate insecticide reduced incidence of TSW in most cases where incidence in nontreated plots was 10% or higher. Cultivars Georganic, and Georgia-10T, had final incidence of TSW that was lower than that of Georgia-06G, or Florida-07 within nontreated plots across 2011–2012. Georgia-10T and Georgia-12Y had final incidence that was lower than that of Georgia-06G, Georgia-07W, Georgia-09B and Georgia Greener across insecticide treatments in 2013. In-furrow application of phorate increased yields across cultivars in 2008–2009, and increased yield of Georgia-09B in 2010. In most other cases, phorate had no significant effect on yield. With higher levels of field resistance in most of these cultivars, especially those such as Georgia-12Y, benefits from use of phorate insecticide for TSW suppression were small, and typically did not result in yield increase. Based on these results, several of these cultivars should allow greater flexibility for insecticide choice for thrips management without increasing the risk of losses to TSW.

Peanut Cultivar Response to Tomato Spotted Wilt over Five Planting Dates

ABSTRACT Tomato spotted wilt virus (TSWV) is vectored by thrips and causes an economically damaging peanut disease in the southeastern U.S. Peanut planting was traditionally initiated when soil temperatures became favorable in April. Planting in the latter two thirds of May is recommended to avoid thrips feeding and reduce tomato spotted wilt (TSW) incidence. This regime concentrates work load for growers and buying points, increases risk of tropical storm damage during harvest, and may contribute to reduced crop maturity. Improved TSW tolerance in cultivars may allow growers to plant earlier spreading risk and work load. Cultivars Georgia Green, Georgia-03L, AT 3085RO, and Flavor Runner 458 were compared with the advanced breeding line EXP 271516 based on peanut foliar condition, pod yield, and grade in 2008 and 2009 in Dawson, Georgia and Headland, Alabama. Peanuts were planted at five planting dates starting in late April through early June each year. Disease incidence was variable according to year, location, and planting date. Planting dates in April and early May resulted in higher TSW incidence. Foliar TSW ratings for the susceptible cultivar Flavor Runner 458 ranged between 48–96% at harvest. Georgia Green had 10–65% TSW incidence while maintaining yields between 3,315–5,440 kg/ha. Other cultivars had better TSW tolerance resulting in higher yield under more intense TSW pressure. Planting in the middle of May or later resulted in the highest yields. Cultivars with improved tolerance to TSW maintained yield above 4,490 kg/ha in early plantings. These results indicate the least risky management is possible by planting the most TSW tolerant genotypes during the current recommended planting dates.

Stability Analysis of Incidence of Tomato Spotted Wilt in Virginia-Type Peanut Cultivars and Breeding Lines

ABSTRACT Tomato spotted wilt (TSW) caused by Tomato spotted wilt tospovirus (TSWV) has become a serious constraint to peanut (Arachis hypogaea L.) production in the Virginia-Carolina production area. Regression stability analysis was applied to TSW incidence data collected in 64 trials conducted over 17 years to determine if an array of 31 virginia-type cultivars and breeding lines exhibited variation in their reactions to increasing levels of general TSW intensity compared with the standard field-resistant cultivar Georgia Green and hirsuta-type line PI 576636. Eight cultivars (NC 7, NC 9, NC 10C, NC-V 11, NC 12C, Perry, Phillips, and Brantley) had mean effects greater than zero (P<0.01) while Bailey, four Bailey siblings, and N96076L, Bailey's resistant parent, all had mean effects less than zero (P<0.01). The deviations of the slope of regression on environmental index (β̂k) for four of the eight susceptible cultivars were greater than zero, indicating greater than average reaction to increased levels of TSW. The β̂k for Bailey indicated that its response to increasing levels of TSW was flat. PI 576636 was confirmed as a highly field-resistant line. The slopes of Georgia Green, the standard TSWV-resistant runner-type cultivar, the Bailey siblings and N96076L did not differ from the average of all lines. The correlation between mean effect and β̂k was r = 0.693, indicating that approximately half the variation in β̂k could be explained by mean effects. However, the regression analysis provided information useful in describing the TSW reactions of the lines and cultivars.

Effect of Plastic Mulch Type and Insecticide on Incidence of Tomato Spotted Wilt, Plant Growth, and Yield of Tomato

Tomato spotted wilt (TSW) is caused by a Tospovirus [tomato spotted wilt virus (TSVW)] and is vectored by thrips. TSW is a major impediment to tomato production worldwide and has been identified as the most significant limitation in the southeastern United States. The objectives of this study were to quantify the impact of polyethylene mulch type (black, metalized, Heat stripe, and Sonoco printed) and insecticide (alternating applications of spinosad and methamidophos) on midafternoon soil temperature under the mulch, reflected photosynthetic photon flux (PPF), vegetative growth, flower number, incidence of TSW, yield, and fruit quality of ‘FL-47’ tomato (Solanum lycopersicum L.). Midafternoon soil temperature during April and May (10-cm depth) averaged 2 to 4 °C higher under black mulch compared with the other mulches. The reflectance of PPF was highest for metalized mulch (up to two-thirds of PPF in full sunlight) followed by Heat stripe, Sonoco printed, and black mulch. In the presence of a full plant canopy, PPF reflectance was greatly reduced. The incidence of TSW [as determined visually and confirmed by enzyme-linked immunosorbent assay (ELISA)] was very high in 2002 and relatively low in 2003. Stem weight was significantly reduced in the black mulch treatment; however, plant height, leaf weight, or total numbers of flowers were not influenced by mulch type. For both years, the incidence of TSW on black mulch was significantly greater than that of the other mulch treatments for most sampling dates. The application of insecticides reduced percentage TSW on the last two sampling dates in both years. In 2002, but not 2003, yield per hectare was affected by mulch type. In both years, mulch type did not influence yield per plant and percentage marketable fruit, and insecticide applications increased yield per hectare, yield per plant, and percentage marketable fruit.

Temporal Relationship of Thrips Populations to Tomato Spotted Wilt Incidence in Tomato in the Field

Thrips-transmitted Tomato spotted wilt (TSW) virus (Family Bunyaviridae Genus Tospovirus) is an important problem in tomato in the southeastern United States. Tobacco thrips, Frankliniella fusca (Hinds), and western flower thrips, Frankliniella occidentalis (Pergande), (Thysanoptera:Thripidae) are the known major vectors of TSW virus in Georgia; however, the temporal relationship of thrips to TSW disease incidence in tomato is not clear. Field studies were conducted in 2005 and 2006 specifically to compare thrips population dynamics to disease incidence in untreated tomato fields. Populations of F. fusca were observed to increase approximately 3 wks prior to increased TSW incidence and correlated positively with TSW when considering this delay. Populations of F. occidentalis positively correlated with TSW occurrence in 2005, but not in 2006. Additionally, tomato fruit yield decreased greater in plants with early TSW symptoms than in plants that developed symptoms later in the season. Both results suggest early-season thrips management targeted at F. fusca during the early-growth stages of tomato could help to reduce the risk of yield loss in tomato due to this disease.

Temporal progress and control of tomato spotted wilt virus in flue-cured tobacco

Tomato spotted wilt virus causes tomato spotted wilt (TSW), a disease that results in economic losses on several crops including tobacco in the southeastern United States. The effect of imidacloprid (IMD) applied as a pre-transplant soil drench alone, in combination with acibenzolar-S-methyl (ASM), or followed by a foliar application of ASM immediately after transplanting on TSW incidence and severity on tobacco was quantified in studies conducted in North Carolina from 2006 to 2008. Pre-transplant IMD application in combination with ASM provided the greatest reduction in TSW incidence and severity; however other treatments provided economically efficacious controls when TSW incidence was <30% in a field. From these results, TSW incidence was classified as Low (<10%), Moderate (11–20%), High (21–30%), or Very High (>30%), classes corresponding to different control recommendations, and subsequently used for modeling temporal TSW progress in a field. The temporal progress of TSW was modeled with data collected from 23 tobacco fields in North Carolina from 2006 to 2008. Cumulative degree-days (DD) and the average class of TSW incidence observed in a field for 5 seasons before the one that data were collected were significant variables ( P < 0.05) for explaining the temporal progress of TSW incidence. DD based on four temperature thresholds (10.5, 18.0, 20.0, and 26.0 °C) were investigated, resulting in four models. Models were validated with data collected in 2009 and the model in which DD were calculated based on the threshold of 10.5 °C had a higher predictability ( R 2 = 0.70) than the other three models. The 26 °C DD model had the poorest predictability ( R 2 = 0.33). These models are currently being validated in North Carolina and the other flue-cured production states of the southeast United States as a tool for implementing disease control recommendations.

Bell Pepper (Capsicum annum L.) Grown on Plastic Film Mulches: Effects on Crop Microenvironment, Physiological Attributes, and Fruit Yield

Plastic mulches are widely used for the production of vegetables. There are numerous studies on the use of plastic mulches for peppers, although relatively few have focused on the microenvironmental and physiological impacts of plastic mulches on bell pepper. The objectives were to determine the effects of plastic film mulches on root zone temperature (RZT), soil water status, incidence of thrips and Tomato spotted wilt (TSW), plant growth, gas exchange, accumulation of mineral nutrients, and fruit yield in bell pepper. The study was conducted in Tifton, GA, in the Fall of 2002 and the Spring of 2003 using eight colored plastic mulches. Plastic mulch color influenced the microenvironmental, physiological, and yield responses of bell pepper plants. Plastic film mulches differed in their soil-warming ability with RZTs in both spring and fall being highest in black mulches and lowest in silver mulches. The percentage of photosynthetically active radiation (PAR) reflected from the mulches was highest in silver mulches and lowest in black mulches. The mean RZT under the plastic mulch decreased with increasing percentages of reflected PAR. The number of thrips per flower and the incidence of TSW in mature plants were not significantly different among plastic mulch treatments. The number of thrips per flower had no relationship with the percentage of reflected PAR or with RZT. Plastic mulch treatments had no significant effect on soil water status. Neither soil water content nor soil water potential had a relationship with RZT. In the fall season, during the first 28 days after transplanting, plant growth attributes were among the highest in silver mulches and the lowest in black mulches. Gas exchange and accumulation of mineral nutrients in the leaves and the fruit were not significantly affected by plastic mulches. Both marketable and total yields were higher on silver mulches and lowest on black mulch in the fall, whereas they were in general higher on silver with a black strip mulch and lowest on white and silver1 mulches in the spring. The reduced plant growth and fruit yields in black mulches during the fall were probably the result of the increased RZTs, and thus higher heat accumulation, that resulted in higher plant heat stress conditions compared with silver and white mulches. Fruit yield decreased with mean seasonal RZTs above 27.5 °C. The optimal range of RZT for bell pepper fruit yield was computed to be 25 to 27.5 °C or less.

INTEGRATED MANAGEMENT OF VIRAL DISEASES IN FIELD-GROWN TOMATOES IN SOUTHERN ITALY

Tomato spotted wilt virus (TSWV) is a Tospovirus affecting field tomato crops worldwide. The virus is transmitted by some species of thrips. The most damaging vectors in Italy are Frankliniella occidentalis and Thrips tabaci. Only the first instar larvae can acquire the virus from an infected plant. After acquisition, the virus replicates in the vector, and the viruliferous thrips is capable of transmission for the duration of its life. Apart from TSWV, other serious threats for tomato production in Italy are the aphid transmitted Cucumber mosaic virus (CMV) and Potato virus Y (PVY), both with necrotic and non necrotic variants. Epidemics caused by TSWV, PVY and CMV occur regularly in southern Italy, where hundreds of millions of tomato plants are grown commercially every year. Insecticides applied on a calendar basis for insect control are not very effective in preventing these vector-borne viral diseases because the viruses can be transmitted to the plant before insects (thrips and aphids) are killed by insecticides. Field experiments were conducted during summer of 2005 and 2006 in the main tomato growing area of the Basilicata region, Lavello (PZ), to determine the separate and integrated effects of UV-reflective mulch (UVRM), Acibenzolar-S-methyl (Actigard) and insecticides for the management of vectors and diseases on tomato. TSW disease pressure was great during 2005 summer but very low in 2006. Disease incidence was measured as percentages of plants infected with each of the three viruses. Aphid populations were evaluated by counting the number of aphids on sampled tomato shoots on one third of the plants on each plot. Tomato yield was evaluated from one third of the plants on each plot. Statistical analysis (analysis of variance) was performed using the SYSTAT 9 Software. The UVRM alone was effective in reducing disease incidence both for aphids and thrips transmitted viruses. A synergistic effect of Actigard with UVRM was observed against the three viruses. The use of the insecticides resulted in a further reduction in the incidence of the three viral diseases on UVRM, and reduced incidence of diseases caused by CMV and PVY in the black mulch and bare soil plots. The combination of UV-reflective mulch, acibenzolar-S-methyl, and insecticides was the most effective in reducing tomato spotted wilt incidence in tomato. The UV-reflective mulch was very effective in delaying and reducing colonization of aphids and subsequent virus incidence. There was no significant difference in the tomato yield between UVRM and black mulch plots. In contrast, yield was strongly reduced in the bare soil plots.

Effects of plastic mulches on root zone temperature and on the manifestation of tomato spotted wilt symptoms and yield of tomato

Tomato spotted wilt (TSW) disease is a serious constraint to tomato production in various regions of the world. The effect of TSW on tomato yield is largely influenced by time of infection. Early infection usually results in severe stunting of the seedling and even death of the plant. Plastic film mulches affect both the incidence of TSW, and plant growth and yield of tomato. The objective of the present study was to determine the effect of root zone temperature (RZT) as affected by plastic film mulch on the manifestation of symptoms of TSW, and growth and yield of tomato plants either artificially inoculated with tomato spotted wilt virus (TSWV) or under natural TSW infection. In artificially inoculated plants as well as in plants under natural TSW infection, vegetative top fresh weight (FW) and fruit FW both increased with the length of time after transplanting that the plants remained free from TSW symptoms. The root zone temperature was highest under black mulch (seasonal mean = 27.5 °C), followed by gray (27.0 °C), silver (25.8 °C), and white (24.8 °C) mulches. The plants grown on black mulch showed the earliest appearance of TSW symptoms, and had significantly reduced vegetative growth and fruit yields compared to plants on the other mulches. In conclusion, utilization of plastic mulches that created conditions of high RZT stress resulted in reduced plant growth and yield and predisposed the plants to earlier expression of TSW symptoms compared to plants grown at RZTs more favorable to tomato plant growth (optimal RZT = 26.1 °C [Díaz-Pérez, J.C., Batal, K.D., Granberry, D., Bertrand, D., Giddings, D., Pappu, H., 2003. Vegetative top growth and yield of tomato grown on plastic film mulches as affected by the appearance of symptoms of Tomato spotted wilt virus. HortScience 38, 395–399]). Since these plant responses to TSW under heat stress occurred in artificially inoculated plants as well as in plants under natural TSW infection, high RZTs probably affected the plants directly, independently of any possible effects on the thrips vectors.

Root Zone Temperature as Modified by Plastic Mulches Affect the Appearance of First Systemic Symptoms of Tomato Spotted Wilt and Fruit Yield in Tomato

Tomato spotted wilt (TSW) is a serious constraint to tomato production in various regions of the world. The effect of TSW on tomato yield is largely influenced by time of infection. Early infection usually results in severe stunting of the seedling and even death of the plant. Plastic mulches have been found to affect both the incidence of TSW, and plant growth and yield of tomato. The objective of this study was to determine the effect of root zone temperature (RZT) as affected by plastic mulch on the timing of appearance of first TSW symptoms, vegetative top fresh weight (FW) and fruit FW in tomato. Under natural TSW infection as well as in artificially inoculated plants, vegetative top FW and fruit FW were both linearly related with number of days after transplanting (DAT) the plants were free from TSW symptoms. The plants grown on black mulch during the fall showed earlier appearance of TSW symptoms, and had significantly reduced vegetative growth and fruit yields. The mean RZT during the first 42 DAT—the time before the plants reached full canopy closure—significantly affected the timing of first appearance of TSW symptoms, tomato plant growth and fruit yield. Vegetative top FW (optimal RZT = 24.1 °C) and fruit FW (26.9 °C) fitted the quadratic relationships with the mean RZT during the first 42 DAT. In conclusion, utilization of plastic mulches that created conditions of RZT stress, particularly heat stress, resulted in reduced plant growth and yield and may predispose the plants to earlier expression of TSW symptoms compared to plants grown under RZTs more favorable to tomato plant growth.

Effects of Plant Spacing, Inoculation Date, and Peanut Cultivar on Epidemics of Peanut Stem Rot and Tomato Spotted Wilt.

Two microplot studies were conducted with peanut (Arachis hypogaea L.) in 2000, 2001, and 2002 to determine the effects of plant spacing, inoculation date, and cultivar on stem rot development caused by Sclerotium rolfsii Sacc., tomato spotted wilt incidence, and microclimate (temperature and relative humidity). Stem rot severity and incidence decreased as plant spacings were increased in 5-cm increments from 5 to 30 cm. Two cultivars with similar susceptibility but different growth habits were compared. Perhaps due to heavy irrigation and extensive vegetative growth, stem rot was similar for 'Florida MDR-98' and 'Georgia Browne'. Plants inoculated later in the year (90 days after planting [DAP]) had less disease at harvest, but often developed more severe symptoms within the first week of inoculation than plants inoculated at 50 or 70 DAP. Canopy microclimate was different than ambient conditions for all treatments; however, differences among treatments were inconsistent and did not explain differences in disease among spacings. Generally, as plant spacing decreased and plant population increased, stem rot increased and tomato spotted wilt was reduced. These data demonstrate that the physical spacing between plants is a critical factor in disease development.

Integrated Management of Tomato Spotted Wilt on Field-Grown Tomatoes.

Epidemics of spotted wilt caused by Tomato spotted wilt virus (TSWV) vectored by Frankliniella occidentalis and possibly other thrips species occur regularly in tomato in the southeastern United States. Field experiments were conducted to determine the effects of UV-reflective mulch, acibenzolar-S-methyl (plant activator), and insecticides on progress of tomato spotted wilt incidence and population dynamics of flower thrips (including F. occidentalis, F. tritici, and F. bispinosa). Whole plots of tomatoes grown on UV-reflective and black polyethylene mulch were divided into subplots of acibenzolar-S-methyl and no acibenzolar-S-methyl, and sub-subplots of insecticide and no insecticide for thrips control. The UV-reflective mulch was more effective than black polyethylene mulch each year in reducing colonization of thrips in May and the consequent primary infections of tomato spotted wilt. Application of acibenzolar-S-methyl further reduced tomato spotted wilt incidence in 2000 and 2002, when disease pressure was great. Reproduction of thrips on tomato was poor in these experiments, but their control in the insecticide-treated sub-subplots prevented secondary spread in both years. The combination of UV-reflective mulch, acibenzolar-S-methyl, and insecticides was very effective in reducing tomato spotted wilt incidence in tomato.

Effect of Tillage System, Phorate, and Cultivar on Tomato Spotted Wilt of Peanut

Tomato spotted wilt (TSW) has become a limiting factor to peanut (Arachis hypogaea L.) production in the southeast United States over the past 6 yr. Cultivars are now selected based on their resistance to TSW and planted during time periods to reduce the incidence of TSW. Three peanut cultivars with different resistance to TSW were used (‘Georgia Green’, ‘MDR98’ and ‘SunOleic 97R’). Conventional‐ or strip‐tilled plots were established after winter wheat (Triticum aestivum L.) in 2000 and 2001 in Marianna, FL. Stand count, severity of TSW, and yield were recorded. Plots were irrigated as needed. Stand count was 10% less in the strip‐tilled plots in both 2000 and 2001. Stand count was affected by cultivar used, with Georgia Green and SunOleic 97R having 20% higher populations than MDR98. Phorate [O, O‐diethyl,S‐(ethylthio)methyl phosphorodithioate] treatment had 7% less stand count in 2001 but not in 2000. Tomato spotted wilt severity was 50% less in strip‐tilled plots in 2000, but there was no difference in 2001. Cultivar affected severity of TSW every year but not consistently. Application of phorate did not affect TSW. In 2000 (a droughty year), the strip‐tilled plots had greater yield (2510 vs. 1900 kg ha−1) averaged across cultivars. MDR98 had the highest yield across treatments in 2000, but yield was not different among cultivars in 2001. Application of phorate did not affect yield in either year. In the strip‐tilled plots, soil moisture was 30% greater and plant canopy 3 to 5°C cooler during 2000 when plants were visibly drought stressed. Use of phorate had no effect on TSW or yield and its use for TSW control is not recommended. Cultivar selection did influence TSW severity and should be considered as part of a TSW control program. Strip tillage resulted in greater yields than conventional tillage in an abnormally dry year.

Effect of Tillage System, Phorate, and Cultivar on Tomato Spotted Wilt of Peanut

Tomato spotted wilt (TSW) has become a limiting factor to peanut (Arachis hypogaea L.) production in the southeast United States over the past 6 yr. Cultivars are now selected based on their resistance to TSW and planted during time periods to reduce the incidence of TSW. Three peanut cultivars with different resistance to TSW were used (‘Georgia Green’, ‘MDR98’ and ‘SunOleic 97R’). Conventional- or strip-tilled plots were established after winter wheat (Triticum aestivum L.) in 2000 and 2001 in Marianna, FL. Stand count, severity of TSW, and yield were recorded. Plots were irrigated as needed. Stand count was 10% less in the strip-tilled plots in both 2000 and 2001. Stand count was affected by cultivar used, with Georgia Green and SunOleic 97R having 20% higher populations than MDR98. Phorate [O, O-diethyl,S-(ethylthio)methyl phosphorodithioate] treatment had 7% less stand count in 2001 but not in 2000. Tomato spotted wilt severity was 50% less in strip-tilled plots in 2000, but there was no difference in 2001. Cultivar affected severity of TSW every year but not consistently. Application of phorate did not affect TSW. In 2000 (a droughty year), the strip-tilled plots had greater yield (2510 vs. 1900 kg ha−1) averaged across cultivars. MDR98 had the highest yield across treatments in 2000, but yield was not different among cultivars in 2001. Application of phorate did not affect yield in either year. In the strip-tilled plots, soil moisture was 30% greater and plant canopy 3 to 5°C cooler during 2000 when plants were visibly drought stressed. Use of phorate had no effect on TSW or yield and its use for TSW control is not recommended. Cultivar selection did influence TSW severity and should be considered as part of a TSW control program. Strip tillage resulted in greater yields than conventional tillage in an abnormally dry year.