Drench Application Research Articles

A novel method for the quantitative assessment of the percolation of Metarhizium anisopliae conidia through horticultural growing media

Incorporation of fungal biological control agents (BCAs) into plant growing media has considerable ergonomic and economic benefits for growers. These agents usually give prophylactic control of target pests and diseases. However, their efficacy is dose dependent and loss of inoculum through leaching could influence the degree of protection they provide. At present there are no protocols to determine the loss of inoculum in the disparate growing media used in horticulture. We describe a method based on a nutrient leaching column to quantify leaching of conidia of the insect-pathogenic fungus Metarhizium anisopliae in a range of growing media. Conidia of this biocontrol agent were applied as a drench or premixed into the medium. Both the application method and growth medium influenced conidial leaching. Inoculum losses were greater following drench application than premixing (95% vs. 15%) irrespective of media type. Comparatively more inoculum was lost from bark and coir following drench application whereas losses were relatively high in peat following premixed application. The leaching column assay provided a simple and accurate method to quantify inoculum loss in real time. This assay could help determine leaching of other fungal BCAs in growing media. It could help in improving pest and disease control by optimizing the rate and frequency of conidial application as well in the design of more efficacious formulations.

Postharvest Decay Management for Stone Fruit Crops in California Using the "Reduced-Risk" Fungicides Fludioxonil and Fenhexamid.

In laboratory studies and experimental packingline trials that closely simulated fungicide treatments under commercial conditions, the "reduced-risk" fungicides fenhexamid and fludioxonil were highly effective in managing postharvest brown rot and gray mold decays of peach, nectarine, and plum caused by Monilinia fructicola and Botrytis cinerea, respectively. Tebuconazole was more effective against brown rot than against gray mold. Additionally, fludioxonil and tebuconazole significantly reduced the incidence of Rhizopus rot caused by Rhizopus stolonifer. In laboratory studies, the QoI fungicide azoxystrobin was not consistent in its decay control activity. The high efficacy of fenhexamid and fludioxonil against brown rot and gray mold was substantiated by low effective concentrations necessary (≤0.063 mg/liter)for 50% inhibition of mycelial growth in vitro. In general, fungicides applied 14 to 16 h after wound inoculation were significantly more effective than those applied before inoculation. These results indicate that the fungicides act mainly as protectants that do not penetrate deeply enough into the fruit to prevent decay from wounds that extend below the fruit epidermis. Laboratory treatments of plum fruit generally were less effective than those of peach or nectarine fruit. Comparative studies using either low-volume spray or high-volume, in-line drench applications over a roller bed demonstrated that drench applications were significantly more effective in reducing postharvest decaysof inoculated plum fruit. Decay incidence using fenhexamid or fludioxonil was ≤1.1%, whereas incidence after the spray applications was between 25.2 and 40.4% for brown rot, between 12.0 and 24.3% for gray mold, or 62.6% for Rhizopus rot (fludioxonil only). This research identified effective replacements for iprodione, a fungicide voluntarily canceled by the manufacturer in 1996.

Biological control of black vine weevil Otiorhynchus sulcatus in Ireland using Heterorhabditis megidis

Abstract Heterorhabditis megidis (UK211) was applied against black vine weevil (BVW, Otiorhynchus sulcatus ) in potted plants in a polyethylene (2002) or glasshouse (2003) and in field planted strawberries (2003). Both potted and field strawberries were artificially infested with BVW larvae. In a 2002 pot planting in the polyethylene house, a single drench application of 25,000 H. megidis infective juveniles per plant in 50 ml of water in mid September, reduced the number of BVW larvae to 1.8/20 plants. A second application in early October gave a reduction of 0.2/20 plants and in the third application, the following March no live weevils were recovered, compared to the control which had 8.2 larvae/20 plants. In a 2003 pot planting in a glasshouse, similar treatments gave a reduction of 5.2, 5.4 and 0.8 larvae/20 plants, respectively, compared to the control where 26.2 larvae/20 plants were recovered. In an artificially, BVW infested field trial, similar treatments gave a reduction to 2.2 larvae/20 plants in the single September treatment, and 2 larvae/20 plants in the single October treatment. The double (September and October) application reduced BVW larvae further to 1.6/20 plants and the triple (September, October and April) application to 0.4 larvae/20 plants, compared to the control where four larvae corresponded to every 20 plants. There was, therefore, little difference between the single and double autumn treatments indoors or in the field, and it mattered little whether the single application in the field was made in September or October under the conditions of 2003. Early spring application gave a significant reduction in BVW in each of the three experiments.

Control of western flower thrips (Frankliniella occidentalis) pupae with Metarhizium anisopliae in peat and peat alternative growing media

Abstract The entomogenous fungus Metarhizium anisopliae V275 was more efficacious than chemical insecticides (imidacloprid, fipronil) in killing pupae of the western flower thrips (70–90% versus 20–50%) in a range of horticultural growing media (peat, coir, bark and peat blends with 10% and 20% composted green waste). Premixing inoculum of M. anisopliae into the growing media gave better control than drench applications in coir and peat blended with 20% composted green waste. Use of M. anisopliae with sublethal dose of the insecticides gives slightly better control than the individual control agents but no clear cut additive or synergistic effects. Overall our study shows that M. anisopliae is efficacious in all growing media and compatible with conventional insecticides and offers much promise for the control of thrips as part of an integrated pest management program.

Effect of Soil Application of AG3 Phosphonate on the Severity of Clubroot of Bok Choy and Cabbage Caused by Plasmodiophora brassicae.

Field trials were carried out to test the effect of phosphonate fungicide (AG3) on the severity of clubroot of bok choy (Brassica rapa var. chinensis) and cabbage (B. rapa var. perkinensis and B. oleracea var. capitata) in commercial Ontario muck fields with a clubroot history. Disease severity also was examined in the same infested soil under greenhouse and microplot conditions. In microplot trials with bok choy, AG3 phosphonate concentrations of 0.07 and 0.14% a.i. applied before or after planting consistently reduced clubroot severity (1-to-4 rating) by 0.8 to 1.6 when planted in May or June. However, only the 0.14% a.i. preplanting treatment was effective in trials in July and August. Postplanting drenches of 0.14% a.i. were consistently effective throughout the season. Fresh weight of bok choy was increased or not affected by phosphonate treatments. Under field conditions, one (0.07, 0.14, and 0.21% a.i.) or two (0.07% a.i.) postplant-ing drench applications of phosphonate significantly reduced the incidence of clubroot by 52 to 87% and severity by 1.7 to 2.5 on bok choy in 2004 but not in 2005. In the 2004 trial, two applications of 0.07% a.i. AG3 phosphonate reduced the severity of clubroot comparably to single applications at 0.14 and 0.21% a.i. rates. Fresh weight of bok choy was increased by 34 to 86% with all phosphonate drench treatments in both years. With cabbage, AG3 postplanting drench treatments consistently reduced the severity of clubroot (1-to-5 rating) by a range of 0.7 to 3.3 under greenhouse, microplot, and field conditions. In the greenhouse, a single drench application of 0.07 and 0.14% a.i. AG3 phosphonate 1 day after transplanting cabbage seedlings to the infested muck soil reduced clubroot severity by 2.6 to 3.3 and increased fresh weight of cabbage tops by 66 to 69%. Similar results were seen with cabbage trials under both microplot and field conditions at all AG3 postplanting drench concentrations.

Residue Evaluation of Famoxadone and Trifloxystrobin in Cultivated Mushrooms

Dissipation of the fungicides famoxadone and trifloxystrobin in basidiocarps of Agaricus bisporus was studied in mushroom growing rooms. The mushroom samples taken at all three consecutive production flushes following single or split applications of the fungicides were extracted with solvents and the residues were determined by using a gas chromatograph equipped with an electron capture detector (GC-ECD). Recoveries from the fortified control samples ranged from 87 to 105%. Following drench applications at 0.1–1 g/m2 of culture bed area, the highest famoxadone residue determined in basidiocarps was 0.1447 mg/kg. Analysis of trifloxystrobin revealed a quantitative relationship between the application rate (0.8–1.8 g/m2) and the residue levels of both the parent compound and its acid metabolite. The maximal combined residues of trifloxystrobin and its metabolite were 0.1313 mg/kg. Short- and long-term dietary risk assessment for both fungicides was carried out using consumption data from World Health Organization and the UK Pesticide Safety Directorate's Ten Consumer Model. The potential acute and chronic residue intakes via mushroom consumption were below toxicologically significant indicators.

(82) Determining Effects of a Uniconazole Drench on Celosia, Petunia, Salvia, and Tagetes

Uniconazole is a plant growth regulator used to inhibit internode elongation on container-grown ornamental plants. Uniconazole is effective on a wide range of plants, but is not commonly used on bedding plants because of concerns about stunting and flowering delay. Our objective was to determine the effectiveness of uniconazole when used as a drench, eliminating the variability inherent in a spray application. Seedlings of Celosia argentea L. var. plumosa L. `Fresh Look Red', Petunia ×hybrida Vilm.-Andr. `Prostrate Wave Rose', Salvia splendens Sell ex Roem. & Schult. `Vista Red', and Tagetes erecta L. `Inca II Gold' in 288-cell plug trays were transplanted 2 days after arrival into 10-cm pots filled with a soilless medium containing no bark. Plants were placed in a greenhouse with a setpoint of 20 °C and under a 16-h photoperiod provided by high-pressure sodium lamps. A single drench application of 0, 0.04, 0.07, 0.15, or 0.30 mg active ingredient/pot was made 11 days after transplant. The uniconazole drench inhibited internode elongation in these species and higher rates provided a greater degree of response. At time of flowering, the 0.30-mg uniconazole drench inhibited shoot length in Celosia, Petunia, Salvia, and Tagetes by 36%, 23% 26%, and 13%, respectively. Drenches of 0.04 or 0.07 mg provided a desirable degree of height control for Celosia and Salvia. For vigorous species like Petunia or Tagetes, 0.15 to 0.30 mg may be more appropriate. We observed a 1- or 2-day delay in flowering of Salvia and Tagetes plants drenched with 0.30 mg, but no delays in Petunia flowering.

Effect of imidacloprid on the reproduction of acaricide‐resistant and susceptible strains of Tetranychus urticae Koch (Acari: Tetranychidae)

Occasional reports linking neonicotinoid insecticide applications to field population outbreaks of the two-spotted spider mite, Tetranychus urticae Koch, have been a topic of concern for integrated pest management (IPM) programmes, particularly in apples. In order to shed light on the factors which may contribute to the occasional field population increase of T. urticae following the application of neonicotinoid insecticides, greenhouse experiments have been set up. Four different T. urticae strains, namely GSS (acaricide-susceptible), WI (organophosphate-selected), USA (a largely uncharacterised strain) and Akita (METI (mitochondrial electron transport inhibitor) acaricide-resistant and cross-resistant to dicofol), were compared for their fecundity without insecticide treatment and for their ovipositional response to foliar and drench applications of the field-relevant dose of imidacloprid (100 mg litre(-1)). Without insecticide treatment, strain GSS laid significantly more eggs (162.50 (+/- 5.43)) than the multiple resistant strain Akita (139.90 (+/- 5.54)) during a 16 day oviposition period. With imidacloprid treatment the highest effect was observed with GSS, with a significantly reduced number of eggs in drench (143.40 (+/- 4.22)) and foliar (144.60 (+/- 5.85)) applications. For strains Akita and USA, no significant differences were observed in oviposition between imidacloprid treatments and controls. The proportion of F1 female offspring decreased significantly with drench application for GSS and WI, while no differences were observed among strains in the survival of F1 immature stages, except for strain USA. The viability of eggs was relatively high (from 82.9 (+/- 4.5)% for USA to 95.2 (+/- 1.2)% for GSS) and not affected by imidacloprid treatments.

Evaluation of Entomopathogenic Fungus Metarhizium anisopliae Against Soil-Dwelling Stages of Cabbage Maggot (Diptera: Anthomyiidae) in Glasshouse and Field Experiments and Effect of Fungicides on Fungal Activity

The effect of two isolates of the entomopathogenic fungus Metarhizium anisopliae (Metchnikoff) Sorokin (389.93 and 392.93) on root-feeding stages of cabbage root fly, Delia radicum (L.), was studied under glasshouse and field conditions. In glasshouse studies, the effect of drenching a suspension of conidia (concentration 1 x 10(8) m(-1), 40 ml per plant, applied on four occasions) onto the base of cabbage plants infested with D. radicum eggs was compared with mixing conidial suspension into compost modules (concentration 1 x 10(8) ml(-1), 25 ml per plant) used to raise seedlings. Drench application reduced the mean number of larvae and pupae recovered per plant by up to 90%, but the compost module treatment had no statistically significant effect. Both application methods reduced the emergence of adult flies from pupae by up to 92%. Most conidia applied as a drench application remained in the top 10-cm layer of compost. Applications of the fungicides iprodione and tebuconazole, which are used routinely on brassica crops, were compatible with using M. anisopliae 389.93 against D. radicum under glasshouse conditions, even though these fungicides were inhibitory to fungal growth on SDA medium. In a field experiment, drench applications of M. anisopliae 389.93 to the base of cauliflower plants at concentrations of 1 x 10(6) to 1 x 10(8) conidia ml(-1) did not control D. radicum populations, although up to 30% of larval cadavers recovered supported sporulating mycelium. Drench applications often exhibited considerable lateral movement on the soil surface before penetrating the ground, which may have reduced the amount of inoculum in contact with D. radicum larvae.

Control Efficacy of Milk Concentration Against Powdery Mildew of Strawberry

The aim of this study was to determine the effect of milk as one of the environmental friendly materials that substitute chemical fungicides for control powdery mildew (Sphaerotheca aphanis) of strawberries <TEX>$(Fragaria{\times}ananassa\;Duch.)$</TEX>. 'Maehyang' and 'Akihime' varieties planted in greenhouses were evaluated for the control of powdery mildew. Applications of <TEX>$5\%,\;10\%\;and\;20\%$</TEX> milk had much better effects on controlling powdery mildew. In particular, <TEX>$10\%$</TEX> milk showed a higher efficacy than other concentrations applied onto straw­berry in greenhouse experiments. Foliar spray application of <TEX>$10\%$</TEX> milk was effective for powdery mildew, whereas drench application was not. Also, foliar spray of <TEX>$10\%$</TEX> milk was able to accelerate more firmness and calcium contents of strawberry fruits than the non-treated. The <TEX>$10\%$</TEX> milk applied with fertilizer salts <TEX>$(Ca(H_2PO_4)_2-H_2O\;and KH_2PO_4)$</TEX> showed there was a similar efficacy to <TEX>$10\%$</TEX> milk alone in greenhouse experiments. White crystals and cracks on strawberry fruits appeared by <TEX>$20\%$</TEX> milk. This result indicated that <TEX>$10\%$</TEX> milk was a useful substitute for fungicides to control powdery mildew of strawberry.

(54) Response of Betulanigra `BNMTF' to Foliar and Drench Applications of Nickel

Mouse ear disorder on container-grown river birch (Betulanigra L.) is a national problem caused by a deficiency of nickel. Symptomatic plants have leaves which are small, wrinkled, darker green, cupped, and have necrotic margins. Research showed that mouse ear could be cured by applications of nickel sulfate (Ruter, 2004). Further research was needed to determine optimal rates of application for sprays and drenches and to determine if phytotoxicity occurs at high rates. A study was initiated at a nursery in South Georgia on 25 June 2003, using river birch in their second growing season in #15 containers. Plants were selected for uniformity of mouse ear disorder. Treatments included a control, urea (0.24 g·L-1) + surfactant (1.0 mL·L-1), 250, 500, 750, and 1000 mg·L-1 nickel sulfate sprays, and substrate drenches applied at 150 and 300 mg of Ni/pot. After 30 days, all plants treated with nickel sulfate had 100% normal growth, except the 150 mg of Ni/pot drench, which had 79% of the canopy showing normal growth. No phytotoxicity was noted. Plants receiving foliar sprays had a 66% to 72% increase in leaf area, a 64% to 68% increase in leaf dry mass, a 31% to 44% increase in stem length, and a 9% to 17% increase in specific leaf area compared to nontreated plants. Drench treatments increased leaf area up to 62%, leaf dry mass to 55% and stem length up to 29% over control plants. Nickel in the foliage of nontreated plants was 2.3 mg·kg-1. For the spray treatments, foliar Ni ranged from 5.5 mg·kg-1 for the 250 mg·L-1 treatment to 9.3 mg·kg-1 for the 1000 mg·L-1 treatment. Though plants at the high rate of drench treatment resumed normal growth, foliar Ni levels were not different from control plants. In general, if plants were treated with Ni, then foliar B, Fe, and Zn decreased.

ORNAMENTAL TOMATO GROWTH AND FRUITING RESPONSE TO PACLOBUTRAZOL

The effects of paclobutrazol on plant growth and fruiting characteristics in a new genetic access '468 BGH' tomato, from Germoplasm Bank of Federal University of Vicosa, were examined in two experiments. In one experiment, paclobutrazol was foliar sprayed 3 times at concentrations of 0, 15, 30, 45, 60 and 75 mg aiL -1 . In a second experiment, paclobutrazol drenches were applied once at 0, 2, 4, 8, 16 and 32 mg aiL -1 . Plant heigth was 20% shorter as paclobutrazol concentrations increased up to 30 mg aiL -1 for foliar application. Similar effects were observed with the internode length. Stem diameter increased as paclobutrazol concentrations increased up to 16 mg aiL -1 for drench application. The plants exhibited smaller leaf area and higher chlorophyll content as the paclobutrazol concentrations increased. Increasing paclobutrazol concentrations decreased fruit diameter but increased the number of red fruits. The number of cluster per plant and the number of cluster with fruits increased linearly by increasing drench paclobutrazol concentrations. Paclobutrazol was effective on controlling growth and fruit characteristics of a potential ornamental tomato '468 BGH'.

EFFECTS OF FLURPRIMIDOL AND ANCYMIDOL ON GROWTH AND POSTHARVEST PERFORMANCE OF Geogenanthus undatus `INCA'

Geogenanthus Ínca' is a new cultivar introduced the foliage plant industry which shows promise in interior plantscaping. The objectives of this study were twofold; to examine the effects of ancymidol and flurprimidol on G. `Inca' growth and determine if plant growth retardant (PGR) application could improve postharvest performance. Four weeks before attaining marketable sizes, the plants were drenched with ancymidol or flurprimidol at 0.0, 0.5, 1.0, or 1.5 mg (a.i.). Plants were then placed in interior-evaluation rooms under 12 μmol·m–2·s–1. Ancymidol or flurprimidol reduced plant height, width, growth index and total leaf area, total dry weight and shoot to root ratio of Geogenathus `Inca'. Flurprimidol increased the deposition of insoluble carbohydrates (starch) and altered the pattern of starch deposition; higher starch content was found in stem tissue compared to foliage tissue. The effects of ancymidol or flurprimidol persisted in the postharvest environment. After 4 months under low irradiance, PGR-treated plants exhibited higher quality, i.e., compact stature and reduced leaf and shoot necrosis. This research has potential significance for the foliage plant industry and it showed that a single drench application at label recommended rates of ancymidol or flurprimidol late in the production cycle can produce desired growth control of Geogenanthus `Inca' in the postharvest environment. Plants retain aesthetic characteristics for extended period thus necessitating lower replacement rate.

GROWING METHODS AND CHEMICAL DRENCHES CONTROL CALLA SOFT ROT

Bacterial soft rot, caused by Erwinia carotovora subsp. carotovora, is the most important disease affecting callas grown in New Zealand. The aim of this experiment was to determine the effects of chemical drench treatments on the incidence and severity of soft rot in callas grown in soil and in sawdust. There were four drench treatments: (1) no drench; (2) one drench application immediately after planting; (3) drench applied after planting, then at 28-day intervals; (4) drench after planting, then at 28-day intervals from the first visible occurrence of soft rot plot. The soil drench was an aqueous solution of 0.05% Kocide ® (350 g/kg copper), 0.05% Terrazole ® (350 g/kg etridiazole), and 0.15% Terrachlor ® (750 g/kg quintozene). Five litres of drench solution per plot was applied to the soil around the base of each plant. More calla plants died when grown in soil than in sawdust for each drench treatment. For both growing media, drenching plants at 28-day intervals resulted in the lowest numbers of dead plants during crop growth and rots in lifted tubers.

Effect of Nickel Applications for the Control of Mouse Ear Disorder on River Birch

Abstract Mouse ear (leaf curl, little leaf, squirrel ear) disorder has been a problem in container-grown river birch (Betula nigra L.) for several decades. The disorder is easy to detect in nurseries as the plants appear stunted due to shortened internodes which give the appearance of a witches-broom. The leaves are small, wrinkled, are often darker green in color, are commonly cupped and have necrotic margins. Plants grown in soil rarely express the disorder. A trial was initiated in June 2003 to determine if a deficiency of nickel was the cause of mouse-ear on river birch. Symptomatic river birch trees (Betula nigra ‘BNMTF’ Dura-Heat™) in their second growing season in #15 containers were selected for uniformity of size and mouse ear. Treatments included a 1) control, 2) 789 ppm Ni sprays, 3) 394 ppm Ni sprays, 4) 0.005 lbs Ni/yd3 as a drench, 5) 26 g/pot triple superphosphate (0–46–0), and 6) 130 g/pot Milorganite. Nickel was applied as nickel sulfate, whereas triple superphosphate and Milorganite contain trace amounts of nickel. At 16 days after treatment, up to 5 cm of new growth was evident on plants sprayed with nickel. Thirty days after treatment shoot length increased up to 60%, leaf area increased 80 to 83%, and leaf dry mass increased 76 to 81% for plants sprayed or drenched with nickel sulfate. Plants treated with triple superphosphate or Milorganite did not resume normal growth. All plants treated with nickel sulfate in 2003 did not show symptoms of mouse ear after initiation of growth in 2004. Based on this research mouse ear disorder of river birch is caused by a deficiency of nickel which can be corrected by foliar or drench applications of nickel sulfate.

Paclobutrazol suppressed vegetative growth and improved yield as well as fruit quality of ‘Tommy Atkins’ mango (Mangifera indica) in Ethiopia

The effects of paclobutrazol on the vegetative growth, reproductive development, total non‐structural carbohydrate of the shoots, and nutrient mobilisation to the leaves of ‘Tommy Atkins’ mango (Mangifera indica) trees grown in the Rift Valley of Ethiopia were evaluated during the 2002/03 season. The trees used were characterised by excessive vegetative growth, erratic flowering, and fruiting with declining productivity that validated the evaluation of paclobutrazol. Uniform trees were selected for a randomised complete block design experiment with two methods (soil and spraying) and four rates of paclobutrazol (0, 2.75, 5.50, 8.25 g a.i. per tree) in factorial combinations. There were three blocks and three trees per plot for each treatment. The results showed that application of paclobutrazol at rates of 5.50 and 8.25 g a.i. per tree both as a soil drench and spray applications were effective in suppressing vegetative growth compared with the control. Consequently, the trees from these treatments had higher total non‐structural carbohydrate in their shoots before flowering. Compared with the control, trees treated with paclobutrazol had higher results for percentages of shoots flowering, number of panicles produced, percentages of hermaphrodite flowers, yield as well as quality of the fruit. Applications of paclobutrazol did not affect the leaf macronutrient content levels analysed (N, P, K, and Ca), and with the exception of manganese, the micronutrient (Cu, Zn, and Fe) levels of the treated tree's leaves were significantly higher than the control.

Response of Hosta to BA Crown Drenches Applied at Division and Establishment

Abstract New offset formation in hosta in response to benzyladenine (BA) drenches applied at division and establishment was examined. Hosta Tratt. ‘Frances Williams’ and H. ‘Francee’ were separated into uniform single-bud divisions and drenched with 50 ml of 0, 100, 500, 1000, 2000 or 3000 ppm (mg/liter) BA just prior to potting (division) or two weeks later when substrate-container interface root development was evident (establishment). A 3000 ppm (mg/liter) foliar spray applied to established plants served as a standard. Offsets were counted in plants treated at division 14 days later at which time BA was applied to established plants. Offsets were counted on all plants 30 and 60 days after BA was applied to established plants and in spring of the following year. Offset counts increased rapidly in both cultivars following drench applications of increasing BA concentrations, whether applied at division or establishment. This positive response to increasing BA drench concentrations was evident 60 days after treatment (DAT) and the following spring, except in H. ‘Frances Williams’ drenched at division. However, benefits of either BA method or time of application were less pronounced in spring, following a period of dormancy.

Mediation of Partial Resistance to Rice Blast Through Anaerobic Induction of Ethylene

ABSTRACT The correlation between anaerobic soil conditions and increased resistance to rice blast disease has long been observed without benefit of an adequate explanation. We researched flood depth, dissolved oxygen (DO), and ethylene relative to expression of partial blast resistance in cvs. M-201, Newbonnet, LaGrue, Mars, and Cypress. Cultivar blast index (BI) and flood DO decreased with increasing flood depth. BIs were positively correlated with DO. Total leaf blast lesions were 3.4 and 3.2 times greater in cvs. M-201 and LaGrue growing in a 5.0-mul liter(-1) DO nutrient solution than when growing in a 0.1-mul liter(-1) DO solution. Treatment with 0.25 mM ethephon, which releases ethylene, lowered BIs of Newbonnet, LaGrue, and Cypress growing upland when applied drench, foliar, or foliar-drench. If flooded, BIs of ethephon-treated cultivars were decreased by drench and foliar-drench applications only. BIs of upland plants were unchanged, whereas BIs of analogous flooded plants increased following treatment with 0.31 mM aminoethoxyvinylglycine (AVG), an ethylene biosynthesis inhibitor. We hypothesize that varying anaerobic conditions mediate production of phytohormones, particularly ethylene, which modify expression of inherent partial blast resistance in these rice cultivars.

Mouse Ear Disorder on River Birch Caused by Nickel Deficiency

Mouse ear (leaf curl, little leaf, squirrel ear) has been a problem for growers of container-grown river birch (Betula nigra L.) since the early 1990's. Mouse ear has been noticed in several southeastern States as well as Minnesota, Ohio, Oregon, and Wisconsin, making it a national problem. The disorder is easy to detect in nurseries as the plants appear stunted. The leaves are small, wrinkled, often darker green in color, commonly cupped, and have necrotic margins. New growth has shortened internodes which gives plants a witches-broom appearance. Plants growing in native soil rarely express the disorder. Several common micronutrients have been evaluated with no results. A trial was initiated in June, 2003 to determine if nickel deficiency was the cause of mouse-ear. Symptomatic river birch trees growing in a pine bark substrate in containers were treated with foliar applications of nickel sulfate and a substrate drench. Topdress applications of superphosphate (0-46-0) and Miloroganite, products known to contain nickel, were also applied. At 16 days after treatment (DAT), up to 5 cm of new growth occurred on plants sprayed with nickel sulfate and foliar concentrations of nickel in the new growth increased five fold compared to control plants. At 30 DAT, shoot length increased 60%, leaf area increased 83%, and leaf dry mass increased 81% for trees receiving a foliar application compared to non-treated control plants. Treating trees with a substrate drench alleviated symptoms, whereas treatment with superphosphate and Milorganite did not. Trees receiving a foliar or drench application had normal growth for the remainder of the growing season. Additional studies are underway to refine methods of application, rates, and sources of nickel suitable for use.

Application methods and dosages of thiamethoxam in thrips control on tomato plants

Thrips is one of the most important vector species of the tomato spotted wilt tospovirus (TSWV) in Brazil. Two different pesticide application methods, drench x spray, using thiamethoxam were compared with commonly used insecticides for thrips control in tomato plants, Debora Plus. The experimental design consisted of a complete randomized block design with seven treatments and four replicates. Dosages of 150 and 200 g of a.i. per ha were used in just one drench application and 50 g of a.i. ha-1 sprayed, at weekly intervals, 48 days after sowing. The control efficacy of thiamethoxam was compared to diafenthiuron (400 g of a.i. ha-1), profenofos + cypermethrin (320+32 g of a.i. ha-1, respectively) and methamidophos (60 g of a.i. per hectolitre of water) in spray application. Cumulative number of plants with tospoviruses and the F. schultzei population from ten flowers per plot were registered. The mean cumulative number of plants with tospoviruses among treatments was not significantly different. No significant difference between thiamethoxam application methods and dosages on F. schultzei control, 24 days after application, were observed for thrips population. One drench application of higher dosages of thiamethoxam proved to be more environmentally advantageous than the pesticide applied at dosages of 50 g of a.i. ha-1 at weekly intervals. The vector control efficacy of thiamethoxam varied from 93 to 95%, independently of the application method and dosages. Diafenthiuron and profenofos + cypermethrin showed less efficacy (78 and 88%, respectively) but greater than those with methamidophos (71%). The products and dosages tested did not cause phytotoxicity in tomato leaves.