Lenny Wells

Cumulative Impact of a Clover Cover Crop on the Persistence and Efficacy of Beauveria bassiana in Suppressing the Pecan Weevil (Coleoptera: Curculionidae)

ABSTRACT The pecan weevil, Curculio caryae (Horn), is a key pest of pecan. Endemic levels of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin can occur in pecan orchards and contribute to natural control of C. caryae. Commercial formulations of the fungus can also be applied for suppression of C. caryae. We hypothesized that a clover cover crop enhances B. bassiana efficacy and persistence (e.g., by protecting the fungus against abiotic environmental stresses). The hypothesis was tested by conducting field trials in a pecan orchard in Byron, GA, in 2009 and 2010. The study included four treatments arranged in a factorial with two levels of fungus (endemic fungus only, and application of a commercial B. bassiana product), and two levels of clover (white clover, Trifolium repens L., and no clover). Fungal persistence was measured by determining the number of CFUs per gram of soil over time (during 42 d postapplication of B. bassiana in 2009 and 29 d in 2010). Efficacy was measured by capturing naturally emerging C. caryae and subsequently determining mortality and mycosis (over 24 d in 2009 and 17 d in 2010). In 2009, greater prevalence of B. bassiana conidia was detected in plots receiving fungal applications compared with no fungus applications, and no clear effect of clover was observed in plots receiving B. bassiana applications in either year. In 2010, B. bassiana prevalence in the endemic fungus plus clover treatment was higher than fungus without clover, and was similar to plots receiving additional B. bassiana applications. Given that we observed enhanced persistence of endemic B. bassiana in 2010 but not 2009, the impact of clover appears to be a cumulative effect. Mortality of C. caryae (averaged over the sampling periods) ranged between 68–74% in plots receiving B. bassiana applications and 51–56% in plots with endemic fungus only. C. caryae mortality and mycosis data also provided evidence that endemic B. bassiana efficacy was enhanced by clover relative to plots without clover (with no clear clover effect on plots receiving fungus applications). Thus, we conclude that natural control of C. caryae can increase when clover is grown in pecan orchards with endemic populations of B. bassiana.

Severity of Scab and its Effects on Fruit Weight in Mechanically Hedge-Pruned and Topped Pecan Trees

Scab is the most damaging disease of pecan in the southeastern United States. Pecan trees can attain 44 m in height, so managing disease in the upper canopy is a problem. Fungicide is ordinarily applied using ground-based air-blast sprayers. Although mechanical hedge-pruning and topping of pecan is done for several reasons, improved management of scab is an important reason in the humid, wet Southeast. Resulting shoot growth on cut limbs of susceptible cultivars could lead to more severe scab. In three experiments over three years, we explored the effect of hedge-pruning trees to ∼12 to 14 m compared with non-hedge-pruned trees. All trees received fungicide treatments (air-blast sprays and ≤3 aerial applications). Hedge-pruning either had no effect, or increased or decreased scab severity only slightly on leaflets, immature, or mature fruit (a -9.95 to +14.63% difference in scab severity compared with the control). However, height in the canopy invariably had a large and significant effect on scab severity, and amounted to a 0.05 to 73.77% difference in severity between the lowest and highest sample in the canopy. Fruit weight depended on sample height, with fruit most often weighing less when collected at greater sample heights. A robust relationship between fruit weight and scab severity was found at the highest sample heights where scab was also most often severe (R2 = 0.21 to 0.67, P < 0.0001). Hedge-pruning and topping pecan tree canopies to manage tree size will enable better fungicide coverage, reducing risk of a scab epidemic as more of the canopy is assured efficacious fungicide spray coverage.

Control of Pecan Weevil With Microbial Biopesticides

Abstract The pecan weevil, Curculio caryae (Horn) (Coleoptera: Curculionidae), is a key pest of pecans Carya illinoinensis ([Wangenh.] K. Koch) (Fagales: Juglandaceae). Control recommendations rely on broad spectrum chemical insecticides. Due to regulatory and environmental concerns, effective alternatives for C. caryae control must be sought for pecan production in conventional and organic systems. We explored the use of microbial biopesticides for control of C. caryae in Georgia pecan orchards. Three experiments were conducted. The first investigated an integrated microbial control approach in an organic system at two locations. Three microbial agents, Grandevo (based on byproducts of the bacterium Chromobacterium subtsugae Martin, Gundersen-Rindal, Blackburn & Buyer), the entomopathogenic nematode Steinernema carpocapsae (Weiser), and entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin, were applied to each treatment plot (0.6 ha) at different times during the season. A second experiment compared the effects of S. carpocapsae and B. bassiana applied as single treatments relative to application of both agents (at different times); survival of C. caryae was assessed approximately 11 mo after larvae were added to pots sunk in an organic pecan orchard. In a conventional orchard (with 1.0 ha plots), the third experiment compared Grandevo applications to a commonly used regime of chemical insecticides (carbaryl alternated with a pyrethroid). All experiments were repeated in consecutive years. The combined pest management tactic (experiment 1) reduced C. caryae infestation relative to non-treated control plots in both locations in 2014 and one of the two locations in 2015 (the other location had less than 1% infestation). In experiment 2, no differences among combined microbial treatments, single-applied microbial treatments or different numbers of application were observed, yet all microbial treatments reduced C. caryae survival relative to the control. In the third experiment, both Grandevo and standard chemical insecticide applications resulted in lower weevil infestation than the control (both years) and there was no difference between the insecticide treatments in 2014 although the chemical insecticide regime had slightly lower infestation in 2015. These results provide evidence that microbial biopesticides can substantially reduce pecan weevil infestations in organic and nonorganic systems.

A Survey of Weeds and Herbicides in Georgia Pecan

Abstract A survey was conducted in 2012 in Georgia to determine the most troublesome weeds in pecan orchards and document common herbicide weed control practices. Weed control practices and infestations in pecan were divided between winter and summer seasons. The most troublesome pecan winter weed species were wild radish and Italian ryegrass, whereas the most troublesome summer season weeds were Palmer amaranth and bermudagrass. Other weeds included crabgrass species, bahiagrass, Florida pusley, purslane species, morningglory species, curly dock, and cutleaf evening-primrose. The most widely used POST herbicide in both the winter and summer season was glyphosate. The most commonly used year-round herbicides with soil persistence were pendimethalin, diuron, flumioxazin, halosulfuron, simazine, indaziflam, and oryzalin. Use of multiple herbicides, PRE- and POST-contact and soil-persistent, with various herbicide mechanisms of action, have benefited pecan producers by providing year-round weed control, despite herbicide-resistant weeds being widely established in this region. Nomenclature: 2,4-D; clethodim; diruron; flumioxazin; glyphosate; glufosinate; halosulfuron; indaziflam; paraquat; sethoxydim; simazine; bahiagrass, Paspalum notatum Flueggé; bermudagrass, Cynodon dactylon (L.) Pers.; crabgrass species, Digitaria spp.; curly dock, Rumex crispus L.; cutleaf evening primrose, Oenothera laciniata Hill; Florida pusley, Richardia scabra L.; Italian ryegrass, Lolium perenne L. ssp. multiforum (Lam.) Husnot; morningglory species, Ipomoea spp.; Palmer amaranth, Amaranthus palmeri S. Wats.; purslane species, Portulaca spp.; wild radish, Raphanus raphanistrum L.; pecan, Carya illinoinensis (Wangenh.) K. Koch. Resumen Se realizó una encuesta en 2012 en Georgia para determinar los malezas más problemáticas en plantaciones de pacana y documentar prácticas comunes de control de malezas con herbicidas. Las prácticas de control de malezas y las infestaciones en pacana fueron divididas entre las temporadas de invierno y verano. Las malezas de invierno más problemáticas en pacana fueron Raphanus raphanistrum y Lolium perenne ssp. multiflorum, mientras que las malezas de verano más problemáticas fueron Amaranthus palmeri y Cynodon dactylon. Otras malezas incluyeron Digitaria spp., Paspalum notatum, Richardia scabra, Portulaca spp., Ipomoea spp., Rumex crispus, y Oenothera laciniata. El herbicida POST más ampliamente usado en ambas temporadas fue glyphosate. Los herbicidas con persistencia en el suelo más comúnmente usados a lo largo de todo el año fueron pendimethalin, diuron, flumioxazin, halosulfuron, simazine, indaziflam, y oryzalin. El uso de múltiples herbicidas, ambos PRE y POST de contacto y persistentes en el suelo, con varios mecanismos de acción, ha beneficiado a los productores de pacana al brindar control de malezas durante todo el año, a pesar de que malezas resistentes a herbicidas se están estableciendo ampliamente en esta región.

Integration of Insect and Mite Management With Disease and Weed Control in Pecan Production

Pecan orchards in the southeastern US are managed to conserve resources, protect the fruit and foliage from injury caused by phytophagous insects, mites, and pecan scab, and remove competition from weeds during the establishment of newly planted trees and in the preparation of the orchard floor as a harvesting surface. Costs associated with pest control are significant each year and the growers use integrated pest management methods to increase the effectiveness of pesticide treatments and reduce control costs. A coordinated research and extension effort over the past 25 years in entomology, plant pathology, weed science and horticulture has reduced the amount of pesticide use by 35%. Four advances have been responsible for the reduction. First, pecan scab sprays are reduced by linking the frequency of applications to the climatic conditions and the cultivar susceptibiltiy. Second, pest-specific insecticides that are toxic to the pests and not toxic to beneficial insects and mites are used to control lepidopterous pests and conserve aphidophagous insects and mite predators. Third, cover crops have been developed to supplement the soil with nitrogen and organic matter and conserve beneficial insects. Fourth, weed studies have led to the elimination of weeds in the first 8 years after planting around young trees, chemical mowing methods in established orchards and selective grass control to increase the growth of clover cover crops. The development and implementation of these and other significant advances in pecan management are reviewed in this chapter.

A comparison of organic fungicides: alternatives for reducing scab on pecan

In the southeastern USA, the most widespread and damaging disease of pecan is scab, caused by Venturia effusa. Although scab can be controlled using conventional chemical methods, organic pecans that attract a premium price mandate the use of organic fungicides. Also, organic production is an environmentally sustainable method. However, where susceptible pecan cultivars are grown, there are limited options for organic management of scab. We conducted experiments to compare organic fungicides to control scab on the susceptible cv. Desirable in 2011, 2012, 2014, 2015, and 2016. The alternatives compared included Bordeaux mixture, compost tea, sodium bicarbonate, Bacillus subtilis, sulfur, cuprous oxide, and extract of the Giant Knotweed (Reynoutria sachalinensis). Rainfall and scab severity differed between seasons. There was consistently low severity on foliage, with little or no difference between treatments. Similarly at the time of the first fruit assessment, the severity was low and the differences in severity small and inconsistent between seasons and treatments. However, by the time of the second fruit assessment, severity of scab had increased and consistent differences among treatments existed (except in the drought year of 2011, when scab severities were very low and similar to the control). In all other years, the control treatment had significantly more severe scab compared to some (2012 and 2014) or all other treatments (2015 and 2016). Extract of the Giant Knotweed as a fungicide was included in 2012, 2014, 2015, and 2016, and fruit on those trees had less severe scab in all years compared to that on fruit of the control trees. In three seasons (2012, 2015, and 2016), applications of Bordeaux mixture resulted in a reduction in scab severity. Compost tea, Sodium bicarbonate, B. subtilis, sulfur, and cuprous oxide significantly reduced scab compared to the control in one or two seasons, but were not consistent among seasons, and were never more efficacious compared to the extract of the Giant Knotweed. Extract of the Giant Knotweed and Bordeaux mixture appear to offer the greatest potential as organic approaches for managing scab in pecan. However, wherever possible, planting of scab resistant cultivars should be considered as a first line of defense.

Response of Young Pecan Trees to Irrigation in a Humid Climate

The prolonged period from tree planting to first commercial harvest of pecan [Carya illinoinensis (Wangenh.) K.Koch] provides incentive formany growers to intensively manage young trees to induce commercial production as soon as possible. This management includes irrigation. However, there remain very few data regarding the irrigation requirements of young pecan trees grown under southeastern U.S. orchard conditions. The objectives of this study were to determine appropriate irrigation rates for young pecan trees and to compare growth of young pecan trees with drip and microsprinkler irrigation. Parameters evaluated for both experiments include trunk diameter growth, stem water potential (water stress), leaf area, leaf length, leaf width, and chlorophyll index. These results suggest that irrigation is beneficial to the growth, vigor, and alleviation of water stress on young pecan trees in the establishment phase grown in the temperate region of the southeastern United States. There was no difference in young pecan tree growth and vigor for microsprinkler irrigated trees at 304 L per week (lpw) compared with 650 lpw from the year of planting through the third leaf. Similarly, drip irrigation at 182 lpw appears to result in equal tree growth comparedwith both drip andmicrosprinkler irrigation at over 600 lpw. Recent pecan price increases have renewed interest in the crop and led to the planting of additional pecan acreage throughout the U.S. pecan belt (USDA, 2012; Wells, 2014). Georgia pecan producers planted at least 391,488 pecan trees and 6203 additional pecan hectares from 2010 to 2014. The majority of these new pecan plantings are equipped with microsprinkler or drip irrigation systems (Wells, 2014). Cultural practices that promote tree growth and vigor during the establishment phase are desirable for maximizing tree fruiting surface (Wood, 1996). Irrigation must be managed appropriately to achieve optimum tree growth and nut production, while ensuring minimal environmental impact. Methods of irrigation affect farm water use, which is a critical issue in many parts of the world, including the humid southeastern United States, where population growth and agricultural expansion are placing increasing pressure on the water supply. Historically, there have been no research based guidelines for managing irrigation of pecan trees during the establishment phase and prefruiting years. Smith et al. (2000) demonstrated improved pecan tree growth with mulch during orchard establishment by helping to conserve soil moisture. However, data regarding the water requirements of young pecan trees and the effect of irrigation on young pecan tree growth and establishment is lacking. Patterson et al. (1990) found no effect of drip irrigation on young pecan tree diameter following the first growing season in a humid climate with 92–124 cm of rainfall; however, growth was enhanced by irrigation in years 2, 3, and 4. Fereres et al. (1982) suggested that due to the uncertainty of the root zone of newly planted almond [Prunus dulcis (Mill.) D.A. Webb] trees in California, wetting of a large volume of soil moisture during the first year of growth was needed to supply adequate water to the developing root system. Method of irrigation can have a strong influence on root distribution. Low-volume irrigation results in a more vertically uniform root distribution near the emitters, whereas overhead irrigation produces more equally dense root systems in apple (Malus domestica Borkh.) (Huguet, 1976). Since root growth is directly correlated with shoot growth (Weaver and Himmel, 1929), root distribution as influenced by irrigation method can have important implications for tree growth and establishment. Research is needed in the southeastern United States to evaluate the effects of drip and microirrigation on young pecan trees in a temperate, humid climate. The objectives of this study were to compare the effects of both methods of irrigation on growth and midday stem water potential of first through third leaf young pecan trees in the temperate climate of the southeastern United States and determine appropriate irrigation rates for pecan establishment in the region. Materials and Methods Study site, experimental design, and sampling Studies were conducted at the University of Georgia Ponder Research Farm located near Tifton, GA, at 31 51# N latitude and –83 64# W longitude. Orchard soils were Tifton loamy sand (fine-loamy, silicieous, thermic Plinthic Paleudult). Trunks were protected with corrugated tree guards (A.M. Leonard, Piqua, OH). The orchard was managed under commercial conditions according to University of Georgia Cooperative Extension recommendations (Hudson et al., 2012). A 3.7-m-wide vegetation-free strip was maintained with the herbicide glyphosate along the tree row in all plots. Row middles consisted of bermudagrass (Cynodon dactylon L.) sod. Expt. 1. Bare-root ‘Kanza’ pecan trees grafted to ‘Elliott’ seedling rootstock were planted from nursery stock. Trees were planted in January 2014 at a spacing of 3 m between trees. All trees were irrigated with microsprinklers at varying rates depending on treatment. Microsprinklers were placed 0.3 m from the tree trunk. Trees were irrigated 3 d per week at 4 h per day from April to September. If rainfall exceeded 2.54 cm within a 24-h period, irrigation was turned off for 3 d. The following treatments were evaluated: 1) microsprinkler irrigation at 304 L per week (lpw) using a 25.36 L per hour (lph) microsprinkler head; 2) microsprinkler irrigation at 650 lpw using a 54.13 lph microsprinkler head; 3) nonirrigated control (NI). Treatments were arranged in a randomized complete block design with four blocks and each treatment represented once per block. All trees were located within a single orchard row. One nonirrigated guard tree was placed between each tree used in the study to avoid overlap of irrigation. Measurements were taken from each tree within each plot. Individual trees received the same treatments in consecutive years. Midday stem water potential (y) was determined using a pump-up pressure chamber (PMS Instruments, Albany, OR) by measuring the y of leaves located near the trunk or a main scaffold branch, which had been enclosed in a foil-covered bag for 20 min (Begg and Turner, 1970). Measurements were made once per month between 1300– 1500 HR from July to September in 2014, June to September in 2015, and May to September in 2016. One leaf per tree was measured on each sampling date to keep measurements within close temporal proximity. Soil moisture was measured with a Field Scout TDR 300 Soil moisture meter (Spectrum Technologies, Aurora, IL) at 20-cm depth within the wetted zone of microsprinklers 1.2 m from the base of the tree on each sampling date at the same time that stem y was measured for each tree. Stem diameter at 76.2 cm above the soil surface was measured on 9 Apr. 2014, 3 July 2014, 19 July 2014, 21 Sept. 2014, 6 Apr. 2015, 14 May 2015, 24 June 2015, 20 July 2015, 24 Aug. 2015, 14 Sept. 2015, 4 May 2016, 13 June 2016, 19 July 2016, and 21 Sept. 2016. Leaf area, leaf length, and leaf width were measured 21 July 2014 and 7 Sept. 2016 using a LI-3000C portable leaf area meter (LI-COR Technologies, Lincoln, NE). Five leaves per tree were measured at each Received for publication 19 Dec. 2016. Accepted for publication 25 Jan. 2017. This work was supported by the Georgia Agricultural Commodity Commission for Pecans. Corresponding author. E-mail: lwells@uga.edu. HORTSCIENCE VOL. 52(3) MARCH 2017 457 Fig. 1. Daily rainfall distribution from 1 Apr. to 30 Sept. during (A) 2014, (B) 2015, and (C) 2016 at the study site. 458 HORTSCIENCE VOL. 52(3) MARCH 2017 sampling date. Leaf chlorophyll index (LCI) was measured 2 Sept. 2014 using a chlorophyll meter (SPAD-502; Minolta, Ramsey, NJ). All leaves measured for leaf area and LCI were fully expanded and selected from one pair of middle leaflets of compound leaves. Rainfall was recorded at a weather station located at the study site. Expt. 2.Bare-root ‘Desirable’ pecan trees grafted to ‘Elliott’ rootstock were planted from nursery stock. Trees were planted in Jan. 2015 at a spacing of 12.2 m · 12.2 m. All trees received one application of dry, balanced fertilizer (10N–10P–10K) at a rate of 0.45 kg/tree in June 2015 and again in Apr. and June 2016. All trees were irrigated with microsprinkler or drip irrigation at varying rates depending on treatment. Microsprinklers were placed 0.3 m from the tree trunk. Trees were irrigated 3 d per week at 4 h per day from April to September. If rainfall exceeded 2.54 cm within a 24-h period, irrigation was turned off for 3 d. The following treatments were evaluated: 1) microsprinkler irrigation at 650 lpw using a 54.13-lph microsprinkler head; 2) drip irrigation using seven 7.6 lph emitters per tree supplying a total of 638 lpw. One emitter was placed 15 cm from the trunk on one side of the tree and three emitters were placed within 120 cm of the trunk on each side of the tree. Emitters 120 cm from the trunk were spaced 60 cm apart from each other on each side of the tree. 3) Drip irrigation using two 7.6-lph emitters supplying a total of 182 lpw. One emitter was placed 15 cm from the trunk of the tree and one emitter was placed within 120 cm of the trunk on one side of the tree. 4) NI. Treatments were arranged in a randomized complete block design with five blocks and each treatment represented once per block. Measurements were taken from each tree within each plot. Individual trees received the same treatments in consecutive years. Soil moisture and midday stem y were determined as above for Expt. 1.Measurements were made once per month between 1300 and 1500 HR from June to Sept. 2015 and May to Sept. 2016. One leaf per tree was measured on each sampling date to keep measurements within close temporal proximity. Stem diameter at 76.2 cm above the soil surface was measured on 6 Apr. 2015,

Effects of Entomopathogenic Fungus Species, and Impact of Fertilizers, on Biological Control of Pecan Weevil (Coleoptera: Curculionidae)

ABSTRACT The pecan weevil, Curculio caryae (Horn), is a key pest of pecan, Carya illinoinensis (Wangenh.) K. Koch. Prior research indicated the potential for use of Hypocreales fungi to suppress C. caryae. We compared the efficacy of two fungal spp., Beauveria bassiana (GHA strain) and Metarhizium brunneum (F52), in their ability to cause C. caryae mortality. The fungus, B. bassiana, was applied to trunks of pecan trees (a method previously shown to be effective in C. caryae suppression) and efficacy was compared with M. brunneum applied to the ground or to the trunk with or without SoyScreen Oil as an ultraviolet protecting agent. Results indicated B. bassiana to be superior to M. brunneum regardless of application method; consequently, the potential for applying B. bassiana to control C. caryae was explored further. Specifically, the impact of different fertilizer regimes (as used by pecan growers) on the persistence of B. bassiana (GHA) in soil was determined. B. bassiana was applied to soil in a pecan orchard after one of several fertilizer treatments—i.e., ammonium nitrate, crimson clover, poultry litter, clover plus poultry litter, and a no-fertilizer control. B. bassiana persistence up to 49 d in 2009 and 2010 was assessed by plating soil onto selective media and determining the number of colony forming units, and by baiting soil with a susceptible host, Galleria mellonella (L.). Fertilizer treatments did not impact B. bassiana persistence. We conclude that standard fertilizers for nitrogen management, when applied according to recommended practices, are unlikely to negatively impact survival of B. bassiana in pecan orchards when the fungus is applied for C. caryae suppression during weevil emergence. Additional research on interactions between entomopathogenic fungi and fertilizer amendments (or other tree nutrition or soil management practices) is merited.