Cogongrass, Insect Biodiversity and Pine Decline Nancy J. Loewenstein, Stephen F. Enloe, Sallie Martin and Ben Brunson Auburn University OBJECTIVES • Impacts of cogongrass infestations on insect communities of southeastern pine forests • Influence of cogongrass management strategies on insect diversity and abundance • Influence of cogongrass on susceptibility of pines to pine decline COGONGRASS, ITS MANAGEMENT AND INSECT BIODIVERSITY (STUDY 1) • Study sites: – 10-year-old planted longleaf pine forests – one in Mobile county, one in Baldwin county, AL – Heavily infested with cogongrass (90-100% cover) – Sandy loam soils • Treatments: – Prescribed fire – Glyphosate – Seeding with mix of native species – Control • Design: – Split plot with CRD – 10 X 10 m plots – 5 replicates per treatment – Non-cogongrass control PRESCRIBED FIRE TREATMENT • Block containing half of the plots was burned in March of 2010 • Good weather conditions to minimize fire severity Still got a bit hot! NJL NJL burned unburned GLYPHOSATE TREATMENTS • April, 2010 - 6 weeks post-burn, pre-flowering , regrowth 12-18” • 2.5% v/v • October, 2010 – regrowth 18- 36” • 4.0% v/v • both treatments applied with a single nozzle backpack sprayer at 55 GPA and 20 PSI SEEDING WITH NATIVE PLANTS • Plots were lightly disked • Broadcast sown • April 2010 • Feb 2011 2010 SPECIES LIST common sunflower Helianthus annuus 35% switchgrass 'Carthage' Panicum virgatum 32% purpletop tridens Tridens flavus 10% partridge pea Chamaecrista fasciculata 15% dixie ticktrefoil Desmodium tortuosum 2% largeflower tickseed Coreopsis grandiflora 2% grey headed coneflower Ratibida pinnata 2% blackeyed Susan Rudbeckia hirta 2% 25 PLS per acre …. $15.81 per lb .... $395 per acre Seed source: Ernst Conservation Seeds OCTOBER 2010 • Coverage of native plants was not high •Cogongrass recovery was fairly strong • Prompted retreating with glyphosate … reseeding in 2011 1=1-2.5%, 2=2.5-10%, 3=10-25%, 4=25-50%, 5=50-75%, 6=75-100% B=burned, G=glyphosate, S=seeded, U=unburned 2011 SPECIES LIST Virginia wild rye Elymus virginicus 19% Indian grass Sorghastrum nutans 19% purpletop tridens Tridens flavus 12% broomsedge Andropogon virginicus 10% partridge pea Chamaecrista fasciculata 30% lance-leaved coreopsis Coreopsis lanceolata 2% perplexed ticktrefoil Desmodium perplexum 2% greyheaded coneflower Ratibida pinnata 2% blackeyed Susan Rudbeckia hirta 2% white wingstem Verbesina virginica 2% spurred butterfly pea Centrosema virginianum 1% 9 PLS per acre …. $22.9 per pound …. $206 per acre Seed source: Roundstone Native Seed 2011 SPECIES RICHNESS 2011 COGONGRASS COVER 40 6 July 5 30 Class 4 20 Sown 3 July Natural October 2 Species Richness Species 10 1 Cogongrass Cover Cogongrass Cover 0 0 B BG BS BGS U UG US UGS B BG BS BGS U UG US UGS 40 October • Seeding increased diversity only when combined 30 with glyphosate treatment • Seeding alone did not reduce cogongrass cover 20 • Seeding may have helped reduce cogongrass cover on the plots that were burned and treated with Species Richness Species 10 glyphosate 0 B=burned, G=glyphosate, S=seeded, U=unburned B BG BS BGS U UG US UGS 1=1-2.5%, 2=2.5-10%, 3=10-25%, 4=25-50%, 5=50-75%, 6=75-100% INSECT COMMUNITIES • Generalist predators (e.g., ants, predaceous beetles and spiders) can serve as bioindicators of sustainability of forest management techniques • Parasitic hymenoptera and hover flies (Syrphidae) respond to vegetation complexity and are useful indicators of landscape- level changes in vegetation • Hereafter referred to as ‘Natural Enemies’ References: Maeto et al., 2009; Maleque et al. 2009 INSECT SAMPLING • 5 pitfall traps (15 cm funnel traps) were placed in each plot • Insects collected every 2 weeks between March and Oct of 2010 and 2011 • Sweep sampling conducted on the same schedule sorting cleaning identifying Back at the lab … NATURAL ENEMIES CAPTURED BY SWEEP SAMPLING • No main effect of fire • Some significant treatment and interaction effects (treatments and fire) … a lot of variation Blue=cogongrass, red=glyphosate, yellow=seeded, • Awaiting results from non- purple=glyposate and seeding cogongrass controls NATURAL ENEMIES CAPTURED BY PITFALL TRAPS • No significant treatment effects Mostly fire ants Mostly fire ants ROOT FEEDING BARK BEETLES BEETLES ( BARK ROOT FEEDING Number of insects 20 25 30 35 40 45 50 10 15 0 5 5/15/2011 5/22/2011 5/29/2011 6/5/2011 6/12/2011 6/19/2011 6/26/2011 7/3/2011 H 7/10/2011 ylastes 7/17/2011 7/24/2011 7/31/2011 spp. 8/7/2011 8/14/2011 ) 8/21/2011 8/28/2011 9/4/2011 9/11/2011 9/18/2011 9/25/2011 10/2/2011 10/9/2011 10/16/2011 10/23/2011 LOBLOLLY PINE DECLINE • Increasingly important issue in Southeast • Caused by a complex of abiotic and biotic stressors • Stressed trees attract root-feeding bark beetles and weevils – Hylastes salebrosus – Hylastes porculus – Hylastes tenuis – Hylastes opacus * – Dendroctonus terebrans – Hylobius pales – Pachylobius picivorus * non-native FUNGAL ASSOCIATIONS • The bark beetles vector wood staining fungi associated with pine decline – Leptographium terebrantis – Leptographium procerum – Leptographium serpens * – Grosmannia huntii * – Ophiostoma spp. * non-native COGONGRASS AND PINE DECLINE (STUDY 2) • Does cogongrass increase tree stress? • Does cogongrass impact bark beetle population levels? • Does cogongrass increase susceptibility to pine decline? • Study site 80 miles northwest of the 1st study • 13-year-old loblolly pine plantation • fertilized in 2006 and 2010 • thinned to 70 BA in 2009 • 10 plots with cogongrass, 10 plots without INSECT SAMPLING • Bi-weekly collections from panel and pitfall traps • Bark beetles and weevils identified and counted • 10% of pitfall insects “rolled” on select media to check for vectoring of fungi PLOT AND TREE DATA • Tree vigor measurements for each plot – DBH – Height – Age – Growth Increment (5 and 10 year) – Basal Area – Crown Ratings – Foliage Sampling – Resin sampling (volume and terpene composition) • Presence of fungi on root samples – Root cores sampled from 2 roots from each of 6 trees per plot – Core is plated on media to test for presence of the 6 fungi listed in previous slide INSECT COLLECTIONS - TOTAL HS-Hylastes salebrosus BTB Other IG XF 3% 3% XP 3% HT- Hylastes tenuis 1% HPO 9% 5% HPO- Hylastes porculus GM 2% IG- Ips grandicolis XCR BTB- Dendroctonus terebrans 9% XF- Xyleborus ferrugineus XP- Xyleborus pubescens XS 5% GM- Gnathotrichus materiarius HP PP XCR- Xylosandrus crassiusculus 1% 2% XS- Xyleborinus saxesenii HT 5% HS 52% HP- Hylobius pales PP- Pachylobius picivorus Other- several Ambrosia species 68% of observed insects were species of interest POPULATION TRENDS 2000 1800 Hylastes salebrosus 1600 1400 1200 1000 of of insects Cogon 800 # Non-Cogon 600 400 200 0 POPULATION TRENDS 70 Pachylobius picivorous 60 50 40 Cogon 30 # of # of Insects Non-Cogon 20 10 0 FUNGAL ISOLATES DATA BTB HPO HS HT HP PP Total Total Rolled 26 96 260 107 42 107 638 Total Fungal 7 7 17 7 17 6 61 Isolates % Insects 27 7 7 7 10 6 10 Infected BTB – Dendroctonus terebrans, HPO – Hylastes porculus, HS – Hylastes salebrosus, HT – Hylastes tenuis, HP – Hylobius pales, PP – Pachylobius picivorus • More trees from the cogongrass infested sites had fungus in their root systems But … • Loblolly on cogongrass infested sites did not produce more resin, although resin analysis may reveal differences in resin composition • No outward signs of pine decline at this time … but, the trees are still young PRELIMINARY CONCLUSIONS • Ecologically based integrated treatment • Seeding alone had little impact on cogongrass cover • Seeding, when combined with burning and glyphosate treatments, may contribute to control and restoration efforts • Response of insect communities (‘natural enemies’) to cogongrass and its treatment is as yet unclear • Several root feeding beetles were found in greater abundance in cogongrass infested pine stands • ~10% were infected with the fungi associated with pine decline • more tree roots had fungal infections in infested plots • no overt signs of pine decline in the stands at this time Acknowledgements • Co-PI’s: • Dr. Lori Eckhardt - Forest Entomology and Pathology, AU … (Ben Brunson’s advisor) • Dr. David Held – Entomology and Plant Pathology, AU … (Sallie Martin’s advisor) • Research Tech: Joe Borden • 2011 Plant Surveys: Gina Todia – Wetland Resources, Environmental Consulting • Study sites: Tommy Swearingen, Austin Rainwater, The Westervelt Company • Funding : USDA-CSREES-AFRI Biology of Weedy and Invasive Species Competitive Grant Program .