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Insect Management in Reduced Tillage Systems Scott D. Stewart University of Tennessee Jackson, TN Presented at 2003 Beltwide Cotton Conferences What is Reduced Tillage? • Reduced tillage practices including ¾ No-till ¾ Ridge-till ¾ Strip-till ¾ Etc. • May not result in the minimum 30% residue required to meet the strict, old definition of “conservation tillage” Reduced Tillage No-till Cotton Following Cotton ¾ May involve the planting of cover crops such as wheat, rye, clover, etc. ¾ Not all reduced tillage systems are the same No-till Cotton Following Wheat Cover Crop No-till Cotton Following Corn Differences in Weed Control (Is it weed control or tillage?) • Conventional-tillage systems ¾ Spring tillage: weed control (and seed bed preparation) often occurs several weeks prior to planting, quickly killing weeds ¾ Fall tillage: weed control may be similar to reduced-till systems • Reduced-tillage systems ¾ Herbicides substitute for tillage, but weeds die relatively slowly ¾ “Burndown” often postponed until shortly before planting ¾ Herbicide tolerant or resistant weeds may remain How Tillage May Impact Insects • Mechanical ¾ Destruction or exposure of soil insects or residue harboring overwintering insect populations • Ecological ¾ Removal of weed hosts for insect pests ¾ Lack of residue/habitat for beneficial insects • Microclimate ¾ Seedbeds may warm-up faster in tilled systems (but temperature fluctuations may be greater) ¾ Soils may waterlog faster (but also dry more quickly) ¾ Affecting plant growth, and thus, susceptibility to insect pests such as thrips (effects may be environment specific) Tillage and Thrips Thrips per 10 plants* Date Disked Strip tillage May 29 23.0 a 23.6 a June 6 131.5 a 70.9 b June 18 35.5 a 16.8 b * Means are averages across aldicarb treated and untreated plots (> 95% of population was tobacco thrips). Lohmeyer et al. (2002), University of Georgia, P < 0.05 Tillage, Cover Crops and Cutworms No-till 12 Wheat Clover 4 Vetch b a b 9 6 3 0 % Stand reduction % Stand reduction 15 Conventional-till 3 b b 2 1 a 0 Tillage system Winter cover crop Leonard (1995), Louisiana State University, P < 0.05 Peas Tillage vs. Herbicides and Cutworms % Stand reduction 40 Herbicide 35 Tillage 30 25 20 15 10 5 0 Six Four Two One Weeks prior to planting Leonard et al. (1993), Louisiana State University, P < 0.05 at all weeks Tillage and Aphids 70 Conven-till a a 60 50 40 30 20 b b No-till Conven-till % Infested plants No. / 10 plants (seasonal) 90 80 100 Reduced-till 10 75 50 25 0 1991 0 Tillage system DeSpain et al. (1990), Texas A&M Data for Corpus Christie,1988, P < 0.001 1992 1993 1994 Year Leonard (1995), LSU Mid-season infestations Tillage and Aphids • “Field studies of aphid infestations …… indicated that aphid numbers were always lower in conservation-tillage or crop-rotation systems compared to continuous-cotton conventional-tillage systems” Leser (1995), Texas A&M (TX High Plains) Tillage and Fire Ants NCSU Cropping / Surface Tillage Rye / Disk Rye / No-till Monocrop / Disk Monocrop / No-till Ants per 10 m row Aldicarb No Aldicarb 54.3 b 55.3 b 133.3 a 145.7 a 48.3 b 50.3 b 113.3 ab 97.3 ab McCutcheon (1999), Clemson University, P < 0.05 Tillage and Heliothines • Tillage can reduce spring emergence of bollworm and tobacco budworm moths emerging from pupae overwintering in cotton fields, but low overwintering populations are usually found in cotton ¾ Hopkins (1972), Harris (1998), Roach (1981), Schneider (unpublished), etc. • If tillage is done in spring, overwintering populations may have already emerged Insects in Reduced Tillage Systems • Cutworms: elevated risk (highly dependent upon use of cover crops and timing of preplant herbicide application) ¾ At-planting or pre-plant insecticides often recommended • Thrips: little net risk (but impacts can vary greatly with environmental conditions) • Aphids: little or increased risk (at least partially dependent upon presence of fire ants) • Bollworm/budworm: increase in overwintering survival ¾ Negligible effect on overall size of population? Other Potential Problems • False chinch bug ¾ More common in reduced-till systems (dispersal from shepardspurse, prostrate spurge, etc.) • Threecornered alfalfa hopper University of California ¾ More common in reduced-till systems ¾ Tended by fire ants • Grasshoppers ¾ Lack of soil disturbances increases hatching success Texas A&M University Other Potential Problems • Spider mites ¾ More common in reduced-till systems using glyphosate tolerant crops (possible dispersal from cutleaf evening primrose, etc.) • Slugs ¾ More common in reduced-till systems ¾ Appears more common following corn • Snails ¾ Increased numbers in no till, but of little economic importance University of California Conclusions • Reduced-till systems are at greater risk to a few insect pests, but these tend to be occasional or minor pests ¾ Cutworms, aphids, false chinch bug, grasshoppers, slugs ¾ Impact on other, more important pests is generally small • Risks are dependent upon timing of pre-plant herbicide applications and weather conditions • Reduced tillage has sporadic but mostly positive impacts on populations of beneficial arthropods ¾ Dependent upon species, use of cover crops, etc. • Greater insect pest problems in reduced-till cotton is not a limiting factor ¾ System specific pest management is sometimes needed ¾ Awareness of potential problems