Download Insect Management in Reduced Tillage Systems

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