Insecticide Seed Treatment (IST) Strategies For Increasing Field Corn And Soybean Yields In Conservation Tillage Production Systems
Introduction
Southern crop production systems have become
much more diversified in recent years and
migrated from near monocultures of cotton, soybean,
or rice. Variability in commodity prices
and increases in production inputs has forced
many producers to consider additional crops
that are more profitable. This trend is likely to
continue during the foreseeable future based
upon annual fluctuations in profit margins for
selected Southern row crops.
Numerous insect pests are capable of injuring
field corn and soybean during seed germination
and seedling establishment. The adoption of
conservation tillage practices that limit tillage,
increase post-harvest crop residue, and allow
the establishment of native winter/spring vegetation
has improved the intra-field soil environment
for several of these pests. Greater pest
diversity and higher survivorship increases potential
injury to seeds and seedlings in field corn
and soybean. For many years, field corn IPM
strategies have included the use of a prophylactic,
soil-applied insecticide treatment at the time
of planting to reduce the impact of these pests.
Those treatments are even more important in
current production systems. Recently, the
widespread adoption of MG IV soybean, early
spring planting dates (March and April), and
conservation tillage also has increased the potential
of injury from soybean seed and seedling
pests. At-planting treatments of soil-applied pesticides
have been available for soybean for many
years, but few benefits were observed when MG
V/VI soybeans were planted in optimum soil environments.
A coordinated Mid-Southern regional
research project has documented
considerable yield increases from the use of insecticides
applied to soybean seed used in earlyplanted
MG IV production systems.
This report will list common seed and seedling
pests associated with field corn and soybean in
the current Southern production systems. In
addition, the use of IST’s will be described as
IPM tools in these crops.
Insect Pests Attacking Field Corn and Soybean
Seedlings
Field corn is usually planted during February
and March resulting in exposure of plants to soil
and weather conditions that delay seedling development.
Therefore, seed and seedlings are
susceptible to insect pests for an extended period.
Insect pest diversity and density in states
along the Gulf Coast are usually much greater
than that observed in northern corn production
states. The most common soil and seedling insect
pests of field corn in Louisiana include
Southern corn rootworms, wireworms, cutworms,
armyworms, seed corn maggots, sugarcane
beetles, red imported fire ants, chinch
bugs, and a complex of stink bugs (Pentatomidae).
Planting soybean during March and April increases
the potential for early season environmental
conditions that could delay seed
germination and satisfactory stand establishment.
This delay in plant development extends
the period of susceptibility to those pests that attack
seeds and seedlings. Furthermore, the
adoption of conservation tillage practices increases
those intra-field pest populations capable
of injuring soybean during the early season.
The most common soil and seedling insect pests
of Louisiana soybean include Southern corn
rootworms, cutworms, bean leaf beetles, armyworms,
seed corn maggots, thrips, and threecornered
alfalfa hoppers.
At-Planting Chemical Control Strategies
Soil-applied insecticides used at the time of
planting have been a critical input for optimum
grain production in Mid-South field corn. In recent
years, most of the soil-applied products
have been replaced by IST’s represented in the
neonicotinoid class (Cruiser, Gaucho, and Poncho).
The results from IST rate definition tests
for field corn pest management have consistently
demonstrated that common commercial rates of
these products are not sufficient for Louisiana’s
pest problems. The broad spectrum of common
and emerging insect pests that attack field corn
seed and seedlings are not consistently controlled
with these treatments. Increasing IST
rates or adding soil insecticides at reduced rates
to the commercial IST has improved corn yields
≥15 bu/acre. Recently, one of the agrochemical
industries (Bayer CropScience) has agreed to
provide the optimum dose of Poncho to commercial
seed companies. Therefore, no additional
at-planting insecticides should be needed for
most situations, with one noteworthy exception:
cutworm management with pyrethroid applications.
Two of these IST’s (Cruiser, Gaucho) have been
recommended on other Louisiana field crops including
soybean. Positive reports of insecticide
efficacy and promising yield increases from other
states have supported this insecticide use strategy,
especially on early-planted soybeans. Results
of the Mid-South regional IST screening
trials have demonstrated seed yield increases of
0-18 bu/acre during the previous four years.
Positive results for later-planted MG V/VI soybean
(such as wheat/soybean double-cropping)
are less consistent.
Current research projects have refined use
rates for field corn pest management and validated
IST performance in early season soybean
production systems. Most national seed companies
will include an IST on field corn or soybean
cultivars sold during 2009.
Considerations for Pest Management
with IST’s in Conservation Tillage Systems
IST’s are a logical extension of the use of transgenic
traits allowing crops to express resistance
to herbicides and tolerance to insect pests.
There are similar benefits between the two plant
protection tactics. In addition to direct improvements
on grain yield and quality, the IST’s improve
planting efficiency and reduce non-target
hazards associated with other soil-applied insecticide
treatments. Several observations and
recommendations for the use of IST’s in field
corn and soybean within conservation tillage
systems are listed below.
• Conservation tillage production systems for
Southern grain crops typically require more intensive
IPM than conventional tillage systems.
• At-planting soil/seed insecticides are critical
plant protection inputs in conservation tillage
production systems for optimizing yields of field
corn.
• Low rates of Cruiser 5F (0.25-0.64 mg
AI/seed), Gaucho 600F (0.25-0.80 mg AI/seed),
and Poncho 600F (0.25 mg AI/seed) are not sufficient
for Louisiana’s field corn pests.
• The LSU AgCenter’s field corn IST results
have provided justification for Bayer Crop-
Science to offer Poncho 500 (0.5 mg AI/seed) on
field corn seed in 2009, the optimum rate for
Louisiana.
• Mid-South Trials on IST’s (Cruiser and Gaucho)
in early-planted soybean suggest seed yield
increases for IST plots of 0-18 bu/acre above
non-treated plots.
• Soybean seedling survival and plant development
was rarely affected by the IST’s, but insect
pests (thrips, bean leaf beetles, three-cornered
hoppers, and a bean-pea weevil [Sitona lineatus])
were significantly reduced compared to numbers
on non-treated plants.
• Yield increases from IST’s on MG V/VI soybean
planted during May and June are less consistent
and are, therefore, not recommended at
this time.
• The IST’s do not provide effective control of
cutworms, and pyrethroid applications are necessary
to reduce plant stand loss from these
pests.
Summary
Chemical control strategies either as soil insecticides
or ISTs’ remain necessary crop protection
inputs for field corn across the
Mid-Southern Region. The shift to early-planted
MG IV soybean production systems has also created
a need for IST’s to maintain adequate plant
development and optimum yields. Recent communications
with the agrochemical industries
suggest that the dose of IST’s offered to seed
companies will provide sufficient control of the
common pest populations in field corn and soybean.
Although IST’s are applied as preventative
applications at the time of planting grain
crops, the value of these specific treatments
should not be underestimated as environmentally
acceptable components of integrated pest
management systems. Δ