World Grain - November 2017 - 74

GRAIN OPERATIONS

Center

119

BTL

WEV

257

1,910 1,370

326

1,000

806

544

BTL

WEV

Total number of stored grain insects found in pitfall probe traps located in
the periphery (near the silo wall) and center of the chilled and ambient aerated (control) silos on Aug. 15, Sept. 22 and Nov. 20, 2015, at the Wakefield Cooperative, Clay County, Kansas, U.S.
GB = Grain Beetle (Cryptolestes spp.); FB = Flour Beetle (Tribolium spp.);
BTL = Sawtoothed or Merchant Beetle (Oryzaephilus spp.); WEV = Weevil
(Sitophilus spp.)

indicated by probe trap catches, especially in September and
November (see Table 1, above left). Had it not been for the
removal of some wheat from the control silo that allowed for
cooling with lower temperature ambient air in the early fall,
a fumigation treatment would have been warranted given that
cold winter weather was still a few weeks away. The chilled
silo was cool enough with the possibility to lower temperatures with ambient aeration further and preserve grain quality
until winter weather arrived.
Recent applications in California with maize, Arkansas
with paddy rice, soybeans and maize, Kansas with wheat and
maize, Pennsylvania with organic popcorn, New York state
with buckwheat, and wheat in Mexico utilizing Grainfrigor
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technology in North America.
In Brazil, grain chilling has been investigated in combination with grain protectants to successfully control stored grain
insects. One comprehensive trial in three 1,100-tonne silos in
the state of Parana documented that chilled aeration with a
bottom and top layer of wheat treated with diatomaceous earth
(DE) resulted in 100% insect suppression and control at less
than half the cost of treating the entire grain mass with DE or
a liquid insecticide (see Table 2, above right).
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paddy rice stored under tropical climate conditions of Costa
Rica also have been investigated using computer simulation.
After six months of storage in Costa Rica, ambient aeration
was not able to reduce average stored paddy rice tempera74

T3
Chilled aeration +
DE (total)
+ ambient aeration

Periphery

T2
Chilled aeration +
DE (enveloping)
+ ambient aeration

Center

T1
Liquid insecticide
+ ambient aeration

Insect
species

Table 2
Treatments

Ambient
aeration
(Control)

Nov. 20

Periphery

Chilled
aeration

Sept. 22

Center

Silo

Aug. 15
Periphery

Table 1

Chilled
aeration

$318

Liquid
insecticide

$1,148

Diatomaceous
earth

$28.5

$830

Ambient
aeration

$48.4

$55.5

$39.7

Total

$1,196

$402

$1,187

Cost comparison (US$) of insect control in a study conducted with stored
wheat in Parana state, Brazil. Each bin was filled with 1,100 tonnes
(44,000 bushels) of new crop wheat. (Source: Lazzari, F. and Lazzari, S.,
personal communication)
*Cost of cooling equipment not included. T1, T2, T3:
Treatments in each bin

tures by more than 4°C (7.2°F), i.e., from 35°C (95°F) to
31°C (88°F). In comparison, grain chilling was predicted to
lower the average paddy temperature to below 15°C (60°F)
LQOHVVWKDQKRXUVZKLFKZRXOGUHVXOWLQH൵HFWLYHLQVHFW
suppression.
SUMMARY
The grain chilling technology requires a substantial investPHQWLQWRDSK\VLFDODVVHWWKDWKDVWRSD\R൵WKURXJKUHDODQG
SHUFHLYHGEHQH¿WV3UHYLRXVUHVHDUFKKDVGHWHUPLQHGWKDWWKH
operational costs of grain chilling is typically lower than the
cost of ambient aeration plus at least one fumigation treatment. However, given the initial cost of purchasing a grain
chiller, the net present cost (NPC) over 10 years is higher
than the cost of ambient aeration plus one fumigation treatment. If multiple fumigations per storage season are required
(as is typical in tropical and subtropical climates) and the
real threat of insect resistance to phosphine is considered,
incorporating the grain chilling technology into an overall
quality management and food safety strategy generates longWHUPEHQH¿W,WDOVRDOORZVIRUFRROLQJRIJUDLQ\HDUURXQG
independent of high ambient temperature and relative humidity conditions.
Dirk Maier is a post-harvest engineer with the Iowa Grain Quality Initiative
at Iowa State University. He can be reached at dmaier@iastate.edu
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