No. 3/April 10, 1998
Corn Herbicide/Insecticide Precautions
The increased occurrence of corn rootworm injury in cornfields
rotated with soybeans, especially in east-central Illinois, has
many producers considering applying a soil-insecticide at
planting. Numerous insecticide choices are available to producers,
but several of these could potentially restrict some corn
herbicide options. In particular, use of certain organophosphate
(OP) insecticides could restrict the use of herbicides that
inhibit the acetolactate synthase (ALS) enzyme, commonly referred
to as ALS-inhibiting herbicides. The precautions and restrictions
are due to concerns for corn injury following use of certain OP
insecticides and ALS-inhibiting herbicides.
Why do combinations of certain OP insecticides and
ALS-inhibiting herbicides cause injury to corn? Most
ALS-inhibiting herbicides used in corn-production systems are
systemic in nature; that is, after these materials enter the plant
they are able to move extensively (translocate) from the site of
uptake. Often, translocated compounds accumulate in areas of the
plant undergoing active cell division (meristems). Both
insecticides and herbicides are considered foreign compounds to
the corn plant. When a foreign compound enters a plant, the plant
attempts to "defend itself" against any potential injury
the foreign compound could cause, by rendering the foreign
compound inert or nonphytotoxic. This process is commonly referred
to as metabolism or breakdown of foreign compounds. A corn plant
has several different pathways to "detoxify" foreign
compounds, but the OP insecticides and many ALS-inhibiting
herbicides share a common metabolic pathway. When one or the other
is present within the plant, the plant is able to metabolize the
compound before it may cause any deleterious effects; but if both
insecticide and herbicide are present, the metabolism pathway can
become overwhelmed and cannot effectively metabolize both
compounds. When this happens, corn injury can result.
What can be done to help minimize the potential for corn
injury from this insecticide/herbicide interaction? Selection
and placement of the insecticide, as well as corn-hybrid
selection, can all be helpful. Table 1 is a summary of
herbicide label information with respect to the potential for corn
injury caused by various OP/ALS-inhibiting herbicide interactions.
As indicated in the table, placement of the insecticide (in-furrow
or T-band), selection of insecticide (Counter, Lorsban, etc.), and
corn hybrid (normal, IT hybrids) can influence the potential for
corn injury from this interaction. The data in this table are for
"normal" corn hybrids, except for products containing
imazethapyr or imazapyr, which require an IT or IR corn hybrid.
(We selected label information for IT hybrids for these
herbicides.) Most of these herbicide labels have few restrictions
about insecticide selection or placement when the respective
herbicide is applied toIR corn hybrids.
Table 1. Herbicide label restrictions for application to "normal"
corn previously treatedwith certain organophosphate insecticides
|
Soil-applied OP insecticide |
Foliar-applied OP |
Corn herbicide |
Counter
Furrow |
20CR
T-band |
Thimet |
Lorsban |
Fortress |
Aztec |
Days before |
Days after |
Nicosulfuron & Rimsulfuron |
Accent |
No |
UCI |
TCI |
TCI |
Yes |
Yes |
7 |
3 |
Accent Gold |
No |
No |
No |
TCI |
Yes |
Yes |
7 |
3 |
Basis |
No |
UCI |
UCI |
TCI |
Yes |
TCI |
7 |
3 |
Basis Gold |
No |
UCI |
TCI |
TCI |
Yes |
Yes |
7 |
3 |
Celebrity B&G |
No |
UCI |
TCI |
TCI |
Yes |
Yes |
7 |
3 |
Primisulfuron & Prosulfuron |
Beacon |
No |
UCI |
TCI |
TCI |
TCI |
TCI |
10 |
7 |
Exceed |
No |
UCI |
TCI |
TCI |
TCI |
TCI |
10 |
7 |
Spirit |
No |
UCI |
TCI |
TCI |
TCI |
TCI |
10 |
7 |
Flumetsulam |
Python |
No |
No |
No |
TCI* |
TCI |
TCI |
-- |
-- |
Broadstrike + Dual |
No |
No |
No |
TCI* |
Yes |
TCI |
-- |
-- |
Hornet (POST) |
No |
No |
No |
TCI |
TCI |
TCI |
-- |
-- |
Scorpion III |
? |
? |
? |
? |
? |
? |
7 |
7 |
Imazethapyr & Imazapyr |
Lightning--IT hybrids |
No |
TCI |
TCI |
TCI |
Yes |
Yes |
-- |
-- |
Contour--IT hybrids |
TCI |
TCI |
TCI |
Yes |
Yes |
Yes |
-- |
-- |
Pursuit--IT hybrids |
TCI |
TCI |
TCI |
Yes |
Yes |
Yes |
-- |
-- |
Resolve--IT hybrids |
TCI |
TCI |
TCI |
Yes |
Yes |
Yes |
-- |
-- |
Halosulfuron |
Permit |
No restrictions on label |
No: Do not use this herbicide if this soil-applied insecticide
was previously applied.
UCI: Using this herbicide on corn previously treated with
this insecticide may result in Unacceptable Crop
Injury.
TCI: Using this herbicide on corn previously treated with
this insecticide may result in Temporary Crop Injury.
*Do not place Lorsban in-furrow if Python or Broadstrike is
to be used.
Foliar OP: Cygon, Diazanon, Disyston, Imidan, Lorsban,
malathion, Penncap-2FM.
Aaron Hager
(hagera@idea. ag.uiuc.edu) and Marshal
McGlamery (mmcglame@uiuc.edu), Extension Weed Science,
(217)333-4424
|