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Although American newspaper
editor Horace
Greeley made famous
the quote, “Go West,
young man,” the Mexican rice borer
(MRB), a troublesome pest for Texas
sugarcane and rice producers, obviously
did not get the memo. Instead,
the MRB – a type of stem borer –
headed east, and on Dec. 15, 2008,
was discovered near Vinton in southwest
Louisiana in a pheromone trap.
At the time, the Louisiana Department
of Agriculture and Forestry
(LDAF) had been working with LSU
AgCenter entomologist Dr. Gene
Reagan’s lab, monitoring pheromone
traps – exclusively for the Mexican
rice borer – every two weeks across
the state. After the first catch, they
ramped up the trap numbers, but the
MRB did not appear again until late
fall 2010 south of Welsh in Jeff
Davis Parish, and the number of
moths quickly increased. In 2011,
MRB larvae were found in Louisiana
rice fields.
According to Dr. Reagan’s
research, the pest moves at a pace
of about 15 miles a year.
“We think this is mostly nonassisted
movement, but that might
change,” says Dr. Julien Beuzelin,
LSU AgCenter post doctoral
researcher in entomology. “When
you have larvae and pupae in sugarcane
and the cane is harvested, it is
possible that by hauling the crop
from the harvesting point to the
milling point in the fall might alter the rate of dispersal.”
Dr. Natalie Hummel, LSU AgCenter entomologist, says another
source may be straw that has been harvested from a rice field, which
potentially could increase the 15-mile-a-year movement. However, all
of the LSU AgCenter entomologists emphasize that this is not a time
to panic, but rather a time to build awareness among farmers and
educate them about practices to help suppress populations and develop
a management plan should the MRB appear in any of their fields.
Identification Guidelines
The first step is to properly identify the pest as its appearance is similar
to the sugarcane borer and rice stalk borer. Following is a description
of the three “outlaws” as published by the LSU AgCenter, LDAF
and Texas AgriLife:
“Mexican rice borer adults are light tan moths with delta-shaped
wings. By comparison, sugarcane borer moths are larger, straw-colored
moths about ¾-inch long with a series of black dots arranged in
an inverted V-shaped pattern on the front wings. Mexican rice borer
adults produce spherical, globular, cream-colored eggs hidden between
the folds of dried leaves. After hatching, young larvae feed inside
fresh leaf sheaths and then bore into the stem or stalk. This feeding
causes an orange discoloration of the leaf sheath.
“Mexican rice borer larvae are whitish with a light-colored head
capsule and two pair of dark purple stripes running the length of the
body. By comparison, sugarcane borer larvae are yellowish or white
with a series of brown spots on the back.
“Rice stalk borer adults are about one-inch long with pale white fore
and hind wings tinged on the edges with metallic gold scales. The front
wings are peppered with small black dots. Larvae of the rice stalk borer
are pale yellow-white with two pairs of stripes running the entire
length of the body and have a black head capsule (very similar to
the Mexican rice borer larva in appearance). In general, the Mexican
rice borer has light-colored hairs and head capsule, while the rice
stalk borer has dark hairs and head capsule.”
If rice fields are located in an area where MRB has been positively
identified, farmers may want to consider a seed treatment application
of Dermacor X-100 as a preventative strategy.
“Dermacor stays present in the plant long enough to have some
activity against stem borers,” says LSU AgCenter entomologist Mike
Stout. “If a farmer is using Dermacor to control rice water weevils, then the seed treatment will help suppress stem borers
if they are present in the field.
“Scouting for MRB is similar to scouting for sugarcane
borer,” he adds. “Look for orangish, yellowish
feeding lesions. At that point, spray a pyrethroid
before the larvae get into the stem. Once that happens,
the pest is protected from the insecticide.”
Since this is a new pest moving into the state, Hummel
says the treatment threshold is just the presence of
MRB to prevent their spread and establishment.
Deadheart, Whitehead Injury
The MRB typically moves into rice from panicle
development to boot. Prior to that, the pest may
already be present in such weeds as Johnsongrass and
vaseygrass, but they wait to lay their eggs in the older
stages of the plant and prefer rice to the grasses.
“Most of the eggs that we find are laid on dry-leaf
materials, which may explain their preference for older plants,” Beuzelin says.
According to the LSU AgCenter, “Rice injury
begins with feeding in leaf sheaths. Borers then tunnel
inside the stem. Signs of early injury in rice are
withering and death of the youngest leaf, resulting in
a condition called deadheart. Most infestations are not
obvious until after the boot stage. Stem feeding during
panicle development causes partial or complete
sterility and the whitehead condition. The white,
empty panicles are lightweight and stand upright.
Feeding inside the stem can also cause plants to lodge
before harvest.”
With this in mind, common sense says to scout
the fields to find larvae at a treatable time.
“Once you see a lot of whiteheads in the field,
there is no point in treating because you have already
suffered injury,” Hummel says. “Don’t apply insecticides
at that time, which would only compound
the amount of money lost on your crop.”
MRB Management Plan In Rice
Because the MRB causes direct yield reduction
via deadheart and whitehead injury, LSU AgCenter
is asking farmers to consider following a MRB management
plan if they have fields in areas where the
pest has been found.
1. Learn to correctly identify the MRB and participate
in population monitoring. If you suspect a
Mexican rice borer infestation, contact your local county agent or LDAF at (225) 952-8100.
2. If you typically have rice water weevils and are in
an area where MRB is present, consider applying Dermacor
X-100. The EPA recently approved a 24(c) registration
for Dermacor X-100 use in water-seeded rice
in Louisiana. If you don’t use Dermacor, aggressively
scout your rice at the susceptible stages and spray a
pyrethroid if larvae are found in the field.
3. Strongly consider stubble management practices.
Reduce the harvest cutting height, unless this conflicts
with environmental regulations regarding duck habitat
management. In the fall, if it’s feasible, consider flooding
or plowing to destroy the stubble because it can
serve as an overwintering host.
4. Consider cultivar selection. “Although there are no
resistant cultivars, we have found that some are more
or less relatively susceptible,” Hummel says. “For
example, some of the hybrids are moderately susceptible,
while others are susceptible.”
5. Consider non-crop habitat management. Manage
grasses, mainly Johnsongrass and vaseygrass, along
field margins and ditch banks in the fall and early
spring to keep MRB populations from multiplying.
In conclusion, Hummel notes, “We’re not trying to
eradicate this pest, but we want to do as much as we can
in management systems to keep the populations down
on an area-wide basis.”
Contact Carroll Smith at (901) 767-4020 or csmith@onegrower.com.
Ongoing Behind-The-Scenes Efforts
In an effort to promote awareness and provide education about
the Mexican rice borer, LSU AgCenter’s Anna Meszaros, research
associate specialist in entomology, has helped coordinate the
Extension outreach, which included creating and organizing MRB
content into the new LSU AgCenter rice insects Web site:
www.lsuagcenter.com/riceinsects. She assisted in planning and
conducting training sessions and has also been an active member
of the LSU AgCenter MRB research team with entomologist Dr.
Julien Beuzelin.
Beuzelin, whose MRB research has been done under the supervision
of LSU AgCenter’s Dr. Gene Reagan and Drs. Ted Wilson and
Mo Way with Texas AgriLife at Beaumont, primarily investigated
weeds and fallow rice fields.
“Year round, the grasses surrounding rice fields host Mexican rice
borers,” he says. “On average, we saw densities from 1.5 to 6
borers per square meter, so weeds can be a substantial source of
borers. That’s why we think it is important to have a comprehensive
management strategy. While we know that borers are not
present in newly planted rice, they still have to come from somewhere.
“Besides weeds, a fallow rice field containing stubble or volunteer
rice can also be a source for MRB and needs to be managed
properly,” Beuzelin adds. “Right now, we haven’t quantified how
much managing these non-crop Mexican rice borer habitats will
decrease the infestation, but we are still working on that and consider
it a priority.” |
