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An
easterly migration
Mexican rice borer damage, range expansion |
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By Vicky Boyd |
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A new pest that bores into rice stems and feeds on panicles, causing
lodging and yield loss, continues to march eastward across the Texas
rice belt. Although the Mexican rice borer has yet to cross into Louisiana,
insect experts say it’s only a matter of time. As a result, entomologists at Texas A&M University and Louisiana
State University recently received a $190,000 grant from the U. S. Department
of Agriculture to cooperatively study integrated pest management of
stem borers attacking rice and sugarcane. Depending on where you farm, you may be plagued by Mexican rice borer,
sugarcane borer, rice stalk borer or a combination, says Mo Way, an
associate entomology professor based at the Texas A&M University
Agricultural Research and Extension Cente rin Beaumont. In some areas west of Houston, rice producers have to contend with
all three borers. In southern Louisiana, sugarcane borer is the major borer pest, whereas
rice stalk borer is the major borer pest in northeastern Louisiana. A pest of both rice and sugar cane As its name implies, it originated south of the border in Mexico. Although
it can significantly reduce rice yields under severe infestations, the
Mexican rice borer is even more damaging to sugarcane. As a result,
it has become the number one insect pest of sugarcane in the Texas lower
Rio Grande Valley. It will also infest and damage grain sorghum and
corn. Since its initial discovery in Texas rice fields, Way and LSU Extension
sugarcane entomologist Gene Reagan have been coordinating a trap line
stretching across the Texas and Louisiana rice belts. Extension agents
in each county check two pheromone traps weekly throughout the rice-growing
season and report the results to Way and Reagan. The goal is to map
the moth’s spread. Results of the 2003 trapping program in western Louisiana sugarcane
and in east Texas show that the Mexican rice borer is now found in the
Texas rice belt counties of Victoria, Wharton, Jackson, Brazoria, Colorado,
Waller, Fort Bend, Harris, Austin Matagorda, Galveston and Calhoun,
placing the pest within 70 miles of east Texas sugarcane, which is transported
for milling into Louisiana. Trap catches during 2003 put the Mexican rice borer within 120 miles
of the western Louisiana border. “What I am afraid of is the longer the rice borer has been in
an area, the bigger the problem it will be over time,” Way says. Based on trap counts and observations, Way says moth populations increase in the spring—around May—then decrease during the mid-summer. They pick up once again in September and October, about the same time the ratoon crop is beginning to mature. The life cycle “You don’t see signs of damage until around PD (panicle differentiation),”
Way says. “Even though the moths are there, they are not going
to the rice until PD, and we don’t know why.” Female moths, about the size of horse flies, lay eggs on dead or dying
rice foliage. Once the eggs hatch, the larvae move to the inside of leaf sheaths
where they are partially protected from natural enemies and pesticides.
The small larvae feed in the sheaths and eventually bore into the culm.
Inside the culm, they feed between nodes to cause “deadhearts”
(dead leaves) and “whiteheads” (panicles with unfilled grains).
In his 6-row-by-16-foot plots with the susceptible variety Priscilla
at Ganado, Way says it wasn’t uncommon to have 100 whiteheads per
plot just in the middle four rows. As a result of the feeding, the rice stalk is weakened and eventually
lodges. After completing five larval instars, or molts, the larva pupates within
the culm and emerges as an adult moth. Way believes the Mexican rice borer has at least two generations, although it possibly may have three or four. That is one of the areas he and Reagan plan to study further. Treatments work but aren’t yet registered Based on his trials, Way says two properly timed treatments of Karate-Z
at 2 ounces per acre provides good control. The first one should be
applied between PD and 2-inch panicle. The second should be applied
at late boot. Karate-Z is not labeled for Mexican rice borer, although
Way says he’s working with Syngenta Crop Protection, the product’s
registrant, to add stem borers to the label. In trials using Icon seed treatment, Way says he’s
seen a 20 percent to 30 percent reduction in whiteheads. “We are seeing some real nice yield responses where
we control the stem borers,” Way says of treatment trials. “When
we rate the plots, we just count the whiteheads in the plots, but I
think there’s partial grain filling, also. There’s a gradation
of damage. There’s less grain filling in the panicles that don’t
whitehead.” In earlier trials, Way examined the effects of treatments
on overall yields by weighing the grain. “Panicles weren’t filling as well [in the untreated plots] as in the treated plots, but that doesn’t show up visually,” Way says. Variety susceptibility varies Contact Vicky Boyd at (209) 571-0414 or vlboyd@att.net. Which borer is it? Full-grown sugarcane borer caterpillars (Diatraea saccahalis)
are about 1 inch long, white to yellow, with rich brown head capsules
and first thoracic segment. Each body segment is marked with round brown
to black spots. Adults are small brown moths with darker brown bands
on each forewing. In the southern part of Texas, the Mexican rice borer, Eoreuma loftini,
has a similar biology and host range to the sugarcane borer. Caterpillars
lack dark spots but have two purple-red stripes similar to dashes on
each body segment that do not connect to the stripes on adjacent segments.
Along the Texas coast, rice stalk borer, Chilo plejadellus,
caterpillars also lack dark spots, but have a pair of continuous light
brown to purplish stripes all along the sides of their bodies. Information courtesy of Texas A&M Internet Hotlinks For management options, visit Texas A&M’s rice Production
STEM borer susceptibility ratings Very Susceptible Varieties: Information courtesy of Mo Way, Texas A&M University
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