Protection of Rice from
Invertebrate Pests - 2010



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Project Leader and Principal  Investigators

Larry D. Godfrey, extension entomologist, Dept. of Entomology, UC Davis




Research into the biology and management of invertebrate pests of California rice continues to emphasize control of rice water weevil (RWW), which was present in 2010 at reduced levels because of unfavorable spring conditions. In addition to research on insecticidal control, scientists also examined rice variety response to RWW infestation. Research continued on tadpole shrimp, a pest of concern in many locations. Armyworms again were not abundant enough for research in 2010. The goal of this work is to refine and advance integrated pest management practices that are cost-effective and protect the rice agroecosystem.

RWW flight and biology

The 2010 RWW infestation was delayed by cool, wet spring conditions. Peaks in flight activity occurred May 13 and from May 28 to June 4. Some weevils were trapped as late as July, very unusual. In total, 1,650 adult RWW were captured in the black light trap at the Rice Experiment Station—about 30 percent of the 2009 total.

RWW primarily reduces rice grain yield by reducing the amount of tillering in plants, rather than affecting grain weight or seeds per panicle. A study was begun to reveal more about the mechanics and physiology of how RWW affects tillering and how larvae damage root systems. Several treatments were set up with different amounts and different timing of stress for RWW. More detailed information on how this pest affects plant productivity could be an important advancement in helping design stable, sustainable, long-term management schemes.

Variety susceptibility studies

Research continued on commonly grown California rice varieties for their susceptibility to RWW infestation and damage.

In controlled ring plot studies with four varieties, yield loss was highest in M-202, and about a third as high in S-102 and L-206. Calmati-202 was most lightly infested with RWW and did not suffer any yield loss.

In field studies with 12 varieties, the medium grains typically suffered the highest yield loss from RWW. M-202 and M-205 upheld this trend. M-401 was the most heavily infested and suffered a significant yield loss, but the yield capacity of this variety partially compensated for the loss. Conversely, M-206 was moderately infested but did not show much yield loss. Similarly, L-206, M-104, and Calamylow-201 did not have measurable yield loss, despite infestation levels believed to be sufficient to cause damage.

RWW chemical controls

Studies in 2010 were conducted in ring plots, small basins, and quarter-acre plots to evaluate experimental and registered insecticides for RWW control. Six different active ingredients were examined in 24 treatments.

In summary, the registered products Dimilin®, Warrior® II, and Mustang® Max are still viable for RWW control. Of these, Mustang® Max was the least effective in 2010 but still provided adequate control. Application of Warrior® preflood was a very effective treatment and produced results equal to or even better than the standard three-leaf application. Mustang® Max did not perform as well preflood and does not appear suited to this type of application.

Trebon® (etofenprox) applied three-leaf provided effective RWW larval control. Registration of this product is currently on hold.

Belay® (clothianidan) appears to have significant potential for RWW management and is progressing toward registration. It is effective both preflood and in three-leaf applications. In three-leaf applications during 2010 tests, this product was as effective as the registered insecticides for RWW control. A “rescue” treatment at five-leaf stage, when larval infestation had already begun, also proved admirable with 70% control. Preflood methods warrant further research. They had shown excellent results in previous years, but the lower application rates used in 2010 produced moderate control.

Dermacor® (rynaxypyr) efficacy as a seed treatment in water-seeded rice afforded only moderate control, similar to results from previous years. However, applied preflood or at three-leaf, rynaxypyr showed promise. In both cases, the higher rates tested were as effective as the best-performing treatments; lower rates showed moderate activity.

In quarter-acre plots with a natural weevil infestation, Belay® applied at three-leaf stage was most effective, followed by Belay® preflood, and a Dermacor® seed treatment. Given the reevaluation of pyrethroid registrations, it is important to continue developing alternative active ingredients and classes of chemistry. These unregistered active ingredients have some favorable properties in regards to nontarget organisms, persistence, and other characteristics.

Tadpole shrimp

Nine insecticide treatments were analyzed for control of tadpole shrimp and protection of rice seedling stands. Trebon®, copper sulfate, Warrior® preflood and postflood and Dermacor® preflood produced the most tadpole shrimp mortality. Trebon® again showed good performance in terms of seedling protection, as did Belay®, Dermacor®, and Warrior® applied preflood.

Nontarget studies

Nine insecticide treatments were compared for their effects on populations of nontarget invertebrates and their potential to upset naturally occurring mosquito management.

Results from 2010 are still being analyzed. Data from 2009 show mosquito populations at fairly high numbers. Mosquito larvae were collected for nine weeks. Four preflood applications from 2009 were evaluated—Warrior® and Belay® as preflood broadcast applications, and DPX-HGW86 and Dermacor® as seed treatments. Belay® preflood appeared to cause the greatest reduction in populations of aquatic insects and other aquatic invertebrates. There was some indication that all the preflood treatments increased mosquito numbers but no consistent trends.

Dimilin®, Warrior®, Belay®, and Trebon® were evaluated with three-leaf stage applications. At 10 days after treatment, all four products significantly reduced aquatic insect levels and three of the four affected levels of other aquatic animals. These reductions persisted at lower levels 16 and 23 days after treatment. Warrior®, Dimilin®, and Belay® appear to have the potential to increase populations of mosquitoes when applied at three-leaf stage. Trebon® did not exhibit the same effect.

Warrior® was also examined for its effect on nontarget organisms when applied mid- to late season (armyworm control). Warrior® belongs to the same class of chemistry used for mosquito control. Mosquito numbers were significantly reduced for five weeks after application. Although this treatment was very damaging to aquatic organisms one week after treatment, their numbers rebounded somewhat. The seasonal average showed a 25% reduction.


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