Insecticidal Seed Treatment And Foliar Insecticide Recommendations In SW LA
DR. BLAKE WILSON
BATON ROUGE, LOUISIANA
With second-crop harvest wrapping up across south Louisiana, we are beginning to shift focus on next season’s management decisions based on what we saw in 2024. Many growers across the state experienced delayed planting due to untimely rains in March, which lead to many acres being planted late. Insect infestations from rice water weevils and stem borers tend to be more severe later into the season and can wreak havoc on a rice crop if not effectively managed. Typically, foliar pyrethroids are rarely needed to control weevils and borers as insecticidal seed treatments (ISTs) such as Dermacor X- 100 and CruiserMaxx have been highly effective on their own and have been a mainstay of rice insect management for over a decade. However, control failures with IST’s were reported across the southwest region leading some growers to seriously consider pyrethroids as a last resort. In on-station university experiments, we can report that Dermacor X-100, normally our most effective product, achieved just 50% control against water weevils (down from 80% or better in the past) and no control of stem borers. This has been a trend we’ve observed in the past couple years but was especially present in 2024. Research is on-going to identify the cause of reduced efficacy and control failures. However, since we can no longer reliably count on ISTs alone, we must consider adjusting how we manage our insect pests.
Prior to the development of seed treatments in rice, foliar pyrethroids were used successfully against water weevils in delayed-flood systems. Application timing is critical due to short residual of pyrethroids and ovipositional habits of female weevils. Before permanent flood is established, rice fields must be scouted for leaf scarring which indicates the presence of adult weevils (Image 1). Female weevils do not lay eggs until permanent flood is established. Therefore, application just before flooding can help reduce overall populations even if total control is not achievable. Application immediately after permanent flood can also be effective. Controls will not be effective if adult weevils persist in fields for several days after flooding.
Poor control of stem borers with seed treatments means scouting for borer infestations will be necessary. Injury from stem borer larvae is most obvious when rice is heading out. Larvae tunnel into rice stems and destroy vascular tissue. This prevents nutrients from reaching the panicle leading to total yield loss for an injured plant. At this point, the damage is done and foliar pyrethroids will not be economical. For this reason, scouting for stem borers should start earlier in crop development around green ring when adult moths begin infesting rice. Females will lay egg clusters on leaves/leaf sheaths and larvae will begin boring into the stem around 1 week after hatching. During this time, leaf sheaths may appear discolored, typically brown to orange, right where the larvae are feeding. Scouting for newly hatched larvae is often difficult due to their small size (≈1 mm long), so focusing on adult moths and discolored stems can make scouting more efficient. Stem borer egg lay is not tied to permanent flood establishment like for water weevils, so timing of pyrethroids for stem borers should be based on presence of moths and injured stems from young larvae.
In addition to using foliar pyrethroids, stacking multiple ISTs of different modes of action (i.e. Dermacor X-100 + NipsIt Inside, Fortenza + CruiserMaxx) has shown to be economical in university research trials from 2019–2020, before product failures were regularly reported. Economic returns from multiple IST combinations may be increased comparatively in the current landscape.
Moving forward, insect management in Louisiana rice production will require more effort from rice producers, crop consultants, and field scouts being able to correctly identify and diagnose insect issues in real time. It is possible we are no longer in a position where we can simply treat with a seed treatment and manage insects without much additional effort. Foliar pyrethroids and stacking multiple ISTs appear to be our next best move. Finally, it’s important to remember that issues with toxicity to crawfish will limit pyrethroid use in and around crawfish ponds. Always follow the label to prevent non-target effects. LSU AgCenter researchers and ANR agents are available to provide insect identification and management recommendations. Please contact your local parish extension office for additional information. ∆
DR. BLAKE WILSON: LSU AgCenter