AgWatch


Insect Update – No News Is Good News

DR. SCOTT STEWART

JACKSON, TENN.
   A quick update this week. There are no major insect issues occurring on a widespread basis. Call about plant bugs indicate variable and average infestations in cotton. For cotton close to or in early bloom and requiring treatment for plant bugs, it would be a good time to consider getting some Diamond or Transform in mix during the next couple of weeks. There are a few spider mites around, but the impacts of infestation are generally pretty mild, mostly due to adequate rainfall and rapidly growing plants. A couple of threshold reminders are below.
   Beginning at the third week of squaring, treat cotton for plant bugs when an average of 15 or more bugs are found per 100 sweeps.     Monitor squares with a goal of maintaining a minimum of 80 percent retention.
   For spider mites in cotton, treatment is suggested when 40 percent of the field is showing signs of infestation and mites are present.
   I’m getting some calls about lodging from stem girdling by threecornered alfalfa hopper in soybean. This often rears it’s head after strong winds, and we’ve had plenty of that. The impacts of lodging are generally minimal when it occurs prior to bloom, especially where there is a good stand. This damage is done when plants are small (< 8-10 inches), so there is not any value in revenge spraying larger beans after lodging is observed. However, scout later planted fields for the presence of hoppers shortly after emergence. Make any treatments when plant are small (< 6 inches tall) if hoppers are being observed in large numbers (best guess is 30+ per 100 sweeps), and especially if stands are relatively thin.  Pyrethroid insecticides or Acephate are effective.
   For those growing non-Bt corn, we are right between generations of southwestern corn borer.  Very few southwestern corn borer moths are being caught, and I don’t expect this to change for the next 7-10 days.  You can read more about managing this pest at http://www.utcrops.com/corn/corn_insects/SWCB.htm. When the second generation moth flight kicks off, treatment is recommended when 10 percent or more of plants are found with egg masses or live larvae, or treat 7 to 10 days after pheromone traps catch an average of 100 or more moths on a seven-day catch. Treatment is generally not recommended once the dough stage (R4) is reached. Insecticides choices for control of corn borers are listed in the Tennessee Insect Control Recommendations for Field Crops (PB 1768). ∆
   DR. SCOTT STEWART: IPM Extension Specialist, University of Tennessee
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