Doane Daily Cotton Commentary

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Georgia:

Be On The Lookout For Budworms In Young Peanuts

From Rusty Harris, County Extension Coordinator

Worth County, Georgia

I have received reports from peanut specialists and county agents from counties in the southwestern corner of the state concerning severe outbreaks of tobacco budworms in young peanuts.

Ordinarily, the threshold is 4 per foot on older peanuts, but young plants cannot tolerate heavy feeding, especially during times of drought and extreme heat. Take time to walk your fields and look closely. Observe all insect activity in the field, and look for three-cornered alfalfa hoppers while scouting for caterpillars.

Tobacco budworm moth

Pyrethroid insecticides should provide adequate control. But monitor fields closely after spraying to ensure resistant populations are not out there.

My concern is that we are using pyrethroids in too many instances in other crops without proper justification based on insect pest populations, thus creating tolerance to pyrethroids. If you have populations at the economic threshold level, spray and scout three days later.

Resistance to pyrethroid insecticides is based on the insect being able to detoxify the poison without being killed. Most populations exhibit varying levels of tolerance to pyrethroid insecticides. Thus, when scouting fields the day after spraying, lethargic insects will be found lying on the ground.

One would think that caterpillars off the plant and on the ground are certainly dead. These days that may not be the case. Those caterpillars basically have the equivalent of an insecticide-induced “hangover.” 

That is why it is critical to scout 3 days after spraying. Survivors will have moved back onto the crop and started feeding again by that time. If active populations are found after spraying pyrethroids, move on to higher priced products such as Steward or Tracer.

Signs of foliage feeding caterpillars will be stripped leaves and the insects themselves. Damage will be obvious when or if you see any. Damage from three cornered alfalfa hoppers can also be a problem early on. Look for girdling around young plants, and look for live insects also.

Be aware that planting peanuts behind burned-off wheat fields puts the crop at high risk for infestation from Lesser Cornstalk Borers (LCB). This is true also for soybeans and snap beans. Moths are drawn to burned fields immediately after burning, and infest young plants quickly after emergence.

The moth lays her eggs directly beside a seedling, just below the soil line. The egg hatches after 2 to 3 days of incubation, then it tunnels directly into the plant and builds its silk feeding tube. The life cycle and feeding habits of the LCB makes it very difficult to control. Granular chlorpyrifos products such as Lorsban 15G do the best, most consistent job by far.

Do NOT expect liquid chlorpyrifos applications to last as long and provide as much residual control as granular chrlopyrifos. Sunlight degrades the molecule of the active ingredient of the liquid form very rapidly, thus killing its activity. Also be cautious of using pyrethroids to control LCBs. The temptation is there to use liquids because of lower price and easier application,

BUT, you don’t get as much control for the dollar as compared to granular chlorpyrifos. Killing an LCB that has established itself in the plant is very difficult, so scout often and treat early before you have a problem. This year may be hard enough to make good grade and yield, so lets don’t give up anything because of not treating on time.

Finally, please DON”T use pyrethroids at every fungicide application just because they are cheap. It creates problems of the worst kind. Besides creating resistant populations of Tobacco Budworms, it also decreases sensitivity to the insecticide by other foliage feeding insects such as Velvetbean Caterpillars. It may also cause uncontrollable outbreaks of spider mites.

The moral of the story would be to scout your peanuts regularly, scout them thoroughly, and don’t use any foliar insecticides until they are needed. Use granular chlorpyrifos for controlling LCBs in peanuts planted behind burned wheat fields.

The following is the url to a University of Florida publication about Lesser Cornstalk Borers:

http://edis.ifas.ufl.edu/IN312

Rusty Harris

County Extension Coordinator

Worth County

204 E. Franklin St, #9

Sylvester, GA 31791

(229) 776-8216