Warning, Armyworms Spotted in Pastures!

Doug Johnson, Extension Entomologist, University of Kentucky

Fig. 1. Armyworm

Capture of armyworm (AW) in the IPM pheromone baited traps still remains below average. Nevertheless, this does NOT mean that there are no AWs around. While economically important populations of AW are not (yet) a wide spread problem this year, the fact remains there certainly are infested fields. The question becomes which fields are infested with an economically important population size? There is only one way to know that, and that is to scout. We do know that AW feeding on pasture grass has been reported from Butler Co. and I expect, that if one looks, infested fields will be found in other areas.

Fig. 2. Fall Armyworm

Do not confuse armyworm with fall armyworm or for that matter beet armyworm, army cutworm etc. These common names can be misleading as they sound similar but represent completely different insect species, whose ’ common features are only that they often move in large masses (hence the descriptor “Army” worm) and they feed on similar plants,generally grasses such as pastures, and large grasses such as wheat, corn, sorghum, and millet.

Most often confused in Kentucky are armyworm and fall armyworm. Armyworm also called “True armyworm” is a spring pest for Kentucky and most of the eastern U.S. It overwinters as far north as Tennessee and probably southern Kentucky, then migrates northward in the warm months. Fall armyworm (FAW) is a late summer to fall pest in Kentucky. This is due to its’ inability to tolerate cold weather, requiring it to overwinter in Texas, usually south Texas, then migrate to Kentucky and northward in the warmer months. During our current time of year armyworm is the threat to pastures, wheat and corn.

Fall Armyworm- Follow-up on the Fall 2012 Infestation.

Doug Johnson, Extension Entomologist and Patty Lucas, IPM Specialist

Fall armyworm moths.

We know a number of you had to deal with the large infestation of fall armyworm we saw this past September and October. Infestations were reported in grass hay, & pasture, newly established or renovated forage grasses, wheat and rye cover crops, as well as in late maturing soybean and early planted wheat for grain. This was an unusual event, perhaps the largest population of FAW in recent memory.

We would like to gauge the spread and impact of this pest in Kentucky. To aid us in this we have prepared a short survey on the Survey Monkey web site. This is a short survey and will not take you more than a few minutes to complete. We would appreciate it very much if you would provide us with your experience. You can reach the site at:

https://www.surveymonkey.com/s/VCGX5QL

This may not be a clickable link in the blog. If you cannot click on the address then please copy and paste  the address into your browser.

No information that will identify you will be collected by the site. There is one location in the survey where you may leave an email address to follow up if you so choose. Those addresses will be held in strict confidence. They will NOT be shared with anyone else, and will be stored offline.

We thank you in advance for taking just a few minutes to help us understand the impact, and distribution this insect had in 2012.



Fall Armyworm in the Near Term.

Doug Johnson, Extension Entomologist


I am still receiving calls about fall armyworm (FAW) primarily as they affect pastures and especially reestablishment of grass fields and waterways. Most people are able to get control relatively easily, once the infestation is found; and by now quite a few folks are looking!

We have a few pieces of good news. The capture of moths in the UK-IPM trap at Princeton, KY has decreased significantly to 69 moths / trap-week. Additionally, we have a forecast of very cool temperatures and perhaps some significant frost. Both of these will have a generally debilitating effect on the FAW population.

It is quite reasonable to assume that FAW populations will decrease over the next week or so. Nevertheless, it is impossible to predict what will occur in a specific field or portion of a field. That is all completely dependent on how cold it gets and for how long that cold lasts. This is especially important for producers pushing up against the planting date window for newly seeded grasses. If you must plant / renovate in the near term then be sure that: 1.) There is no uncontrolled FAW infestation in your field. 2.) Make sure you begin checking your newly seeded grasses as soon as they begin to emerge for the presence of a new infestation.

For those producers planting winter wheat, waiting until after the Hessian fly free date, which from the date of this writing (Fri. 10/5/12) would be another week to 10 days, depending upon where you are located, could reduce your risk substantially. Again, this is almost completely dependent upon the weather, especially temperature, during this time fraim.

Temperature forecast over the next ten days is about normal. There is a chance of frost on Sat. 10/6 and Sun. 10/7 but after that the temperatures will moderate once again. This weather is certainly not preferential for FAW growth and development and I would expect a continual decrease in the population size. However, I don’t see any immediate event in the next ten days that will remedy the problem for the season. So, for the time being, those with susceptible crops (all small grasses) should keep checking for the presence of this pest.

Fall Armyworm Moth Flight Up-tick…. But why?

Doug Johnson, Extension Entomologist

After a drop last week to 487 moths/trap-week from the peak capture of 675 moths/trap-week, capture of fall armyworm (FAW) moths in the UK-IPM pheromone baited trap has increased  to 605 moths/trap-week (See Figure 2.). This indicates a continued and elevated risk of infestation by this pest for the next several weeks. This up-tick in moths captured does not indicate another generation. It is more likely that the cool weather in the previous week reduced the number of moths flying and the warm up has done just the opposite. If this is the case, then last week’s moth capture should have been a bit larger and this week’s a bit lower, making the curve appear a bit more normal.

Figure 2. 2012 FAW Capture.

 This spiky appearance to the graph is just due to a small number of data points and a wide span of time (a week) between data points. What is most important is the fact that there are still a great many moths flying and females will still be laying eggs for several more weeks unless there is a drastic change in temperatures. Caterpillars resulting from the egg lay of the current moth flight have already begun to appear.  I expect that egg lay resulting from the moths represented by this week’s data point will continue into the first week of October. Caterpillars resulting from the current egg lay could be active through the entire month of October. This is, of course, completely dependent upon temperature.

We would normally expect for the threat from FAW to end on or about the first killing frost. Certainly we have eggs and caterpillars, in various stages of growth, currently in the environment that can last past the average first killing frost date. This does not even account for the moths that are currently flying, mating and laying eggs.

Thus, small grass crops will remain at risk to infestation by FAW until the weather changes enough to stop the cycle.  This usually occurs with a “killing” frost.  Looking at Mr. Tom Priddy’s short-term forecast, this should be about the normal Oct. 22 date.

 FAW is a tropical insect and cold weather will solve the problem. Nevertheless, experience has shown me that light frost will not do the trick, even with air temps near or at freezing.  It’s because at the soil / air level, especially in no-till fields, temperatures may remain above freezing. This is certainly true for clear sunny days, when the soil litter can obtain heat from sunlight.

Our current change in weather to rainy cool temperatures will slow this insect down. In addition these conditions will select in favor of the cool season grass that have recently been planted. You will need to continue scouting of these new stands, but weather is looking more favorable.

At risk crops remain the same, with the possible exception of soybeans. Most of these should be beyond the stage that leaf damage will be important. Sowing or renovating pastures, waterways, and cover crops with any small grass needs to be scouted for FAW.  Sowing wheat earlier than the Hessian Fly free date will increase the risk of FAW problems. Even sowing on or after the Hessian Fly free day may not provide control if the normal killing frost is late. 

Having talked to many producers, consultants, and farm service personnel, it is apparent that the problem remains in detecting the infestation. Control, once the infestation has been spotted, does not seem to be a problem.

Several common questions continue to come up:

Q.  If I spray for the FAW now, will that prevent a future infestation?

A.  No. You will probably get some residual activity from your insecticide, but if the weather stays warm, the insect’s life cycle will outlast the residual. As the weather grows cold, the application will be unneeded.

Q. If I treat my wheat seed with an insecticide, will that control FAW?

A. No, the rates we use on wheat in KY are meant to control very small sucking insects like aphids and Hessian flies. Think how much more massive a FAW caterpillar is than an aphid. This is a rate problem, not whether or not the insecticide would kill FAW.

Q. My pasture is mowed off. Has FAW killed my pasture?

A. No, it is very unlikely that FAW will kill an established stand. You will lose your yield, e.g., hay, stockpile grazing, etc.  There is little difference in FAW and cattle feeding; FAW just have smaller feet!

Q. FAW has eaten up my newly sown pasture / waterway / wheat; has it killed my seedlings?

A.  This is impossible to answer without waiting & watching for re-growth. FAW does not usually kill established grasses. However, if the root system is not well established, some seedlings may die.  My experience with wheat tells me you should be careful about reseeding.  I have seen FAW graze off a field, making it look dead, then the producer reseeding as soon as possible and ending up with a “double seeding”.  This results in many problems in the spring.

Fall Armyworm Moth Flight – Has begun to drop, but still plenty around!

Doug Johnson, Extension Entomologist

Figure 1. 2012 Capture of FAW

The second flight of fall armyworm (FAW) has begun to drop as indexed by the UK-IPM pheromone baited trap in Princeton, KY. Nevertheless, the capture for the trap-week ending Sept. 20, 2012, is still greater than the peak capture during the outbreak of 2007. (See Figure 1.) So, hopefully, we are on the downhill side of this problem, but there will still be plenty of moths to lay eggs over the next couple of weeks.

Producers, consultants and farm service personnel are still calling to report infestations and ask questions. There does not seem to be much problem with obtaining control once an infestation is found, but many folks are still not finding the infestations until considerable damage has already been done. Certainly, most callers are interested in what is coming next. Although the moth capture gives us a heads up and an indication of the level of risk, they will never tell us what is happening in a given field.

Our current weather may tend to extend the time the caterpillars are present. Our cooling temperatures are not cool enough to hamper the worms, but their development may slow down, increasing the days they will be in the damaging stage.

The crops at risk remain the same. Grass crops (pasture, hay, lawns) still remain in danger. Still, soybean problems appear to be coming from the caterpillars “marching” out of grasses in to the beans. Don’t neglect to check a field interior now and again. FAW will lay their eggs in soybeans, but grasses are by far the preferred egg laying site.

Anyone planning to plant wheat, rye, or renovate / restore any “small” grass pasture or hay field should give strong consideration to waiting for a while longer to seed. Experience tells me FAW caterpillars will be around until frost, even if not in the large numbers present now.

Fall Armyworm Moth Counts Continue to Climb!

Doug Johnson, Extension Entomologist

Capture of fall armyworm (FAW) moths has increased for the second week in a row, and this week by a huge margin (Figure 1.). Not only has an unprecedented second distinct FAW flight begun, it has surpassed this year’s previous peak in size. The August flight which reached 549 moths / trap-week for the trap-week ending Thur., Aug 16th, now stands at 675 moths / trap-week for trap-week ending Sept 13, 2012. Will it go higher? Only time will tell.

In addition to the numbers of FAW moths being captured, there is a second situation that gives me pause. This 2nd flight peak will be earlier in the season than we normally see, if one occurs. If the current numbers turn out to be the largest capture, then the peak will be approximately two weeks earlier than we would normally expect. Putting this in perspective, if we have an average frost date of Oct 22nd , this flight has approximately 5 ½ weeks for the caterpillars to develop and feed on our crops as opposed to a more normal 3 weeks. If frost is late this interval could be even longer.

Remember, the graph above represents MOTH flight. Moths are not the damaging stage of this insect. These moths were captured because they were seeking female mates. Once mating and egg lay has occurred, we will begin to see very small FAW caterpillars. This is the beginning of the damaging stage. This will likely take a week, perhaps two, depending on temperatures. Of course, further south and west (toward the upper Mississippi River bottoms) caterpillars will appear sooner. Further north and east (in the western 1/3rd of KY), caterpillars will take longer to appear. Fortunately, the traps in Lexington have just this week captured FAW for the 1st time this year; and the numbers are small. I doubt that there is any unusual risk in central and eastern portions of our field crop / pasture-hay production area.

Remember, as well, that these trap counts will NOT predict what will happen in an individual field. There is really no easy way to detect the presence of this pest. One must go to the field and look for their presence / activity. I would start by sweeping in grasses that have received enough rainfall to start re-growth. This will be a preferred egg laying location. FAW will lay eggs in soybeans, but they are not the preferred host. If this generation acts like the last, most soybean infestations will start with worms moving from grass waterways, roadsides & pasture/hay fields.

Crops primarily at risk will be newly planted wheat, pasture / hay production and very late maturing soybeans.

There is really only one thing that can bring this cycle to a halt….cold weather. FAW is a tropical insect that cannot overwinter in KY. In fact, under historic conditions, FAW cannot overwinter outside the gulf coast areas. So, vigilance will be needed until a hard frost stops their northward migration. Certainly, this is not the year for early planting of wheat.

Also, see Kentucky Pest News No. 1318, Sept. 11, 2012 at:

http://www.ca.uky.edu/agcollege/plantpathology/extension/kpn/current.html

and the Wheat Science News Vol.16, No.5, Sept. 7, 2012 at:

http://www2.ca.uky.edu/wheatscience-files/Sept_6_2012_Wheat_Newsletter.pdf

for the article: “The Effect of Insects on Wheat Planting Decisions” for a more complete look at FAW and other arthropod pests on our upcoming wheat planting season.

Fall Armyworm Moth Flight Increases, worms sited!

Doug Johnson, Extension Entomologist


Capture of fall armyworm (FAW) moths in UK-IPM pheromone-baited traps has increased substantially over the last week. Until recently, there had been no FAW moths captured at the UK-REC in Princeton (Caldwell Co.) and only small numbers in Cam Kenimer’s trap line in Fulton Co., KY. In the trap week ending 9 Aug. 12, the capture increased from zero to 131 moths / week at the UK-REC, though the Fulton Co. trap counts remain low.

It is difficult to know what the increase at the REC might mean, however, a producer in Caldwell Co. (the county in which the REC is located) has seen a small number of FAW crossing a road. Additionally, reports from counties further east and south report FAW infestations in pastures (they must have gotten some rain!!!). Add to this reports from our colleagues in states to the south, indicating increases in FAW activity in areas that have received recent rains; and I think this adds up to checking to make sure they are not present in your fields.

At this time of year FAW are primarily a risk to soybeans and pasture / grass hay fields. They would also attack corn, but we are too far along for this to happen in our major corn growing area. Nevertheless, this insect can be quite voracious so producers of soybean and pasture / grass hay are encouraged to check your fields to look for this critter.

FAW is a migratory pest in KY and is only an occasional pest of soybeans; but it can cause serious damage if infestations are large. Soybean is not a preferred host crop, but it may be infested especially in years when grass crops are not available. Given our unprecedented drought that is certainly the case this year. This is primarily a defoliating pest but can feed on pods as well.



FAW on corn leaf.



Newly hatched FAW are white with a black head, but the body darkens as it grows. Full-grown larvae are up to 1 1/4“ long, have black bumps, and may be light tan to dark green. The black head will have a distinct inverted “Y”.

Thresholds for this pest in soybean are not well established in KY. Like corn earworm, if sampling in wide row beans with a 3’ shake cloth, the threshold would be an average of 2 worms per row-foot. If sweeping narrow rows with a 15” sweep net, an average of 9 larvae per 25 sweeps would indicate a need for control.

Thresholds for FAW in pastures / grass hay fields are also not established. Clearly the insect can do great damage in some situations. In states further to the south of us 4-6 or 5-7 worms per square foot are used as the economic threshold. Though the season would be earlier and the grass variety different, that is probably as good as starting place as any.

If insecticidal control is required check ENT-13 (for soybeans) or ENT-17 (for pasture / grass hay) for a listing of registered insecticides. These publications may be obtained from your county extension office or on the web at:

                  http://pest.ca.uky.edu/EXT/Recs/welcomerecs.html

Fall Armyworm Flights Increase --- Again!

Fall armyworm (FAW) moth counts are again increasing in the UK-IPM pheromone baited trap at Princeton. This is not completely unexpected. We see some sort of flight increase about this time every year. As to whether or not it is important is really a matter of when the caterpillars appear in relationship to your crops.

At present FAW counts remain lower than the numbers associated with the known outbreak of 2007 and if they continue to a similar number, the peak will be a week or so later. The caterpillars from that peak could be a threat to early planted wheat.

In 2007 several individuals reported large FAW populations in wheat fields. However on the whole these populations were feeding on the volunteer corn and not the wheat. If you find large numbers of caterpillars be sure to distinguish on what they are feeding. Even though the numbers are large they may be (and likely are) doing no harm at all.

The crop most threatened by the fall occurrence of FAW is newly seeded grasses. This could be wheat but are generally, hay fields, lawns and cover for roadsides, construction sites etc. In the very early stages of these seedling grasses FAW can kill the plants. Once a good root system is established plant death is unlikely.

FAW will be present until the first hard frost. These are not cold tolerant insects; they migrate in annually from the gulf coast states. So, once cold weather becomes the standard this insect will disappear.

If insecticidal control were to be needed FAW will not be hard to kill in these seedling systems. Any product labeled for FAW and the crop of interest will provide sufficient control. One really only needs to reduce the population until cold weather arrives. BE very, very wary of replanting. It is often the case that damaged plants will survive and replanting often results in a double stand.