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Extension Entomology

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Bagworms are Here!

–by Dr. Raymond Cloyd

Bagworms are Here!

Now is the time to start taking action against that “infamous” insect pest known as the bagworm (Thyridopteryx ephemeraeformis). Throughout Kansas, bagworm eggs have hatched and the young caterpillars are feeding on both broadleaf and evergreen trees and shrubs. Bagworms are primarily a pest of conifers but have expanded their host range to include a number of broadleaf plants, including: rose, honeylocust, and flowering plum. Hand-picking small caterpillars (along with their accompanying bag) and placing them into a container of soapy water will kill them directly. This practice, if feasible, will quickly remove populations before they can cause substantial plant damage.

For those not interested in hand-picking, a number of insecticides are labeled for use against bagworms including those with the following active ingredients (trade name in parentheses): acephate (Orthene), Bacillus thuringiensis subsp. kurstaki (Dipel/Thuricide), cyfluthrin (Tempo), lambda-cyhalothrin (Scimitar), trichlorfon (Dylox), indoxacarb (Provaunt), chlorantraniliprole (Acelepryn), and spinosad (Conserve). Many of these active ingredients are commercially available and sold under different trade names or as generic products. However, several insecticides may not be directly available to homeowners. The key to managing bagworms with insecticides is to apply early and frequently enough in order to kill the highly susceptible young caterpillars that are feeding aggressively on plant foliage (Figure 1). Older caterpillars that develop

 

Figure 1. Young Bagworm Feeding On Conifer (Author-Raymond Cloyd, Kansas State University)

 

later in the season (Figure 2) are typically more difficult to kill with insecticides. Furthermore, females feed less as they prepare for reproduction, which reduces their susceptibility to spray applications and any residues. The bacterium Bacillus thuringiensis subsp. kurstaki is active on young caterpillars; however, the active ingredient must be consumed to be effective, so thorough coverage of all plant parts and frequent applications are required. This compound is sensitive to ultra-violet light degradation and rainfall, which reduces residual activity. Spinosad is the active ingredient in a number of homeowner products, including: Borer, Bagworm, Tent Caterpillar and Leafminer Spray; Captain Jack’s DeadBug Brew; and Monterey Garden Insect Spray. These products work by contact and ingestion (stomach poison) although they are most

 

Figure 2. Older Bagworms (Author-Raymond Cloyd, Kansas State University)

 

 

effective when ingested and can be used against older or larger bagworm caterpillars (Figure 3). Cyfluthrin, lambda-cyhalothrin, trichlorfon, chlorantraniliprole, and indoxacarb may be used against both the young and the older caterpillars. However, thorough coverage of all plant parts, especially the tops of trees and shrubs, where bagworms commonly initiate feeding, and frequent applications are required. The reason multiple applications are needed when bagworms are first detected is because young bagworms “blow in” (called ‘ballooning’) from neighboring plants on silken threads. If left unchecked, bagworms can cause significant damage, and ruin the aesthetic quality of plants. In addition, bagworms may actually kill plants, especially newly transplanted small evergreens, since evergreens do not usually produce another flush of growth.

 

Figure 3. Captain Jack’s DeadBug Brew (Author-Raymond Cloyd, Kansas State University)

If you have any questions regarding the management bagworms contact your county horticultural agent, or university-based or state extension entomologist.

 

 

Alfalfa Update

–by Dr. Jeff Whitworth, Dr. Holly Schwarting & JR Ewing

Alfalfa weevil larvae have been hatching throughout north central and south central Kansas for the last couple of weeks.  However, as of 9 March, there doesn’t seem to be much feeding or development yet (Photo1).  There are also a few of these tiny larvae that are dead (Photo2).  Because these larvae are so small and vulnerable it is difficult to determine the cause of death.  At least some of the mortality could be related to weather fluctuations that have reached mid 70’s for several days but also dropping into the mid to low 20’s some nights.

 

 

 

Most of these larvae are so small that they are well enclosed within the plant terminals to the point that they cannot be dislodged by shaking the stems into a bucket, as the most accurate sampling method specifies.  This can definitely cause you to underestimate larval populations.  Probably the easiest solution is to hold off sampling until the middle of next week, if the weather turns cooler as predicted.  There are a few more mature larvae present, along with adult weevils (Photos 3, 4). Adults will probably continue depositing eggs for a few more weeks, thus extending the period of larval hatching.

 

 

There are also a few pea aphids present.  Populations do not seem to be increasing now, and there are lady beetles and parasitoid wasps actively attacking these aphids.  Also, reports of cowpea aphids in south central Kansas bear watching.  These aphids are usually more numerous in warmer summer months.  They can add stress to plants by feeding, but they also produce copious quantities of honeydew which can become covered with sooty mold.  This may further stress alfalfa by interfering with photosynthesis, especially with small plants coming out of winter dormancy and experiencing dry conditions and fluctuating temperatures.

 

 

 

 

Alfalfa weevil status

–Jeff Whitworth, Extension Entomologist: Holly Schwarting, Entomology Research Assoc.; Steve Watson, Agronomy; Mary Knapp, Weather Data Library

Thanks to the unusually warm winter, alfalfa weevil larvae are already present in some areas. Many more will no doubt be hatching in the next few days to weeks. Alfalfa weevils will continue to hatch and larvae continue to develop any time temperatures exceed 48°F.

 

Thus, it looks like larvae will be emerging, and damage progressing, relatively quickly. Whether this warm weather will compress the alfalfa weevil larval feeding so that the period of damage is not as stretched out as usual remains to be seen. There are also lady beetles active in the alfalfa fields, as well as a few pea aphids. The treatment threshold we use for alfalfa weevil insecticide applications is 30-50% infestation, i.e. 1 larva/2-3 stems.

 

Alfalfa weevils are cool-weather insects. Adults lay eggs in alfalfa fields in the fall or even the winter. Most of these eggs survive the winter. Eggs hatch and larvae emerge after accumulating enough degree days or thermal units, normally in early spring. Alfalfa weevil adults also lay eggs in the spring, but in many cases the first larvae to emerge are from eggs that were laid in the fall and overwintered.

 

That said, an anomaly we encountered in the fall of 2016 was a significant infestation of relatively large (2nd and 3rd instar) larvae from mid-November to mid-December. Alfalfa weevils normally overwinter as eggs or adults – not larvae. In the last week we could find none of these more mature larvae, or any pupae. So, hopefully they perished in the colder weather.

Figure 1. Alfalfa weevil larvae collected Nov. 16, 2016 in Dickinson Co.

 

 

Figure 2. Alfalfa weevil larva collected Feb. 22, 2017 in Dickinson Co.

However, as of February 22 we did start finding newly hatched larvae in north central Kansas (Figure 2). Obviously the larvae hatching out now are coming from eggs deposited prior to Jan. 1, 2017. The return of below freezing temperatures may kill those very small, young larvae, especially if they stay in the plant terminals. But, they may survive if they crawl down the plant and get in the plant residue where they will be protected. So, scouting should continue as follows:

 

 

Early scouting for alfalfa weevil

 

Scouting for alfalfa weevil larvae should start after plants break dormancy – which means now. A degree day or thermal unit accumulation system can be used to predict when to initiate scouting. Insect development is controlled by temperature. This can be used to help manage these pests. Weevil activity has been tracked in Kansas for the past few years and has been used to generate recom­mendations (Table 1).

 

 

Table 1. Approximate degree days required for alfalfa weevil development

Degree Days or Thermal Units Stage Importance
25–300 Eggs develop and hatch In stems
301–450 1st and 2nd instars Leaf pinholing – start sampling
450–600 2nd and 3rd instars Defoliation
600–750 3rd and 4th instars Defoliation
750+ Pupa to adult Adults – some feeding – oversummering

 

To calculate a degree day, record the daily high tempera­ture anytime it exceeds 48ºF. For example, if there is only one day in January that the temperature exceeded 48ºF, take that temperature and add the lowest temperature for that day, or 48ºF, whichever is higher. Then divide by 2 to calculate the average tempera­ture for that day. Next, subtract 48ºF.

As an example, say there was one day in January when the high temperature was 60ºF and the low was 35ºF. You would use 48ºF as the default value for the low instead of 35ºF. The calculation in this case would be:

[(60 + 48)/2] – 48 = 54 – 48 = 6 degree days (or weevil development units)

 

The following chart from K-State’s Weather Data Library shows examples of the degree days that have accumulated for the period for Jan. 1 – Feb. 21, 2017 and for last fall:

 

 

Do not be too quick to treat for alfalfa weevil. Wait until the field reaches the treatment threshold. Treating too early is not only unnecessary, it can also have detrimental effects by killing beneficial insects.

 

For more details, see Alfalfa Weevils, K-State publication MF-2999, at your local county Extension office, or http://www.bookstore.ksre.ksu.edu/pubs/MF2999.pdf

 

 

Other early spring alfalfa insects

 

While scouting for alfalfa weevils, you will probably also notice a few pea aphids. These are also early season potential pests. However, in the past few years pea aphids have seemed to be adequately controlled by adult lady beetles. This year seems to be starting that way as well, with a few pea aphids, but also many adult lady beetles present.

Figure 3. Pea aphid on alfalfa leaf.

 

Also, producers need to keep an eye out for army cutworms as there were some reports of army cutworm activity last fall. Army cutworms start feeding again any time temperatures are above 50 degrees F. Armyworms are another potential problem, but probably a little later in the spring.

 

Those are the early season pests which have the most potential for damaging alfalfa prior to the first cutting. For more information on control, see K-State publication MF-809, Alfalfa Insect Management 2017, at: http://www.bookstore.ksre.ksu.edu/pubs/MF809.pdf

Alfalfa and Wheat “Worms”

–by Dr Jeff Whitworth and Dr Holly Schwarting

Wheat and alfalfa fields throughout south central and north central Kansas should be monitored for signs of defoliation.  Many pests can defoliate either crop this time of year, i.e. grasshoppers and flea beetles (usually around borders), and “worms”.  These larvae are most commonly armyworms, fall armyworms, and/or army cutworms.  Identification is important for these “worms” because armyworms and fall armyworms will feed until the temperatures cool into the mid-20’s or they pupate, whichever comes first.

armyworm

fall-armyworm

 

Army cutworms, however, are and have been hatching from eggs deposited by moths as they return from over-summering, probably in Colorado.

army-cutworm

These army cutworm larvae will feed a little this fall, overwinter, then start feeding again in early spring.  So, if the “worms” causing the defoliation now are relatively large, ½ inch or more, they are probably armyworms and/or fall armyworms.

 

We have been hearing about and seeing a mixture of both armyworms and fall armyworms (see pics below).  These small worms start by causing small “windowpanes” in wheat or alfalfa.  No army cutworm infestations have been verified yet.

small-worm-1

small-worm-2

windowpane-feeding_wheat

Flocks of birds in wheat or alfalfa fields in fall or early spring are often indicative of a “worm” infestation as the birds are feeding on the larvae.  Fields with 25-30% of the plants showing “windowpane” feeding need to be monitored frequently as these larvae consume more as they get larger.  Treatment should be applied before stands become threatened.  For more information on treatment thresholds and management options please see the Wheat Insect Management Guide: http://www.bookstore.ksre.ksu.edu/pubs/mf745.pdf

Alfalfa Weevils

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevil larvae were first detected in north central Kansas on 3 March. Mr. Chuck Otte, Ag and Natural Resources Agent, also reported finding small larvae on 5 March in Geary County and Mr. Tom Maxwell, Ag and Natural Resources Agent, also reported finding small larvae and pinprick-sized holes in new alfalfa leaves on 9 March in Saline County. So, ready or not, alfalfa weevil larvae are here and, I would bet, many more will be hatching in the next few days to weeks. Alfalfa weevils will continue to hatch and larvae continue to develop any time temperatures exceed 48°F – and those temperatures have been much more common over the last few weeks than usual. Forecasts for the next 7-10 days also look for warm conditions. Thus, it looks like larvae will be emerging, and damage progressing, relatively quickly. Whether this warm weather will compress the alfalfa weevil larval feeding so that the damage is not as stretched out as usual remains to be seen. There are also many lady beetles present in the alfalfa fields we have checked as well as a few pea aphids. Treatment thresholds we use for alfalfa weevil insecticide applications are 30-50% infestation, i.e. 1 larva/2-3 stems.

For more information on alfalfa weevils, please visit:

http://www.bookstore.ksre.ksu.edu/pubs/mf2999.pdf

eggs in stem

Overwintering alfalfa weevil eggs in stem

alfalfa weevil

Early instar alfalfa weevil larvae

pinprick feeding damage

Pinprick feeding damage

 

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