Kansas State University

search

Extension Entomology

Tag: defoliation

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 Update

–Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevils are still active throughout north central Kansas.  Even fields that had insecticide treatments which were well timed and effective have been having more larval feeding.  These fields need to be treated again as soon as possible as these larvae are still capable of considerable defoliation for the next week or so, especially as we continue to see the fluctuating temperatures.  Remember, these are contact insecticides so coverage is very important.  Also, please pay attention to the pre-harvest interval (PHI) for whatever product you use as many fields are getting close to that first cutting.

AW larva 28 Apr

AW damage 28 Apr

Soybean Pest Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Double cropped soybeans are still very much in the reproductive stages throughout north central Kansas.  Thus, they are still vulnerable to a variety of pests – and pest populations seem to be increasing.  Green cloverworms (see pic) have been feeding on leaves for the past couple of weeks but are starting to cease feeding to begin pupating.  They rarely cause actual yield loss but usually cause concern because of the amount of defoliation they often cause.  While green cloverworms don’t feed on the pods or seeds, adult bean leaf beetles and corn earworm larvae (a.k.a. soybean podworms) do (see pics).  Both species, bean leaf beetles and corn earworms, seem to be increasing throughout south central and north central parts of the state.  The corn earworm larvae will usually feed on the seed within the pod and will only feed for about 10-14 days.  However, bean leaf beetles will continue to feed until harvest, or they disperse to overwintering sites.

green cloverworms

 

Adult BLB

BLB pod feeding

 

CEW pod feeding

 

There are still a few soybean aphid populations in north central Kansas, however there are more winged adults present which probably means they are mostly finished feeding and preparing to migrate to overwintering sites (they probably do not overwinter successfully in Kansas – we hope).

We have received several calls this week relative to these “interesting little green worms” in soybeans.  These are silver spotted skipper larvae and will feed on leaves but should not defoliate enough, on a field-wide basis, to impact yield.

silver spotted skipper

 

Alfalfa Pests

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa continues to cause concern throughout north central and south central Kansas due to defoliation by “worms”.  There seems to be a combination of garden (alfalfa) webworms, fall armyworms, armyworms, yellow striped armyworms, etc. feeding on the foliage.  Generally, if the alfalfa is within 10 days of swathing or if the “worms” are mature, (maybe ½ inch long for webworms which are naturally smaller than the others; or ¾ inch long for the others), it probably is best to just cut the field and not treat.  If treatment is justified, please pay attention to the pre harvest interval (PHI) for whatever product is used.  These worms won’t feed on the foliage after it is cut, but they may feed under the windrows holding back the regrowth and causing striping in these fields.  For more information on these insects and their control options, as well as PHI’s, please visit: http://www.bookstore.ksre.ksu.edu/pubs/MF809.PDF

Old “Defoliated” Friends Revisited

–by Dr. Bob Bauernfeind

One of my favorite most succinct introductory slides simply says:

#1

While attentiveness, care and pampering are especially important in the early years after newly transplanted trees first become “family members”, there does come a point-in-time when they become “Big Boys and Girls”.  Look at mature trees lining city streets, in park and recreation areas and in the countryside —- all thriving on their own.  This despite having to contend with different insect pests.

Most alarming for homeowners is the compromised appearance of trees when foliar feeding species come-to-town.  The situation is such that their presence first becomes apparent (after-the-fact) when the offending species are approaching the end of their feeding phase-of-development — a time at which they are of such size that they ravenously feed on and rapidly deplete available foliage thus drawing attention to their presence.

Defoliations may vary in intensity from a few bare branches to the entire canopy.  As alarming as a complete defoliation might appear, it should be regarded as but a cosmetic issue.  Probably more objectionable is the visible and audible “rain-of-frass”, as well as streams of descended mature larvae roaming about in search of pupation sites.  Early-season defoliations are of temporary duration because trees rapidly produce a new flush of growth restoring normalcy.  On the other hand, new foliage production is scant late in the season at a time when leaf abscission is imminent after the cessation of seasonal photosynthetic activities.  Come springtime, trees again will fully leaf out — seemingly none the worse-for-wear.

People may ask, “What did I do wrong?  Couldn’t I have prevented this?”, to which I would respond, “You did nothing wrong.  Outbreaks are unpredictable!”. As mentioned earlier, a person is unaware of the presence of specific pests which (as “wee ones”) scrape and nibble away not producing any noticeable foliar damage to give away their presence.

Come the questions, (1) “Well, once I notice the damage, shouldn’t I spray?”, to which there is not an absolute response.  Consider the size (and possibly) number of trees, and the unlikely capability of an individual to apply/achieve thorough spray coverage. (2)  “Well couldn’t I hire a service to spray for me?”, to which the response might be, “If the service provider is “booked” and unable to get to your tree(s) in a timely fashion, by the time they do arrive, caterpillars/larvae may have already completed and ceased feeding —- little point in spraying at that point.

Balancing the cost of hiring a spray service against what-is-to-be-gained by spraying at a time that tree appearance has already been compromised may make the decision to be to simply allow the situation to run its course.

“Is there a need to “kill-them-now” to prevent a repeat?”  While this seems to be a logical thought, in reality, we really have little control over future events.  Nature sort of has its own checks-and-balances.  Whether unfavorable environmental conditions or biological entities (diseases, predators, parasites) reduce or eliminate potential future “seed” for pest populations, or, if pests themselves naturally disperse, one may never again experience a repeat situation.  Individuals who have experienced defoliations and who have seen their trees recover are convinced of the need to let nature run-its-course.                            

Defoliations:  before and after

Greenstriped Mapleworms on silver maples

#2

 

Yellownecked Caterpillars on oak 

#3

 

             Walnut Caterpillars on black walnut (red arrow = limb pruned out in 2011)

#4

 

Foliar Dessication:  Before and After

Some foliar-feeders are relatively small in size and therefore incapable of skelotinizing and defoliating tree hosts.  Rather, their feeding activities are reduced to nibbling/consuming the epidermal tissues of leaves.  Both the upper and lower epidermis (with their thicker “waxy” cuticles) protect the more delicate inbetween high-in-moisture-content internal cellular layers. Deprived of their protective outer layer, leaf dessication leads to leaf death — the resultant being the unsightly browned/burnt appearance of trees.

Mimosa Webworms on honey locust

#5

 

Elm Leaf Beetles on elm

#6

 

In this incidence, I do not have a current image of the trees above.  They no longer exist.  However, not due to to the depredations of elm leaf beetles.  Rather, simply, they were in the way of progress.  A highway expansion project necessitated their removal.  They were no match against “man”.  Soooo painful to watch trees ripped out roots-and-all by powerful excavating equipment.  But again, the lesson being that the asthetically unacceptable foliar appearances resulting from insect activities are but an occasional temporary fleeting occurrences …. leading to the following:

On a return trip to Manhattan Monday, I noted the presence of fall webworms along the roadway — sometimes one or two in an occasional tree here and there, or  (in this instance) numerous web masses.

#8

 

#7

 

These did not develop “overnight”  Judging by their size, these colonies likely were initiated 4-5 weeks earlier.  Again under the banner of defoliators, people may worry about the impact of feeding depredations.  Minimal!  Probably a more verbally expressed concern is the unsightlyness created by the webbing, as well  “creepy” clumps of caterpillars within.

#9

 

A common recommendation is to prune out webbed branches.  One must consider the accessibility of web masses — those beyond reach simply allowed to remain.

#10

Pruning might be doable if just a branch or two —- but possibly unacceptable and disfiguring when trees are heavily infested with web masses.

If within reach, consider an implement (of sorts) to “rake out”/remove  webbing.  And what implement could be more handy (yes, pun intended) than one’s own hand.  There is no need to fear the dry webbing and/or dried fecal deposits and squirmy caterpillers within.  As webbing is removed, also removed will be the objectionable dead/dry foliage and the fallwebworms.  Simply dispose of the gathered material.  All that is left behind is the leafless (but still living) branch and it’s intact buds which will produce the ensuing year’s foliage.

#11

 

 

And Still Talking About Ash Trees – Brownheaded Ash Sawflies

—by Dr. Bob Bauernfeind

Based on reports posted by Department of Entomology Diagnostician regarding her having received specimens of adult brownheaded ash sawfly, I went out to a site where ash trees have been heavily infested the past couple of years. And, they are back. Though from a distance all appears normal, upon closer look, “pinhole feeding” is underway. By enlarging the image, the still-wee-larvae responsible for the “nibble holes” can be easily seen.

To treat or no-to-treat becomes an individual’s decision. Should trees become defoliated, they will rapidly recover, producing a flush of new foliage.

Brownheaded Ash Sawflies

Alfalfa – Weevils and Aphids

—by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevils continue to be very active in north central Kansas. The recent cooler weather has slowed down development a little but they are still feeding. We determined development from larvae collected on 20 and 22 April. Here is what the population breakdown looks like:

20 AprilNo. larvae   23 April No. larvae
12 1st Instars 4
25 2nd Instars 16
15 3rd Instars 30
   numerous Pupae numerous

alfalfa weevil

So what does this mean? Alfalfa weevil larval feeding will continue for another 7-10 days, depending on the weather. Egg hatch and consequent larval feeding has been going on since 13 March in north central KS. Insecticides applied since that time have provided adequate protection, for the most part.

field trial

This photo shows KSU chemical efficacy trials with many different products being tested, and the obvious untreated plots plus the border around the plots. The rest of the field was treated with Stallion® by MKC in Abilene, KS and, as illustrated here seemed to work relatively well with 1 application. Remember, feeding will continue for at least another week and therefore treatment (or re-treatment) may still be appropriate.

Alfalfa aphids, mainly pea aphids, are becoming more numerous throughout north central Kansas. Treating for alfalfa weevils probably pretty much decimated the natural enemies/beneficials and they will not repopulate as quickly as the aphids migrate in to infest fields.

 

Subscribe

Follow this blog

Get every new post delivered right to your inbox.