Pecan nut casebearer arrives late

  

    Every year I scout my pecan orchard for pecan nut casebearer damage to young nuts. Damage from this insect is easy to recognize by the pile of insect frass at the base of a nut and the silken threads that connect the damaged nut to the pedicel (photo at right). Left unchecked, a single pecan nut casebearer larvae will destroy 3 to 4 nuts in a cluster. 

    The first evidence of casebearer nut damage this year occurred a week later than normal. However, now that this first summer generation has started, the above average temperatures predicted for the next 10 days will cause the casebearer population to expand rapidly. I found the first damaged cluster on Wednesday June 16th and started spraying early Thursday morning.

    When spraying during a heat wave, I try to start at first light and quit around 11:00 am. Once temperatures start to approach 90 degrees F spray droplets can evaporate before they ever hit the foliage. 

Pollinated flowers vs. Fertilized Nuts

        Long before I found the first casebearer damaged nut, I knew things were running late by watching the developing nuts. When a female flower becomes pollinated the stigma becomes dry and black, however, it takes a little time for the pollen tube to grow down into the nut and become united with the ovule. Once the nut is fertilized, it starts to swell and the sepals (leaf like projections just below the stigma) will point straight up. This year, nuts didn't show the normal signs of fertilization until June 14th. A day after most sepals were pointing up, I found my first casebearer. Over the years, this relationship between nut development and the first sign of casebearer activity has been very consistent.  In fact, I now use observations of nut development as the primary method for timing a pesticide application to control casebearer.

Scouting for pecan pests

    Every year I have inspected hundreds of pecan nut clusters in early June to determine the date of first significant nut entry by pecan nut casebearer. Casebearer has been a perennial insect pest that can destroy an entire nut clusters shortly after pollination. However, I have searched all month and could not find a single nut damaged by the feeding of a pecan nut casebearer larva (photo above). In fact, my trees look clean of all insect problems at this point (no webworms or walnut caterpillar)

   As part of my regular scouting routine, I always visit some large native pecan trees in a cemetery just across the road from my home. These trees are never sprayed and provide me with an opportunity to see pests develop unchecked during the growing season.

  

   This past May was cooler and wetter than normal and by the first week in June I found pecan scab infections on native pecan tree leaves (photo at left).   The black spots that dot the leaflets and leaf rachis seem like a minor infection but theses scab lesions will provide provide enough spores to cover young developing nuts with scab lesions. Scab infection early in the nut expansion phase (late June - early July)has the potential to causes serious yield loss.

    Since last Saturday (26 June 2021),  we have entered an extended rainy period that promises to provide ideal conditions for the spread of pecan scab (rain every day for 6-7 days). In my orchard, I gave up waiting for pecan nut casebearer scab and applied a fungicide for disease control back on June 12th. These trees will need a second fungicide spray as soon as I can get in the field and apply it. I'll spray all my trees, even scab resistant cultivars like Kanza. In the past, I have found that the secondary diseases that cause early defoliation usually get their start during mid summer wet periods. By keeping healthy leaves all season long, I canl ensure a good return crop in 2022.    

Pecan Nut Casebearer arrives late

    I've been scouting my orchard every other day for the past 10 days watching for the first signs of pecan nut casebearer activity. After inspecting over 100 nut clusters, I found a single casebearer egg and even one nut damaged by a casebearer larva.

    Pecan nut casebearer eggs are difficult to spot in the field because of their small size. However, when I do find them, they are always placed near the tip of the nut just below one of the four sepals. In the photo at right, the red arrow points to a single white casebearer egg. When the egg hatches, the emerging larva will crawl to the base of the nut and start chewing its way into the nut's interior. 

   The damage caused by casebearer feeding is very distinctive. In the photo at left, the yellow arrow points to a pile of insect frass at the base of a nut. As the larva tunnels into the nut it pushes all its excrement out the entrance hole creating a pile of brown waste between the nut and the peduncle. In addition, the larva ties the nut onto the stem with numerous fine silken threads. This prevents the nut from falling off the tree before the larva can move to other nuts in the cluster. A single casebearer larva will destroy 3 to 4 nuts while completing its life cycle.

 

  I'll be making a pesticide application aimed at controlling casebearer on Monday June 15. That's 5 days later than my average spray date of June 10th.

A bad case of pecan leaf phylloxera

    I have been scouting pecan trees for signs of pecan nut casebearer activity and have made a couple of important observations. I haven't seen any casebearer as of today, June 7th and every native pecan I've looked at is loaded with nuts. It looks like 2019 will be a year of over-cropping and it may beneficial to skip the casebearer spray and to allow casebearer to help thin the nut crop.

    During my rounds of looking at wild pecan trees for casebearer activity, I came across a tree with the worst case of pecan leaf phylloxera that I have seen in a very long time (photo at right). The pecan leaf phylloxera is an aphid-like insect that causes the tree to form galls around these plant sap-feeding insects. Note that the galls are confined to the leaf blades.
   

    Once the galls are formed, there are no control measures for this pest. Later this summer, all seriously gall infested leaves fill drop from the tree. 
    Insecticide treatments are effective for control of this pest but must be applied before galls form over the insect. For pecan leaf phylloxera, a single insecticide application made at leaf burst will control this pest. Mark infested trees this summer and plan on spraying those trees next spring.
    You can read more about the pecan leaf phylloxera in a previous post.

First nut entry by pecan nut casebearer

    When we scouted our trees this morning we found 3 pecan clusters infested with pecan nut casebearer larvae (3 out of 300 clusters inspected). Casebearer damage is easy to spot. The larva always enters at the base of the nut and creates a pile of brown frass in the narrow axis between the pedicel and nut (photo at right).
   We plan to spray our grove over the next few days adding an insecticide for casebearer control and a fungicide for scab control. The weather forecast for this weekend is hot and dry. To get the best spray coverage of the pecan foliage, I'll start spraying at daybreak and quit when temperatures top 80 degrees (F).

  

This is why scouting for pests is so important

   For the past week, I've been expecting to see damage from pecan nut casebearer start to take off.  In fact, I have my sprayer filled with water and ready to go. The problem is, we can't find enough casebearer damage to justify spraying
   Three times per week we scout our orchard for signs of insect damage (photo at right). The results of each of our scouting runs can be found by clicking on the Pecan Nut Casebearer tab (The tab is located just below below this blog's header). We have yet to find more than 1% damage.
   In a normal year, we apply a fungicide to control pecan scab at the same time we apply an insecticide to control casebearer. Its now mid-June and we still haven't applied any pest control chemicals. So starting next Monday (June 19th) we are going to start spraying a fungicide to protect our pecans from scab.  If the casebearer population stays low, we won't be including an insecticide with this spray.
   In late June, we might see fall webworm or walnut caterpillar move into the grove. If these insects appear, we will include an insecticide in the spray tank when we make our second scab spray (around July 1).

Spraying for pecan nut casebearer

    We began spraying for pecan nut casebearer this morning (photo at right). After discovering 1% cluster damage yesterday and checking the weather forecast for the next week, I decided we better get started.
    Temperatures for today (June 9) thru Sunday ( June 12) are predicted to reach the low 90's each afternoon. Insect development is stimulated by warm temperatures so this year's casebearer infestation should build quickly. In addition, rain is forecast for early next week so I added a fungicide to this spray to provide protection against infection by pecan scab.
    For casebearer control, I decided to use up some of the insecticides we had on hand. Part of the orchard will be sprayed with Eraser (Chloropyrifos) and part with Warrior II (lambda-Cyhalothrin). For a fungicide, we applied Quilt which has two active ingredients: propiconazole and azoxystrobin. We also added a non-ionic surfactant to the spray tank.
   We like to get started spraying as early in the morning as possible. At this time of day, the winds are calm and the humidity is high. Both of these factors contribute getting better coverage of the leaves throughout the entire tree canopy. You can see in the photo above that early morning spraying creates a mist that swirls through the canopy covering both upper and lower portions of the leaves. 

First evidence of pecan nut casebearer activity

   Every spring we monitor the development of the first summer generation of pecan nut casebearer. This morning I looked at 300 nut clusters in our native grove and found a single nut that displayed the tell-tale signs of casebearer feeding (photo at right). Judging from the light tan color of the frass pile, the lowest nut in the cluster was attached very recently. The frass pile will turn dark brown as it sits exposed to the weather. Look carefully and you can see fine silken threads that extend from the frass pile to the the peduncle of the nut cluster. These threads serve to keep the nut attached to the tree while the insect feeds inside.
    I like to wait until we record 2 to 3 percent damage before applying an insecticide to control this pest. With only a single damaged nut found, its still too early to spray. Keep up to date on our latest casebearer observations by clicking on the casebearer tab above. We scout our trees every Monday, Wednesday, and Friday

Pecan nut casebearer's winter home

     Mid-winter is not the usual time to be thinking about pecan nut casebearer, an early-summer, nut-feeding insect pest (photo at right). But if you have been a regular reader of this blog, you will know that we spend a lot of time monitoring this insect during the months of May and June. I have even placed a special tab at the top of this blog so you can follow the progress of moth flight and first significant nut entry each summer. But have you ever wondered where and how the pecan nut casebearer overwinters?

    Yesterday, I was looking at a pecan twig under a dissecting microscope and I found the casebearer's winter home. Nestled at the base of a pecan bud was a small partially grown caterpillar wrapped in a protective case called a hibernaculum. In the photo at left, note how small the hibernaculum is compared to the dormant pecan bud and leaf scar. No wonder it is nearly impossible to spot hibernacula in the field.
    The larva will emerge from its winter home shortly after budbreak and begin feeding on the expanding new pecan shoot. Once the larva grows to full size it will pupate in the stem of the damaged shoot. An adult moth emerges from the pupal case in May and is part of the generation of moths we catch in pheromone traps. This generation of moths eventually lay eggs on nut clusters in early June.

Following the evidence: Pecan nut casebearer damage development

    This spring I've put together a separate page on this website to keep you posted on pecan nut casebearer activity (see tab above). But today, I wanted to show how the activity of casebearer larvae can be traced by careful observation of frass piles (frass=insect manure).
    As casebearer larvae feed on the inside of pecans, they push all their frass outside into a nice neat pile. In the photo above, the red arrow marked "A" points to a pile of dark, granular frass created by a casebearer feeding inside that nut.
   But that's not the entire story. If you look carefully, the red arrow marked "B" points to a small frass pile at the base of a bud. When casebearer larvae first hatch, they often feed on buds before moving onto the nut cluster. Note that the frass pile at the base of the bud is much smaller than the pile formed at the base of the nut. The smaller pile was created by a smaller, first-instar larvae. By the time the insect moved into the nut, the larvae had grown larger and was eating far more plant material.

    The photo at left is a close up of the frass pile found on the nut seen in the photo above. There are two things to notice. First, fine strands of white webbing are strung between the nut and the pedicel. This webbing serves to prevent the damaged nut from dropping off the tree,  keeping the insect within the tree's canopy.
   Next, notice that there are two different colors of insect frass in the pile. The lighter colored frass was just expelled from the nut betraying the fact that there is still an actively feeding larvae inside the nut.

    The photo at right shows a clear evidence trail of how a single casebearer larvae destroyed three nuts in this cluster. The larvae started at the base of the cluster. At the time of first nut entry, the basal nut was still small and could not provide enough nourishment for the growing larvae.  Once the caterpillar ran out of food in the first nut its moved onto the next nut up the stem. This second nut had grown slightly larger but still didn't meet all the nutritional needs of casebearer. So the larvae moved onto a third nut.
   Looking at the piles of frass at the base of each nut, notice that the size of the granules changes from nut to nut. The first nut attacked has the smallest frass granules indicating a small larvae had fed inside the nut. In sharp contrast, the frass pile at the base of the third nut has large granules that are light in color. Just by looking at the frass, I can tell a full sized larvae is actively feeding on this nut and will probably pupate inside.
    The photo above also demonstrates how webbing, spun by the larvae, holds the nut onto the tree even after a damaged nut aborts. The lowest nut in the cluster is literally holding on by a thread. At a later date, the last nut damaged by casebearer will also abort from the tree. Again, insect webbing will hold this nut in the tree but this time the nut will contain a pupal case. By not dropping to the ground, the survival of both pupae and the emerging adult moths is increased.

Spraying for scab and casebearer

    With all the rain we have received over the past couple of weeks, my concern for keeping  pecan scab under control has grown.  So when the weatherman gave us a break from the rain for the next 3 days, I thought it best to start applying a fungicide.  "But what about casebearer control?',  you might ask.
    For the past week, we have been monitoring pecan nut casebearer trying to determine the best spray date for insect control. All last week, this year's casebearer population was stuck at 1% damage.  But today casebearer damage levels started to trend upwards, as we recorded 2.67% cluster damage. So it turns out that today is also a good day to start insecticide applications.
    The weather for spraying pecan trees over the next few days will be far from perfect. A combination of high winds and high temperatures will make the effective application of pesticides almost impossible. To make sure we get good spray coverage of our trees, we will limit our spray operation from the morning's first light until the winds pick up mid morning.
    For this first spray of the 2014 season, we will apply Lorsban insecticide and Stratego fungicide. The best tip I can give you on spraying pecan trees is to slow down your tractor speed and make sure you get complete coverage over the entire canopy. Complete coverage is especially vital for getting  fungicides to work properly.

Casebearer activity slowed by cool, wet weather

Nut cluster damaged by casebearer larvae

   If you have been following our casebearer counts (posted under the special "Pecan Nut Casebearer" tab above), you will notice that damage by first summer generation larvae has remained at 1% cluster damage all week. Will damage levels ever increase above 1% this year? If so, when?
   Insect activity is greatly influenced by the weather. Casebearer moths are nocturnal creatures. When overnight temps are low (in the 50's and lower) or when rain showers occur during the evening hours, adult activity is greatly reduced. If you look at our moth catch data, you'll find that the numbers bounce up and down. We always caught high numbers of moths following a period of warm, clear nights.
   The long range forecast, predicts a return to summer like temperature during the second half of next week. That's when I predict we will start seeing a rapid rise in casebearer damage. In the mean time, we will continue scouting.  

First nut entry by pecan nut casebearer in 2014

    We spotted the very first evidence of pecan nut casebearer larvae feeding on pecan nuts today. Casebearer larvae typically bore into the base of a nut leaving a pile of frass and some fine webbing that attaches the nut to the pedicel (photo at right). A single larvae usually requires 3 nuts to complete its life cycle.
   It looks like we will probably need to make an insecticide treatment to control this pest sometime towards the end of the week. Timing will depend on the weather and how fast the damage level increases. 
   You can follow the development of this year's casebearer population at the Pecan Experiment Field by clicking of the "Pecan Nut Casbearer" tab above. 

Pheromone traps for monitoring pecan nut casebearer

   We use a rope and pulley system to install pecan nut casebearer traps up into the canopy of our pecan trees (photo at right). Since these insects spend their entire life cycle in pecan trees, we need to place the traps in a location where casebearers are flying. Male casebearer moths enter our traps when they detect the female sex pheromone being released from a small rubber septum placed inside the trap. The moth then gets stuck in the sticky goo spread on the inside floor of the trap (see photo below).

    We usually capture our first male moths during the middle of the pollination season and we found one moth last night. In the photo at left, the casebearer moth is pointed out by a red arrow. This arrow also points to the ridge of scales on the wings that helps to identify this small, gray moth as a pecan nut casebearer. You can also see the grey rubber septum that emits the female sex pheromone.  The rubber septum is roughly 3/4 inch in length and the casebearer moth is 3/8 inch long.

Casebearer damage near peak

    Here's the figures on this year's pecan nut casebearer population in an unsprayed native pecan grove at the Pecan Experiment Field (above). As of today, 10.7% of nut clusters in this orchard have been damaged by casebearer. I don't expect the damage level to go much higher at this point, probably leveling off at around 12% damage for the year.

Watching casebearer larvae work

   

Two nuts have been destroyed by a single casebearer larva

    Pecan nut casebearer larvae continue to feed on pecan nut clusters. This morning, we found 5.3% of nut clusters infested with a casebearer larva in untreated plots. The larvae are starting to move into a second nut in the cluster (photo above right).
    If you look carefully at the photo, the full story of how these pecans were destroyed is revealed.  The smaller, brownish nut at the bottom of the photo was attacked first. As soon as this nut was damaged by the casebearer larva, the nut stopped enlarging and began the process of aborting from the tree. By the time this photo was taken, the damaged nut had formed an abscission layer and had separated from the stem.  With great foresight, the casebearer larva wisely attaches the nut to the tree with several strands of white silk. This prevents the nut from falling to the ground and allows the larva to remain in the tree. Since one pecan is not enough to satisfy all nutritional needs of a growing caterpillar, the casebearer larva moved to the lowest nut in the cluster and began tunneling inside. You can tell that the caterpillar had grown larger in size by the time it got to the second nut because the pile of frass (i.e. insect poop) at the base of the nut is larger and more coarse.

    There are times when a casebearer larva never finishes it meal of pecans. In the photo at left, two nut were destroyed by a casebearer. Judging from the size of these damaged pecans, the larva should have attacked the third and final nut in the cluster. However, it looks like an insect predator might have gotten to the casebearer larva before it could attack the third nut. During my survey this morning, I spotted several wheel bugs actively searching the pecan canopies for insect prey. Casebearer for breakfast--what a lucky wheel bug!

Casebearer damage at 3.3%

   

The entire nut cluster can be destroyed by a single casebearer larvae

    We scouted our "no-spray" native pecan grove today and found 3.3% of the nut clusters infested by pecan nut casebearer larvae. The warm, dry weather we are currently experiencing has caused insect development to move quickly. All northern pecan producers should be carefully scouting their orchards at this time. The window for effective economic control of this pest is rapidly drawing to a close.

Casebearer update 19 June 2013

 

    We found 1% nut entry by first summer generation pecan nut casebearer larvae this morning.
We captured 2 additional moths in all 5 of our pheromone traps. I looked at the weather forecast early this morning and discovered we would have good conditions for spraying today (low wind, temperatures below 85 and little chance of rain). Besides applying an insecticide we also made our first application of a fungicide to control pecan scab.

Casebearer update 16 June 2013

    Today we found the very first pecan damaged by a pecan nut casebearer larvae. If you look carefully at photo at left, you will see a small pile of insect frass near the base of the nut on the left side of the cluster. Pecan nut casebearer larvae always enter on the upper side of a nut close to the point where the nut is attached to the peduncle. When scouting for PNC damage look for the pile of frass along with some fine white webbing the insect strings between nut and peduncle.
  

     In addition, we are still catching moths in our pheromone traps (data below). Based on today's findings we are planning to spray our pecan trees for PNC and pecan scab starting on Wednesday the 18th of June.

Casebearer Update 14 June 2013

 

    We scouted our pecan trees for signs of casebearer (PNC) activity again today. As of today, we have yet to find nut entry by any first generation larvae. We are still catching male moths in pheromone traps (data above) but the numbers seem to be dropping off. Pecan nuts are just starting to show signs of enlargement indicating that the PNC egg laying period is rapidly approaching. At this point, we are preparing our sprayers to apply this year's first spray sometime next week. Monday's scouting report should help pinpoint an optimum spray date.