Spraying for weevil control

     Its been a relatively dry summer this year so I decided to delay making my first weevil spray until after we got a good soaking rain. Well, during the early morning hours of August 21st we received our first good rain (0.96 inches) in several weeks. This rainfall event should allow pecan weevils to emerge from their underground cells and find their way to the nearest pecan nut cluster. The photo above shows both a female (longer snout) and male adult weevils.

   The first order of business for these insects is to move to a pecan nut cluster in the hope of finding a weevil of the opposite sex. After mating, the female will start puncturing pecans to discover if the nuts are suitable for egg laying. She will not deposit eggs inside the nut until the kernel inside has entered the gel stage.

   

    I cut several pecans open today and found that even early-ripening cultivars were still in the water stage (photo at left). As I mentioned in my previous post, pecan kernel development is much later than normal the year due to unseasonably cool Spring temperatures.

    The combination of a concentrated weevil emergence due a triggering rainfall event and a nut crop not ready for weevil oviposition means that weevils will just keep probing nuts until kernels start to firm up inside the shell. A pecan that gets punctured during the water stage will drop off the tree (both weevils and stink bugs cause nut drop).

    To prevent a possible significant amount of weevil induced nut drop, I decided to spray my orchard with and insecticide. In spraying the orchard, I started at dawn this  morning (22 Aug 2021) and quit around 10:30 am as air temperatures climbed above 85 degrees F. The forecast for tomorrow is afternoon temperatures in the mid 90's (F), so I'll be getting up early tomorrow morning to finish the job. 

    With cooler temperatures and high humidity, early morning is the best time for spraying. The water droplets that blow out of the sprayer stay airborne longer and do a better job at coating all the surfaces of the pecan tree's canopy. For this weevil spray I used Warrior II insecticide. I'll probably spray again in 10 to 14 days depending on soil conditions and rainfall patterns.    

 

Spraying to control pecan weevil

      It has been hot and dry most of the summer in extreme SE Kansas. The lack of rainfall has effected nut size (smaller nuts than normal) and has delayed the emergence of pecan weevil.

    During most years pecan weevil adults emerge from the soil starting in early August (male and female weevils pictured above). However, during periods of drought, soil hardness prevents adult weevils from tunneling out of their subterranean pupal cases.

   We finally received 3/4 inch of rain last Saturday which should have been just enough moisture to soften the ground and allow weevil emergence. I was all ready to start up the sprayer on Sunday, but then I looked at the weather forecast. More significant showers were predicted for my area on Monday, Tuesday, and Wednesday. To avoid wasting insecticide by spraying one day and getting it washed off the next, I decided to wait until the danger of heavy rain was past. 

    Turns out, we never did get any heavy rainfall earlier this week, just plenty of cloud cover and fog. So I decided to make an application of Sevin insecticide today.  My orchard does not have a history of heavy weevil infestation but I have a neighbor that has un-managed native trees. When and if I get weevil damage, it is usually a result of weevils migrating into my grove from the adjacent property. Hopefully, today's spraying will keep visiting weevils from getting established in my grove.

Making my last weevil spray

    It has been a difficult year to make decisions on timing insecticide treatments to fight pecan weevil. During the month of August we received 9.9 inches of rain, with rain falling 16 out of the 31 days in the month. However, I did manage to get the grove sprayed 3 times in August with my last spray applied August 31. 
   With plentiful rainfall this month, all the farm ponds in the area are full. That a good thing because, I use pond water to fill my sprayer tank (photo at right).  However, the excessive rainfall also meant that every time I sprayed for weevil this year,  I had pull my spray-rig over water saturated soil. I'm now very glad I spent the extra money to buy a 4-wheel drive tractor.

Spraying for pecan weevil

   I was up at 4:30 am this morning to spray my pecan orchard before the sun came up and it got too hot to achieve good spray coverage. My aim was to make sure pecan weevils weren't able to lay eggs in any of the pecans.  Pecan weevils (pictured above right) are "snout" beetles that can puncture the shuck and shell of a pecan to lay eggs inside the nut. The result are legless worms that devour the entire nut kernel.

    A key behavior of pecan weevil females is that will not start laying eggs until the nuts enter what is commonly known as the gel stage. The photo at left shows a 'Gardner' pecan that I cut open this morning. The kernel cavity is still largely filled with liquid endosperm but, just inside the kernel seed coat, a gelatinous layer of pecan kernel has begun to form. This translucent tissue is what we call the gel stage.
    With the soil moisture at near capacity, I  knew weevils had already begun to emerge and  would be ready to start laying eggs. Today promised to be sunny but very hot, so getting an early start on spraying was critical. I like to finish spraying for the day before the temperatures rise above 85 degrees F.
    When I first started spraying it was still dark. With all the tractor lights on, I could see just enough to navigate down the rows of my pecan breeding plot. However, spraying in the early morning hours has its advantages. The humidity is highest at this time of day which allows the mist created by the sprayer to travel further though the air. Before long, the first hints of dawn allowed me keep spraying without fear of getting lost in a maze of tree trunks.
   In 10 to 14 days, I'll need to spray again for late emerging weevils.
    

Making a pecan weevil spray

    After a week of showers it was time for me to make an insecticide application for pecan weevil. So, I attached my sprayer, put the tractor in 4-wheel-drive, and slogged my way over saturated ground to apply Warrior II insecticide to protect my nut crop (photo at right). It has been 12 days and nine inches of rain since I last sprayed (mainly for stinkbugs). This time my objective was to kill all weevils in the grove before they can lay eggs inside the nuts.
   I'll need to wait to see how things go during the last part of August and early September before deciding whether or not to make a second weevil spray in a few weeks.

Spraying for stinkbugs and weevils

   Today, I made an application of Warrior 2 insecticide to my pecan grove (photo at right).  This insecticide application was made primarily to keep stink bugs in check and to kill any early emerging pecan weevils that might have migrated into my grove from the neighbor's un-managed native pecan grove.
    At this point in the growing season, my Kanza nuts are approaching full water stage. It is too early for weevils to lay eggs but both stink bug and weevil feeding can cause serious nut drop. With our below average nut set this year, I definitely want to prevent any potential nut loss.

    My grove was established by grafting volunteer seedlings to cultivars such as Kanza, Hark, and Lakota. As a consequence, the orchard looks like a native grove with trees growing at random locations. Since the trees are not planted in rows one question often comes up: "How do you keep track of which trees have been sprayed?".  Since I use a Savage sprayer, I take into account that it is most efficient to spray in one direction at a time. I usually spray to the right side of the tractor (as pictured above). I start on the edge of the grove and spray inwards. When I get to the end of the field. I turn the tractor so that I'm 40-50 feet away from my initial path through the orchard.  Still spraying towards the right side of the tractor, I end up spraying the other side of the trees sprayed during my initial pass. When I weave through the orchard, I keep track of where I am by looking for the tire impressions I made in the tall, wet grass 40-50 feet to my right.  Once I get to the other end of the field, I turn around and retrace the tire marks I just made (the second pass through the orchard). Driving in the opposite direction on the same path and spraying to the right means I'll be spraying trees not yet receiving insecticide treatment. In the photo at left, look at the ground-cover  carefully, you can see bent over blades of grass that mark the trail I took through the grove.  I know its hard to see in the photo, but from my tractor seat I can see it clearly. By sticking to this travel pattern, I'm certain to cover every tree n the grove.
     A couple more notes on spraying. I like to spray early in the morning. The high humidity and calm winds at that time of day helps the sprayer deliver the pesticide to the entire canopy. Since I'm using a late model tractor to spray the grove, I have a digital reading of ground speed. With my 12 speed tractor, I drive in 3rd gear and average 1.9 miles per hour.  I operate the fan at full throttle.      

Getting ready to battle pecan weevils

    When the calendar turns to August, I immediately think about controlling pecan weevils. If the soil contains enough moisture, male weevils  will start emerging in late July. By early August, females will appear. Both sexes migrate to pecan nut clusters in the hopes of finding a suitable mate (photo above).

    During this courtship phase, male and female weevils will feed on nuts causing nuts, that are still in the water stage, to drop from the tree. Female weevils will continue to probe nuts until the pecan kernel inside the nut starts to firm up. Once a female finds solid kernel they will lay 5-7 eggs inside the nut.  Our job, as pecan growers, is to prevent females weevils from laying eggs.

   

   Today, I walked over to a Kanza tree to check on nut development. With recent rainfall, the nuts are growing rapidly (photo at left). This is the time of year when nut clusters are clearly in the tree's canopy and I start looking forward to a successful harvest season.

    I pulled off a Kanza nut and cut it open to determined the stage of kernel development (photo at right). At this point, Kanza is about 3/4 water stage. It will be mid-August before Kanza kernels will start to firm up and become susceptible to weevil oviposition.
    In my orchard, the weevil population is very low so I'm not overly anxious to start spraying for weevil. However, I am planning to spray for stinkbugs next week and that spray should take care of any early emerging weevil adults. My biggest concern is that fact the my neighbors native pecan grove doesn't appear to have a crop this year. That means, any weevils that emerge across the fence will probably migrate over to my orchard. 
    From past experience, migrating weevils are not captured in trunk mounted traps. So this year, I'll be making a weevil spray as soon as my Kanza nuts enter the dough stage in an effort to stop migrating weevils from becoming established in my orchard.
    If you want to monitor pecan weevil emergence in your grove, I'd suggest that you build some Circle pecan weevil traps. Step by step instructions for building traps can be found HERE.

  

Pecan kernels filling - pests on the prowl

    The other day I cut open pecans from a few cultivars of pecans and discovered just what I expected. My pecans had started the kernel filling process (photo above, right). At this point during the growing season, the seed inside the shell has formed a thin layer of kernel tissue just under the seed coat. The amount of kernel deposition by late August is both weather and cultivar dependent. Earlier ripening cultivars will fill their kernels sooner that later ripening cultivars.

     As soon as pecans start to fill their kernels, two important pecan pests attack: Pecan weevils and squirrels. Since we've experience above normal rainfall for the month of August pecan weevils have been emerging continuously since late July (photo at left). However, female weevils will not lay their eggs inside the pecan until kernels start to fill. So with the kernel filling process underway, we applied our second weevil spray to our trees this week (August 23 & 24) to control both pecan weevil and stinkbugs.  For growers with high weevil populations be prepared to make a third weevil spray in early September.
    

    The kernel filling process also marks the time when squirrels start cutting open pecans in search of a meager meal of partially formed nut meat. This kind of squirrrel damage largely goes unnoticed by growers but we have begun to collect lots of nut fragments in drop cages set under native pecan trees (photo at right). Although, we might never claim complete victory over squirrels, we've been trapping squirrels in coni-bear traps since early summer to help reduce the resident squirrel population.    

Spraying for weevil, stinkbug, and scab

    We had a good rain shower over the weekend which came at a perfect time to promote nut growth and kernel fill. But 1.5 inches rainfall also provided plenty of moisture to softened the soil and allow pecan weevil to start emerging. So today we fired up the sprayer (photo at right).
   Today's pesticide application was aimed at controlling three key pests; Pecan weevil, stinkbugs, and pecan scab.  We generally spray the grove in early August for stinkbug control but the wet weather dictated that we also control weevil and scab. We used Warrior 2 for insect control and Quilt Xcel for disease control.   
    Applying a fungicide this late in the season has proven beneficial during wet summers to control not only pecan scab but also pecan anthracnose and downy spot. Judging from the forecast we are in for a cool wet August.

Time to set out pecan weevil traps

    Today, we set out several pecan weevil traps on trees that we expect to find plenty of weevils (photo at right).  With all the rainfall we have received this week, soil conditions should be perfect for weevil emergence. However, only a very few weevils usually emerge during the last week of July. The bulk of the weevil population emerges in mid-August if soil conditions remain moist.
    The long term forecast calls for hot and dry weather next week. As the soil dries and become hard, weevils will be unable to move out of their underground homes and adult weevil emergence will stop. The emergence period will not continue until we receive more rain. By setting out weevil traps, we will know exactly when weevils become active in the grove.
   Complete instructions for building your own weevil traps are given HERE.  

Spraying for pecan weevil

   In our little corner on SE Kansas, we've had over 6 inches of rain in a 5 day period. While the rain is welcomed at this time of year to help fill pecan kernel, wet soil conditions have lead slow steady emergence of pecan weevils. So today,  with sunshine, calm winds, and cool temperatures, we applied a second dose of insecticide to keep weevils in check (photo at right).  This time we applied Sevin insecticide making sure our air-blast sprayer covered the entire tree canopy.

Spraying for stinkbugs and early pecan weevil

    As I mentioned in yesterday's post, we've been seeing quite a few nuts drop from stinkbug feeding. On top of that, the 2 inches of rain we received yesterday should bring out the first flush of pecan weevils. So this morning we decided to take advantage of a cooler day with light winds to spray our pecan grove (photo above). This is only the second time we've sprayed our native trees in 2015 so we included both an insecticide and a fungicide. We used Warrior II for stinkbugs and weevil and Headline for scab.

Tight green shucks point to pecan weevil attack

     By this date in late October, all northern pecan cultivars and local native pecans have fully ripened and split shuck. But as leaves start to drop, you might notice a few pecans up in the trees that still have bright green shucks that are still tightly bound to the shell. On closer inspection, you might find a hole in the shuck. This hole could be the exit tunnel for a hickory shuckworm moth but if you take your knife and cut away the shuck you might find the hole continues straight through the nut shell (photos at right).  If the hole goes straight into the nut, what you have discovered is the exit hole for a pecan weevil larvae.
    The weevil larvae that developed inside these pecans completely devoured the kernel inside then chewed a hole through the shell and shuck to exit the nut. Once outside the nut weevil larvae drop to the ground, burrow into the soil, and form an underground cell. The larvae will pupate in the soil before emerging as and adult 22 months later (weevils have a two year life cycle).    

    I pulled a nut cluster off a tree because I noticed all three nuts in the cluster had not split shuck (photo at left). At first look, I saw only two of the nuts had weevil exit holes. But what about the third nut?

    Turning the cluster over, I found the third nut was also destroyed by pecan weevil (photo at left). Since a single adult female weevil can lay eggs in 7 to 15 nuts, it seems likely that the larvae in these three nuts originated from the egg laying activities of a single mother. It is also interesting to note that exit holes occur at seemly random locations on each nut. This may mean that once a larva finishes eating all the kernel inside the shell, the closest exit point is always the best.  

Pecan weevils emerge

    After a hot and very dry month of August, a large storm spread over our area on the 1st day of September. Along with an amazing lightning display and high winds, this storm dumped 5 inches of rain on our pecan grove. The much needed moisture will help fill out pecan kernels but has also created the prefect soil conditions for pecan weevil emergence. Today we collected up to 5 weevils in a Circle trap.
    When weevils emerge from the soil they crawl and fly up into the nearest pecan tree. Once in the tree's canopy, both male and female weevils search out a nut cluster (photo above). After arriving at the nut cluster, male and female weevils will find each other and mate. Several days after mating, the female weevil will begin laying eggs inside the nut.

   

    It is fairly easy to tell the difference between male and female weevils. Female weevils have a much longer proboscis than their male counterparts. In the photo at left, the male weevil is the insect on the upper right. The female is located on the lower left side of the photo. Looks like these two will be doing the weevil tango before too long.

   To remind everyone that weevils can and do fly, I was also able to photograph a weevil adult preparing to take flight (photo at right). A weevil will raise its two hard wing-covers to reveal a pair of translucent, copper-colored wings. A pecan weevil may not be the best aerial acrobat, but this insect will fly from un-managed, weevil-infested, native trees into your orchard just to find a place to lay eggs. That it one reason why we have been setting up traps outside of our orchard. I don't like to be caught unaware by migrating weevils.
    We will be spraying for weevil starting Thursday Sept. 4. 

Rain, weevils, and nut development

   It rained a little over one inch on Thursday and that's usually enough moisture to loosen up the soil and allow pecan weevils to start emerging. But female weevils can't lay eggs inside a pecan until all the embryonic fluid inside the expanding nut is replaced by kernel tissue (i.e. water stage changes to dough stage).

   Over the past several weeks, I have been cutting open nuts of several pecan cultivars to determine stage of kernel development. However,  I thought it would be a good idea to check on the status of our native crop. So I climbed up into our hydraulic lift and grabbed nut samples from 9 native trees (photo above).
   The first thing you should notice is that native pecans are generally smaller than the improved cultivars I photographed earlier this week. The second thing to notice is the wide variation we find among natives in size and shape. After cutting into each of these nuts I found that many of these nuts are still expanding.

    The photo at left shows the cross-section of each native nut. By cutting into each nut I found that kernel development ranged from 1/4 kernel expansion (nut B) to the very first stage of kernel deposition (nut H). None of these nuts would be suitable for pecan weevil egg laying.
    The early pecan weevils that will emerge this weekend will migrate to nut clusters seeking a mate and feeding on developing pecans. Nuts in the water stage and punctured by weevil feeding will stop expanding and drop from the tree.
    If your grove has a history of heavy pecan weevil damage you might consider applying an insecticide to reduce the weevil population as early as next week. At the Pecan Experiment Field, we will be applying an insecticide starting on Monday that will be aimed primarily at stinkbug control but should also control early emerging weevils.

Rainfall and pecan weevil emergence

Pecan weevil larva feeding on pecan kernel tissue

   A large part of being a successful pecan grower is learning how to adapt to changing weather conditions. This year nut development was delayed by a cool spring and has remained at least two weeks behind normal all season long. But this summer we also experienced  above average rainfall in late July and early August that promoted early pecan weevil emergence.
    Late developing pecans. Early weevils. This year's weather patterns have created a unique pest control challenge. In the chart below, I've recorded both rainfall and weevil trap catches. We had over 15 inches of rain from July 21 until August 12. Since that time, the rain has completely stopped and at this point things are starting to look dry again.
    We captured our first weevil on July 31 with emergence peaking from August 5 to August 21.  As our soil has started to dry out the number of weevils we have captured dropped off dramatically.

  

     The combination of early weevil emergence and late kernel development has meant that, for the entire month of August, adult weevils could not find a place to lay eggs. However, pecan weevils are patient creatures. They simply feed on developing pecans (causing nut drop!), while they wait for the pecans to start creating kernel.  Because of the large number of weevils that emerged in early August, we sprayed our pecan grove starting August 14. Now I'm wondering, when it rains again this month, will we get a second flush of weevil emergence? Late emerging weevils will find plenty of places to lay eggs now that our pecan crop has started to fill kernel. And I certainly don't like finding weevil larvae in my cracked pecans at harvest time. This year, we'll be checking our weevil traps well into October.

Pecan weevil nut drop

   We discovered this cluster of Posey nuts while collecting leaf samples today (photo at right). The nut cluster had 5 nuts with three of the nuts streaked with brown necrotic areas. This didn't look good.
  

    I pulled off one of the damaged nuts for a closer look (photo at left). On one side of the nut I found an obvious puncture wound in the shuck (at end of red arrow). I could tell this puncture extended all the way into the kernel because of the shiny black stain on the outside of the nut husk. The kernel was punctured allowing liquid endosperm to leak out of the nut, onto the shuck and turning black as it oxidized.  In three days we would be finding dry, blackened pecans on the ground.

      I cut open one of the damaged nuts to inspect the kernel. The interior of the nut had lost its normal, light-green coloration. The entire contents of the nut had turned brown. Between the size of the puncture wound and the brown discoloration of the kernel, I can state with confidence that this nut was a victim of  pecan weevil feeding. Not only that, it was probably just one adult weevil damaging all three nuts in the cluster.
   Because nut development is so far behind normal, pecan weevil feeding damage will be an all too common problem this year. This is exactly the kind of feeding damage we were trying to prevent when we sprayed last week. Looks like we missed one.

Controlling stinkbugs and pecan weevils

    With all the rain we've had in early August, pecan weevils have been emerging nearly every day since late July. However, with nut development two weeks late, the female weevils are not yet laying eggs inside the nuts. For now, weevils are feeding on nuts and causing nut drop.
    Stink bugs are also feeding on pecans at this time. These insects also puncture pecan nuts and are currently causing nut drop. With significant nut feeding injury from both weevil and stink bug, we decided to spray our pecan grove (photo at right).
   We starting spraying the grove on Wednesday August 14 and finished up on Friday. We used Warrior II to control weevil and stink bug then added a fungicide (Stratego) to fight scab. We added the scab spray because most pecans are still expanding (a time when nuts are susceptible to scab infection) and recent rains and saturated soils have brought us lots of disease enhancing humidity.
   If pecan weevils continue to emerge over the next 2 weeks, we will need a second insecticide treatment when nuts enter the dough stage of kernel development.  

Pecan weevils: Identifying the sexes

   With all the recent rains we've received, pecan weevils have begun to emerge and are being captured in our traps. The pecan weevil is a member of a group of insects called the snout beetles. As you can see in the photo at right, the pecan weevil has a long proboscis with a pair of antenna attached. This insect can vary in color from rusty brown to brownish grey. The body of and adult weevil is approximately 3/8 inch long.
     Female adults are usually larger than their male counterparts. Females also feature an much longer snout, often stretching longer than the length of her body. Female weevils use their proboscis to puncture the shuck and shell of pecan and hickory nuts. Once they puncture the nut, they insert their ovipositor in the hole and lay 5 to 7 eggs within the nut's shell.

Pecan weevils emerge right on schedule

   We set up some weevil traps earlier in the week and right on schedule we caught our first adult weevil (photo at right).  The weevil in the photo is a male, and that's a penny at the bottom of the photo to give you an idea of the size of this insect.
   Over the last week we have received plentiful rainfall which translates into ideal soil conditions for an extended adult emergence period. Males weevils emerge first, followed by the females that should start emerging by next week.
    Although adult weevils will feed on nuts and cause nut drop while nuts are still sizing or in the water stage, the females will not be able to lay eggs inside the nut until the kernel starts to fill. With this year's late nut development schedule, I expect to see a lot of weevil induced nut drop during the first half of August.  Since they will be the first to develop kernel tissue, early ripening pecan cultivars will be especially attractive to female weevils looks for egg-laying locations

 

     If you have not installed pecan weevil traps in your orchard, build a few traps and attached them to trees that have had a history of heavy weevil infestations.  The traps will let you know when weevils are emerging and allow you to plan insecticide treatments. Check back on this blog to see when and why we decide to make our first weevil spray for 2013.