Early August pest control

    Every August, I spray my pecan grove during the first week of August to reduce stink bug populations. I know stink bugs are active in the grove when I start seeing dropped nuts on the orchard floor. If you look over the outside of a dropped nut, you'll have a hard time finding any puncture marks. However, cut open the dropped nut and you'll find that the inside of the nut has turned dark brown or black (photo at right).
    The unusually wet summer we've had this year has made pecan pest control even trickier. Heavy rainfall starting on the first day of August and again a week later has saturated the soil allowing pecan weevils to start emerging. Under moist soil conditions throughout the month of August, weevils will not flush out all at one time. Instead they will emerge slowly over the entire month. So this year, my early August stink bug spray is also aimed at controlling any early emerging weevils.
    The hot, humid weather we've had all summer long has also made conditions perfect for the spread of pecan diseases. Although pecan scab is our primary disease problem, wet conditions late into the summer means that pecan anthracnose and downy spot will also become problematic. To keep all these diseases in check this summer, I made my forth fungicide application with my early August spray.
    Determining the best day to spray was also a problem. It didn't look like I could afford to let things dry out completely so I just had to pick a day with the lowest rain chances and pray I would get at least 8 hours of drying time to allow the pesticides to do their job. I like to start spraying at first light. The winds are calm and the high relative humidity allows the spray to drift up through the entire tree canopy allowing me to get excellent spray coverage.
   In two weeks, I'll be spraying the grove again. This time with an insecticide specifically aimed at pecan weevil. 

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.      

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.

More than black spots on pecan kernels

   Over the past several years we have been making a special effort to prevent stink bugs from feeding on our nut crop. For the most part we've been fairly successful. However, we didn't start our stink bug control program early enough in the season to prevent black spots from developing on the kernels of very early ripening cultivars. The photo at right shows several Osage pecans damaged by stink bug feeding. As a very early ripening cultivar, Osage enters the dough stage at least a week before many of our standard northern pecan cultivars (Kanza, Pawnee, Major, Giles etc.). To prevent this type of kernel damage on Osage, we should have made a late July pesticide application in addition to our normal stink bug prevention program that begins during the first week of August.
    Stink bug feeding can cause more than just black spots on the kernels. Note the pecan in the lower right portion of the photo. A red arrow points to a large blackened area on a kernel half. When stinkbugs feed on pecan kernels, their digestive fluids kill a portion of the kernel leaving behind the characteristic black spot. However, during feeding, the stink bug can also introduce bacteria or fungi inside the shell. These organisms break down kernel tissue and cause large areas of the kernel to turn black. Ultimately, controlling stink bugs will prevent both types of kernel damage pictured above.   

Spraying for stinkbugs and aphids

   We've waited all during the month of August for enough rain to cause pecan weevil to emerge. And we are still waiting. In the mean time, two other insect pests have become potential problems.
    In the absence of pecan weevil sprays, stink bugs can build up in the orchard especially when the weather turns dry. Stink bugs feed on a wide variety of plants but always prefer a green and juicy host plant. Under dry conditions, the ground cover and surrounding fields start to dry up and pecans become the most desirable food available. We decided to spray this week to keep stink bug populations under control.
    Since we were making a pass through the orchard with the sprayer, I decided to add an aphicide to the mix to knock down the population of black-margined aphids currently coating pecan tree leaves with honeydew. We used Hero insecticide to control stinkbug and Provado for the aphids.    

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.

Mid-summer nut drop

    A quick walk out into the pecan orchard at this time of year and you might spot several green nuts on the ground (photo at right). A quick look at the fallen nuts and you will probably find some scab lesions or large patches of discolored shuck tissue. However, the primary reason these nuts have dropped during the first week of August is stinkbug feeding. It is often difficult to identify stinkbug damage by inspecting the exterior of the shuck. If you look carefully, you might find stinkbug feeding scars on the outside of the nuts but, with numerous scab lesions also present, these small feeding scars might be hard to see.
    The easiest way to confirm stinkbug feeding is to cut open dropped nuts and inspect the developing kernel. If the interior of the nut including the developing kernel is dark brown you can be assured that stinkbugs have attacked the nut.
   This morning we received nearly 2 inches of rain which should stimulate the emergence of pecan weevil. These weevils will also start feeding on nuts causing a nut drop similar to the drop caused by stinkbugs. You can distinguish weevil feeding from stinkbug feeding by the size of the hole drilled through the shuck. Weevils make a much larger hole in the shuck and often leave a pattern of foot marks around the feeding site. Weevils will continue to feed on nuts until kernels reach the dough stage.
   Once this rain system passes all the way through our area, we plan to spray our pecans to control the stink bug population and kill off early emerging pecan weevils.    

Spraying for stinkbugs and shuckworm

   After fighting through some mechanical problems with our tractor and sprayer, we finally sprayed the pecan grove to control stinkbugs and shuckworm today (photo at right). We had planned to spray earlier in the week in response to the nut drop we have been seeing but we ended up having to wait for parts to arrive.
    We applied Warrior II at the rate of 2.56 oz/ac. But, "How much do I put in the tank?" you might ask. Many growers are frustrated by fact that suggested rates on pesticide labels are given as amount of product to apply per acre rather than amount to mix in 100 gallons of water. Pesticide manufacturers are not trying to make your job more difficult, they are only following EPA mandates.
   The proper way to determine how much pesticide to put in the tank is to determine how much water is needed to spray an acre of pecan trees. However, we have found that the amount of water needed varies with both time of year and tree size. We use less water per acre during springtime casebearer sprays and more water per acre during late-summer weevil sprays. There are just more leaves to cover late in the season than earlier in the year. In addition, large native trees take far more water per acre to cover than a young orchard of grafted trees.
    With experience, I have learned to assume we apply 100 gallons of water per acre in calculating how much pesticide to add to our 500 gallon tank. I then use the maximum recommended rate as listed on the pesticide label. In spraying the grove, I never rush the process. I drive slow enough to make sure to get complete coverage of the canopy. The leaves need to be covered, not dripping wet.    

Early August nut drop

    Over the past week, I've noticed  quite a few green pecans have dropped to the ground (photo at right). Since all our pecans are still in the kernel expansion phase of nut development (i.e. the water stage), any insect that punctures the nut will cause nut drop. At this time of year we have three insects currently feeding on nuts; hickory shuckworm, pecan weevil and stinkbugs. I picked up a handful of dropped pecans and used my knife to determine why the nuts were aborted.

    In our orchard, the vast majority of nuts dropping from trees were damaged by stinkbug feeding. I also found evidence of hickory shuckworm activity. Nuts damaged by stinkbug were still filled with embryonic fluid (water) but the inside of the seed coat had turn dark brown to black in color (nut on right in photo above). In contrast, hickory shuckworm infested nuts were dry inside and I could see signs of larval tunneling. In the photo above, the red arrow points to a tunnel created by the shuckworm. I did not find any weevil punctured pecans in our orchard.
   We will be spraying the orchard this week to combat shuckworm and stink bug. We'll use Warrior II insecticide at the rate of 2.56 oz/acre.

Stinkbugs create a nasty suprise

Leaf-footed Bug

    This past fall the Kanza trees I planted near my home produced their first big crop of pecans. So many nuts in fact that the wife and I decided to harvest the nuts for our own use. Yesterday, I finally got around to cracking our Kanza crop and was disappointed by the number of nuts that had been attached by stink bugs. However, the amount of damage I found was very typical for back-yard, unsprayed pecan trees. There are numerous species of stink bugs and leaf-footed bugs (photo at right) that feed on pecans but all species leave behind bitter-tasting, black spots on the kernel. 

    The photo at left illustrates the type of damage I found caused by stink bugs. The nut on the far left was attacked during the water stage of nut development causing nut fill to cease and the entire kernel to become black and papery. The three other nuts were attacked after the nut had entered the dough stage. Each black spot on the kernel represents a stink bug feeding site.
    Stink bugs are a serious problem for back yard pecan growers. At the Pecan Experiment Field we use pesticides and an air-blast sprayer to keep these kernel feeding pests at bay. But these restricted-use pesticides and the equipment needed to apply them are generally not available to to the small scale pecan producer.  Carbaryl insecticide is widely available to home-owners and is recommended for use to control pecan weevil.  Carbaryl sprays, aimed at pecan weevil, will help reduce stink bug injury but will not eliminate the problem.
    You will notice that the amount of stink bug damage will vary widely from year to year. This is largely due to weather patterns that influence insect populations and the availability of alternative host plants for stink bugs to feed and reproduce.
    One thing is for sure, I'll be picking out a lot of stink bug damaged nuts while I'm shelling out the Kanza nut I picked up at home. 

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.  

Controlling stinkbugs

    During the water stage of nut development, pecans seem to become especially attractive to stink bugs and leaf-footed bugs. Stink bug feeding at his time of year causes nut drop. In a couple of weeks when the nuts stage into the gel stage, stink bug feeding will leave a black spot on the surface of the kernel.
    As part of our annual pest management program, I apply an insecticide at water stage to control kernel feeding bugs. Today we applied Warrior II, a synthetic pyrethroid that is formulated to remain active for at least 2 weeks.  This spray will also control any pecan weevils that may have emerged up through the cracks of out drought parched soil.

Pecans in the water stage

   Spring came early this year and many of our summer fruit crops ripened 2 to 3 weeks early. Not so for pecan. This summer's heat and drought has slowed pecan kernel development to a point where kernel development now is right on schedule. It's early August and nuts are in the water stage (photo at right).
   The water stage of pecan kernel development can be defined as the point in time when the shell and kernel seed coat have become fully sized and the interior of the kernel is filled with liquid endosperm. Cut a nut open at full water stage and your hands will be soaked by the water that comes pouring out.
   In the photo above, Osage and Kanza are in full water stage while Maramec is still expanding it's kernel (its in 3/4 water stage). At this point, you can also see that the shell has become hardened especially near the nut apex and the inner shell packing material between kernel halves is starting to be compacted by the expanding kernel, turning orange in color. 
    Understanding the stages of kernel development is important for understanding how kernel feeding insects damage pecans. If a pecan weevil or stink bug punctures a nut during the water stage (or any time before water stage) that nut will drop off the tree. Once kernel deposition starts (the gel stage) insect damaged nuts will remain on the tree until harvest.

Summer nut drop

     During mid-summer, there are a few critters out there that can cause pecans to drop. This summer, we set up drop cages to collect dropped nuts so we can monitor the causes for nut loss. Here are a few of the nuts we've found.
    The pecan pictured at right fell from the tree after being attacked by the hickory shuckworm. The bright white spot on the outside of the nut identifies shuckworm as the reason for the drop.  After hickory shuckworm females lay there eggs in the husk of a pecan, they cover the site with some scales rubbed off from their lower abdomen. This results in a raised spot of what looks like white fluff. We see hickory shuckworm damage every July but damage levels are rarely large enough to warrant control measures.

      Stink bugs and leaf-footed bugs can cause mid-summer nut drop (photo at left). The tell-tale signs of activity for these kernel feeding bugs are two fold. On the outside of the shuck, you should see small black feeding scars as well as large areas of damaged husk tissue. Cut open the nut and you will find the internal portions of the nut stained dark brown to black. These insects are primarily a late season pests but this summer's drought has caused an early migration of bugs into pecan groves. Fortunately, we are seeing only low number of these kernel feeding insects at this point. I typically apply an insecticide in early August specifically aimed at controlling stink bugs and leaf-footed bugs.

     We found one surprising nut drop--a pecan half eaten by a squirrel (photo at right). Squirrels usually do not start cutting into pecans until mid-August, when kernels enter the dough stage. However, this extended drought must be putting a lot of pressure on the squirrel's normal food sources. This must also be the reason we have been having great success trapping squirrels over the last month--they are starving.
 

     Nuts that drop from drought typically look dried up (photo at right). The shuck is completely rock hard and dark in color. However, inside you will find that the developing kernel is still white. This is in contrast to the stink bug damaged nut that has a darkened kernel (above). Fortunately, we have not seen a lot of drought induced nut drop so far this year.

Fewer black spots on kernels in 2011.

    Its not until you crack open a sample of  this year's pecan crop do you discover the level of damage created by stink bug feeding. As I mentioned in an earlier post, the black spots found on pecan kernels are the result of feeding by stinkbugs and/or leaf-footed bugs (photo at right).
    Last year (2010) we found quite a bit of stink bug damage. This year (2011) the number of kernels with black spots are far fewer. I wish I could come up with a good explanation for the year-to-year variation in stink bug damage but it turns out that the movements and population numbers for this group of plant feeding bugs are very hard to predict.
    Over the past several years, our  control strategy for kernel feeding bugs has been to apply an insecticide (Warrior II) in early August. Subsequent insecticide applications aimed at pecan weevil also help decrease stink bug populations. These control measures are not perfect but seem to keep kernel damage down to less that 1% of kernels.

Time to control weevil and stinkbug

   We had over 4 inches of rain last week. The rains came slow and over several days so every drop soaked into the ground. The only down side of the rain is the effect it has on pecan weevil emergence. The rain softened the soil and adult weevils have started to emerge.
    Today we started spraying the grove to control pecan weevil and to slow down stink bug feeding (photo at right). Most nuts are in the water stage so weevils aren't laying many eggs at this point but the amount of nut drop we are seeing has prompted my decision to apply "Warrior" insecticide to our grove.

     Here's a photo of an adult pecan weevil looking for just the right spot to puncture a pecan. We've kept pecan weevil populations at the Experiment Field very low with over 30 years annual control measures. At this point, stink bugs may be a larger problem for us than weevils. 

Stink bug nut drop

    During early August, several species of stink bugs migrate into pecans groves and start feeding on developing nuts. If a stick bug punctures a nut to feed on the kernel during nut enlargement, that nut will drop from the tree. In the photo at right, The red arrows point to puncture marks left after stink bug feeding. This nut was punctured 3 times (the upper red arrow points to two punctures very near each other). We found this nut in one of our drop cages that collect all the nuts that fall from the tree during the course of the season. It usually takes 3-5 days after the damage occurs for the nut to drop off the tree, so this nut was probably attacked by a stink bug late last week

     If you cut the nut open (photo at left), you will note that the developing kernel has turned dark brown to black. The yellow arrow points to the developing kernel that is less that 1/2 way to full water stage.
    In the photo, you will notice that the cut surface of the shuck has turned black. This occurs when shuck cells are exposed to the air and is not a sign of stink bug feeding. However, the darken areas inside the shell are the result of insect attack.
    This year the weather has been so dry that even stink bug populations seem suppressed. It may be that a total lack of succulent plant growth earlier in the season has made it difficult for stink bugs to  grow, reproduce, and build their population numbers. We'll be watching our drop cages for signs of increased stink bug activity.

Black Spots on the Kernel

It is not until you crack open a pecan that you discover that stink bugs have been feeding in your orchard. In the photo at left the large, sunken black spots on the kernel were caused by one of several large bugs, including the southern green stinkbug, the brown stinkbug, and the leaf-footed bug. We commonly lump all these insects together and call the damage they create, stink bug damage. The black spots are created when stink bugs feed on pecans when nuts are filling their kernels (mid to late August). This group of insects have a needle like mouth part that can pass through the shuck and hardened-shell to get to the kernel. As the insect feeds, it secretes digestive fluids into the nut that actually breaks down some of the kernel, so the insect can feed on a kind of pecan slurpee. These digestive juices are what cause the black spot on the kernel.
     For those of you that are picking out pecans for your family, be sure to break out these black spots and discard them. The black spots are bitter and will ruin a good pecan pie.