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 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.    

June beetles cut off new growth

   Last week, we experienced several days when early evening hour temperatures remained in the low 70's. That's when I heard the familiar sound of large "June" beetles crashing into the windows of my house starting shortly after sunset.  I looked through the window glass and spotted a European chafer crawling on the sill. After spotting this insect, I knew that I could go outside the next morning and find new leaves and shoots chewed off young pecan trees (photo at right). I've written about this pest in an earlier post, but this week I wanted to talk further about the adult beetle behavior and why they only damage young pecan trees.

    The European chafer produces one generation per year. Female beetles lay their eggs in the turf  and C-shaped grubs that hatch from these eggs spend all year feeding on the roots of grasses. Each spring larvae pupate and become adult beetles. These beetles emerge from the turf during early evening hours and swarm to low lying tree branches or shrubs. By cutting off tender leaves and shoots, the European chafer creates an ideal place for additional beetles to land facilitating the search for a suitable mate.
   European chafers are ground dwelling insects so when then fly onto young pecan trees they generally migrate to lower limbs. In the photo at left, you can see that the lowest two limbs of this tree have been attacked by beetles while the upper portion of the tree is untouched. As pecan trees grow larger and lower limbs are pruned off, European chafers will no longer present a problem because these insect can't stand heights.  
    Spring emergence of adult beetles lasts about 2 weeks. At my location, emergence is trailing off and will be over soon. 

Sapsuckers drill new holes each spring

  

     Rows of shallow holes carved into pecan trunks is the sure sign of Yellow-bellied sapsucker activity.
In the photo at right, two new holes have been drilled to the right of three holes made the previous season by this bird.
    Sapsuckers drill holes in the bark starting at pecan bud swell. These birds create the holes in order to feed on the abundant and sugary sap that is flowing up the tree trunk in early spring. You will find that sapsuckers prefer certain pecan cultivars over others. I have never seen a 'Stuart' pecan tree that isn't riddled with sapsucker holes.
 

Sapsuckers are migratory birds (photo at left). They overwinter in Central America and spend the summer breeding season in the far northern States and Canada. This means that in our area, yellow-bellied sapsuckers are just 'passin thru' each spring and fall.  They drill holes in the bark and feed on sap in the spring, then primarily feed on insects during the fall migration.
     Although truck damage can look awful, a well tended pecan tree can withstand sapsucker feeding without significant yield loss. 

Hickory shuckworm

    Today I peeled back the shuck of a Maramec pecan and found a couple of hickory shuckworm larvae (photo above). The red arrows point to the head of one larvae and the tail of another. These caterpillars feed on the shucks of pecans leaving tell-tale black tunnels in the shuck. The tunneling seems to be concentrated near the base of the nut but you can find tunnels throughout the shuck.
     Hickory shuckworm is a minor pest in our northern pecan groves. Northern pecan cultivars fill their kernels and ripen their nuts faster than the shuckworm can destroy the shuck and cause economic damage. Hickory shuckworm populations are kept relatively low in well tended pecan groves because insecticides applied in August to control stink bugs and pecan weevils also control shuckworm.

    Hickory shuckworm larvae are small white caterpillars with a red heads (photo at left). Note that these larvae are confined to the shuck and have well defined legs. Pecan weevil larvae are also white with red heads but are completely legless. Unlike shuckworm, pecan weevil larvae are usually found inside the shell of the nut. 

Time for weevil control

  Wide spread rainfall over this past weekend has enabled pecan weevil adults to emerge from the soil in large numbers. Growers from Kansas, Oklahoma, and Missouri have all reported catching lots of weevils in their 'Circle' weevil traps.The time to control this perennial pecan pest is NOW!
     We started spraying our pecan orchard this morning and this year we are using Sevin XLR insecticide. Other isecticides labeled for pecan weevil control include Warrior II, Silencer, Hero and Proaxis.
   The photo shows a female pecan weevil looking for just the right spot to drill through shuck and shell to enable her to lay 5 to 7 eggs inside the pecan. To control pecan weevil, you must prevent female weevils from laying eggs.

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.

Fall webworm hatching

   Last week we found an egg mass of the fall webworm. This week we found hatched out larvae feeding comfortably in their loosely spun web (photo at right). Just like newly hatched walnut caterpillars, first instar fall webworms do not have large enough mouth parts to bite through an entire pecan leaf. Instead these young larvae just scrape off the outer layer of cells on both sides of the leaf. In the photo, the leaflets nearest to the cluster of caterpillars has just been scraped clean of its outer layer. As these leaflets dry, they will turn brown just like the other leaflets under the web.
   We are not finding a large number of first summer generation webworm colonies at this time. However, since it looks like we are facing a walnut caterpillar outbreak this summer, insecticides applied to control walnut caterpillar will also control fall webworm.

Walnut caterpillar hatching

    Just like fall webworm, walnut caterpillars have arrived right on schedule--late June. Today, we found a couple of newly hatched walnut caterpillar colonies (photo at right). Newly hatched larvae are quite small and olive green in color.

    I looked around the foliage near the colony of feeding caterpillars and found the egg mass from which they hatched (photo at left). Looking closely at the egg mass, I learned two things. First, the egg mass is much larger than normal. And second, not all the eggs hatched indicating possible parasitition by the wasp, Trichogramma minutum. The laying of large egg masses is often a precursor for an outbreak of walnut caterpillars. The fact that less than 10% of the eggs were parasitized means that wasp parasites were not numerous enough to keep walnut caterpillar in check.  Everything I saw today, points to a walnut caterpillar outbreak, at least in and around the Pecan Field.

     To scout for newly hatched walnut caterpillar colonies look for brown, skeletonized leaves in the canopy of your pecan trees (note brown leaf in center of photo at right). The mouth parts of newly hatched larvae are so small they can not eat the entire leaf. Instead, the young insects scrape both upper and lower surfaces of the leaf, turning the leaf brown. The photo below shows a close up of the brown, skeletonized leaves and a feeding colony of first instar walnut caterpillars.

     

Fall webworm right on schedule

     This year, pecan trees broke bud nearly 3 weeks early. First-summer-generation pecan nut casebearer came as least 2 weeks earlier than normal. So what should we expect when it comes to summer-foliage feeding caterpillars? The answer came today when I found my first fall webworm egg mass (photo at above).
    Mid-June is the normal time period for the very first webworm egg masses to be spotted. It seems fall webworm moths didn't get the memo that bud break was early in 2012.
    Fall webworm egg masses are easy to identify by the white "fluff" scattered over the top of the egg cluster. This "fluff" is actually moth scales that the female scrapes off her body in an effort to disguise the eggs to avoid attacks by egg parasites.

    By early July you should see webworm colonies in their dirty white webs (photo at left). Fall webworm has two generations per year in our area. A second generation appears in late August.
    Depending on the number of colonies we see per acre, we can control this pest with a wide range of insecticides. Currently, the action threshold for fall webworm is 5 colonies per acre. Make sure to scout your orchard carefully to spot the colonies when they are still small (the size of your fist). Young larvae are much easier to control than larvae nearing the end of their life cycle.

Curled-up pecan leaves

    Growers are seeing some curled-up leaves in their orchards this year. Over the past week, I have spotted two types of leaf distortions in our pecan grove.
     In the photo at right you can see that the 5 leaflets on the end of this leaf are twisted and cupped. This type of damage was caused by the potato leaf hopper during the period of leaf expansion. The holes in the leaflets were caused by sawfly feeding, also earlier this growing season.

    If you take a close look at the underside of a curled-up leaflet, you will note brown necrotic areas along the main midrib and all major veins  (photo at left). When the leaflet was small and very tender, the potato leaf hopper inserted it mouth parts into the vascular system of the leaflet to feed on nutrient rich plant sap. This feeding behavior causes the vascular system to become clogged, stopping the flow of carbohydrates needed for further leaf expansion. Areas of the leaf that rely on those clogged veins for water and nutrients become yellow (lack of nutrients) or turn brown (lack of water). The leaflets curl because affected areas stop expanding while areas that are adjacent to functioning veins continue to expand.
     Potato leaf hoppers migrate through our area every spring. The damage caused by this insect varies from year to year and you will see several trees species affected (including pecan, walnut, ash, & maple).  We do not recommend treating for this transitory insect and just let the tree grow additional leaves to replace the damaged ones.

     A second type of curled up leaf is caused by the leaf roll mite. In the photo at right, note that the margin of the leaflet is rolled into a tight, hardened gall-like structure. As the mite feeds on the edge of a leaflet during leaf expansion, it causes distorted cell growth, creating the "leaf roll".  Leaf roll mites are fairly rare in a native pecan grove and we don't take steps to control what amounts to minimal damage.

Galls on pecan stems

   This spring has provided excellent conditions for the development of galls created by pecan stem phylloxera (photo above). Pecan growers in Kansas, Missouri, and Kentucky are all finding trees covered with stem galls. The scientific name for this insect is Phylloxera devasatrix and like the name implies, this phylloxera species can have a devastating effect--distorting pecan tree growth and eliminating nut production.

    If you open the galls at this time of year you will find it filled with hundred of winged aphid-like insects (photo at left). When the gall cracks open, the winged phylloxerans will fly out, mate, then mated females will find a hiding place in the rough bark of the tree.  While hidden in the bark the female's body will become filled with eggs that will remain dormant until budbreak the following year.
    At budbreak the eggs hatch and "stem mothers" crawl out to the emerging pecan buds. Once she finds green tissue,  a stem mother begins to feed on plant sap, secreting a compound that caused the tree to grown a gall over the insect. After the gall is formed stem mothers lay eggs inside their galls. These eggs hatched into the winged form of the insect.

    To control phylloxera an insecticide needs to be applied at the outer scale split stage of nut development (photo at right). The insecticide is aimed at controlling crawlers before they become imbedded inside a gall.
    If you see a tree infested with pecan stem phylloxera, mark that tree now. Next spring, spray only the marked trees.
    The pecan leaf phylloxera is a related species that creates galls on pecan leaf blades. The control timing for pecan leaf phylloxera is at leaf burst; so make sure you identify which species is attacking your trees before planning insecticide treatments for next spring.

Pecan catocala

    Hidden in the bark of a native pecan tree, I found the largest caterpillar that feeds on pecan foliage (photo at right).   The catocala caterpillar can grow to 3 inches long but it is often difficult to find because its grey mottled appearance is the perfect camouflage for hiding in the bark of pecan trees.  The caterpillar remains hidden and motionless during the day and feeds on pecan foliage after dark. The nocturnal behavior and perfect camouflage helps catocala larvae from becoming a tasty meal for hungry birds.  Catocala caterpillars chew large angular sections out of pecan leaflets giving the foliage a tattered appearance.
    The pecan catocala is a member the Noctuidae family and is commonly known as an underwing moth. I always find one or two caterpillars per year in our pecan grove but populations never grow large enough to cause significant damage to our trees.
   (Remember, you can click on the photo to enlarge it. The caterpillar is in the lower center of the photo with its head pointing down.)

June beetles cut new pecan shoots

    It almost looks like a ten-foot-tall deer has browsed out the tops of a young pecan tree (photo at right).  You can look over the entire tree and not find a trace of the offending creature that clipped off this spring's new growth. You can, however, find clipped-off leaves scattered under the tree.
   This kind of damage is caused by what is commonly known as June beetles.  There are numerous species of June beetles found in Kansas but the one that I've recently noticed crashing into my kitchen window after dark is the European chafer, Rhizotrogus majalis.

    The European chafer is a major pest of cool season grasses. This insect's C-shaped larvae (photo at left) live in the soil feeding on grass roots.  In late spring, larvae pupate and adult beetles emerge from the soil swarming to small trees or shrubs in search of a mate.

    Adults emerge after dark during warm (above 65 degrees) clear nights. It is during this adult swarm that the adult insect feeds on tender shoots, clipping off the foliage of young pecan trees. Adults are active only at night, hiding in the turf's thatch during daylight hours. The adult phase of the European chafer (photo above) lasts only one to two weeks before mated females burrow into the soil to lay eggs. There is only one generation of European chafers per year.

     Damage caused by the European chafer (photo at right) can slow down the growth of young trees but they usually recover when new buds break and form new leaves.  Control of this insect would require an insecticide treatment of the orchard floor in August to kill larvae in the soil. However, the cost of insecticide treatment is hard to justify considering that most damaged trees have yet to reach the age of commercial nut production.

Hickory shoot curculio

    Have you seen flagging leaves and shoot dieback on this year's new pecan shoots (photo at right). If you have, you are most likely seeing an attack of the hickory shoot curculio.
     After resting dormant all winter in ground cover thatch, adult curculios (Conotrachelus aratus) become active in the spring as pecan shoot growth commences. When the first leaf on new pecan shoots is about one half expanded, female curculios start searching of locations to lay eggs.

     Hickory shoot curculio females use their mouth parts to carve a moon shaped depression into the base of a leaf petiole (photo at left). In that depression she will lay an egg. The larvae that emerges from the egg will first tunnel into the leaf petiole causing the leaf to wither and die. It will continue to feed by tunneling into the center of the new shoot making its way towards the terminal, often killing the entire shoot.

     If you see signs of hickory shoot curculio activity, cut open an infested shoot and you should find a white, legless larvae with a red head (photo at right).
    Once the larvae hatches and begins to burrow into pecan shoot tissue, it is impossible to control this pest with an insecticide. In other words, once you see the damage it too late to take action this year. If your pecan grove has a history of curculio attack plan on controlling adults early next spring.

     You will probably never see an adult hickory shoot curculio in the field (photo at left) but watch the development of springtime pecan shoot growth to time an insecticide treatment. Spray when the first leaf on the new growth starts to unfurls all its leaflets.
     Hickory shoot curculio is one of those sporadic pecan pests that seem to appear out of nowhere and then a couple of years later disappear altogether. I've only seen a few curculio infestations that warrant chemical control. It seems that naturally occurring biological control agents usually keep this pest in check.  

Yellow pecan aphid

    I was look looking at our crop of pistillate flowers when I spotted a few drops of honeydew on the leaves. Honeydew is the tell-tale sign that aphids are feeding on the foliage. In this case, I found yellow pecan aphids (photo above). Aphids feed on the underside of the leaves usually right along the midrib, just like the wingless nymph above. The winged adult didn't like the bright sunshine and was already moving off to find a feeding spot in the shade.

   Early season aphids are not normally a problem in our native pecan groves because we have plenty of beneficial insects to keep them in check. In looking through the foliage, I found a cluster of lady beetle eggs laid on the underside of a pecan leaflet (photo at right). Lady beetle adults respond to the presence of honeydew and lay their eggs in a location where they know that there will be plenty of aphids around to provide food for their larvae.

Where does pecan scab overwinter?

   Pecan scab is the most serious disease attacking pecan leaves and nuts. Every fall infected leaves and nut shucks fall to the ground often getting ground up by the action of pecan harvesters. So where does pecan scab come from every spring with the start of a new growing season?
    If you look carefully at the twigs of scab susceptible pecan cultivars, you'll usually spot overwintering scab lesions on the bark and even on bud scales. In the photo at right, the red arrows point to black, sunken scab lesions. Some lesions are large and quite noticeable while others are much smaller. All can produce the spores that lead to scab infections of new leaves and nuts.

   At the top of the twig pictured at left is last year's peduncle. The peduncle is the stem like structure that holds all the nuts in a cluster. Look closely at the photo and you can see where three nuts were attached last year. Also note that this peduncle is loaded with scab lesions (click on the photo to enlarge it for a closer look). Old peduncles are one of the primary sources of scab spores at the start of a new season.
   In Kansas, we have found that it cost effective to concentrate control measures on protecting the nuts from contracting scab. Our first fungicide spray is usually applied soon after pollination is complete. Additional applications may be necessary during wet summers.

Splits in pecan twigs

    I had this photo emailed to me from Missouri (love the duct tape). The red arrows point to splits in the bark of one-year-old pecan twigs. The numerous splits made collecting high quality pecan scions difficult. What caused this damage? The answer is directly related to the emergence of large, noisy insects that appear only every 13 years.
    In 2011, parts of Missouri were treated to the emergence of 13 year cicadas. These insects spend most of their life cycle (13 years) under the soil slowly feasting on tree roots. Adults emerge in mid summer, mate, and then females gouge a split in the bark in which they lay their eggs.  Besides pecan, cicadas lay eggs in the twigs numerous species of hardwood trees. Once the eggs hatch, the nymphs fall to the ground, tunnel into the soil and feed on tree roots.

     You may not be familiar with the looks of the 1.5 inch long adults (photo at left) but I'm sure you've heard the loud mating calls on hot summer nights (a shrill sound the rises to peak before slowly fading). There are hundreds of species of cicada with life cycles that range from 1 to 17 years. Last year's emergence of the 13 year cicada flooded the forests of Missouri with a cacophony of cicada calls and caused immense damage to tree twigs.
    Tree twigs will heal over in time, especially if your pecan trees receive plenty of water and nutrients during the upcoming growing season. Look at the photo of the twigs above, and you can see that the tree has already formed callus tissue around each bark split.

Flatheaded appletree borer

 

 

   The flatheaded appletree borer is a common pest of young pecan orchards. You rarely see the insect, but during early spring, you can easily spot the results of its activity in the crotch of a branch. In the photo at right, you can see a pile bark shavings created by the adult phase of the borer, a  buprestid beetle called  Chrysobothris femorate.  The adults chew their way out of the tree to escape from tunnels created by the insect's larval stage during the previous growing season.

   Even old exit holes created by adult flatheaded appletree borers are easily spotted near branch attachments. In the photo at left, note the oval shaped exit hole in the side of the tree at the point of a branch attachment. Once the adults emerge, they mate and female beetles begin laying eggs about a week later. Females beetles can lay as many as 100 eggs and search the tree's bark for deep crevices that offer some protection for the eggs. This female behavior is the reason larvae tend to develop at branch attachment points especially branches that have developed a bark inclusion.
    Eggs hatch in 15-20 days and the resulting larvae start to create tunnels under the bark feeding on the inner bark, cambium, and new wood. Healthy pecan trees fight flatheaded appletrees borers by producing excessive sap flow that can prove lethal to developing larvae. Trees weakened by stress often suffer the greatest damage from these borers, sometimes resulting in limb loss.

    The larvae are legless and can grow to 1.25 inches long. Several body segments just behind the insect's head are enlarged and flattened (photo at right). These segments are actually part of the insect's thorax, but appear to be a large flat head, thus the common name. Once larvae become fully developed they burrow deep into the wood of the tree to form a pupal chamber, where the insect over winters. Larvae pupate in the early spring and the adult beetles chew their way out as described above. 
    Although we find flatheaded appletree borers in most young pecan orchards,  the damage caused by this insect is usually not serious enough to warrant a control program. The best defense against borers is the keep your trees healthy with adequate nutrients, water, and weed control.  
 

Identifying pecan trunk injuries

     Today, I enjoyed a late winter walk through our native pecan grove.  In the bright sunshine and without a canopy of leaves, the immense size of pecan trees really struck me.  Many trees are now over 3 feet in diameter and over 100 years old (photo at left).
     As I walked around, I was able to spot some common problems associated with tree trunks. Many of these problems are man-made, the result of pruning trees or mowing the ground cover. Let's take a look.

   A healthy trunk is straight with flared roots at the very base of the tree (photo above). The tree trunk at right has a swollen base that features rough, pebbled bark. This type of trunk is the result of an infestation of wood boring insects that attack a tree already under stress.   The stress is usually water related--either too little water (shallow soils) or too much flooding (high water table). You can tell this tree is in trouble when you look at the tree's crown (photo below).

      The canopy of the tree with a swollen base has several dead limbs and has very narrow crown (photo at left). This tree is not crowded by adjacent trees, it is just simply a tree in decline.  If you are planning a tree thinning operation in your grove, this type of tree should be among the first to be removed.

   Here's an all-too-common trunk problem that I like to call mower blight (photo at right). If you hit a tree trunk with a mower and pop off the bark, you have opened up the tree to wood rotting fungi. The kind of wood rot pictured here took years to develop yet the tree has remained productive. However, there will come a time when advancing decay will make this tree subject to wind throw.  Pecan trees seem to tolerate a lot of abuse but its best to avoid hitting trees with farm equipment.

      A lopsided trunk (photo at left) is usually associated with an old pruning wound. Forty years ago this was a forked tree. At that time, one of the forks was removed to encourage the development of a single trunk.  This tree must have had two fairly large forks at the time of pruning because the crease in the side of the tree is a remnant of the old pruning wound.   However, it seems the pruning was done correctly (pruned on a slant) and the trees remains healthy.

    If the pruning cut to remove a fork in a tree is not preformed correctly,  massive wood rot can occur. Here's an example of a tree fork that was removed with a horizontal cut (photo at right).
The flat surface of the pruning wound held moisture from rainfall and accelerated the rate of fungal wood rot. At this point, the decomposition  of the wood is so advanced that it is proving a place for weeds to grow. Cutting a forked tree to one trunk is a good idea, but the way you make the cut is critical for preserving tree trunk health.