Thursday, May 31, 2012

Post-pollination nut drop

    When I'm scouting for pecan nut casebearer, I always notice some level of post-pollination nut drop. The other day, I was able to photograph a single nut cluster that exemplifies two common causes of post pollination nut drop.

     In the photo at right, note the small, rusty-colored nutlet that has completely separated from the peduncle and is just about to fall to the ground. This type of nut drop is due to poor pistillate flower development. In other words, the tree didn't have enough energy to fully create a healthy female flower. In most cases, pecan trees shed these weak flowers early in the growing season, usually during the pollination season.
    The olive colored nut at the top of the peduncle is an example of a second type of nut drop. This pistillate flower was most likely pollinated but the egg inside the ovary was never fertilized. Lack of fertilization can be the result of improper pollen tube growth or a genetic miscue between egg and sperm.  In the photo you can also seeing the beginnings of an abscission zone forming on the peduncle right above the healthy nut (small crack). In shedding the unfertilized nut, the tree will also shed the upper part of the peduncle above the abscission zone.
    This year we are experiencing an "on" year for pecans. The vast majority of our pistillate flowers were healthy and are now developing into a bumper crop of pecans. In contrast, during "off" years we seem to see a lot more post-pollination nut drop of both types illustrated by the photo above.    

Monday, May 28, 2012

Pecan nut casebearer: May 28th Update

    We scouted our native pecan grove this morning and found 2.67% of the nut clusters damaged by pecan nut casebearer. I'm still seeing a bumper crop of nuts on the trees so we do not plan to control this year's casebearer population.
     Recent weather conditions have been ideal for the development of pecan nut casebearer--dry and hot. The slow rate if damage increase we've seen so far points to a relatively light casebearer infestation for 2012. However, we need to keep watching.

Friday, May 25, 2012

Pecan nut casebearer: 1st entry May 25th

     This morning we found 1.67% of our pecan clusters with pecan nut casebearer damage (photo at right). You can identify casebearer damage by the pile of brown frass at the base of the nut and the appearance of fine webbing between nut and peduncle.
    It usually takes 2-3 nuts to satisfy the hunger of just one insect.  Damage levels will peak in 7 to 10 days after first entry. If you plan on controlling this pest, you will need to spray before damage levels hit 5% cluster infestation.

Thursday, May 24, 2012

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.

Wednesday, May 23, 2012

Pecan nut casebearer update

     Three times a week we scout our native pecan grove for signs of pecan nut casebearer feeding. As of Wednesday, May 23rd we have found almost every terminal bearing nuts but only 1 damaged nut. The cool evening temperatures we've experienced over the last three days have slowed both nut development and insect activity way down. However, the weatherman is predicting much warmer temps for the second half of the week. That means we should see increased casebearer activity by the weekend.
    This year's crop load is very heavy (photo at left) so we will not be spraying our grove for casebearer this year.  Instead we will be concentrating our pesticide dollars on scab control.  The weather has been unseasonably dry lately so current scab pressure remains low. However, when we do get a change in the weather, we'll be ready to spray our trees with a fungicide.

Tuesday, May 22, 2012

Pecan bark flaking off?

Kanza Bark
    The other day a pecan grower expressed his concern about the cultivar, Kanza. "It looks like Kanza is susceptible to sun scald. The bark is flaking off". Well the bark looks like it is flaking off (photo at right) but the sun has nothing to do with it. Kanza, like its Major parent, has bark that exfoliates in blocky patches.
    When trees grow in diameter the older (and outer) bark can not stretch to cover the increased girth. As a consequence the outer bark cracks. The shape and pattern of these cracks are genetically controlled and do not indicate any inherited weakness.
    There is huge variation in bark appearance among pecan trees. Growing behind my office are three seeding trees, all the same age and roughly the same diameter. All three trees are in perfect health. Bark appearance among these trees ranges from furrowed to shaggy (Photos below).

Monday, May 21, 2012

Directive pruning young trees

     Grafting a pecan tree is only the first step in developing a strong, nut-bearing tree. Directive pruning is essential for developing a new graft into a tree with a strong straight trunk. Last week we worked on some of the trees we grafted last summer (photo at right).
     Left on their own, young pecan trees will develop multiple leaders and a bushy top. In this photo, you can see at least three new shoots growing in competition to be the central leader.
   Once I remove all the suckers growing below the graft, I move to the top of the tree and select the one new shoot to become the central leader.  You usually find 3 to 4 strong shoots all growing from the top 2 to 3 inches of last year's wood. By choosing the lowest of the strong upright shoots to become my new central leader, I can make a single pruning cut and remove all competing shoots (photo at left).
      Once the cut is made, you can clearly see that I have a new single central leader. Now this shoot will receive all the tree's energy and grow rapidly in both height and girth.
    To make sure I don't loose the tender growth of my new central leader to wind or bird damage, I tie the new shoot to a bamboo stake using plant tie ribbon.  Before leaving this tree, I pinch off the growing points of all lateral branches below the central leader. This slows down the growth of the laterals and focuses all of the tree's resources on growing a strong straight trunk.  

Friday, May 18, 2012

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.

Thursday, May 17, 2012

Pecan Nut Casebearer 2012

    Pecan nut casebearer is one of the primary nut feeding insects that pecan producers must monitor closely (photo at left. Note frass and webbing). During years of low nut production, casebearer larvae can completely wipe out what few nuts are set on a tree. In contrast, casebearer feeding can act as a beneficial nut thinning agent during years when trees set an excessive crop.
    With the this growing season nearly 3 weeks ahead of normal, we got way behind in our normal spring work and failed to get pheromone traps up early enough to capture the flight of first generation adults. However all is not lost. From our experience of monitoring casebearer and pecan nut development for more than 30 years we can predict that first nut entry will occur next week most likely, May 22. Since all northern pecan areas experienced the same early spring this year, The normal differences we see in the timing of budbreak, nut development, and insect appearance from south to north have been nearly erased. As a consequence, everyone should expect first nut entry sometime next week.   
     How can we tell about casebearer by just looking at nuts?   Pecan nut casebearer does not attack until the nuts have been fertilized and the nut begins to swell in size. Look at this pair of photos.
The nuts cluster on the left is pollinated but the pollen tube has yet to grow down to the ovary to fertilize the egg. Note the small size of the nutlet and the fact that the 4 leafy bracts just below the stigma stick outwards. The nuts pictured on the right are fertilized. The small nuts have enlarged and the 4 bracts are now sticking straight up. The nuts in our grove are nearly all fertilized and are now ready to for egg laying by female casebearer moths.

    To spray or not to spray, that is the question. We've been following nut set and casebearer damage levels for many years and have developed a decision tree to determine if spraying for casebearer is really necessary (pictured above).  We start by counting the number of nuts in a cluster on at least 300 nut bearing terminals. If the average cluster size is above 2.9 we have determined that spraying for pecan nut casebearer is not cost effective and in fact nut casebearer  may act as a beneficial thinning agent.  This year our native pecan trees have an average cluster size of 3.8. We may be looking at a record breaking crop in 2012.
    This decision tree was developed for native pecans. Improved cultivars most likely have a higher cluster size threshold for not treating than native trees. However, with the nut set I'm seeing on all our trees, I won't be spraying anything for casebearer this year.

Thursday, May 10, 2012

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.)

Wednesday, May 9, 2012

Bark graft bursting

   A few weeks back, I showed you how I top-worked a pecan tree using the bark graft.  Now, I can show you that the graft has been successful and the new shoots are already 3 to 4 inches long. However, there is something more in the photo to see. The scion is producing catkins and may even develop pistillate flowers in a week or two.
     I'll leave the catkins alone. But if the shoots growing from the scion produce nutlets, I'll prune them off. At this point in the new graft's development, I want nothing but vigorous vegetative growth. I'm hoping to push the scion enough to grow over at least 1/2 of the stock's stump by the end of the growing season.

Tuesday, May 8, 2012

3-flap graft, 3 weeks later

    Three weeks ago I described how to make a 3-flap graft.  This past weekend, I found the buds on the scion greening up and  the rootstock already trying to out grow the new graft. In the photo at left, note that the buds on the scion have expanded to about one-inch-green. Below the graft are two red-tinged shoots that have already grown over 12 inches in the past 3 weeks. Reddish growth is a characteristic of juvenile tissue and is common among pecan seedlings.
    Left alone, the junvenile shoots would out-grow the buds emerging from the scion and eventually shade the scion's growth. I've even seen a sprouted scion die from lack of sunlight caused by shading from rootstock suckers. To force the tree to concentrate all its energy towards scion growth, I trimmed off all sprouts below the graft (photo at right).
    I'll be back to this tree in a couple of weeks to tie the scion's new growth to the bird perch to prevent wind damage.

Monday, May 7, 2012

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.

Friday, May 4, 2012

Inside a bark graft

   Bark grafting is one of the important techniques I use to propagate pecan trees. But have you ever wondered how a bark graft scion actually grows together with the rootstock? I cut open a one-year-old bark graft so you can see exactly how the grafting process works (photo at right).
    In the photo, you can clearly recognize the scion on top but you can also see that it was placed between the bark and the wood along the side of the stock. The stock is identifiable by the flat cut surface made before the scion was inserted. Even three of the staples that I used to hold the graft firmly in place are visible. Look how much wood has grown over the staples in just one year.
    Taking a closer look, we can discover how a tree seals over a graft union. Wood tissue from the scion never actually joins with the wood tissue of the stock.  Note how callus tissue from the scion is rolling over the cut surface of the stock but the wood never actually joins together. The long brown line that marks the scion and stock boundary is another location where wood tissue meets wood tissue and the two never fuse. 
     It is only where cambium tissue from the scion meets cambium from the stock that the tree can grown new wood and bark to cover over the wounds created by grafting. At first, most of the new wood and bark created by the fusion of cambium tissues is located outside the scion-stock boundary. But as the stock and scion continue to grow, new wood is created to cover the cut surface of the stock.
    This photo also illustrates how trees work to block the spread of wood decay that results from tree wounding. On the right side of the tree, a new layer of wood has grown since the graft was made. Note the faint brown line that marks a boundary between this new layer and the discolored wood associated with the pruning wound. Trees develop a specialized boundary layer (the brown line) to wall off decay organisms from reaching new wood tissues.
     A photo of the inside of a much older bark graft can been seen here.

Thursday, May 3, 2012

Mirids on pecan flowers

    Most pecan growers like to look for pistillate flower clusters during the pollination season.  A flower cluster on most every terminal (like this year) is a sure sign of a good nut crop in the Fall. However, when looking for pistillate flowers, you might spot one of the common plant bugs that feed on pistillate flowers (photo above) or on catkins.
    Here's a closeup of the insect (photo at right).  Plagiognathus albatus is a plant feeding mirid (family Miridae) that I see every year during pollination season feeding on pecan flowers (both male and female). This insect does not cause economic damage to the nut crop and disappears from trees at the conclusion of pollination season. We have plenty of insects to worry about controlling in a pecan grove. This mirid is not one of them.

Wednesday, May 2, 2012

A good flood

     Pecan trees are native to the flood plains of major rivers in central and southcentral U.S. These trees are adapted to periodic flooding, and along the Neosho River we seem to have at least one flooding event per year.
     Last Monday night, the area around Chetopa, KS received over 10 inches of rain in a three hour period, swelling creeks over their banks and rapidly filling the Neosho River.  The river spilled out onto the flood plain on Tuesday and peaked on Wednesday.  This flood looks to be a fast rising and relatively fast falling event.
    A flooding event has both positive and negative impacts on the pecan grove. Floods can kill the groundcover and promote denitrification (loss of soil nitrogen). But floods also bring a layer of nutrient-rich silt to the orchard, recharge the water supply deep into the soil profile, and wash away any old pecans left on the ground following last year's harvest.
    This week's flood is high enough to cover the entire orchard but not high enough to cause damage to machinery and buildings.  If we have to live with flooding on the Neosho, this flood was a "good" flood.