Tuesday, August 30, 2016

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.    

Monday, August 29, 2016

Late summer graft maintenance

    In late summer, a new graft always seems to want to develop a bushy top (photo at right). This is especially a problem when fairly large trees are top-worked with a bark graft and the scion grows vigorously. The tree in the photo was grafted about 5 feet above the ground on a stump around 2 inches in diameter. In a single growing season, the scion has developed over 5 feet of new growth. Its no wonder I needed an 8 foot tall orchard ladder to get a good look at the top of this tree.

    Perched up on the ladder, I photographed the bushy top of this tree. As I suspected, numerous stalked buds had grown into lateral branches and the tree was rapidly losing its central leader (photo at left).
    Removing stalked buds has always been a priority of mine when training a young graft, so how I let this tree get so far out of control?  The answer is simple. The tree got too tall too fast for me. I usually do all my young tree training from the ground, walking from tree to tree, pinching off stalked buds when needed. When a ladder becomes part of that equation, tree training doesn't seem to happen as often as it should. 
   The primary reason I'm so insistent on removing stalked buds can be seen in the photo at right. Notice the deep crevice the has developed between the main stem and the branch that grew from a stalked bud. Left to grow, this crevice will only become more pronounced leaving the branch prone to snapping off at the point of attachment.
   Since I was up on the ladder, I removed all weakly attached branches with a pair of clippers.

     Lower down the stem of the same tree, I could easily spot where I removed stalked buds earlier in the summer.  The photo at left shows a short stub of a stalked bud that I had pinched out with my fingers. Below the stub is a plump secondary bud that will probably stay dormant until next spring when it will burst forth to create a firmly attached lateral shoot.

   In the mean time, pruning out all the branches that grew from stalked buds helped to re-establish my central leader (photo at right). Look carefully at the main stem and you will see all the pruning cuts left behind after removing poorly attached lateral branches.

   The photos above show the tree before (left) and after (right) pruning. Stepping back away from the tree I could easily see that I was successful in removing the bushy top and reclaiming a single central leader.

Wednesday, August 24, 2016

Squirrels feeding on pecans already

   All summer long, we have been collecting nuts that drop from native pecan trees in drop cages. In most cases these dropped nuts were damaged by stink bugs, shuckworm, casebearer, or pecan scab. However, today we found evidence that squirrels have begun feeding (photo above). A squirrel seems to be able to sense the stage of kernel development inside a green-husked nut and will crack open nut as soon as it begins depositing kernel tissue. This usually means that the earliest ripening trees in the orchard will suffer the greatest amount of squirrel damage.
   We have been trapping squirrels all summer long and hopefully we have reduced the squirrel population around our pecan grove. However, looks like we have at least one squirrel that needs a good dose of lead poisoning.  

Monday, August 22, 2016

Kernel filling: 22 August 2016

    August is the month when pecan kernels start to fill. This morning I collected some nut samples from several cultivars and cut them in half to reveal the stage of kernel fill. Warren 346 is one of the earliest ripening cultivars we have in our collections and, as you can see in the photo above, this nut is rapidly approaching full kernel fill. The Peruque nut has laid down a layer of kernel tissue all along the inside surface of the seed coat. The Kanza nut still contained ample water but I could see evidence that kernel deposition has started as the seed coat wall appears to be thickening. For a close up look at the kernel filling process, check out this post: Pecan kernel filling.     

    When I cut open nuts from several mid-season ripening pecan cultivars, I found all three cultivars still in the water stage (photo above). However, you can still see differences in the development of the kernel. As the seed coat becomes filled with water, the water accumulates under pressure and presses outwards to expand the region where pecan kernel will form. Note now the kernel space inside the Lakota nut is much larger than the Waccamaw and Greenriver nuts. Lakota has advanced further towards kernel filling than the other two cultivars.

   I've mentioned a clone we've labeled SWB617 in previous posts. We think this tree originated as a  Giles seedling so I thought it would be interesting to compare SWB617 with Giles in terms of nut development (photo above).  The Giles nut was still in the water stage while SWB617 had started to deposit kernel inside the nut. However, I spotted a potential kernel filling problem inside the SWB617 nut. Notice how thick the layer of kernel has formed on the dorsal side of each kernel half. Compare that to the thin layer that has developed next to the inner wall partition (blue arrow).  
   Uneven kernel deposition is a sign that the tree is under stress and is having difficulty pumping enough energy into the seed. Two common stresses that cause poor kernel fill are lack of available soil moisture and excessive crop load. Water seems to be the culprit in this case. However, all is not lost. A good soaking rain this weekend could relieve the water stress and this nut would still go ahead and fully fill out its kernel.     

Friday, August 19, 2016

Nut Development: Shellbark hickory vs. Pecan

  Over the past several weeks, I've been recording the development of several pecan cultivars. Hopefully, you have been able to see differences in the rate of kernel development between early ripening cultivars and later ripening cultivars.
    Today, I want to highlight the differences in nut development between two distant cousins in the hickory family--Shellbark hickory and pecan. The shellbark hickory produces a huge fruit that appears to be at least 3 times larger than a pecan fruit (photo above right). To check on the development of the nuts inside these fruits, I cut each fruit in half.

     The pecan shell had only just started to harden up and I could slice through the entire fruit with a pocket knife. In contrast, I had to use a band-saw to open up the hickory. In the photo at left, the huge difference in stage of kernel development between species is very clear. The shellbark hickory is fully packed with kernel while the pecan is still in the water stage.
    The cross section of the hickory nut also reveals some major negative characteristics associated with shellbark hickory as compared to pecan. The hickory has both a very thick shuck and shell. At harvest the shuck of the hickory remains woody, clings to the nut inside,  and is difficult to remove from the nut. Pecan nuts fall from the shucks after a good hard freeze. The thick shell of the hickory and the bony partition between kernel halves make extracting nut meat difficult. In contrast, the Kanza pecan shells easily producing a high percentage of kernel halves.    

Wednesday, August 17, 2016

Black-margined aphids create sticky leaves

   This week, I noticed the appearance droplets of sticky sap spotting the leaves of our pecan trees (photo at right). In fact, when standing in the shade of one of our pecan trees, I could feel tiny droplets of plant sap hit my arms and face. It seems we have begun our annual outbreak of pecan aphids and they are covering the tree and everything under the tree's canopy with honeydew.   

     I pulled a few leaves off a tree to look for aphids.  What I found were numerous adults and nymphs. In the photo at left, note that only the adult aphids have wings. The black markings on the outer edge of each wing identifies this insect as a black-margined aphid. The wing-less insects represent immature stages of aphids call nymphs. Note in the photo that there are several sizes of nymphs. Young aphids molt their exoskeletons as they grow larger leaving behind white cast skins on the underside of leaves. There is one cast skin in the photo, can you find it? (upper center of photo).
    Rain is forecast for this weekend and a heavy rainstorm can often cause a dramatic drop in aphid populations. If we do receive significant rain, we will need to spray for pecan weevil next week and if aphid populations persist we probably add an aphicide to our weevil spray.   

Friday, August 12, 2016

Pecan development: 12 August 2016

    Another week of summer has past and its time to check on nut development.This week Kanza has achieved full water stage. Pawnee seem to be catching up to Kanza. Pawnee kernel halves have grown to full length but seed coat still needs to expand in volume to called full water stage. In comparison, Giles is still expanding in nut size with kernels barely past the 1/2 water stage.   

   This week, I cut open some early-ripening, northern, pecan cultivars. Usually, by this time in August,  Peruque nuts have started to fill out their kernels with nut meat. However, this year Peruque is still in the water stage. Mullahy nuts are starting to form a jell layer  just inside the seed coat. Of these three northern pecan cultivars, Goosepond kernel development was most advanced. White kernel tissue was starting to fill the inside of the seed coat.

Thursday, August 11, 2016

Pecan scab causes nut drop

   Over the past few years, we have set out nut drop cages to monitor the causes of nut abortion over the summer months.  The trees in this trial are not treated with insecticides or fungicides and it's been amazing to discover how many pests can cause nut loss. The tree that has suffered the greatest nut loss this year is a native pecan trees susceptible to pecan scab. The photo at right are just a few of the pecans that fell of the tree in early August. Every nut is covered with scab lesions.

    After finding numerous scab infected nuts in the drop cages, I decided use our hydraulic lift to find out what was going on up in the tree. The photos above show two nut clusters produced by the same native pecan tree. The photos were taken with exactly the same camera settings to allow for direct nut size comparisons. The heavily scab covered nuts (left photo) are much smaller than the still green nuts spotted with scab lesions (right photo). In a previous post, I explained how scab impacts nut grown and kernel fill. But in the photo above I was able to document how scab can cause nut abortion. The orange arrow points to a small scab-infected nut that is just about to fall from the tree. In fact, after taking the photo, the nut fell in a gust of wind.
   By cutting open the nuts that had fallen from the tree, I came to understand that scab causes nuts to abort when the infection starts early during the fruit expansion period. All the nuts I've found on the ground ceased growing before kernels reached the 1/2 water stage. This tells me that the scab infection on these nuts started right after nut fertilization and advanced to full shuck coverage by early July. Nuts that become covered with scab lesions later in the season usually remain attached to the tree and fall during harvest as blackened stick-tight.

Tuesday, August 9, 2016

Mid-summer tree shaking to improve kernel quality

    As the pecans on our trees approach full size, it's a lot easier to see the crop load produced by each pecan cultivar. The photo at right shows a Pawnee tree with limbs already bending down with an over-abundance of pecans.  Left un-managed, this overloaded pecan tree will end up producing a lot of poorly filled nuts this fall and will struggle to produce female flowers next year. Today, I'm going to use my trunk shaker to remove a portion of the crop.

   The prime time for crop load management is during the water stage of kernel development (photo at left). At this point, the tree has invested only a minimum amount of tree energy into building a pecan fruit. In constrast, the kernel filling process and the creation of high-oil-content kernel requires a huge amount of energy.
    We wait until full water stage to thin the crop because the nuts are only now heavy enough to fall when the tree is shaken. 

     I used a tree shaker equipped with doughnut pads to shake off a portion of the crop from my over-loaded Pawnee trees.  In mid-summer, the cambium layer under the bark is still actively growing and can be damaged by improper tree shaking. In addition to using doughnut pads, I apply silicon lubricant between the outer rubber flap and each doughnut pad. The lubricant will allow the rubber flap to slide around when shaking the tree instead of vibrating off a portion of the tree's bark.

    Trees over-loaded with nuts shake easily. A couple of  short-duration, hard shakes will rain down plenty of green-shucked nuts (photo at left). Using a tree shaker to remove a portion of the crop has one disadvantage; nuts are not removed evenly throughout the canopy. After shaking, you'll find more nuts fall from the top of the tree and fewer nuts are dislodged  from low limbs. That's why I always look at the mid-portion of the tree's canopy to judge if I've removed enough nuts.
    The one thing you can't do while summer tree shaking is look at all the nuts on the ground. The typical human response to an orchard floor covered in green nuts is to start thinking about lost nut production. However, shaking off nuts in August actually means that you'll see far fewer poorly filled nuts blowing out of the pecan cleaner after harvest.  

Sunday, August 7, 2016

Fall webworm females laying eggs to start second summer generation

    I was mowing my pecan grove  when I spotted a female fall webworm moth laying a cluster of eggs (photo at right). This egg mass represents the start of a second generation of caterpillars that will create a large white web in the canopy of a pecan tree.
    In our pecan orchard, we will not be applying an insectide specifically aimed at controlling fall webworm.
We will be spraying our pecan trees for stink bugs this week and for pecan weevil later in the month. These sprays will also serve to keep fall webworm populations under control.
    Unsprayed trees will see numerous fall webworm colonies by late August.

Thursday, August 4, 2016

Pecan development: 4 August 2016

    For some reason, the normal timing of pecan fruit development is a little off this year. Today, I collected nut samples from several cultivars and cut them open to check on kernel development. The first two cultivars I looked at were Pawnee and Kanza (photo at right).  The Pawnee kernel is at 1/2 water stage while the Kanza kernel was nearing the full water stage. This year our Pawnee nuts seem to be developing about 10 days behind a normal year  while Kanza is right on schedule. I have no logical explanation for this observation and it make me wonder if Kanza will split shuck before Pawnee this year.
    Next, I cut open nuts from three well known northern pecan cultivars (photo at left). Of these three, Mullahy was most advanced with full kernel expansion and a trace of kernel deposition. Peruque is at full water stage while the Colby kernel was three quarters expanded. When I cut these nuts open, I found the shells of Peruque and Mullahy were starting to harden while the Colby shell was still soft and easily cut.

   I cut open two cultivars that normally ripen at similar times as Kanza and Pawnee. Hark usually splits shuck at the same time as Kanza. However, this year Hark kernel development is well behind the Kanza nut shown above. Judging from the current state of nut development, Hark will ripen later than Kanza this Fall.
    Posey usually splits shuck at the same time as Pawnee in early October. When you compare the development stage of Posey to Pawnee this year, the kernels are very similar. Posey and Pawnee should ripen together again this Fall.

   The final comparison I made was between Lakota and Giles. Typically, these two cultivars share a similar ripening date in mid-October. However, this year Lakota looks to be about a week ahead of Giles in terms of kernel development. It will be interesting to see how ripening dates for these two cultivars compare this Fall.

Tuesday, August 2, 2016

Mid-summer tree training of newly grafted pecan tree

   During the first summer after grafting a tree, I spent a lot of time pruning and training the scion's new growth to ensure I create a tree with a dominant central leader. The tree pictured at right is an example of a bark graft I made this past spring. I've already pruned the scion down to a single shoot back in late-May and removed stalked buds in mid-June. Looking at the photo, the scion appears to be growing straight and tall just like I want it to grow. However, on closer inspection this tree needs a little attention.  

    My first order of business is to prune off all the trunk sprouts growing below the graft union (photo at left). Its amazing how fast these shoots can grow. If left on the tree,  trunk sprouts can compete with the scion for sunlight, slow the growth of the scion, and retard the callusing over of the graft union.When pruning off these sprouts, I make sure to cut flush with the trunk to help retard regrowth later in the summer.
    Just above the graft union, the tree has started to produce lateral limbs (photo at right). These new shoots are developing from secondary buds along the area of the stem were I had removed all the stalked buds back in June. By leaving all these lateral shoots in place, I'll be encouraging the tree to fill out its canopy well below the central leader. In addition, the leaf area provided by these lateral branches will help strengthen the scion's main stem and increase the tree's ability to capture energy from the sun.

    At the top of the tree I found that numerous stalked buds had started to grow and I was in danger of loosing my central leader (photo at left).  I've seen this kind of brushy top develop on almost every young pecan I've grafted. If I don't re-establish a central leader now, I'll be faced with making even larger pruning cuts next spring.

     I re-established the central leader by removing several competing shoots with a single snip of the hand shears. In the photo above, I've marked the location of my cut with a red line. After the cut is made I'm left with a single shoot to become the new central leader. Below this one cut, I also removed all stalked buds and any shoots that had developed from stalked buds.

    Comparing photos of my tree before and after pruning reveals that the pruning cuts I made had little impact on overall tree appearance (photo at right). But that's the point of frequent summer pruning. I'm directing the tree into growing in ways that with result in good tree structure. Making small cuts now will prevent me from having to make massive corrective pruning cuts in the future.