Wednesday, June 22, 2011

Training new grafts

   The grafts we made in late April are growing rapidly. Pecan trees seem to love this hot dry weather and new shoots are bursting out everywhere (photo at right). Now is a good time to do some pruning to direct all the tree's energy into establishing a strong central leader.
    In pruning a new graft, the first thing that must be done is to dig through all those leaves to discover which bud on the scion is growing the best. With this tree, the top bud on the scion had already grown 20 inches in height. The lower bud was not as vigorous, so we pruned it off. We also removed most but not all of the growth below the graft union (photo at right). Note that we use a bamboo stake attached to the tree to train the new central leader and prevent wind damage. The bamboo is 6 feet tall and makes a great training stake and bird perch (if  birds light on the tender central leader they can break out the terminal bud). It also looks like Sonja got a little carried away with the plastic tape we use to tie up the grafts.
    Here is a close-up of the graft union (photo at right). The red arrow points to the wound left behind after we pruned off the lower bud. Note the vigor of the shoot that developed from the upper bud. Looks like we'll have a 5-6 foot tall tree by the end of the summer.
   In a couple of weeks we will remove all growth below the graft union then cut off the grafting tape tied around the base of the scion. We don't want anything to slow this new graft down.

Tuesday, June 21, 2011

Pecan scab development 2011

   Over the past several years, pecan scab has developed into a massive problem for northern pecan growers. This year in SE Kansas weather conditions in May were perfect for scab infection of new leaves (photo at left) and new stem growth (photo below).
    I hope I convinced all growers to apply a fungicide with their casebearer spray (insecticide) to stop the spread of the scab fungus onto the nuts of scab susceptible cultivars. Today, I went out to scout the grove for scab infections on nuts and found that the combination of a fungicide application in early June and hot dry weather has prevented new infections on the developing nut crop.(Photo below)
    The question becomes--will additional fungicide applications be necessary?  The answers depends on you location. It seems that rain has been falling everywhere except extreme SE Kansas. We are dry and will probably skip additional scab sprays this year. In other northern pecan areas, rainfall has been abundant. This means a second fungicide spray should be applied 2 weeks after the 1st spray was made. Keeping scab off of expanding nuts is critical for achieving full nut size and kernel quality.

Friday, June 17, 2011

Casebearer winding down

   Today, when we scouted the trees in our "No-Spray" plots, we discovered two things. First, most of the active casebearer larvae had moved into the third nut of the cluster (photo at left). At this point in the development of the pecan, it usually takes 3 nuts for a single larva to grow large enough to pupate.
   The second thing we learned was that our "No-Spray" plot was effectively sprayed last Monday when the neighbor's spray plane treated the Experiment Field along with the commercial groves north and south of us. The number of clusters damaged in our no-spray plots hit 6% on Monday and stayed at that level the rest of the week. Casebearer larvae inside nuts at the time the pesticide was applied were sheltered from the spray and continued to feed on the cluster.

Thursday, June 16, 2011

Haying a pecan grove effects nutrient budgets

    Many native pecan producers like to cut a hay crop from their groves as a good way to "clean up" the orchard floor. The grove pictured at left looks picture perfect and has a valuable hay crop that can be sold or fed.
    Unfortunately, most growers that regularly hay their groves do not figure in the cost of replacing the soil nutrients that are removed when the hay is trucked off the farm. For every ton of hay harvested, an estimated 30 pounds of nitrogen, 7 pounds of phosphorus and 42 pounds of potassium are removed from the pecan grove.
    Nitrogen and potassium are also used in large amounts to build pecan crops. By removing these important nutrients with a hay crop you are effectively robbing soil fertility away from the much more valuable pecan crop.
    There are two options in dealing with the ground cover. First you can just brush hog down all the vegetation and return all the nutrients and organic matter back into the soil. Or second, you can plan to cut the hay from the grove but increase the amount of N and K you apply in the spring to compensate for expected nutrient removal.

Bacterial wetwood

     Have you ever noticed a wet spot on the side of a pecan tree trunk and wondered why the tree was oozing sap?  Look closely at the wet spot and you will note a thick slimy liquid oozing out of a crack in the bark and flowing down the outside of the tree, staining the normally gray bark dark brown.
     This condition is called bacterial wetwood or slime flux. Bacteria enter the woody tissue of the tree through a broken branch or pruning wound and start working to decay the wood.
    In response to wounding, pecan trees develop lignin fortified internal walls to block bacteria and fungi from penetrating the entire woody interior. The tree's defense mechanism works well in stopping wood rotting organisms from moving deeper into the wood or expanding radially. However, the tree's natural defenses are weakest above and below a wound.
    When you see wetwood, look straight above the weeping bark and you usually find a large pruning wound.  Here's what happens. Bacteria enter the tree at the pruning wound and work downward through the wood. Once the bacteria move far enough away from the pruning wound (and source of oxygen), the wood rotting process becomes anaerobic,  producing methane and nitrogen gasses. The gas pressure becomes so great it actually bursts the bark open and bacterial ooze streams out.
    There is no cure for this disease. You can only work to prevent bacterial wetwood by encouraging tree growth and rapid wound healing. A limited amount of wetwood on a large pecan tree does not seem to limit nut production.

Tuesday, June 14, 2011

Setting squirrel traps

    I've been told a single fox squirrel can cause 200 pounds of pecan losses in a single year. With that amount of crop loss, "old bushy tail" may be the most serious pest of pecans. Squirrels can damage your pecan crop in many ways. As soon as the nuts enter the dough stage in August, squirrels begin cutting nut clusters off trees and eating the entire pecan. Once the shucks split in the fall, squirrels not only eat pecans but they begin to steal your crop by storing nuts in tree cavities and burying them in the ground.
    One of the ways we work to reduce the squirrel population around our pecan grove is to set traps. We use #110 conibear traps (photo at right) mounted on small shelves constructed from 2 by 4 lumber and attached to tree trunks.
   Deck screws are used to attach the 2 x 4 shelf to the trunk of the tree. Mounting the trap on a shelf seems to limit the type of animals caught by the trap to squirrels.
     Notice that we have driven 4 roofing nails into shelf to hold the trap in position. To position the nails on the board, draw 2 lines across the 2 x 4 near the center of the board. The lines should be 3/4 inch apart. Hammer 2 nails on each line about 1 1/4 inches apart.  The large heads of the nails are what actually holds the trap in place.
    When setting the trap, hold the trap open and place over the nails. Squeeze the trap tightly against the nails then set the trap catch. Note that we use pecans to bait the trap but several types of nuts will work. Make sure to bait the trap before setting it ( I don't want to hear about broken fingers!).


Monday, June 13, 2011

Pecan leaf phylloxera

   During this time of year you may notice small, yellow galls growing between the veins of pecan leaves (photo at left). These galls are created by the pecan leaf phylloxera.
     Phylloxera are small, aphid-like insects that overwinter in the rough bark of pecan trees. In early spring, just when the first new leaf bursts from expanding buds, phylloxerans crawl out onto the emerging leaves and start to feed. As leaves expand,  phylloxerans secrete a substance that causes pecan leaves  to grow a galls around each insect.

    Once inside the gall,  phylloxerans produce two generations of offspring that all feed on plant sap from inside the gall. In June, the gall opens up on the underside of the leaf (photo at right shows galls cracking open ) to allow winged adults to fly out of the gall and mate. Mated females then hide under rough bark where their bodies become filled with the eggs that will start next year's population of phylloxerans.
    If phylloxera galls become so numerous they seriously distort leaves, you will see early defoliation of infested leaflets starting in July. To control phylloxera, an insecticide should be applied early in the spring at leaf burst before galls start to form.

Casebearer nut entry update June 13

   We found 6% cluster damage from pecan nut casebearer in unsprayed trees today. This damage level indicates that casebearer damage will increase rapidly over the next 5 days at our location.
   We sprayed our grove last week. We had only a tenth of an inch of rain on Sunday morning, and I'm seeing no casebearer damage in sprayed plots.

Friday, June 10, 2011

Walnut caterpillar eggs

    I was doing some summer pruning a couple of days ago and spotted this egg mass (at left) on the underside of a leaflet. These are the eggs of the walnut caterpillar (Datana integerrima), a major defoliating pest of pecans.
    When I see one of these egg masses, I carefully observe the eggs for a while waiting to see if any parasitic wasps show up. The tiny black wasps, Trichogramma minutum, seem to dance over the egg mass and lay their own eggs inside the caterpillar eggs. These wasps usually keep walnut caterpillar in check, but unfortunately, I didn't see any on this egg mass.
    We will need to keep close tabs on walnut caterpillar this summer, watching of signs of a population outbreak that requires an insecticide treatment.

Casebearer nut entry update June 10

   With all this hot weather we've had,  I expected this year's pecan nut casebearer population to increase faster than normal. But I was wrong. Today we found 1.7% damage to nut clusters in non-sprayed plots. This rate of increase is similar to previous years--the damage starts off slowly but then accelerates 5-7 days after the 1st damaged clusters are spotted. We'll see what happens when we scout next Monday.

Wednesday, June 8, 2011

Casebearer nut entry update June 8th

    Today we found 1% of our nut clusters with an active pecan nut casebearer larva feeding on young nuts. The weather forecast has a 20 to 40% chance of rain through Sunday but in this heat the casebearer population will increase rapidly. To protect our below- average crop from serious nut loss, we are planning on making a pesticide application starting tomorrow morning. We will be using Lorsban insecticide and Headline fungicide.
    If you plan on spraying your trees this week, start at dawn and shut down when temperatures hit 85 degrees F.  Also, check out weather forecast predictions using the National Weather Service website. By typing in your local city and state you can get a local forecast that includes an hourly prediction of temperature and wind speed. Tomorrow it looks like we will get only about 3-4 hours to spray with our airblast sprayer. Wind gusts up to 22 mph  are predicted starting at 10 am and the temperature will hit 85 degrees by noon. On Friday, the winds are supposed to die down but the temperature will still hit 85 by noon.

Tuesday, June 7, 2011

Forcing your grafts

   We've had a pretty good grafting year. One of the reasons for our success is that we only graft trees when they are ready.  The photo at left shows one of Sonja's bark grafts that has already put on 5-6 inches of new growth. But also note that the trunk below the graft has sprouted numerous shoots. These competing shoots will need to be pruned off.
    There is also a very important lesson to be learned from this photo. New growth from the seedling rootstock has the characteristic red coloring associated with juvenile pecan trees. In contrast, the shoots emerging from the scion are totally green, an indication the scion comes from mature (or nut bearing) wood.
    If you ever suffer winter dieback of young grafts, the color of emerging shoots will tell you if at least some of the scion cultivar survived the winter.

    Here's a photo of the same tree with all the suckers trimmed off below the graft union. Removing the suckers will force all the tree's energy into the new graft, accelerating its growth rate. Our next step will be to attach a training post next to the tree. We will tie the graft's new growth to the post to ensure the graft is not broken in the wind.

Casebearer nut entry update June 7th

  Pecan nut casebearer has begun attacking nuts in SE Kansas. On June 6th, Tom Circle found the first signs of larval feeding in his grove near Strauss, KS. On June 7th, we searched over 500 nut clusters and found only one cluster with signs of nut entry at the research station near Chetopa. Because of the extreme heat we've been experiencing, the development of this year's pecan nut casebearer population may be fast. But at this point, we are going to continue scouting until we record at least 2% damage.
    Pecan nut casebearer damage is easily recognized by the pile of frass at the base of a nut and the white webbing that expends from nut to stem (photo above).

Pecan nut development: Pollination and fertilization

    The photos above show two important stages of pecan development. The photo on the left was taken May 19th and shows a cluster of recently pollenized pistillate flowers. The photo on the right was taken June 6th and shows the initial nut expansion that follows fertilization and embryo development. Besides the obvious difference in size, notice the position of the 4 leafy bracts just below the blackened stigma. The bracts on pistillate flowers extend outwards from the nutlet while the bracts on the fertilized nut point upwards.
    The early stages of  nut development are important to recognize because they can be used to time your scouting efforts for early-season pecan pests. Pecan nut casebearer and pecan scab do not attack the pecan crop until nuts become fertilized and begin expanding in size.

Intercropping pecans with soybeans

    Yesterday we spent the day preparing the soil and planting a soybean crop within our double row pecan orchard (photo at right). We established this pecan orchard back in the fall of 2002 and have raised soybeans, wheat, or oats between the trees since that time. 
   The double row system was designed to put tree care first. It features a grass alley way between each double row of pecan trees to allow easy access to the trees all season long.

    In this photo taken a few years ago, you can see recently grafted trees, an oat intercrop, and the grass alley between the double pecan rows The pecan trees are planted 40 ft apart within each row. Trees in adjacent rows are offset so that the distance between the double row is 22.5 feet and trees are 30 feet apart on the diagonal. The space between each set of double rows allows at least 50 feet for grain crop production.

Sunday, June 5, 2011

Lecanium scale

   Once in a while you might notice a shiny brown bump on your pecan twigs. Try to rub off this bump and you will find a dome shaped outer shell filled with white grains. This shiny brown dome is a protective shell created by an insect called lecanium scale (photo above).
    Lecanium scales spend the winter on twigs and branches in an immature or nymphal stage. Development resumes in the spring and mature females produce large numbers of eggs which are protected by their soft waxy covering. The white grains you discover under the waxy shell are the eggs.
     Crawlers that hatch from these eggs move to leaves, settle, and feed on sap during the rest of the summer. They move back to twigs and branches prior to leaf drop and settle for the winter.
     Lecanium scale is rarely a problem in well managed pecan groves. Insecticides applied to control major pecan pests often control scale insects in the nymphal stage. In addition, lecanium scale is often kept in check by beneficial insects. You might notice small holes in the waxy shell indicating that the scale has been visited by tiny wasps, whose larvae devour scale eggs.                      

Friday, June 3, 2011

Planning for scab control

    After several years of wet summers, pecan scab is now on every northern pecan grower's mind. This disease infects the sucks of expanding nuts decreasing nut size, reducing kernel fill, and causing the shucks to stick tightly to the shell at harvest. The photo at left shows nuts that were severely infected with scab early in the season (top left), nuts that suffered little or no infection (bottom right) and varying degrees of infection in between.  We do have cultivars that have resistance to this disease (ie. Kanza, Lakota, Oswego, Major, Shepherd) but native pecans and scab-susceptible, improved cultivars require a fungicide program to prevent scab infections on nuts.

     In northern pecan groves, our pecan scab management program focuses on controlling scab infections on nuts. Pecan scab overwinters as sunken lesions on pecan stems that can lead to infection of  expanding leaves early in the season. These early infections on leaves are rarely troublesome in our area and usually occur only on the most scab susceptible cultivars (a Colby leaflet with dark scab lesions is shown above).
      We start our scab control program when pollinated nuts show the first sign of nut enlargement. This actually occurs a couple of weeks after pollination when the egg inside the pistillate flower becomes fertilized and the embryo starts to grow. It is interesting to note that pecan nut casebearer moths seem to lay their eggs only on nuts that have viable, growing embryos. Because these two pests attack nuts at the same time in the life cycle of the pecan, we usually combine our first fungicide treatment with an insecticide to control both scab and casebearer.
      Depending on weather conditions a second fungicide application may be required 2 weeks after the first application. Last year we sprayed our native pecans twice and high-value, scab-susceptible cultivars 3 times. I'll be posting this year's scab spray program as the season progresses.

Wednesday, June 1, 2011

Leaf Roll Mite

     Long, strapy  leaflets that have curled-up leaf margins are the sure sign of a leaf roll mite infestation. The adjacent photo shows two pecan leaves; The leaf on the right is normal while the one on the left has been attacked by leaf roll mite. These eriophyoid mites are extremely small and visible only under high magification. Leaf roll mites attack only expanding leaves. They feed along leaflet edges causing the leaflet to roll upwards and inwards to form a protective area for the development of mite offspring.
   A closer look at a mite infested leaflet (at right) reveals that the leaflet margins have become thickened and almost gall like.  Leaf roll mite damage is often confused with herbicide injury but only a mite infestation will cause rolled-up and thickened leaflet margins. 
     Leaf roll mite is a minor pest that rarely requires treatment.  You usally need to look long and hard to find infested trees and those trees seem to grow out of the damage.