Friday, June 27, 2014

Pecan scab present and ready to spread

    The other day, a grower called to ask if I had seen any signs of pecan scab this year. If you remember, we had a serious problem with scab last year and lost a large part of our 'Giles' pecan crop to the disease.
     During our conversation, he mentioned that he had looked over his nut crop and found no trace of the disease. The photo at right shows a cluster of 'Giles' nuts I cut from a tree this afternoon.   Everything looks clean and healthy. However, a closer look over the entire shoot revealed that scab was very much present on the tree.

    Below the nut cluster pictured above and on last year's wood, I found a series of small scab lesions (photo at left). These black, scruffy lesions are one of the primary locations the disease overwinters on the tree. Under conditions of high humidity and warm temperatures, scab spores can be released from these lesions and infect expanding leaves or nuts.

    I looked carefully over each of the leaves on the entire fruiting shoot and discovered the terminal leaflets of one of the leaves were spotted with scab lesions (photo at right). The fact that only three leaflets on the shoot had numerous scab lesions tells me that we've had a single, very-brief scab-infection-period this Spring so far.
    How do I know that? First, I know that the scab fungus most effectively colonizes plant parts that are rapidly expanding. Second, I know that the terminal three leaflets are the last leaflets to expand when a new pecan leaf unfurls in the spring. Sometime this past Spring, weather conditions promoted the release of scab spores from old lesions. At the same time, these three leaflets were at the perfect point in their expansion to become infected by the disease. Weather conditions must have dried up quickly after this initial infection period because later expanding leaves show no sign of scab.
    The nuts pictured at the top of this post have stayed scab free so far this year because we applied a fungicide along with our casebearer spray and the nuts have yet enter their period of greatest susceptibility--rapid fruit enlargement. However, we must remain on our guard because scab can spread quickly under the right weather conditions.

Thursday, June 26, 2014

Newly hatched walnut caterpillars found

   While scouting for pecan nut casebearer damage yesterday, we discovered a newly hatched colony of walnut caterpillars (photo at right). At this point in their life cycle, the caterpillars are so small that they can't get their mouth parts open wide enough to chomp through the entire leaf blade. Instead, these first instar larvae simply scrape off green tissue from both surfaces of the leaf. Once walnut caterpillars molt into the second instar, they will be large enough to make entire leaflets disappear.

    I turned over the leaf and found the egg mass where this colony started (photo at left). Walnut caterpillar moths lay row after row of small white eggs in a large cluster. The eggs that look like empty cups are simply eggs that have already hatched. You can see a few eggs that are solid white indicating that a larvae has not yet emerged. However, if the egg hasn't hatched by this point it probably has been parasitized by a trichogramma wasps.
     The walnut caterpillar has two generations per year in Kansas. The first generation hatches in late June to early July while a second generation appears in August. Walnut caterpillars feed together in large colonies. When it comes time to molt the entire colony moves to the underside of a large limb or the trunk and sheds their exoskeletons together in a large clump. You can see photos of later instars in posts I've made during previous growing seasons (2011 & 2102).

Wednesday, June 25, 2014

Following the evidence: Pecan nut casebearer damage development

    This spring I've put together a separate page on this website to keep you posted on pecan nut casebearer activity (see tab above). But today, I wanted to show how the activity of casebearer larvae can be traced by careful observation of frass piles (frass=insect manure).
    As casebearer larvae feed on the inside of pecans, they push all their frass outside into a nice neat pile. In the photo above, the red arrow marked "A" points to a pile of dark, granular frass created by a casebearer feeding inside that nut.
   But that's not the entire story. If you look carefully, the red arrow marked "B" points to a small frass pile at the base of a bud. When casebearer larvae first hatch, they often feed on buds before moving onto the nut cluster. Note that the frass pile at the base of the bud is much smaller than the pile formed at the base of the nut. The smaller pile was created by a smaller, first-instar larvae. By the time the insect moved into the nut, the larvae had grown larger and was eating far more plant material.

    The photo at left is a close up of the frass pile found on the nut seen in the photo above. There are two things to notice. First, fine strands of white webbing are strung between the nut and the pedicel. This webbing serves to prevent the damaged nut from dropping off the tree,  keeping the insect within the tree's canopy.
   Next, notice that there are two different colors of insect frass in the pile. The lighter colored frass was just expelled from the nut betraying the fact that there is still an actively feeding larvae inside the nut.
    The photo at right shows a clear evidence trail of how a single casebearer larvae destroyed three nuts in this cluster. The larvae started at the base of the cluster. At the time of first nut entry, the basal nut was still small and could not provide enough nourishment for the growing larvae.  Once the caterpillar ran out of food in the first nut its moved onto the next nut up the stem. This second nut had grown slightly larger but still didn't meet all the nutritional needs of casebearer. So the larvae moved onto a third nut.
   Looking at the piles of frass at the base of each nut, notice that the size of the granules changes from nut to nut. The first nut attacked has the smallest frass granules indicating a small larvae had fed inside the nut. In sharp contrast, the frass pile at the base of the third nut has large granules that are light in color. Just by looking at the frass, I can tell a full sized larvae is actively feeding on this nut and will probably pupate inside.
    The photo above also demonstrates how webbing, spun by the larvae, holds the nut onto the tree even after a damaged nut aborts. The lowest nut in the cluster is literally holding on by a thread. At a later date, the last nut damaged by casebearer will also abort from the tree. Again, insect webbing will hold this nut in the tree but this time the nut will contain a pupal case. By not dropping to the ground, the survival of both pupae and the emerging adult moths is increased.

Tuesday, June 24, 2014

Notes of this year's grafts

   Over the past couple of weeks, I have been trimming and training my successful grafts. The new growth I've seen on my grafts this year have been outstanding. The photo above is just one example of a tree I grafted with a Kanza scion placed on a 1.5 inch diameter seedling pecan tree using a bark graft. Before I shot this photo, I removed all rootstock suckers, pruned the graft to one shoot, removed stalked buds, then tied the new shoot to a bamboo stake. I protected the entire tree from deer with a 5 foot tall welded wire cage.

   In trimming this tree, I noticed a couple of things that I thought important to point out. The first has to do with the small piece of grafting tape I tied around the scion. I applied the grafting tape to seal in the moisture inside the plastic bag that surrounds the graft union. But look how thin the 1/2 inch tape has already been stretched by the rapidly growing scion. The original scionwood I placed on the tree was roughly the same diameter as the pruning cut you now see at base of this year's green growth.  In just 6 weeks time, the scion stick has  increased in diameter two fold. To prevent possible girdling by grafting tape, I removed the tape but left all other graft wraps in place (photo above).

   In previous posts, I have written about the tree training problems that can be caused by allowing stalked buds to develop on a tree's central leader. I have usually associated the appearance of stalked buds with the growth of young trees but I've never before have I seen stalked buds develop on a new graft--that is until this year.
    At right is a series of four photos that show the buds growing on the graft shown at the top of this post. The first photo (at right) shows the buds on the lowest portion of the scion's new shoot. Here the buds appear small and tightly appressed to the stem.

    Moving up the stem, I found that the lowest bud pictured in the photo at right was small and tight to the stem. However, as I looked up the stem the buds started to develop short stalks.


    Further up the new shoot, stalked buds were longer and looked like they might start sprouting leaves soon (photo at right). If I allowed these buds to remain on the tree, it wouldn't be long before the tree would develop a brushy top with no clear central leader and numerous narrow-angled branches.
   Could it be, that I've just discover the origin of the phrase, "nip it in the bud"? I had to nip off these stalked buds before they could create tree structural problems.
    Finally, I looked at the very top of the new shoot (photo at right). Here I found that stalked buds were developing at the base of leaves that were still expanding. Amazing!
  In training this new graft, I removed every stalked bud on the scion's new shoot, from top to bottom. In 2-3 weeks, I'll revisit this tree, pruning where needed and pinching out any new stalked buds that form.

Saturday, June 21, 2014

Impacts of grazing cattle in a pecan grove

Beef cattle grazing in a native pecan grove
   One of the most common forms of ground cover management in native pecan groves is to pasture cattle. Cattle grazing offers two advantages for a pecan producer: A second source of income from the same parcel of land (pecans + beef) and a significant reduction in orchard mowing costs. 
    The grazing of animals under tree crops is an age old agricultural practice that started soon after man first learned to tend livestock. Travel to almost any Mediterranean coastal area and you'll see the small, rock-walled sheep paddocks with ancient olive trees still dotting a landscape first created by ancient Romans.

   Cattle may help diversify farm income but grazing the pecan grove impacts the ground cover and the trees in ways not easily recognized.
    In the photo at left, the pecan grove on the left side of the fence is pastured while the grove on the right side is mowed. Cattle are picky eaters. Over time, intensive grazing will change the composition of the plants that make up the ground cover. The tall weed growing on the pastured side of the fence is ironweed. This plant has stems as tough as iron, can grow 5 feet tall and is totally avoided by grazing cattle. On the right side of the fence,  you see mostly Canadian wild rye, a common native in our river bottom and great cool season forage grass. You don't see wild rye in the grazed area because the cattle have already chewed it into the ground.
   Grazing has both positive and negative impacts on the pecan grove ground-cover composition. On the plus side, cattle will help control poison ivy and wild grape, keeping those troublesome vines from climbing trees. Over-grazing, on the other hand, fosters the growth of undesirable plants in the ground cover. Mowed-off ironweed stems can damage the rubber fingers of your pecan harvester. Nutsedge, another plant cattle will not eat, will quickly carpet the orchard floor during the summer months. Nutsedge secretes allelopathic substances into the soil that can inhibit the growth of other plants and possibly reduce pecan tree vigor.
    Last year, I saw and explosion of chickweed in thin, over grazed pecan groves. Chickweed is a winter annual weed that germinated in the fall after the cattle were removed from pecan groves in preparation for harvest. Chickweed made such a thick mat of intertwined vegetation that harvesters were unable to effectively pick up the nut crop.

    The biggest impact cattle have on the pecan grove is on soil nitrogen. In the past, I've talked to cattle experts and asked, what I thought was a simple question-- "How much nitrogen does cattle production use per acre?" The knee-jerk response I got was--"Cattle don't use nitrogen, they add nitrogen via urine and manure." Well I knew that couldn't be right. A 100 lb. calf in the spring turns into a 700 lb calf by fall and part of that weight gain is nitrogen containing proteins and amino acids.
   I finally discovered some beef research that estimated the nitrogen uptake by a grazing cow/calf pair. The only problem with reading beef research is everything is reported in animal units not on a per acre basis. So, in calculating nitrogen use by cattle, I will assume that each cow/calf pair utilizes 4 acres of grazing land.
    It is estimated that a cow/calf pair ingests 280 lb. of nitrogen during the grazing season. Of the nitrogen ingested, 10 lbs are retained by the animals and 270 lbs are excreted as urine and manure. But here's the problem. The nitrogen returned to the soil surface via urine and manure is so concentrated in a relatively small area that it overwhelms the soil system and 30-50% of the nitrogen contained in cattle excretions end up volatilizing into the air.
   On a per acre basis, grazing cattle remove only about 2.5 lbs. of N per acre as increased body weight. However, nitrogen volatilization from cattle urine and manure causes a net loss from the pecan grove of between 17.5 to 33.75 lbs. N/acre. Taken together, cattle grazing in the pecan grove removes between 20 and 36.25 lbs of nitrogen per acre.
   Cattle do have a place in native pecan groves but knowing the impacts of grazing on the system is important for growers to understand.  Growers should practice good pasture management techniques to limits the spread of troublesome weed species and be careful not to over graze the orchard floor. Growers should also consider increasing their spring fertilizer nitrogen application by 30 lbs N/acre to replace the N lost to cattle production.

Thursday, June 19, 2014

Time for summer pruning of young trees

    Rain and warm weather makes pecan trees grow and grow fast! The other day, I was out looking at some of our young trees and noticed that stalked buds had already formed at the top of the central leader (photo above). If these buds are allowed to grow, the tree will end up with a developing a bushy, "lolly-pop"  top with no prominent  central leader. To maintain a single leader, I simply pulled the stalked buds (or shoots developed from stalked buds) off the tree with my fingers. The photos above show the central leader before and after all stalked buds were removed. Be careful to look for stalked buds all the way to the top the the leader. The stalked buds were smaller near the top but I could easily see them and snap them off.

    I developed the 2-foot rule for summer pruning to help growers maintain a prominent central leader on their young pecan trees. But after I pruned out all the stalked buds on this year's new leader growth, I noticed how following the 2-foot rule last year has influence the growth of new lateral shoots this year. Look carefully at the photo at right and you can see several new shoots developing on last year's wood (grey bark). These new shoots are developing from secondary buds below last year's pruned off stalked buds.

    Here's a close-up view of the developing new shoots (photo at left). You can see last year's pruning cut and the new shoot growing out below that cut. Now, note how the shoot is developing a nice wide angle branch attachment. That's exactly the type of strong branches we want on a pecan tree.

Monday, June 16, 2014

Spraying for scab and casebearer

    With all the rain we have received over the past couple of weeks, my concern for keeping  pecan scab under control has grown.  So when the weatherman gave us a break from the rain for the next 3 days, I thought it best to start applying a fungicide.  "But what about casebearer control?',  you might ask.
    For the past week, we have been monitoring pecan nut casebearer trying to determine the best spray date for insect control. All last week, this year's casebearer population was stuck at 1% damage.  But today casebearer damage levels started to trend upwards, as we recorded 2.67% cluster damage. So it turns out that today is also a good day to start insecticide applications.
    The weather for spraying pecan trees over the next few days will be far from perfect. A combination of high winds and high temperatures will make the effective application of pesticides almost impossible. To make sure we get good spray coverage of our trees, we will limit our spray operation from the morning's first light until the winds pick up mid morning.
    For this first spray of the 2014 season, we will apply Lorsban insecticide and Stratego fungicide. The best tip I can give you on spraying pecan trees is to slow down your tractor speed and make sure you get complete coverage over the entire canopy. Complete coverage is especially vital for getting  fungicides to work properly.

Sunday, June 15, 2014

Repairing a wind damaged tree

    During the early morning hours, a line of strong thunderstorms rolled through the area. High winds and pounding rainfall woke me up and kept me awake as I listened to the storm whip tree limbs back and forth. Later in the day, I discovered that the wind had broken out the top of a young Greenriver tree (photo at right).
   My first thought was--"Now what do I do? The central leader is gone?".  I walked up to the tree for a closer look at the damage.
    At the point of breakage I discovered two things. First, the vast majority of the wood that broke was healthy (photo at left). A small portion of the stem had been damaged by a flatheaded wood borer. The yellow arrow points to dark tunnels made by the larvae tunneling in the area near the crotch of a side limb. Since the limb broke in the direction away from the wood borer damage, it seems that the insect tunnels created a spot of weakness that allowed a 60 mph gust of wind gust to snap out the top of this tree.
    The second thing I noticed was that the bark had become separated from the wood below the break point (red arrow). By looking over the damage carefully, I formulated a plan to help this damaged tree re-develop a central leader.

    Just above the lowest side limb and just below the area where the bark had separated from the wood, I pruned the tree (photo at right) using my chainsaw. I made a sloping cut that will help foster rapid wound healing. Now all I needed to do was to force the remaining limb to become the tree's new central leader.
    My first step in the tree retaining process was to attach an 8 foot long 2x4 to the trunk of the tree using duct tape (photo at left). I prefer duct tape over nails or screws because it is much easy to remove once the tree wound has healed over. Note that I attached the 2x4 on the side of the tree opposite the one remaining limb.
    Next, I used a orchard ladder to reach the upper portion of the 2x4 and adjacent side limb. Using a nylon rope, I pulled the side limb to an upright position and tied the limb to the 2x4 (photo at right). At this point, the rope is only a temporary fastener. Over time, movement of the tree in the wind can cause a rope to rub right through the bark.  Its time for more duct tape.

    With the rope still holding the limb in place, I used duct tape to secure the limb to the 2x4. To ensure that the duct tape will hold, I applied four layers of tape around tree and 2x4. After taping the limb in place, I removed the rope. At this point, all I have is a side branch raised to an upright position.
    Since I had to remove so much of the tree to repair the storm damage, I decided to postpone  all further pruning until next year. This summer this tree will sprout many new limbs while trying to replace as much of it's lost top as possible. Hopefully, a new central leader will emerge from all the new growth and can begin the tree training process all over again starting next March. I'll keep the 2x4 in place  and the branch tied up until the pruning wound on the main trunk heals over.

Friday, June 13, 2014

Casebearer activity slowed by cool, wet weather

Nut cluster damaged by casebearer larvae
   If you have been following our casebearer counts (posted under the special "Pecan Nut Casebearer" tab above), you will notice that damage by first summer generation larvae has remained at 1% cluster damage all week. Will damage levels ever increase above 1% this year? If so, when?
   Insect activity is greatly influenced by the weather. Casebearer moths are nocturnal creatures. When overnight temps are low (in the 50's and lower) or when rain showers occur during the evening hours, adult activity is greatly reduced. If you look at our moth catch data, you'll find that the numbers bounce up and down. We always caught high numbers of moths following a period of warm, clear nights.
   The long range forecast, predicts a return to summer like temperature during the second half of next week. That's when I predict we will start seeing a rapid rise in casebearer damage. In the mean time, we will continue scouting.  

Monday, June 9, 2014

First nut entry by pecan nut casebearer in 2014

    We spotted the very first evidence of pecan nut casebearer larvae feeding on pecan nuts today. Casebearer larvae typically bore into the base of a nut leaving a pile of frass and some fine webbing that attaches the nut to the pedicel (photo at right). A single larvae usually requires 3 nuts to complete its life cycle.
   It looks like we will probably need to make an insecticide treatment to control this pest sometime towards the end of the week. Timing will depend on the weather and how fast the damage level increases. 
   You can follow the development of this year's casebearer population at the Pecan Experiment Field by clicking of the "Pecan Nut Casbearer" tab above. 

Thursday, June 5, 2014

Juvenile vs. mature pecan leaves

    Last night I was out in my pecan grove checking grafts when I came across the tree pictured at right. Wow! What a colorful display. All the shoots and leaves sprouting from the rootstock were crimson red. The shoots sprouting from the scion were green.
    What you are actually looking at is the difference between juvenile pecan leaves (the red ones) and sexually mature leaves (the green ones). If you look carefully, you can see that catkins were produced by the the sexually mature scion.
   Seedling pecans must grow through an extended juvenile stage before they become capable of producing catkins and pistillate flowers. This juvenile stage usually lasts between 15 and 20 years. Juvenile pecan trees produce leaves and rachises with a noticeable red tinge. Leaves of juvenile trees also tend to be more pubescent (hairy) than leaves of mature trees.
   When grafting a tree, we place a sexually mature twig (the scion) on a juvenile rootstock. Because the scion is sexually mature, the shoots growing from that scion will be sexually mature. This simple fact is the reason grafted trees start bearing pecans at such an early age as compared to seedling (not grafted) trees.
   After taking this photo, I pruned all the trunks sprouts (red leaves) off this tree to focus all the tree's energy into the scion. I also attached a bamboo stake to the trunk, pruned the scion to one shoot, and tied that new shoot to the stake. I've got more grafts to trim tonight but so far the 2014 grafting season looks to be a 100% success year.

Tuesday, June 3, 2014

Forcing a bark graft

   Five weeks ago I top-worked a Jayhawk tree over to a new cultivar by placing a bark graft on the tree's central leader. Today, I returned to this tree for a little post-grafting maintenance. After some much needed rain fell over the weekend, the tree was exploding with rapid shoot growth including multiple shoots growing from the scion (photo above).  I like to prune newly grafted trees frequently during the first summer of grow and the first of June was a great time to get started.

    My first step was to remove all trunk sprouts growing on the central stem below the graft union. I also removed any new shoots that had sprouted from lower lateral limbs that were growing in direct competition with the central leader. Before and after pruning photos are shown above.

    My next step was to choose a single shoot growing from the scion and train that shoot to a bamboo stake. In the photo series above, you can see that the scion sprouted three, equally-vigorous shoots. I pruned out the lower two shoots and kept the shoot growing from the top of the scion. I made this choice based on the direction this upper shoot was growing--right in line with my bamboo stake. I then used some flagging tape to tie the remaining shoot to the stake to prevent wind damage to the tender shoot.

    Next, I moved to pruning the rest of the tree. All the cuts I make on lateral branches below the graft are aimed at reducing competition with the central leader, slowing the growth of lateral limbs, and directing more of the tree's energy towards the scion. My first step was to inspect the tree and remove any limbs that tended to grow upward.
    The red arrow in the photo above points to an upward growing limb. I removed this limb by pruning back to the point it connected to a major lateral limb. The photo above-right shows the tree after pruning.

    I then walked around the entire tree making directive pruning cuts on the tree's new grow.  Whenever a pecan tree starts growth in the spring, a cluster of buds breaks near the terminal of last year's shoot.  From this cluster of new shoots I leave the one shoot that is growing outward, away from the graft union. I prune out all other new shoots (photo at right). I then pinch out the terminal of the one shoot that remains in order to slow its growth.
    The photo below shows my tree after pruning and training. You should note that the new graft is fully exposed to sunlight and remains in the central leader position. I'll need to revisit this tree in a few weeks to prune where necessary and to keep the rapidly growing graft tied to the stake.