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.

Bud break and young trees

    Last summer, I shared with you the observation that you can't always trust information on cultivar performance collected from young trees (trees under 8 inches in diameter). Young trees are more prone to drought stress, nut maturity is often delayed, and nut size and shape are often different on young trees than on mature trees. These inconsistencies between young and mature trees are largely due to the fact that young trees do not have a root system that is large enough to dominate the landscape and out-compete surrounding vegetation for water and nutrients. 
     This spring, I've noticed that bud break on young trees is delayed as compared to nearby mature trees. The photo at right was taken on 26 March 2012. Both twigs were cut from trees grafted to Lakota. The twig on the left was taken from a mature tree measuring 12 inches in diameter, while the twig on the right was collected from a young tree only 4 inches in diameter.
     It seems that this difference in bud break development is not unique to Lakota. Young Pawnee and Kanza trees also were delayed in breaking bud as compared to mature trees of the same cultivar.

Spring fertilization

   After the flood waters receded and all the in-field puddles dried up, we decided to spread some fertilizer today (photo above). We usually apply nutrients in mid March when we notice outer scale split  but decided to wait until after a predicted wet period that had the potential to cause flash flooding. I'm so glad we did. With the cost of urea at $660/ton, we needed to make sure our trees received the nutrients instead of just washing away down river to Grand Lake.
   This year, bud break came early and we are applying fertilizer later than normal (most native trees are slowing swelling buds). We applied the same amounts of fertilizer as last year: 150 lbs. of urea per acre (69 lbs N/ac) and 100 lbs of potash per acre (60 lbs K/ac). The cost of this application, including spreader rent, turned out to be $80.66 per acre. That's a $18.16 per acre increase over last Spring's fertilizer application. Despite the price increase, regular fertilizer application remains the best investment you can make for your trees.

Flowering type noticeable at bud break

    Pecan trees have one of two flowering habits. Those trees that shed pollen before their pistillate flowers become receptive to pollen are said to have protandrous flowering (also known as type 1 flowering). Pecan trees that shed their pollen late in the pollination season and produce receptive pistillate flowers before they shed pollen are called protogynous ( also known as type 2 flowering). Having catkins and pistillate flowers mature at different times on a tree is nature's way to ensure cross pollination.
    You can easily see which flowering habit a cultivar will have by close observation of bud break. Here is a photo of emerging new growth from two pecan cultivars: Oswego and USDA 75-8-5. Oswego is protogynous while USDA 75-8-5 is protandrous. Note that the catkins on the protandrous cultivar are already well developed while  catkins on the protogynous cultivar are barely showing (red arrow points to emerging catkins).
    Besides watching for the time of pollen shed, you will note that catkins produced by protandrous cultivars are short and fat while the catkins produced by protogynous cultivars are long and narrow.

Bud break comes early in 2012

    Last week our pecan trees were under water. So, today was the first time I was able to get around the Pecan Experiment Field to check on this year's bud development. Wow, things have really popped. Of the cultivars I looked at today, Greenriver was farthest advanced (photo at right). Not only had Greenriver buds broken but the new growth had already moved into the leave burst stage.
   

    Today, many of the cultivars I checked were in the bud enlargement stage of spring growth development. Pictured at left is a twig cut from the Kanza cultivar. It was only a week ago that Kanza was still fully dormant.
     Spring temperatures, especially night time temperatures,  have been above normal for this time of year. These warm temperatures have advanced bud break about 2 weeks over last year. The long range forecast looks for continued warm temperatures with no late frosts predicted.

     Not all pecan cultivars are so far advanced. In the photo at right are two twigs I cut today; one from the Chetopa cultivar (left twig) and the other from the Giles cultivar (right twig). Chetopa has progressed to outer-scale split while Giles has nice plump buds with outer scales still intact. Both of these cultivars originated from the Chetopa, KS area and may have have a higher level of spring frost avoidance built into their genetics as compared to cultivars originating from other parts of the pecan's native range. 

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.

Drought is broken

Cattle continue to graze in a partly flooded pecan grove near Chetopa

  Last summer we suffered through heat and drought. In several posts, I shared photos of the soil in our pecan grove cracked open by dryness.  After a warm and dry winter, it has rained every day for 5 straight days dumping around 7 inches of rain on the Pecan Experiment Field and the surrounding area. The heavy rainfall has caused our first flood of 2012 (photo above). As floods along the Neosho River go, this week's "average" flood is more of a nuisance than a disaster. I'm just glad, I was watching the long range forecast and made the decision to delay our March fertilizer applications. With urea costing over $600 per ton, I wanted to make sure our trees received the fertilizer rather than watch all that nitrogen wash down stream. Once things dry up next week, we will get the fertilizer buggy rolling.

USDA cultivars under test

USDA 61-1-X

    Pecan growers are always searching for new, high-quality, disease-resistant cultivars to be included in their orchards. Over the years, we have tested a lot of cultivars that originated with the USDA pecan breeding project. Both Kanza and Lakota were released by the USDA and K-State as the result of our testing efforts. Now, two more USDA clones are showing some promise in trials we are conducting in Kansas and Missouri.
     USDA 61-1-X was developed by crossing Barton with Starking Hardy Giant. The nut is medium sized (6.5 g/nut) and produces an average of 57% kernel. Flowering is protandrous. If this cultivar proves to be scab resistant like its Barton parent, USDA 61-1-X may be just what we are looking for to pollinate the scab-resistant, protogynous cultivars Kanza and Lakota. USDA 61-1-X ripens early, about the same time as Colby.  Both Barton and Starking Hardy Giant have strong alternate bearing tendencies so we will need to watch this USDA cultivar over time to see if alternate bearing develops.

    USDA 75-8-5 resulted from a cross of  Osage and Creek. The nuts produced by this clone are large (7.5 g/nut) even when produced by young trees. The nut produces 55% kernel. Trees are very precocious and have produced well in both SE Kansas and SE Missouri. We have not seen scab develop on this clone at this point. Based on current observations,  USDA 75-8-5 ripens shortly after Kanza. Flowering type should be protandrous since both the parents shed their pollen early (protandrous flowering).  USDA 75-8-5 is another cultivar to watch as a possible pollinator for Kanza and Lakota.

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.  
 

Zapp! A potential new cultivar appears in Illinois

Zapp pecan

    Sixty miles east of St. Louis, Ralph Voss has become known as Illinois' pecan king. Ralph and his family have been involved in the pecan business for over 25 years, harvesting native nuts in the Kaskaskia river bottoms and growing grafted trees on their farm outside of Carlyle, IL. Part of Ralph's pecan business is to offer custom cracking for backyard pecan growers.  Using a Quantz air cracker, Ralph has seen thousands of seedling pecans pass through his shop. One large pecan, caught his eye--a nut from a backyard tree brought in by the Zapp family (photo above). He soon had permission to collect scionwood from the tree's owner and grafted a couple of trees on his own farm.

     Zapp looks to be about the same size as Stuart (photo at left) and may even be a Stuart seedling. However, Zapp ripens about a week earlier than Stuart or about the same time as Lakota. So far, Zapp has shown good resistance to pecans scab in Illinois. We will be grafting Zapp into field trials at the Pecan Experiment Field this Spring so we can observe the performance of this clone in Kansas.

Orchard renewal

    Back in the 1970's, Mohawk and Maramec were among the most highly recommended pecan cultivars in Kansas and Oklahoma. Both nuts are very large and produce large beautiful kernels especially when the trees are young (under 20 years old). As we gained experience with Mohawk and Maramec, we discovered their fatal flaws.  As Mohawk trees mature they become increasing prone to alternate bearing. During the "on" years Mohawk produces so many nuts that the tree can not fill the kernel. In additon, the tree becomes so drained by over production it become very susceptible to winter cold injury. Maramec has just the opposite problem--the trees are under-productive. Maramec is also very susceptible to pecan scab and often suffers cold injury.   

    This year, we decided to remove a group of Mohawk and Maramec trees to make room for more reliable and scab resistant cultivars (photo at right).  We also removed several Coy trees and a couple of natives to give us a 2-3 acre patch of open ground to plant new trees. (Coy is an old and unproductive cultivar only propagated in the Chetopa, KS area).

    In the aerial photo at left, I've marked the area we cleared (red box). Besides removing some very unproductive trees (Mohawk, Maramec, & Coy), we will now be able to utilize several areas that were previously open space for planting new trees.