Pecan scab in a dry year

    While I was walking over our pecan grove checking cultivars for shuck split, I was surprised to find pecan scab. I thought that a summer of heat and drought would eliminate scab disease from the face of the earth. No such luck! Here is a photo of scab infected 'Giles' pecan tree taken this year. You can see scab lesions (black spots) on the shucks, leaflet midribs, and leaf rachii. Infections on all those plant parts means we actually had multiple scab infection periods throughout the season. How do I know this by just looking at a photo?  Here is my thinking.

     The scab fungus infects pecan tissues that are rapidly expanding. As new leaves develop in the Spring, the leaf rachis grows rapidity first, followed closely by expanding leaflets. Now look at the photo at right. Note that scab lesions appear on the oldest leaflets at the base of the leaf while the younger leaflets near the end of the leaf are largely scab free. This tells me that we had a scab infection period early in the growing season but as conditions turned hot and dry new scab infections ceased.

      So if the hot dry weather stopped the spread of scab, why can I find scab on this year's nut crop (photo at left)? The answers lies in this summer's rainfall events. During the second week of August we finally received some much needed rain. Up until that point, the nuts of most cultivars had hardly grown in size. It was like the trees were waiting for a rain to develop normal sized nuts. When the rains came, we received multiple showers over 6 days. The trees responded with a burst of growth in nut size. The combination of a wet week and rapidly growing nuts provided ideal conditions for the spread of scab. However, since this infection period was so late in the season, the amount of scab observed this year will have little impact on shuck split and kernel quality. But remember, scab will be back next year and we should be prepared to control this important disease.
   

Pawnee starts shuck split

    Our Pawnee pecans have started to split their shucks during this last week of September (photo at right). Shuck split in late September is nothing special for Pawnee, but I took this photo to make a point. Like any fruit crop, pecans do not ripen all at the same time. Only one of the three nuts in this cluster has split open. Most pecan cultivars ripen (or split their shucks) over a 7 to 10 day period.
     If you ever spot a pecan on a tree that opens significantly later than other nuts on the tree or doesn't open at all, it indicates one of two things: The nut inside is a blank or the nut is infested with pecan weevil.

Pecan kernel cracks open shell

   The rain we received in mid September has saved this year's pecan crop from drought-induced, total disaster. Last week, I wrote that the September showers promoted kernel filling and the prospects for quality pecan kernels look so much better. But, I also warned that a sudden rainfall after a prolonged dry period can lead to shell splitting (photo at left).
   At this point, I haven't seen a lot of shell splitting. I actually had to search a while to find this Henning nut (at left). What happened to this nut is exactly what it look likes. The kernel expanded so much following the rain that the shell burst open. Note that the shell split, not only along the suture, but also laterally near the base of the nut.
    Nut splitting can lead to serious kernel quality problems. Notice the black spot (with white center) on the kernel near the tip of the nut. A kernel rotting fungus has already attacked the exposed kernel.  As this nut dries before harvest, the kernel will shrink and the shell will close up, hiding the kernel rot.  Only after cracking a sample of our 2011 crop,  will we discover the amount of damage caused by nut splitting and kernel rot. Oh, how I hate surprises at the grading table.

Checking for shucksplit

    The weather has finally cooled off and the 2011 pecan crop is racing to maturity. Some of our earliest maturing cultivars have already split their shucks ('Henning' pictured at right), revealing this year's nut crop. At this point, Henning nuts are still full of moisture and need to dry before they gain full flavor.

    If you are interested in checking the ripening progress of pecan cultivars that have not yet split their shucks, all you need is a pocket knife.  Cut into the shuck about 1/4 the down from the tip of the pecan and try to peel off the a portion of the shuck. If the pecan you are checking has begun the final nut ripening process, the shuck should pop off the nut easily, revealing that the shell is starting to color. I cut a 'Kanza' nut (pictured  above) this morning and found that the top half had separated from the shuck.
    Take a closer look at the Kanza nut (above) and you can see that space has developed between the shuck and shell. The shuck splitting process starts at the end of the nut and work towards the base. Ultimately, shuck split is a two step process: 1st the shuck and nut separate, then 2nd, the sutures in the shuck separate and the shuck splits open. The entire nut ripening process usually takes 9 to 14 days. 

'Giles' pecan kernel fill

     Historically, the cultivar Giles has been a heavy producer of pecans. So heavy, that kernel fill often suffers during "on" years. This year, our Giles trees have a good to heavy crop  and with all the dry weather we've experienced this year, I was afraid most of our Giles nuts would end up on the cleaning pile (ei. poorly filled, light nuts). The photo at right is a cross section of a Giles nut cut last week (14 Sept. 2011, before the rain). You can see lots of air spaces and poor kernel development.

    A week later (photo at right), Giles' kernel development is much improved thanks to 3.5 inches of rain over last weekend. Although you can still see a line running down the middle of each kernel half, it looks like we will have no trouble marketing our Giles crop this Fall.
     There are a couple more things you can notice in the photos about kernel filling . Look carefully at the shell packing material between the two kernel halves. As the kernel has expanded, the partition between halves has become compressed and appears more woody. Also compacted by kernel deposition is the packing material that fills the dorsal groves. Note the color change from orange to tan.

    Part of the reason our pecans are filling so well is because the dry weather started early in the nut sizing period (July). This means that nut expansion was inhibited by lack of rain and our trees produced smaller nuts than in previous seasons.  The photo at left shows a cross section of this year's Giles nut compared to a Giles nut grown in the past. Look at the shape of the shell of both nuts. This year's Giles is shorter and more tapered at the base than the "normal" Giles nut. The good news is that a smaller nut is easier to fill with kernel (less kernel to make) and buyers always like to see plump kernels when they are paying top dollar for northern pecans.

September rain fills kernels

    Over the weekend, 3.5 inches of rain fell in the Chetopa, KS area. Its been so long since I've heard the sound of raindrops on the roof, I could hardly sleep. It is amazing how drought stressed plants react to a sudden supply of water.  In my wife's apple orchard, the rain was welcomed but has lead to a massive amount of fruit cracking (photo above right). As soon as the roots started pumping water from the water soaked soil into the tree, the fruit started to swell in size. Since the fruit's skin couldn't grow fast enough in response to the rapid fruit growth, pop, the skin cracked open.

Lakota, 14 Sept. 2011

    So this morning, it was time to see how the rain  influenced our pecan crop. At left is the cross section of a Lakota nut that I posted last Wednesday (Sept. 14).  In that post, I mentioned that Lakota was still depositing kernel but if rains didn't fall soon, nut quality would be poor. Well the rains came, but was it enough to make an impact on kernel fill?

Lakota, 19 Sept. 2011

  

    Here's a cross section of Lakota today, Sept 19, two days after a major rain event. Wow, what a difference. This Lakota nut is now packed with kernel. Notice that all the voids have been filled with nut meat.
     Just like the apple pictured above, pecans can also suffer fruit cracking. Late rains can swell the kernel up so much that it pops open the shell and splits the shuck. This can lead to kernel rot and ultimately crop losses. However, we are so late in the season, I don't expect to see a lot of shuck splitting. I'm just hoping for better kernel fill over the entire grove. 
    

Drought effects nut fill

     A hot dry summer has played havoc with this year's pecan crop. The dry weather during the 1st half of the summer decreased nut size dramatically. Back in early August, we received some welcomed rains that seemed to perk up our trees. But unfortunately, the rain turned off again and the 100 degree plus temperatures returned. Hot, dry weather in late August through early September has had a major impact on nut fill.
     This morning, I cut open some nuts to check on the progress of nut filling and made some interesting observations.  The first cultivar I checked was Pawnee.  I had expected Pawnee to have nut filling problems this year because of its large nut size but was pleasantly surprised when I found a fairly well packed kernel. However, our Pawnee nuts will not be perfect. In an earlier post, I mentioned that kernel filling starts at the seed coat and works inward. Note that the top of each kernel half has grown much thicker than underside of the kernel. This will mean that, at harvest, our Pawnee nuts will have a concave appearance on the bottom of each kernel half.

    Next, I cut open a Osage nut, thinking that a super, early-maturing nut may be better filled. You can see in the photo that kernel deposition was similar on both upper and lower portions of each kernel half. At this point in the season, Osage has already started the process of shuck separation from the shell and kernel deposition is effectively complete. Note that there are still obvious voids in the kernel. This type of drought damage translates into a dry, crumbly kernel at harvest.

     Lakota ripens almost 2 weeks later than Pawnee and you can see that the nut filling process is still underway. If you zoom in on the photo, you can see translucent areas where kernel is still being developed. Amazingly, we are getting some rain today, with more forecast later in the week. Will these rains help Lakota fill out their kernels? Time will tell, but I think most of our cultivars and all of our native pecans will produce nuts with much lower percent kernel than in normal years.

A ray of hope

 

     Morning light filtering through a native pecan grove quiets the soul and lifts the spirit.

Dominating the landscape

     Last week, I wrote about tree age and response to drought. When I drove into work this morning, I noticed that our soybean crop provided the perfect example of how pecan trees come to dominate the landscape. In the photo at right, note the large native pecan tree marked with a yellow bar. The roots of this tree have suppressed the growth of the adjacent bean crop (out-competed the beans for water). The red arrow points to a distinctive line in the field of soybeans that marks the extent of the pecan roots domination over the bean crop. Even 60 feet away from the tree,  the beans are struggling for water. Outside the tree's influence the beans maybe drought stressed but the plants are 30 inches tall.  It is important to note that a tree's underground influence on its environment extends far beyond the "drip line" of the tree's canopy.

Grafting success

     Over the past several years, I've been preaching the importance of waiting until a young tree tells you when its ready to be grafted.  Here's proof that waiting until the tree is ready yields great results. We used a bark graft on this tree in early May and have grown a strong, central-leader tree that's now over 6 feet tall (even in a drought year!).
   There is one thing I want you to notice on this tree. In mid-August we removed all the wrappings from the graft union and painted that area of the tree with white latex paint. The paint prevents sun scald to the graft union (just like the aluminum foil) but more importantly the white paint gives us an obvious visual cue as to which trees have been grafted and the exact location of the graft union. In a field of 140 young trees,  the white paint on successful grafts will make it easy to locate trees that still need grafting in 2012.
      Grafting is the first step in training young pecans into strong, central-leader trees. To learn more about the tree training process go my 7 post series called "Training young trees" .