Brown fuzz on pecan kernels

    Patches of a brown fuzzy material loosely adhering to the surface of pecan kernels are a common sight this fall (photo at right).  This is not a disease but simply some of the internal shell packing material that has become stuck to the kernel.
    During the 2011 and 2012 growing seasons, the brown fuzzy patches were caused by a summer droughts. This year the problem was just the opposite. The summer of 2013 was cooler and wetter than normal. In fact, nut development ran two weeks behind normal all season long. By the end of the 2013 season, many pecan cultivars ran out of time and heat to fully pack the inside of the shell with kernel.
    If the expanding kernel does not fully compress all the packing material tightly against the inside of the shell, some of that packing material can adhere to the kernel. Note that the brown fuzzy material is generally concentrated towards the upper end of the kernel half. This is the part of the kernel that fills last during nut development.  It seems that time simply ran out for kernel filling as shorter days and falling temperatures promoted nut ripening and shuck splitting. 

Drought induced kernel defects

   I was out in the grove checking trees to determine which cultivar we were going to harvest next. As I walked under a Pawnee tree, I grabbed a few nuts and cracked them to check their kernel quality. Among the nuts I sampled, I found two that displayed common drought induced kernel defects (photo at left).
    The nut kernel at the top of the photo is covered in a fine light tan fuzz. Kernel fuzz is not a disease but simply a portion of the internal shell packing material that adheres to the surface of the kernel. Fuzzy kernels occur when insufficient soil water (i.e. drought) retards kernel expansion, preventing the kernel from tightly packing internal shell materials against the inside of the shell. Kernel fuzz is easily scraped of the kernel and does not represent a health risk if eaten.
    Another kernel defect, directly related to a shortage of water during the kernel filling process, is a shortened kernel half (nut at the bottom of the photo).  In this case, one side of the kernel didn't grow out to the end of the nutshell  because there wasn't enough water available to plump out both halves of the kernel. Short kernel halves have no impact of kernel eating quality but their occurrence reduces the total percent kernel harvested from a tree.

Fuzzy pecan kernels

   One of most common questions I receive about pecans is about a kernel defect commonly called "kernel fuzz". In the photo at right are two 'Giles' kernels, each covered with patches of brownish tan "fuzz". Using your fingernail, you can easily scrape off the flaky brown patches to reveal a normal looking kernel underneath.
     Kernel fuzz is not a disease and the brown material that is adhering to the kernel surface is not dangerous to eat. It only tastes dry and bitter. The fuzzy material on the kernel is actually part of the nut's inside shell packing material.
    In a previous post, I presented photos of the nut filling process of 'Giles' pecan nuts. I explained how the expanding kernel compacts both the inner wall partition and the packing material that surrounds the kernel inside the shell.  Fuzzy kernels occur when the kernels don't exert enough pressure on the packing material to compact it tightly together and against the shell. This occurs under two circumstances--not enough water or not long enough growing season.
     Dry weather during kernel fill can inhibit full kernel development, causing poorly filled kernels. These poorly filled kernels are often covered in fuzz especially towards end of the kernel. The 'Giles' kernels pictured above are an excellent example of fuzzy kernels caused by drought.
    Growing late-maturing cultivars in an area that doesn't provide enough summer heat also leads to fuzzy kernels. In this case, long-season pecan cultivars just run out of time to fill the kernel before the cool days of fall arrive. Kernel expansion ceases prematurely in response to cooler temperatures and shorter day length. The packing material isn't compressed fully and the result is fuzzy kernels. In Kansas,  we find the southern cultivar, 'Stuart', and seedlings of 'Stuart' prone to fuzzy kernels.

What's wrong with my pecans?

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   I often receive pecan samples from home owners that have a pecan tree or two in their yard with a note simply saying--"Whats wrong with these pecans?". So I thought it might be a good idea to describe how I determine the problems associated with these type of samples. The sample pictured above came from a gentleman from the Wichita, KS area. The note that came with the sample stated that the pecans produced by his tree rarely fill well and some nuts have an "off" flavor.
    The first step to determine the cause of poor pecan performance is to determine if the nut comes from a grafted tree. These nuts were smaller than most cultivars and the thick shell confirmed the nut to be a seedling. Before cracking the nut open, I noticed that the shell markings that are normally dark black on a pecan were lighter and reddish on the submitted sample. This told me this pecan did not receive a long enough growing season to complete normal nut development. I cracked open the nut and found more evidence that this pecan is not adapted to the Kansas growing season.  Three kernel defects were present--hollow kernels, kernels that don't extend the full length of the shell, and brown fuzz adhering to the kernels. All 3 of these defects indicate that this tree ran out of time (length of growing season) to fill the kernel properly.
   The "off" flavor of some kernels were caused by stinkbug feeding. This problem shows up as darkened areas on the kernels. A full explanation of this malady can be found in a previous post call "black spots on kernels".
  So now its time to make recommendations. There are no remedies for poor genetics. The tree that produced the pecan pictured above likely originated from a seedling tree (or nut) collected in Texas and moved to the Wichita area. During years when we experience a longer-than-normal growing season the nuts will fill better. Stink bugs can be controlled in the commercial pecan orchard setting but the chemicals used are not compatible with application  within suburban neighborhoods.
   This nut sample provides yet another example of why proper cultivar selection is critical for successful pecan production in the North.