JUNE 2003
Texas Cooperative Extension, Texas A&M University, College Station, Texas

   

 

PECAN CARE
Rebounding from the freeze


By Dr. Larry A. Stein, Professor and Extension Horticulturist
Texas A&M University, Uvalde, Texas


hat started out to be a most promising spring for most fruit and nut growers has been shattered by late freezes in March and April. The "old timers" were not too far off this year when they said you needed to get by Easter before you were safe from potential freezes. Let's hope Easter is early in 2004.

It seems that pecans, even natives, were not so "smart" in 2003. Typically, other trees are "out" for days before pecans and the lowly mesquites emerge from their winter slumber. However, even their late emergence was not enough to prevent injury this year. Still, it appears the damage is minimal to pecans for the most part with damage being confined to the lower limbs. Degree of damage was also variable depending on location in the state.

It remains to be seen how the lower limbs will respond; i.e. some may be able to set and retain some nuts or just be barren. Those lower limbs are usually only good for knocking your cap off when trying to shred or do whatever. Still they are usually an easy place to check for casebearer eggs and entries.

Pecans are one of the few crops where you get a "second chance." Not so for other fruit crops such as peaches or plums - the first bloom is all you get; apples and pears are usually not hit so hard, because they grow a shoot and then the flowers appear, which is similar to pecans. These freezes were so late that even some annual field crops were injured. Still, although expensive, they can be replanted.

So, where do pecans get their second chance? Most growers are well aware of the fact that pecans have multiple buds at each node; in fact, they have at least three such buds. The first bud is the biggest and is known as the primary bud; the second is not as big and is the secondary bud and the last visible bud is the tertiary bud. When a primary bud breaks or forces on a tree, which is mature and capable of producing pecans, the first thing which emerges from the bud is a set of catkins (male flowers) on each side of the shoot. A "set" consists of three individual catkins, so each bud produces six catkins. The main shoot comes from the middle of the bud which typically grows four to six inches and hopefully terminates in a cluster of female flowers which, if properly pollinated, will form a cluster of pecans. So at the time of the freezes, a lot of these primary buds had already forced, meaning the catkins and shoots were already showing.

As stated earlier, location in the state and position on the tree determined the amount of damage; the buds on the lower limbs froze worse than those in the top of the tree and in many cases, there was no visible damage at all in the top of the trees. Still, any buds and shoots that were out when the temperatures dropped into the upper 20s were susceptible to the cold. So, if all the primary buds on the tree were out, and they got frozen back, then the tree, if not severely damaged, would push from the secondary buds described earlier.

If the tree was in a healthy state and was "programmed" to produce pecans, the secondary buds can indeed grow a shoot and produce more female flowers. However, these secondary buds produce no catkins; which is where the problem comes in. No catkins means no male flowers and/or pollen. However, when these freezes occurred not all of the primary buds had forced on all the trees. Hence, there were sufficient remaining primary buds to produce ample pollen. Also, the primary buds in the tops of the trees were not injured so this pollen was available as well. So, all in all, it looks like we experienced a very good nut thinning on many lower limbs.

It will be interesting to follow the secondary buds on these shoots, which were hit pretty hard, to see if indeed they produce female flowers and get pollinated. Again, just when you think you have it figured out, Mother Nature throws you a "curve".

The importance of zinc sprays has been mentioned many times before and zinc is no less important to native trees than it is for improved trees. The "catch" is that usually most natives are able to get enough zinc from the soil for satisfactory growth. Generally, improved varieties grow more and hence need more zinc. Still, a couple of zinc sprays will drastically increase even the native leaf surface area in most years which goes a long way to improving the amount of light captured and food manufactured. So, in this year when a lot of expended energy was lost to the cold, it is critical that you help the trees recover this leaf area with foliar zinc sprays. The trees do not care which zinc source you use, just make sure to use either NZN, zinc nitrate or zinc sulfate.

We like to see a minimum of two zinc sprays on native trees, one at bud break and the other with the casebearer application. So, if at all possible, do not skimp on your zinc sprays in 2003.

Finally, now is the ideal time for top working or changing non-productive native trees in your grove to more productive and/or better quality pecans. There is nothing wrong with propagating a "good native" which does well in your grove; or a small, high quality improved variety such as 'Sioux' or 'Caddo' could be used. Still, experience tells us that it is only good to change these native trees if we are going to properly care for them. If we were not going to manage them, then it would be better to leave them as natives.

Experience also tells us that it is best to graft the smaller trees as opposed to the larger ones. True, one could be in production in a shorter period of time if they went up high in these larger native trees and put 20 to 30 grafts in the tree. Still, the labor to not only perform this surgical feat but to do the aftercare as well makes it almost impossible. So, you would be better off to "work" the smaller trees from the back of a pickup with two to three grafts. If you simply must change a larger tree, you would be wise to cut the tree way back this year and allow vigorous regrowth to occur and then graft the tree next spring. It is much easier to graft a smooth vigorously growing shoot than it is an old, rough bark shoot.

For those of you needing a refresher on grafting, check out our latest information at the following web sites:

http://aggie-horticulture.tamu.edu/extension/prop.html.
This site includes some new illustrated procedures for both the four flap and inlay bark graft.

The following site contains quick-time streaming videos of both procedures:

http://aggie-horticulture.tamu.edu/propagation/grafting-movies/index.html.

If some of you would like to have a VCR tape of these procedures, it can be purchased by contacting the Extension Horticulture Office in College Station, TX., at 979-845-7342.

(The previous article was reprinted with permission from "Pecan South" magazine, Texas Pecan Growers Association, 4348 Carter Creek Pkwy, Bryan, TX 77802. Telephone 979-846-3285.)


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