Pecans Drop Leaves in Drought Conditions

We are in a drought in south Mississippi. Sure, some areas have had more rain, some less, but things are very dry overall. By my calculations (with data from Weather.com which may or may not be the most accurate) since June 1 we are 20.75 inches in deficit from the average in Poplarville.

Month     AVG     2015     Deficit

June       5.3 in    0.88 in   -4.42 in

July         6.4 in   1.35 in    -5.05 in

August    5.4 in   0.93 in    -4.47 in

Sept.       3.9 in   1.13 in    -2.77 in

Oct.         4.1 in   0.06 in    ????

So, as you can tell things are not good in terms of rainfall.  Pecans, in particular, need a good bit of rain especially during the crucial time of nut filling.  Which, as it turns out, is when the rain stopped falling this year.  Un-irrigated orchards suffered tremendously, with many trees having no nuts at all and then eventually losing a massive amount of leaves, like the tree below.

A defoliated pecan tree. Leaves dropped due to drought conditions.

A defoliated pecan tree. Leaves dropped due to drought conditions.

Unfortunately this is a common sight around south Mississippi. I hear that things are a little better in central Mississippi and not bad in north Mississippi in terms of pecan production this year.  Many trees have also tried to send out new growth to compensate for the lost leaves.

New leaves appearing in October on drought stressed pecan trees.

New leaves appearing in October on drought stressed pecan trees.

These new leaves and shoots have a high probability of being damaged by cold weather when it finally comes for good. This new growth will not have time to properly harden off for the winter. Defoliation can lead to poor return bloom next year as well as overall tree stress which can affect yields and fruit quality.

If your tree is in this shape what can you do?  If you have the capacity to water the tree do so.  If not, then there is nothing to do but hope for more rain.

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Beware Buying Fruit Plants at the Big Box Stores

I only write this as a public service message.  Don’t get me wrong, I am not necessarily blaming big box stores for their inventory.  I don’t know how some of the varieties are chosen and how they are labeled, but the consumer must be wary when shopping at these locations.  This past weekend I visited a big box store for a few items I needed.  I didn’t need any fruit plants, but I decided to take a look at what was available.  Needless to say, I was dismayed at the selection.  Where do I begin?

Available grape vine varieties: Concord, Flame Seedless, Black Monukka, Mars, Thompson Seedless.  Problem: All of these are not resistant to Pierce’s Disease and will die within a couple of years at most. There were no muscadine varieties available at this location in south Mississippi.  It boggles the mind. Solution: Do some serious research before buying grapes in the Deep South. Muscadines are the best option.  Some bunch grapes do have potential, but are not usually very common in the nursery trade.

Available blueberry varieties: Legacy, O’Neal. Problem: There is no problem with these per se, except that one was mislabeled as a rabbiteye variety (Vaccinium virgatum) and the other a wild blueberry species (Vaccinium darrowii) when they are actually southern highbush (Vaccinium spp.).  I did not see any rabbiteye varieties (although I did not look at every plant).  Rabbiteye varieties are the best option for a homeowner here.  Solution: Southern highbush blueberries are partially self-fertile but will do better with a pollinizer.  Rabbiteye varieties require planting two different varieties with overlapping bloom times.  None of this information was available on the labeling at the store.  Local nurseries will have a better selection.

Available pecan variety: Elliot. Problem: There were two tags on the tree.  One said ‘Elliot’ pecan and the other said “ungrafted seedling”, which means it is NOT Elliot, but seedling of Elliot. This is very misleading.  Someone thinking they were getting an Elliot may end up disappointed.  A seedling of Elliot may or may not have some of the Elliot traits that make it desirable to grow.  Pecan trees also need to have two different varieties with overlapping bloom periods in order to produce nuts.  In this case there was only one type available. Solution: Local nurseries may not have the best selection.  The internet is your friend in this case.  Most pecan trees come from AL, GA, or TX, although if you search hard enough you can find some in MS.  A homeowner should choose varieties that are resistant to pecan scab.  If you don’t and do not plan to control the disease, it is really a waste of your time, money, and effort.

Available bramble variety: Boysenberry. Problem: Boysenberry is a hybrid raspberry x blackberry cross that originates from the west coast of the U.S. and is not especially tolerant of high heat conditions.  Coupled with the high humidity and prodigious spring rainfall it is a recipe for poor plant production.  It was also mislabeled as Rubus ursinus. Solution: Many blackberry varieties are available that will grow and produce in the Deep South.  Raspberries fair less well because they too do not tolerate the heat as well as blackberries.  I have seen blackberry varieties available at local nurseries recently, namely Kiowa, Apache, and Brazos (!).  These are far better options than Boysenberry in our area, although the thorny types will have problems with rosette (double blossom) fungus.

There were probably other fruiting plants that I didn’t look at too closely at to see if there were problems with them as well.  The real lesson here is this:  Know what you are looking for and why.  Realize that all blueberries or grapes or pecan are not created equal.  Some do well here and some do not.  Mislabeling is not a new thing in the nursery trade, but seeing the grievous errors in these examples made me cringe.   Before buying at the big box store near you, educate yourself on the crop you wish to purchase, talk to the folks in the garden center, and if you are not satisfied go somewhere else.  Contact your local county Extension office for more information on fruit crops for your area.  Or feel free to contact me.  I can help.

Pollination in Pecans

Pecans are wind-pollinated.  Trees are monoecious, meaning both male and female flowers are on the same tree. Thus, self-pollination is possible, but ultimately undesirable.  There are two main pecan flowering types: protandrous and protogynous.  When male flowers release their pollen before female flowers are receptive, those flowers are protandrous (also called Type I).  When female flowers are receptive to pollen before pollen is shed from the male flowers on the same tree it is called a protogynous flower or Type II.

Some protandrous (Type I) pecan trees include Caddo, Cape Fear, Cherokee, Cheyenne, Creek, Desirable, Gafford, Giles, Jackson, Oconee, Oklahoma, Pawnee, Peruque, and Western.  Some protogynous (Type II) pecan trees are Burkett, Candy, Choctaw, Elliot, Forkert, Kanza, Kiowa, Mahan, Maramec, Mohawk, Mount, Oakla, Podsednik, Schley, Shoshoni, Stuart, Sumner, and Wichita.

Pecan has what is called dichogamous flowering, when male and female flowers mature at different times.  Dichogamy promotes cross-pollination within and between species.  It is also known as heterodichogamy.  Dichogamy may be an intermediary step between synchronous dichogamy and dioecy (male and female flowers on separate plants).  The degree of dichogamy is variable within pecan trees and can be affected by weather.  Moist, warm springs favor male flowers, whereas cool, dry springs favor female flowers.  Some members of the hickory family may switch flowering type depending on the environment in the year.  This has been documented in Shagbark (Carya ovata) and Mockernut (Carya tomentosa) hickories. Complete dichogamy means that no self-pollination is possible.  Incomplete dichogamy results in some level of selfing.  Dichogamy encourages cross pollination and discourages self-pollination.  Self-pollination can lead to inbreeding depression in some plants.

Inbreeding depression occurs when two closely related individuals mate.  Some species have a strong negative response to this situation, whereas some have an intermediate response, and some little to none.  There can be ramifications of selfing, including fruit abortion, suppressed kernel development, and low plant vigor.  The unfit do not survive, thus resulting in a reduction in the number of successful mating individuals within a population.  Selfing also limits the gene flow from other populations.  Genes from other populations help to perpetuate individuals that adapt to environmental stresses.  Species with a strong tendency against self-pollination have greater genetic diversity within populations.  Within pecans, the level of inbreeding is low or inbred seedlings die early and never enter the mating process.

Thompson and Romberg (1985) reported that a single gene determines dichogamy in pecan trees.  This means that the trait is qualitative, or is controlled by a single gene or very few genes.  They reported that protogyny is the dominant trait and protandry is recessive.  This is common throughout the hickory family.  Beedanagari et al. (2005) found that protogyny and green stigmas were linked traits as were protandy and red stigmas.  These traits were tightly linked with little recombination.  This means that the more tightly linked the traits are, the rarer the recombination possibility will be.

There are benefits to dichogamy, with the largest being genetic variation.  More genetic variation leads to better pecan tree survival, continued evolution, and better climate adaptation.  Inbreeding, mating of close relatives or selfing, tends to bring out bad traits and thus ultimately makes the tree non-competitive with its non-inbred neighbors.

References

Beedanagari, S.R., S.K. Dove, B.W. Wood, and P.J. Conner. 2005.  A first linkage map of pecan cultivars based on RAPD and AFLP markers. Theoretical and Applied Genetics 110:1127-1137.

Thompson, T.E. and L.D. Romberg. 1985. Inheritance of heterodichogamy in pecan. Journal of Heredity 76:456-458.

Basic Pecan Production Practices

Last week I was in Wiggins and gave a presentation on basic pecan production practices to an enthusiastic group of attendees.  Many were wanting to renovate their existing trees, but some were interested in planting a new orchard.  I promised that I would post that presentation on this blog, so lo and behold, the link to the PDF is below.

Basics of Pecan Production

There is considerable interest in Mississippi about pecan production, but most of it is for homeowner use and not commercial.  Most of the commercial production is in the Delta, but South Mississippi has a rich history in pecan production.  Unfortunately, hurricanes have had a devastating effect on orchards over the years.

Hopefully the tips in the above presentation will get you started on putting your pecan trees back into production.  It is not always an easy, quick, or inexpensive proposition, but it is always rewarding.

Fall Webworms in Pecan Trees

I have been meaning to write this for some time now, but other things have taken my attention away.  So, Dr. Wayne Porter beat me to it and posted this on his blog, “Gardening in Mississippi”.  It has a great description of the insect and how much damage to the tree it actually does.  I tell most folks that it does no harm to the large trees and is only a concern on small, young trees.  Read on below for more details:

“It is not even fall and they are back! I am getting calls from people asking, “What is that web stuff on my pecan trees!” That stuff is the webbing created by the fall webworm.

The fall webworm appears on pecans in summer as well as in the fall. The fall webworms build larvae nests on the ends of branches. In our area they appear mostly on pecans and up to 90 other deciduous trees.

Damage is caused by caterpillars that eat leaves within the nest and enlarge the nest as they grow. Damage to the tree is seldom serious, but several severe infestations can defoliate and stress a tree, particularly small ones. The adult insect is a one inch, snowy white moth, with dark spots on its wings. The caterpillars are one inch long and covered with silky hair. Their color varies from pale yellow to green with a black stripe on the back and yellow stripe on each side. People usually do not notice the caterpillars until the large, white webs with skeletonized leaves appear.

Although the fall webworm is not considered a deadly pest it does gets lots complaints due to its ugly web that detracts from the aesthetic value of the tree.

You usually do not need to worry about losing your tree is because the webworms are eating leaves relatively late in the growing season. Therefore the defoliation is much less damaging to the tree than had it occurred earlier.

Control of this pest is rarely needed or even effective. You could use stick or high water pressure to break their silk web nest and expose them to their natural predators: birds, yellow jackets, and wasps. Also, you could prune infected branches and burn or otherwise destroy them. Some people attach some newspaper to the end of a long pole, set it on fire, and burn the webs in place.

If using pesticides for the webworm, there are a few that are effective. For severe infestations, spray nests and leaves with Sevin, permithrin, spinosad, or malathion, according to label directions. The best way to apply these chemicals is to spray them around the nest, on branches that the worms may spread to, and inside the nest after first breaking it with a stick. There is an organic product called “B.t.” (Bacillus thuringiensis), sold under the product name of Biotrol, Dipel, or Thurcide. To apply break up newly formed nests, then spray with B.T. in early evening during mid-summer when the caterpillar nests are small. B.t. is slow acting so be patient.

Natural control is preferred whenever possible so poke that hole in the web and let Mother Nature take charge.”

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Pecan Phylloxera

Yesterday at the Beaumont Field Day I spoke on bunch grapes.  But, this post is not about bunch grapes, but rather something else I noticed next to where I was standing.  Directly on the other side of the fence from the station sits a pecan orchard.  With the late freezes we had this year there were few nuts on the trees, but there was a good amount of pecan phylloxera.  Pecan phylloxera cause galls to develop on the pecan trees, usually on leaves or on stems.  They can seriously impact yield if left uncontrolled.  Of course now is too late to control the insect — it must be done early in the season around budbreak and before leaf growth is 1 inch.  This is one case where the insect is akin to a disease — once you see the symptom it is too late to control.  The insect populations can vary from year to year, so they may not be a big problem every year.  For homeowners this insect is next to impossible to control on a large tree because the entire tree would need to be sprayed.  If one had the proper equipment, carbaryl or a dormant oil could control it.  The better option is to have trees that are resistant to the insect — something like ‘Elliot’, ‘Candy’, or ‘Jenkins’ (there are others as well).  Control in a commercial situation is relatively easy because commercial growers have the equipment and access to insecticides, but timing is the key.

Pecan Phylloxera (Phylloxera notabilis, P. russelae, P. devastatrix)

Description: The adults and nymphs are tiny, soft-bodied, cream colored insects resembling aphids.  They are rarely seen.

Life Cycle: Phylloxera overwinter in the egg stage in protected places on branches. The young insects appear in spring about the time the buds unfold.  The insect inserts its (beak) into new leaf or terminal growth and a gall forms that soon envelopes the insect.  The insect matures within the gall and lays a large number of eggs.  Young hatch from these eggs and develop into winged forms.  Usually, in late May or early June the gall splits open and releases the insects.  Infestations may start on one tree and spread out to others.  There are several generations per year.

Symptoms: Galls appear on leaflets or growing terminals.  Leaflets with 4 or more galls may drop.  Severe infestations may produce partial defoliation of affected trees and may interfere with photosynthesis.  Terminals infested by P. devastatrix have galls where the nut clusters would normally develop.  This is the most damaging phylloxera.

More good info on this insect is available at the links below:

http://msucares.com/newsletters/pests/bugwise/2011/bw02_2011.pdf

http://www.lsuagcenter.com/NR/rdonlyres/B26C67FB-C3E7-4BFE-98B8-4D123BBE2074/61951/pub2547PecanPhylloxeraLOWRES.pdf

http://www.aces.edu/counties/StClair/documents/NRPecanTreesLee2012.pdf

http://aggie-horticulture.tamu.edu/galveston/Gardening-Handbook/PDF-files/GH-027–phylloxera-gall-on-pecan.pdf

http://entoplp.okstate.edu/ddd/insects/phylloxera.htm

Image from LSU agcenter.

Hypoxylon Canker of Pecan

Hypoxylon canker  is a devastating disease of hardwood trees in the southern U.S.  I had never seen this disease before until last Friday.  I visited a pecan orchard where several trees were dead and others were in the last throes of life.  The bark was falling off the trees, but the real tell-tale sign (at least to me) was on the dead trees — they had hard, black, tar-like sections under the bark.  I asked the orchard caretaker if he applied tar to wounds on the tree.  He said no.  It was then I was sure of the problem.  So, what to do about it?

Unfortunately, there is not a lot to do.  Tree removal is the best option.  Hypoxylon canker strikes trees that have been stressed.  These pecan trees had been severely stressed during Hurricane Katrina, but also to drought conditions in recent years.  The Hypoxylon fungus does not infect healthy trees, so keeping trees watered and fertilized will help avoid this disease.  Once established, it can be spread by spores from tree to trees, therefore it is imperative to get the infected trees out of the orchard.

The symptoms can vary depending on the tree species, but the first sign is usually thinning out of the canopy (fewer leaves, dying branches, etc.).  This publication has some great photos of the symptoms:

(http://txforestservice.tamu.edu/main/article.aspx?id=1262)

Below are the black tar-like symptoms:

Photographer Information

Name: Robert L. Anderson
Organization: USDA Forest Service
Country: United States

Holes in Tree Bark

I often get questions regarding holes in trees, especially pecan trees.  The holes are not random, but rather in straight lines.  I wrote an article on this a couple years ago for the Oklahoma Pecan Growers Association newsletter (Stafne, E.T. 2010. Trunk damage from sapsuckers: Cause and effect. In: M. Smith (ed.). OPGA newsletter vol. LI no. 2:1-2.)

Here is the text:

Have you ever noticed certain pecan trees with holes?  Lines of holes in perfect rows, row after row?  The cause is not always obvious.  Holes like these are caused by one thing, but may be confused for another.  Wood borers are often blamed, yet they do not possess the acumen to make the holes into perfect lines.  Holes in perfect lines are most definitely caused by another creature – the Yellow-bellied sapsucker (Sphyrapicus varius).

Sapsuckers are close relatives to woodpeckers.  They overwinter mainly in Mexico and Central America and spend the summers in the U.S. and Canada.  Oklahoma is directly in their migratory pathway and pecans are one of their preferred food sources.   The birds are about 7 to 8 inches long with a black head and a white stripe extending down its neck.  The yellow-bellied sapsucker has a red forehead with some pale stripes on the chest with a black border to the throat area.  Its back is black with white bars and has black wings with some white as well.  The yellow breast (or belly) fades to a creamy white from front to rear.  The tail is often black with white bars.

It is often thought that the birds are after insects under the bark.  While this might be true in some cases, they are more likely after the tree sap that exudes once the bark and wood have been penetrated, hence the name sapsucker. The damage caused by the holes themselves is minimal; however, those holes can be entry points for fungi and bacteria (Photo below).  Numerous holes on the same tree may actually weaken the trees, causing stress and susceptibility to other maladies.  Rarely, the tree may be girdled if an excessive amount of holes are made that surround the entire trunk.

Control of the sapsucker is not easy.  Sapsuckers are a migratory, non-game bird and are protected by federal law.  Options for control can include exclusion by wrapping the tree trunk with burlap or other material to discourage the birds from returning.  Another option is frightening techniques like visual or sound devices.  Sometimes, however, these deterrents do not work or work only for a short period of time.  Tactile repellents such as Tanglefoot may be another option to discourage landing upon the trunk.

Above all, one should remember that unless the damage is severe, the tree will likely show little or no problems.  It may be best to just let these elegant creatures have their nourishment from a few of their favorite pecan trees and for us to learn to live together in harmony.

Holes in bark from Yellow-Bellied Sap Sucker

Holes in bark from Yellow-Bellied Sap Sucker