Back to October 2016

Stay on Top of Pest Monitoring, Shading Issues

This pecan tree has extensive black aphid damage. (Photo by Larry Stein)

As this Labor Day came and went, I couldn’t help but think of my good friend Horace Brown, now deceased, and his first pecan pie of the season. The Browns had some of the earliest ripening native pecans in the country, and so, Horace was not content to have an apple pie for Labor Day, but rather he had to have a pecan pie. Most years Mr. Brown was picking these early ripening nuts out of the shuck and drying them so indeed he could have that Labor Day pecan pie made from fresh pecans.

And so the harvest season is upon us as the earliest nuts are beginning to open, but what a mixed bag of tricks it remains. For those who have a crop, it has gotten larger in some cases, and for those with not much, I reckon the varmints are finishing off the few nuts they had.

What a year it has been — very wet spring and, my, how did the trees grow! Many trees looked better than they had in years. Then we had a bit of dry time with some heat, but then beautiful, beautiful rains came in August. It was the wettest August on record for the state of Texas with an average of 5.7 inches falling across the state.

Not only did it help the irrigated improved orchards catch up, but it is allowing the native pecan crop to fill beautifully. Often that rain does not fall until mid to late September so to get it in August was indeed very nice. However, in many cases the rain in August caught us sleeping. For most, it would have been time to spray for shuckworm, stink bug and weevil in the areas that have them, but when the rain came, spraying was put on the back burner. And it was only when the yellow splotches started to show on the leaves and the leaves themselves begin to drop, that we realized there was an issue (see extensive black aphid damage to the leaves in photo).

Many of us have come to appreciate a good rain for its ability to wash off the aphids, but this seems to mainly apply to the yellow aphids as the black aphids were feeding away during the rain. Please take the time to see the diversity in your native trees. You will find some trees are terribly affected by the black aphids and others not so much. The same is true for improved varieties as ‘Pawnee’, ‘Choctaw’ and ‘Caddo’ are notorious for getting black aphids. It has been my experience that this holds true from year to year, so those native trees that are most affected this year would be where you would want to scout for the black aphids next year. In many cases the black aphids are now gone, not sure if they were parasitized or what, but keep on the lookout because this is not the time of year for leaf drop.

Typically black aphids start in the more shaded areas of the orchard or grove. Hence, you may have a shading issue that is causing the black aphid issue so you need to keep track of the sunlight hitting the grove floor. The best situation remains one-half sun and one-half shade on the grove or orchard floor when the sun is directly overhead. The big challenge that everyone has is that trees continually grow and so, even though you may have gotten it right for a while, it is an on-going process and if you don’t stay on top of it, the trees will indeed crowd and your overall production will drop.

Often trees will tell you that they are beginning to crowd. Typically the production will decline and also the nut quality will become poorer. Then as larger and larger limbs appear on the ground under the trees, you realize that you are in trouble. At first, it is just the small limbs that shade out and later it is the larger limbs. So, as these limbs die from the lack of light and the limbs fall out of the trees from wind or from the extra weight of water from a rain storm, make a note to check the areas around where trees are losing limbs. If there are other trees that are encroaching on each other, you need to come up with a plan to address the issue. You need to decide which are the trees to leave and which need to go.

In addition, one of the best indicator plants for lack of sunlight is Bermuda grass. Bermuda grass only grows in sun and common Bermuda grass is an okay ground cover in native pecan bottoms. Please realize we are talking about common Bermuda grass and not the forage Bermuda grasses like Coastal, Jiggs or Tifton 85. These forage Bermuda grasses have no place in pecan operations as they are too aggressive and will rob the trees of both water and nutrients. So typically we let common Bermuda grass take over native pecan bottoms; but, when you are out and about, note exactly where this grass does the best. Upon close observation you a, e going to find that where the grass receives full sun, it does very well and as the shade comes in, it grows much less.

If you have leaf drop and the reason is not from black aphids, then you need to investigate what is causing the issue. There has been scab on even native pecans this year so that is a possibility. The other issue could be downy spot; the leaves develop a splotchy appearance on the bottom with a hint of white to brown spots. As the fungus grows in the leaf, it causes the leaf epidermis to collapse and the leaves dry out and die in late summer to early fall. Again as the leaves drop, the tree can no longer fill the nuts. Trees with serious leaf loss should be prime candidates for removal.

Finally as we near nut drop on the native pecans, it is important for growers to pull the livestock out of these areas. We have never had an issue from manure contamination of pecans in Texas and there is no need to have one now. You need to allow at least 45 days for the manure to break down although more would be better. Realize that cattle and other livestock will not only consume, but they can crush the nuts as well. In addition they can rut up the orchard when it is wet, which can hinder the harvest operation. Here is hoping for a golden and bountiful harvest!

Author Photo

Larry A. Stein

Larry Stein is a professor and Extension Specialist for Department of Horticultural Sciences at Texas A&M University.