It is a common misconception when people see a sap-like substance on the trunk, leaves, or ground surrounding their pecan tree that the tree itself is dripping sap. In reality, this sap is not coming from the tree at all but from an infestation of aphids living on the tree’s leaves. These tiny insects secrete a sticky substance called honeydew. Find out more about why your pecan tree is dripping sap below.
What You'll Learn Today
- Why Is Sap Oozing Out Of My Pecan Tree?
- Why Is There So Much Sap This Year?
- Will Aphids Kill A Pecan Tree?
Why Is Sap Oozing Out Of My Pecan Tree?
Honeydew, the sticky substance secreted by yellow or black margined aphids, it’s actually the excretion of the insects. You got it, it’s aphid poop!
On first inspection, it can seem like the tree itself is oozing this sticky goop. The reality is it’s coming from large numbers of aphids that are busy sucking the life out of your tree. Pretty soon, their waste starts to run down the trunk and can be found on the leaves and ground below.
Aphids are prey small, usually around 0.039 (4/64ths) to 0.078 (5/64ths) of an inch (one or two millimeters) in length. They are winged insects with soft bodies that live off the sap in the leaves of plants.
These pests may be tiny, but they can wreak havoc! The Black pecan aphid is a lot more destructive than the yellow. It only takes three of these little beasts to create irreparable damage.
When black margined aphids feed, they inject a toxin into the leaves, causing them to first turn yellow, then brown, before eventually dying and falling from the tree.
Black Margined Aphids (Monellia caryella)
These small fly-like insects are yellow and can be identified by the narrow black stripe they have running along the outer edge of their wings. The wings themselves are held flat against their body.
Many generations of black margined aphids will be born, grow and feed over the summer. It takes only six days for one to go from birth to being an adult.
During the summer months, adult females give birth to live young. It is only in late fall when females will lay eggs under tree bark, where they remain protected for the winter, and freshly hatched nymphs emerge in spring.
The nymphs and adults both feed on sap they extract from the leaves of the tree. They then excrete honeydew, the sticky substance that people often confuse for tree sap.
Sooty mold thrives on honeydew, and this can be really problematic for the tree as it prevents proper photosynthesis.
These aphids are most active in early to late summer, and vigilance should be used to check trees for their presence regularly.
Prevention & Treatment
Insecticides can be used to kill these aphids. These should be special aphid-selective insecticides that only kill insects that feed on sap.
To prevent tolerance buildup, insecticides containing different active ingredients can be used in rotation, but they should be applied as a spray to the leaves so the insects ingest the most significant load possible, which helps to prevent tolerance problems.
Other solutions can be to plant winter cover crops such as legumes. This helps increase the number of beneficial predatory insects such as lacewings and lady beetles in spring.
Yellow Pecan Aphids (Monelliopsis pecanis)
Not surprisingly, this type of aphid is completely yellow or greenish-yellow in color. Their wings are held at an angle to the body like the ridge of a roof, rather than flat like those of a black-margined aphid.
Yellow aphids have a lifecycle very similar to that of the black margined aphid. Eggs are laid in bark crevices over winter, and newly hatched nymphs emerge in the spring and start feeding on the young tree foliage. All of these nymphs will be female.
Over the spring and summer, many generations of aphids are born, all female, as these aphids can reproduce without males. Only in fall do males appear, which is how the females make and lay eggs to survive the winter. From birth/hatching to adulthood takes one week.
Yellow pecan aphids infest the trees slightly later than black-margined aphids. They have mouth parts that pierce the outer coating of the leaf veins and suck nutrients and water from inside.
The excess sugars are then excreted in the form of honeydew, which can be found on the leaves. When the aphids reach sufficient numbers, honeydew will even begin to run down the trunk of the tree.
Prevention & Treatment
We looked at how to deal with the black-margined aphids above, and yellow aphids can be controlled similarly. Commercial pecan orchards tend to use Imidaclorpid, Chlorpyrifos, Dimethoate, or Endosulfan, but these chemicals are not generally available to home growers.
A natural alternative to chemical insecticides would be Neem oil. This can be mixed with water and sprayed onto the leaves.
There are also some pecan species that are more resilient to aphid attacks, such as Pawnee.
Black Pecan Aphids (Melanocallis caryaefoliae)
The final type of aphid that attacks pecan trees is the black pecan aphid. Unlike the yellow and black-margined pecan aphid, this one does not excrete honeydew as yellow, or black-margined aphids do.
These are the only black aphids that attack pecan foliage.
Adults are found in shades of black or green, although nymphs are paler. They have pale yellow antennae with black segments along the length.
They have dark red eyes and short cornicles, tube-like structures at the rear of the aphid that face backward. Black aphids are the only species that attack pecan trees to have these appendages.
Each year, starting in spring and continuing to early winter, multiple generations of these aphids will attack pecan trees. The largest infestation is generally seen during early fall.
You will notice small, square, bright yellow spots appearing on the leaves where these aphids have been feeding. These are seen between the veins of the leaves, and the spots will change color from yellow to brown before killing the leaf and causing it to drop from the tree.
Pecan nuts require good foliage to provide the energy to form the nuts. Too few leaves will reduce the quality of the nuts, and this can continue into subsequent seasons.
Prevention & Treatment
Check the leaves of your pecan trees from mid-summer until late fall. Both the top and bottom sides should be looked at every four or five days.
If you have a large number of pecan trees, then checking as many as you can 50% should give you a good idea of the situation.
If you find signs of the blackfly, use foliar applications of imidacloprid. Although a soil-applied version is also available, this will not be sufficient for black pecan aphids.
Other insecticides may also work but check on the packaging. Remember to only use insecticides that will not harm any beneficial insects but will reduce aphid numbers.
In this video, see how to deal with aphids on your pecan trees:
Why Is There So Much Sap This Year?
In some years, the number of aphids can be more problematic than in others. This means that not only will extra damage be done to your pecan trees, but there will be even more sticky honeydew to deal with as it drips from leaves and oozes down the trunks of your trees.
The reason for larger than normal aphid populations includes something causing your pecan trees undue stress or a particularly mild winter.
Trees can become stressed by many things, such as:
- To much or too little water
- Poor soil conditions – heavy clay or very light sand
- Insufficient nutrients in the soil
- Inability to photosynthesize
- Too many trees growing close together
A mild winter will also allow more of the eggs laid during fall to survive and hatch into new young the following spring. When conditions are right, aphids will reproduce at lightning speeds building a massive colony in days.
If you don’t want to use insecticides and planting a cover crop to develop natural predators isn’t an option, you can try growing plants around the border of your orchard to attract predator insect species instead.
These plants should be chosen because they entice “beneficials” insects that will attack and destroy the aphids.
Such beneficials include:
- Seven-spotted lady beetles (Coccinella septempunctata)
- Convergent lady beetles (Hippodamia convergens)
- Ash gray lady beetles (Olla v-nigrum)
- Twice-stabbed lady beetle (Chilocorus stigma)
- Asian lady beetle (Harmonia axyridis)
- Lace wings (Chrysopidae) varieties (Chrysopa rufilabris, Chrysoperla carnea, Chrysopa nigricornis)
- Parasitic wasps (Trioxys pallidus & Aphelinus peri pallidus)
The names of some broad-spectrum chemical controls include:
- Warrior II
- Mustang Mazz
Will Aphids Kill A Pecan Tree?
Although it is not usual for a pecan tree to die from an aphid infestation, it can happen if the numbers are high enough and the tree is weak.
Black aphids are generally known to cause the most damage. The main harm these insects do is to feed on the nutrients in the leaves, which causes the leaves to die prematurely, thus preventing the tree from being able to photosynthesize.
If this process continues over several growing seasons, the tree may eventually become too weakened to survive.
That sticky stuff all over the leaves, trunk, and surrounding your pecan tree isn’t tree sap, after all. In reality, it’s actually insect poop. Aphid insect poop, to be exact.
Of the three types of aphids which attack pecan trees, two are the main culprits for producing large amounts of sticky goo – otherwise known as “honeydew,” which is a very romantic name for what it is!
Yellow pecan aphids and black margined aphids are the problem and should be controlled to prevent damage to the tree and to the crop of nuts the tree will hopefully produce.
To discover more about growing pecan trees and, of course, delicious pecan nuts, take a look at our other articles!