Are the green shucks and gelatinous kernels appearing in pecans falling from trees this season caused by environmental stress or herbicide damage?
Juan Carlos Cabrera-Garcia, local field specialist in horticulture for the University of Missouri Extension, offers a few ways to help tell the difference between environmental stress or herbicide damage.
“I have received calls from people having issues with green shucks falling off pecan trees,” said Cabrera-Garcia. “The tree doesn’t fill the meat and sometimes the kernel is gelatinous inside. Some callers suspect that this issue may be caused by accidental herbicide drift. However, based on the specific symptoms and how widespread the issue is this may be an environmental stress rather than herbicide damage.”
Although the exact mechanisms are not known, Cabrera-Garcia said, embryo abortion can happen if the weather is too hot and dry when the kernel is filling. September was a hot and dry month which may explain why the green pecan nuts are falling off the tree. Some growers have reported the kernels are gelatinous inside and this is a sign of rotted embryos.
“Pecan trees are often planted near corn, soybean and cotton varieties that are resistant to auxin based herbicides (i. e. 2,4-D and dicamba),” Cabrera-Garcia said. “These trees are at risk of being exposed to these herbicides through drift and volatilization.”
Cabrera-Garcia explained, the symptoms of accidental damage from these herbicides appear as deformed leaves (cupping or leaf curling), die-back of foliage, dead limbs and arrested nut development.
These symptoms should be evident when the herbicides are applied in April-June (when fields are prepared for planting) and in the fall months (when defoliants are used in cotton fields). Notice that falling green nuts with gelatinous kernels has not been identified as a symptom of auxin herbicide damage.
Early in 2019, a report from a long term study made by researchers at the University of Georgia was published in the HortTechnology journal. The focus of this study was to determine the effects of auxin herbicide drift on pecan trees.
Cabrera-Garcia said, “The trees were sprayed with 2,4-D and dicamba formulations at rates of 0, 0.01, 0.1, and 1% by volume. In this report, the trees were severely injured by the herbicides but the yields were not affected. The authors suggest that the trees can compensate for the injuries and produce in a similar manner to unaffected trees. You can find the publication at HortTechnology Volume 29 Issue 3 pages 360-366 https://journals.ashs.org/horttech/view/journals/horttech/29/3/article-p360.xml.”
Cabrera-Garcia offers steps to follow if you suspect that your trees have accidental herbicide damage. Document all possible evidence: record the date and location of the damage, write down a description of the observed symptoms, take photos of the symptoms, document yields, and file a formal complaint (within 30 days of the alleged damage) through the Missouri Department of Agriculture Bureau of Pesticide control (573-751-5504 or https://agriculture.mo.gov/plants/pesticides/incidentreport.php).
“At MU Extension we can help with documenting damage, however we do not perform residue testing or file complaints on your behalf,” Cabrera-Garcia said. “Residue testing is done by the MDA after they receive and review a formal complaint.”
Cabrera-Garcia stressed, if using auxin based herbicides on a regular basis, make sure to protect yourself by following the guidelines posted in the product label. Avoid using old formulations of these products, manage equipment to prevent drift, and apply the products in weather conditions specified by the label. Avoid putting yourself at risk of having legal issues, bad relationships with neighbors, and ruining your reputation in the community.
“At MU Extension we can help you with resources and trainings to prevent pesticide spray drift,” Cabrera-Garcia said.