As mentioned in a previous post, orchard floor management is a component of field maintenance by which undesirable vegetation is eliminated or controlled via the three methods of cultivation involving mechanical, chemical, or cultural practices. At Terviva’s 150 acre pongamia orchard in Texas, I have focused on both chemical and mechanical practices for weed control.
Within chemical practices, the use of the herbicide glyphosate has allowed for effective control of weeds in the Texas orchard. This systemic herbicide gives lasting control, that in conjunction with regular mowing, helps keep weed competition at a minimum for the trees. The use of a shielded boom sprayer mounted onto a utility vehicle allows for a quick and efficient means to apply herbicides while also disallowing for any possible occurrences of the herbicide drifting onto the trees during application. “Drift,” as defined by the Texas Pesticide Application handbook, refers to “movement of airborne pesticide, usually in a dust, spray, or vapor, away from a release site.”
However, despite my prudent herbicide application methods, an occurrence of herbicide damage due to drift still unfortunately happened to a few of the trees last year. The pongamia orchard is bordered on two sides (East and South) by farmland that is often used to grow grain crops. One grain crop in particular, sorghum, is often sprayed with glyphosate to dessicate the crop and increase the harvest yield. Unfortunately, as a sorghum field to the south of the orchard was being aerially sprayed, a prevailing southerly wind and misapplication by the pilot resulted in glyphosate drifting onto a nontarget area, the PONGAMIA trees!
As typical with glyphosate’s mode of action that prevents a plant’s ability to synthesize various amino acids, the leaves of the affected trees yellowed, wilted, and often shedded off.
To make matters worse, a tree that has been affected by herbicide damage is often much more susceptible to secondary afflictions from such pests as insects and fungi. The affected trees in the orchard held up well in regard to their level of stress and resistance to secondary afflictions, but the new regrowth did exhibit another tell-tell sign of herbicide damage in the form of wavy and curled leaves. This form persisted for some of the trees for the remainder of the growing season, but as rains occurred that spurned new growth, all the aforementioned visible symptoms to the trees became less and less prevalent.
It has since been a little over a year since the glyphosate damage from the drift occurred on a portion of the trees, and anecdotal observations based on the trees’ current status seems to fortunately show no prevalent visible lasting effects on the trees: no dead trees, no yellowed/wilted or curly leaves, and no obvious stunted growth. This points towards the trees’ robustness and vigorous growth characteristics having overcame what was hopefully minimal amounts of herbicide exposure. However, only time will tell if any lasting effects on the affected trees’ performance will manifest itself in the future. The two pictures below show the same drift affected area of the orchard from shortly after the incident occurred, to its appearance last week.
Keith Kutac is TerViva’s Operations Manager and provides technical support and advice for customer plantings while also actively managing 150 acres of pongamia trees along the Texas Gulf Coast. While Keith was attaining his B.S. in Biology from Texas A&M University, he worked at both the Texas A&M and USDA pecan orchards learning management techniques that are now being practically applied towards pongamia.