As much as agriculture is about growing a certain plant, so it is also about not growing other plants. These “other plants” is a reference to undesirable vegetation (weeds) that manifests itself in gardens, fields, and orchards across the world.
“Weeds” is a term that refers to vegetation that is undesirable for a crop due to a plethora of reasons that may range from aesthetics to their ability to serve as a repository of harmful pests and pathogens. The top concern for the presence of weeds amongst a crop though is the direct competiton for the crop to obtain water, sunlight, nutrients, and space. This competition can have an immense effect on a crop’s performance, and according to the Texas A&M Agrilife handbook on pest control for crops, “four pigweeds per acre can reduce beet yields by as much as 1 ton per acre.” This innocuous sounding number of only four pigweeds causing so much loss in a crop relays into the frightfully astounding ability of 1 acre of land being capable of producing over 500,000 individual pigweed plants over the course of a growing season.
Through my little over a year experience managing Terviva’s 150 acre pongamia orchard located on the Texas Gulf Coast, I have come across all these issues in the constant battle known as orchard floor management. Texas alone has over 4000 species of plants, with virtually every acre of land having the potential to be a unique management situation due to variability in “climate, geography, topography, soil and human activity (Texas Agrilife Pest Control in Fruits, Nuts and Vegetables).” These factors of variability are then amplified when discussing the introduction of a novel crop, such as what Terviva is doing with the commercialization of pongamia. The absence of tried and proven management techniques for a novel crop lends itself to the utilization of endemic practices of the particular planting areas, finding parallels with various existing crops, and always being open to developing and experimenting with new or modified techniques drawn from necessity.
There are many more examples of weeds and their effects on vegetables, but in a closer comparison to a tree orchard agricultural system such as pongamia, the handbook states that “weed competition is the leading cause of failure in newly planted pecan orchards,” However, weeds and their detrimental effect in an orchard goes beyond the initial planting, and their presence through an orchard also hinders machinery or people performing activities such as field maintenance or harvesting throughout the viable life of the orchard.
The management of weeds is performed via three methods: mechanical, chemical, and cultural. Mechanical practices involve the use of various implements that mow the weeds or till the soil, while chemical methods involve the use of herbicides in a selective manner. Cultural control may employ facets of both mechanical and agricultural practices while also including cover crops or selective irrigation to derive a site specific management plan that is unique to the orchard’s needs.
Since April of 2012, I have employed a cultural method that utilizes timed herbicide spraying that is in conjunction with regular mowing. As weeds emerge in the spring, I apply the broad spectrum systemic herbicide glyphosate in an approximately 80 inch band on each side of a row of trees. This method of spraying is to promote a “bare sod” strip of orchard floor that allows for increased water and nutrient utilization by the trees in the strip. This is then followed up with mowing the remaining unsprayed turf strip in between rows that is conducive for both controlling weeds in this area and improving access for workers and equipment during wet conditions. Selectively spraying and regular mowing has also helped with the succession of the vegetation community in the orchard to transition from broadleaves to grasses, with grasses being much less competitive and detrimental to the health of the orchard floor. This control of the broadleaves via these two methods disrupts the broadleaves life cycle and its production of seeds while stimulating grasses to outgrow them.
So as I continue to manage the pongamia orchard in Texas, new lessons both good and bad will likely happen as the ever moving target of weed management occurs. Orchard floor management is a dynamic situation that may involve very localized and novel management techniques that may then be hopefully used in a synergistic fashion for other geographies.
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.