Authored by Pat Minogue
Pat Minogue is an Associate Professor of Silviculture at the University of Florida, School of Forest Resources and Conservation.
As an introduction to our recently published Guide to Using Imazapyr for Site Preparation in Southern Pine Plantation Establishment, it is helpful for landowners to understand the value of earlier site prep. This article outlines the benefits and gives some general information on using herbicides in site preparation.
Landowners looking for the most cost-efficient and effective ways to maximize the value of their pine seedling investments need to stay up to date on “best practices” in silviculture and land management. A body of research has shown that our best pine growth is with earlier site prep (starting in about mid June) rather than the current late season practice. Not only do we get better growth response in June, but there are also other benefits from earlier site prep, including:
- Earlier timing means greater applicator availability. During the “crunch time” later in the season, it can be difficult to find a crew to get the job done. Everybody is already booked.
- Earlier timing gives better flexibility and a wider window for site prep burning. Typically you want to wait six weeks after application to burn to let the herbicide translocate down into the root system, but if we’re doing all the work in the fall and planting in early winter there is much less time to get the burning done if the weather is not cooperating.
- Earlier timing also allows us to prioritize our pine release applications for later in the season when we can electively control the hardwood growth with better pine tolerance and less chance of injury or mortality to the pines.
The ONE CAVEAT to early site prep is that following harvest, hardwood resprouts should be waist high or taller to ensure efficient herbicide uptake.
Timing is not the only issue. Get the right chemical mix.
As the price of site prep chemicals has dropped, the natural inclination is to use more since they are cheaper. But more is not always better. Another common problem area is the use of multiple herbicides such as imazapyr, sulfometuron and metsulfuron methyl that all have the same mode of action, and can easily exceed the threshold for pine tolerance when combined at rates labeled for the individual herbicides. Too much herbicide can stunt or kill your valuable pine seedlings. Longleaf and slash are especially susceptible to these persistent, soil-active herbicides, but loblolly can also be affected. Symptoms of overdose spraying can include pine mortality, but are often more subtle, such as stunting of growth, development of multiple buds at the pine leader and, in the case of sulfometuron and metsulfuron methyl, yellowing of the pine needles.
Based on research and extensive field observations throughout the southeast during the nearly three decades since imazapyr was introduced, we have developed a matrix for site prep rates based on pine species, soil type and the timing between site prep applications and planting, to optimize planted pine seedling growth and survival while avoiding seedling injury caused by residual herbicide.
In the University of Georgia publication A Guide to Using Imazapyr for Chemical Site Preparation in Southern Pine Plantation Establishment, Table 1 gives the suggested highest imazapyr product rate using formulations containing 2 lb. acid equivalent imazapyr per gallon to optimize growth and to minimize planted loblolly, longleaf or slash pine seedling phytotoxicity and Table 2 gives the suggested highest imazapyr product rate using formulations containing 4 lb. acid equivalent imazapyr per gallon to optimize growth and minimize planted loblolly, longleaf or slash pine seedling phytotoxicity.
Pat has more than 30 years experience in agricultural, forestry and environmental research working with USDA ARS Beltsville, North Carolina State University, Auburn University, Cyanamid, BASF and as a private forestry and environmental consultant in the southeastern and western United States. He has been a licensed forester in Alabama and Georgia for many years, and was instrumental in developing herbicide technology for reforestation and improved productivity and health of southern pine and hardwood forests.
For more valuable information on invasive species, forest health, natural resource and agricultural management through technology development, program implementation, training, applied research and public awareness at the state, regional, national and international levels, visit Center for Invasive Species and Ecosystem Health at the University of Georgia.