Pecan Herbicide Programs

There are reports of budbreak in the state. Many growers are in the process of getting out herbicide strip applications. There are many herbicide options for pecan growers to choose based on weeds, pre and post emergence, and herbicide activity. UGA Extension Pecan Horticulturalist Dr. Lenny Wells has these thoughts on herbicide choice:

1. Glufosinate and Paraquat would be better selections for burndown than glyphosate under newly planted and young trees because they are contact materials and any potential drift would cause very limited and only temporary damage unlike the systemic glyphosate. Just be sure to protect the bark from any herbicide.
2. Burn down herbicides should include glyphosate where grass is a major issue. Just be careful about drift where using this material under young trees. Paraquat and Glufosinate normally will not give long term control on a thick covering of Bermuda grass.
3. Include pre-emergent herbicides in your program. Again, we have many options here. Alion is an excellent pre-emergence material that gives long lasting control. It has a high price tag, but will significantly cut down on the number of applications you need to make, which offsets the cost. Use the 5 oz/A rate in the first year that you use Alion. After that, you can drop down to the 3.5 oz/A rate. Previously Alion was only labeled for trees 3 yrs of age or older. I was recently told by Bayer representatives that this has changed and can be used on 1st year trees and older. We have tested it for a number of years on 1st year trees at high rates and have never seen a problem.
4. Flumioxazin (Chateau) is also an excellent pre-emergence herbicide for use on trees 1 year and up. Its residual is not quite as long as Alion, but it’s close. Even if you are using Alion, rotation between Alion and Flumioxazin from one year to the next is a good idea to manage resistance and limit the over-use and buildup of indaziflam (Alion) in the orchard.
5. We have many other options for pre-emergence which can be utilized in pecan orchards. These include Surflan, Simazine, Prowl, and Diuron. Isoxaben (Trellis) and rimsulfuron (Metric, Solida, and Pruvin) are recent additions to this arsenal. Of these, Surflan, Prowl, Isoxaben and Rimsulfuron can be used on 1st year trees and up. Trees must be 2 yrs old for Simazine and 3 years old for Diuron. Also, do not use Diuron on sandy soils. Consult the current UGA Pecan Spray guide here for a complete list of herbicides available for pecan and their uses.
6. Tank mixing burndown and pre-emergent herbicides will reduce the number of trips made over the orchard but be sure to have at least 75-80% bare ground when using a pre-emergence material. Most of them need good soil contact to be effective.