Here is an article by Dr. Lenny Wells discussing herbicide strips in Pecan Orchards.
With increasing production costs and lower prices last year, growers are looking for creative ways to reduce the cost of production. With this thought in mind, more than one grower has asked me recently, “Do I really need this herbicide strip all year long?”
If you’re talking about an orchard with young trees still in the establishment phase or an orchard not yet bearing, you definitely need to maintain a herbicide strip. Weed competition is one of the biggest drains on growth of the tree and length of time to production.
A few years ago, Dr. Mike Smith at Oklahoma State demonstrated that young tree growth is significantly affected by the weed free area surrounding it. He measured trunk diameter growth on trees with a weed-free area of varying sizes around the tree. Those with the largest weed free area were 18% larger by the 5th-6th years. It does appear that in the first year or so, when the root system is smaller, you can get by with a smaller weed-free area; however, it should be increased to the standard size weed free area by year 3 because tree roots should have grown significanlty by that time.
Eliminating weed competition is key to getting trees into production as quickly as possible. Dr. Smith’s work demonstrated a 334% increase in yield by year 7 on trees with the largest weed-free area.
But, for a mature tree, letting your herbicide strip go won’t necessarily affect the tree or its production all that much. There will be a little competition for nutrients and water but mature, established trees compete well with most grasses and herbaceous plants. The herbicide strips’s main advantage in a mature orchard is to make the wind-row harvest process run smoothly. Therefore, most growers will still need to burn it down as harvest approaches. One confounding factor with this is that too much dead, herbaceous material in the strip can trap nuts when trying to blow them out of the tree row at harvest. If you decide to cut back on the maintenance of your herbicide strip in mature orchards to save money, be sure to mow it (mowing across the rows) prior to the burndown for harvest to try and limit the amount of debris left in the strips which may interfere with harvest.