Most apple buyers visit farms and purchase the tasty fruit at the farms’ markets or even pull them straight off the trees. Yet, most people probably never consider that growers must keep orchards clear of weeds so the trees can bear those beautiful apple varieties. This article focuses on the weeds most prevalent in the North Carolina region.
So what weeds give North Carolina-based growers the most problems? Wayne Mitchem, Southern Region Small Fruit Consortium coordinator and tree fruit weed management Extension associate at North Carolina State University, said weeds that affect apple growers in the region include large crabgrass, fall panicum, pigweed, lambsquarter, smartweed species, morningglory species, Carolina geranium, dandelion, curly dock, mouse-ear and common chickweed, purple deadnettle and horseweed.
“In newly planted orchards, we recommend growers protect the trunks and use Chateau (flumioxazin) for preweed control,” Mitchem said. “A sequential application of 6 to 8 ounces per acre applied shortly after transplanting and 60 to 80 days later with either paraquat (Gramoxone) or glufosinate (Rely) works very well. If there is a need to control perennial grasses, clethodim (Select), Poast (sethoxydim) or Fusilade (fluazifop) are all available.
“In established orchards, Alion (indaziflam) has performed very well for growers across the Southeast,” he said. “The label allows for good flexibility in that we can use sequential applications of 3.5 fluid ounces per acre in the fall or mid-March followed by five fluid ounces per acre in late May to late June and get residual control through harvest.
“The addition of Zeus Prime XC (carfentrazone-ethyl + sulfentrazone) to the herbicide portfolio is something I think growers should be excited about, too,” Mitchem added. “It can be tank-mixed with oryzalin (Surflan) and applied at the same times as Alion, and it is very effective. The Zeus + oryzalin tank mix may not persist as long as Alion, but it is very good.
“Two advantages Zeus Prime has over Alion is it will provide excellent control of yellow nutsedge due to the sulfentrazone component in the herbicide while the carfentrazone component gives a little extra heat to glyphosate for added burndown of emerged weeds,” he added. “It is also important to not forget Sinbar (terbacil) + diuron (Karmex), diuron + rimsulfuron (Matrix), and rimsulfuron + oryzalin (Matrix + Surflan) programs, which have also proven effective and good options to use in a preherbicide rotation.”
Other established orchards
For established orchards, Mitchem recommends use of a generic glyphosate product at one quart per acre with 2, 4-D amine at 1 pint per acre for nonselective post-control in the late winter and early spring. “Depending on the preherbicide and timing program they are using, this may or may not be used with a pre-herbicide,” he said.
A second option is to use a glufosinate herbicide at 32 ounces per acre with 2, 4-D amine at 1 to 1.5 pints per acre or TreeVix (saflufenacil) at 1 ounce per acre plus a spray-grade ammonium sulfate at 8 to 10 pounds per 100-gallons of spray solution. He added that growers have applied combinations just as effectively using a glyphosate.
“As we move into the late spring and summer, I prefer we use only paraquat or glufosinate for nonselective post-weed control,” Mitchem said. “Work in Michigan and several other places has shown that multiple applications of glyphosate into the summer can have some long-term effects on tree health and has even been linked to fruit storage problems.”
Mitchem said that bermudagrass continues to cause problems for apple growers. “As growers move to higher density, smaller trees, I think it will become more problematic,” he said. “As tree size has decreased, there is less shading of the orchard floor, resulting in a reduced, competitive advantage for the tree over a weed-like bermudagrass that does not thrive in a shady environment.”
Mugwort and nutsedge concerns
He also is seeing more mugwort (wild chrysanthemum) and yellow nutsedge. To control bermudagrass in established orchards, Mitchem recommends using sequential applications of Poast. On the other hand, mugwort is more of a challenge. In conducted trials, he said Alion and Zeus Prime have shown promise when applied sequentially starting in late March, followed by a late May or June application in back-to-back years. He suggests that Sinbar will additionally suppress mugwort. In addition, he said a 3 percent solution of glyphosate as a spot spray works well when mugwort is in full bloom.
“Of these three weeds, yellow nutsedge may be the easiest to deal with because of the herbicide options we have available,” Mitchem said. “Sandea (halosulfuron) is as good on yellow nutsedge postemergence as you can ask for. Zeus Prime is very good as well, and between the two, yellow nutsedge in orchards can be effectively controlled.”
Essentially, weeds can suppress tree growth and fruit size, according to Jim Travis, a former Penn State University tree fruit plant pathologist. Weeds also can take away soil moisture and rob the soil of nutrients. Additionally, he said that weeds promote fruit rots and spots when sunlight is blocked by weeds and when air movement is curtailed by these same weeds.
Practicing general weed maintenance in the orchards and in nearby fields can help keep trees healthy and bearing fruit, according to the University of Florida. Growers also are advised to prevent weeds from producing seeds. One way is to clean farm equipment of weed seed.
Lastly, growers are wise to consider applying herbicides to control weeds at different times during the growing season. The result will be happy customers when they pick up a ripe, delicious apple or pluck one straight off the tree.