Although planning and managing the orchard floor isn't a simple proposition, the premise is basic: managing plants other than the tree that's being grown for fruit production.
"Weeds compete with the crop for water, nutrients, sunlight and space, and can be alternate hosts for insect and disease pests," said Dr. Bradley Majek, Rutgers Agricultural Research and Extension Center. "Weeds also provide cover for rodents, and can interfere with pollination and reduce harvest efficiency."
Grass clippings from between blocks or rows might be useful as mulch for tree rows.
PHOTOS BY SALLY COLBY.
In the case of healthy trees that are yielding well in rows that appear to be fairly well controlled, weeds such as dandelions can interfere with pollination. "That grower paid for someone to bring in bees, and the bees are pollinating dandelions," said Majek. "It's a few degrees colder up [in] the tree, and it's windier up there, and bees prefer dandelions. It's a perfect example of why you don't want dandelions in the orchard, but there's a much more important reason."
Weed season bloom begins with dandelions and continues with white clover, which blooms from spring through summer and fall. By mid and late summer, more weeds such as white snakeroot and goldenrod are flowering. Not only is there a constant bloom of weeds throughout the season, Majek pointed out a statement that appears on many insecticide labels: do not apply when there is bloom in the orchard. "The orchard is full of natural pollinators," said Majek, "and if you go in with spray, you aren't doing them any good." The best plan to eliminate this and other issues is through maintaining a weed-free orchard floor.
Majek said that between the 1950s through the 1970s, many growers clean-cultivated orchard floors from early spring through late fall. Growers who used this method did so because it eliminated weeds and encouraged water penetration. However, Majek said that clear cultivation after the first year has the potential to prune roots, raise oxygen levels in the soil and oxidize organic matter. "Continuous cultivation exposes the soil to erosion, and roots that are pruned are more vulnerable to disease," said Majek. "The decrease in organic matter destroys soil structure." Damaged structure means reduced water penetration and nutrient holding capacity and eventually more soil compaction.
Clean rows between the trees in this young orchard will help encourage pollination of fruit flowers rather than weeds, prevent runoff and maintain soil organic matter.
The first consideration for managing the orchard floor is the impact on the soil. "Not just this year," said Majek, "but next year, and 10 years from now, so that the next orchard you plant has soil that is as good as or better than the soil you're working with today."
Desirable orchard floor vegetation should be minimally competitive with the trees while providing good traction for orchard equipment. The roots of orchard floor vegetation should be shallow, fine and fibrous. Vegetation should not be an alternate host to insects or disease, and should be inexpensive to maintain and easy to control. "Consider the impact of the orchard floor on insect pests and beneficials," said Majek. "We want to encourage beneficials and give them a place to hide, but not to the point that we're providing a food source for insect pests."
Ideally, sod for the orchard floor should be established in late summer prior to the planting year. While preparing the site, consider what species of sod will work best and how that sod will be managed the first few years so that it lasts the lifetime of the orchard. Majek said that pH and fertility should be addressed, and established perennial weeds must be eliminated. Field drainage should be improved through tiling, leveling or other suitable means.
Of the sod species, Kentucky bluegrass and perennial rye are relatively high-maintenance plants, while fescues are better adapted. "Of the tall fescue types, Kentucky 31 is tall growing and vigorous, but needs to be mowed," said Majek. "Hard fescues almost never need to be mowed, but they're hard to establish. A compromise is a turf-type tall fescue that isn't as tall and vigorous as Kentucky 31 but is easier to establish than the hard fescues." For planting between tree rows, Majek recommends a 95 percent hard or tall fescue and 5 percent ryegrass at a rate of 25 to 50 pounds per acre.
Heavy weeds compete with fruit trees for nutrients and may interfere with spray applications intended for the trees.
For planting between rows, Majek said that a drum-type seeder with a roller, such as Brillion, results in a firm seedbed. He also suggests planting perennial rye where trees will be planted the following year. "That will grow for a few months, then you'll kill it," he said, adding that the goal is root decay by spring planting time. "It'll provide a mulch that will help the trees for that first year. If you plant the rye on September 1, think about killing it around December 1." Majek advises a modest application of nitrogen at seeding, and then again early the first and second springs.
Once the sod is established, mowing should remove no more than one-third the height of the grass. Use appropriately timed weed control when necessary. "The idea that we can apply an herbicide once a year, control all the weeds for 364 days and not have carryover on the 365th day is probably not realistic," said Majek. "We can do a much better job controlling weeds if we think in terms of the weed control year beginning in late fall when the soil temperature drops below 50 degrees and until it freezes. We want to have one good rain on residual herbicides before the ground freezes, which means late November to early December."
Majek said that weed control application can be done when most of the fall work is finished. "You'll get good winter annual weed control, daylight levels are low, there will be an activating rainfall, and you can use a lower application rate because it only has to last until June."
The future of floor management might include more use of mulch, either organic or fabric. Considerations include whether or not a mulch will reduce the amount of herbicide used, how mulches affect tree growth and yield, and if new problems will be created by using mulch. Majek said that one concern with mulch is rodent damage. "Voles like it under that plastic landscape fabric, so something has to be done to discourage voles." Trials have shown that the use of Bravo on top of and under landscape fabric eliminated vole problems. "Landscape fabric suppressed weeds for about three or four years," said Majek. "Leaf mulch only works for about a year. It breaks down and encourages weeds unless you add more mulch."
Majek said that trees in a trial comparing mulch to herbicide programs performed better, but that the increased tree growth and early yield increase could not be explained as being fully due to weed control. "We have questions that we still need to answer: What impact does mulch have on fertility, on rootzone temperatures, and on rootzone moisture?" Majek added that grass clippings that come from row middles and placed on top of fabric might make a difference. "We're growing useful mulch every year between the tree rows and dumping it back on the sod," he said. "What we have to find out is whether we can mow the sod so that we can put that mulch in the tree row."
The author is a freelance writer who farms and raises Great Pyrenees in south-central Pennsylvania.