Good weed control is most important early in the season, but fall may be a better time to get the job done.

Good weed control is most important early in the season, but fall may be a better time to get the job done.

Good weed control is essential in modern orchards, where trees are planted at high densities on weak, shallow-rooted rootstocks and can’t handle much competition for water and nutrients.

Given their choice, growers would like to have a simple, one-shot chemical program that would kill all the weeds in late spring and keep them down, at least for the summer during the vegetative and fruit growth stages. Some use such a program, but many don’t find time to address weeds in the spring.

“The key problem in weed control is growers don’t get their herbicides on at the right time,” said Penn State University horticulturist Dr. Robert Crassweller. “Weed control is the last thing they think of as they finish up pruning and get ready for spraying and thinning. So they miss the early spring window of opportunity.

“They should be putting herbicides on in early April in Pennsylvania,” he added.

Crassweller’s been stressing fall applications, thinking growers might be able to find a window after harvest but before the first hard freeze. That’s a good time to attack winter annual weeds, he said, and it’s also a good time to go after perennials like brambles, Canada thistles, wild grapes, Virginia creeper, and poison ivy.

Across most of the Northeast and Midwest, the orchard floor management system of choice is a ­vegetation-free strip where trees grow, between grass-covered, mowed alleys. Tillage is rarely used.

“Cultivation with a disk harrow damages a lot of roots near the surface,” said Dr. Douglas Doohan, an orchard weed management specialist at Ohio State University who keeps abreast of the newest developments in weed control in Midwest orchards. “It’s not the wisest practice.”

Chemical companies continue to develop new and improved herbicides, so there’s no shortage of materials to choose from. About 35 are listed for use on tree fruits, although some are names given to mixtures of ingredients. That doesn’t include all the names for glyphosate, which is now a generic product that comes with 35 brand names. There are many fewer active ingredients than products.

An emerging problem has been the heavy reliance on glyphosate and the idea that one material can do everything. One key problem, according to Dr. Robin Bellinder at Cornell University, is a growing number of weeds are resistant, and relying on this one herbicide will cause a shift in the weed spectrum toward resistant species.

Second, a growing number of weed specialists are concerned that glyphosate may be doing more damage than once thought, especially to young trees. Orchardists have used tree wraps, paint, and shields to keep the chemical away from sensitive tree trunks, but the newest concern is the effect it may be having on shallow roots or perhaps through suckers.

“A number of growers who have used it over the years feel it leads to gradual tree decline,” Doohan said. “The research has not yet been done, but the theory is that somehow active ingredient is getting into the trees, reducing their health even at very low doses.”

New products

Many of the newer products being registered are contact materials, claiming to do what glyphosate does but doing it to resistant weeds, or claiming to do what paraquat does while being safer for the applicator, or claiming to be low in volatility so they can be used around sensitive crops like grapes, unlike glyphosate or 2,4-D amine. Some are mixtures of products trying to be the perfect combination for some special situation. Not all of them are registered for use in all fruit-growing areas.

Bayer CropScience has launched a new formulation of Rely (glufosinate-ammonium) called Rely 280, which is also less expensive than the original version. Rely 280 is a nonselective contact herbicide registered for post­emergent weed control of broadleaf weeds and grasses.

DuPont’s Matrix (rimsulfuron) was registered for use on fruit two years ago and is also touted as providing broad-spectrum pre- and postemergence control of many broad-leaved weeds and grasses and improving the burndown of contact herbicides. It is not for use on new plantings.

Treevix (Kixor) is new this year from BASF. It has both contact and residual activity on broadleaf weeds, but no grass activity.

FMC has two relatively new products, Aim (carfentrazonle-ethyl) and Spartan (sulfentrazone), both of which are contact materials touted as safer to use than paraquat. Aim doesn’t suppress grass. Spartan has broader activity. It is a preemergence material that is very effective against morning glories and nutsedge, according to the company. Spartan has been used in other crops for many years.

Venue (pyraflufen ethyl), from Nichino America, provides season-long control for nonbearing fruit crops and should be applied either prebloom or postharvest. It has contact activity on young weeds.

Rage, from FMC, controls weeds through two modes of action, providing both contact and systemic herbicide effects. It is a mixture of two ingredients, glyphosate and carfentrazonle-ethyl.

Recoil, from Nufarm, is a combination of glyphosate and 2,4-D.

Reglone (diquat dibromide), from Syngenta Crop ­Protection, is a contact herbicide like paraquat and without residual action.

Alion (indaziflam), from Bayer CropScience, is broad spectrum and controls both broadleaves and grasses, and provides residual control for about three months.

The 2010 Midwest Tree Fruit Spray Guide, combining the recommendations of eight Midwest land-grant universities, outlines 11 programs for preemergence weed control in apple and pear orchards and another 12 for postemergence control.

States in the Northeast have similar guides—like the Pennsylvania Tree Fruit Production Guide.

Lack of materials isn’t the problem, Crassweller said, although the search is always on for the silver bullet. Growers need to know their weed problems and then choose the combination of timing and materials to address them.

New challenges for the future might include finding materials that will allow growers to keep more ground covers, like flowers or other plants that harbor beneficials while suppressing undesirable weed species.

Bellinder says that stewardship requires multiple approaches, and advises growers to find several programs that work for them and then rotate them.