With the phasing out of methyl bromide, California berry growers are facing more weed control challenges than growers of other specialty crops.

Chris Mathews is farm manager at Garroutte Farms in Watsonville, Calif. He deals with sticky weed control issues due to the crop mix, as well as the organic portion of the business. Garroutte Farms grows 300 acres of strawberries, blackberries and raspberries.

“On fumigated strawberry ground, we can get our hand weeding costs down to about $550 an acre,” Matthews told a session at the recent California Weed Science Society meeting in Monterey, Calif. “In some soils, of course, you're going to see a $1,000 plus an acre in hand weeding.”

Garroutte Farms has been moving to full bed mulch earlier in the season to improve weed control. The full plastic mulch installed at pre-planting gives a longer period of weed control, according to Matthews. Additionally, herbicides in the furrow can reduce weed pressure as well as the need for hand weeding. Matthews has been working with Chateau in row middles at pre-plant.

“We sprayed Chateau once the plastic was in place,” he says. “So far, we've had very good control. An herbicide application will cost you $40-$50 an acre. Chateau has been working. I can potentially see big savings. It's not going to eliminate hand weeding, but it will help.”

Weed control in caneberries is another issue, complicated by not only the expense of hand labor, but also some agronomic considerations that are unique to raspberries and blackberries.

“Weed control in caneberries is very different,” says Mark Bolda, Santa Cruz County UC farm advisor. “It's very distinct from other crops and also has ramifications far beyond weed control.”

In Monterey County, the Light Brown Apple Moth (LBAM) is a serious problem in caneberries that can be made worse by weeds. “Weeds and trash around the edge of the field can lead to increased pest pressures so it is important to keep those areas clean along with the rest of the field.”

Another interesting phenomenon in caneberry production is the very definition of a “weed”. “Caneberries reproduce by vegetative canes, not seeds,” Bolda says.

“That means you have to balance the vegetative canes with the fruiting canes. Essentially the early vegetative cane (also referred to as a primocane) is a weed, where the later vegetative cane is not.”

One option to manage a vegetative cane is to cut it out. Another option is using herbicides, which can also help manage weeds within the field. Since hand labor is so expensive, growers and researchers often look for ways to manage primocanes with herbicides. Unfortunately, the choices are limited.

Goal is not registered in California, but is being used in the Pacific Northwest for primocane control. Shark is registered in California, but is not persistent in the soil. Paraquat is registered, but difficult to work with, Bolda says.

Matthews has also worked with Shark and Goal Tender for primocane control. “Both controlled the initial primocane they came in contact with,” he says. “The results were similar to Gramoxone or maybe even better. However, Gramoxone is hard to work with.”

Longer-term control also poses a challenge. “I was hoping that I would get more residual control with Shark and Goal Tender, but they didn't work as well as I thought they might,” Matthews says.

Tillage is also limited in usefulness for weed control since caneberries often have uneven hedgerows and thick growth. It's difficult to get at the weeds. Hoop houses offer many production advantages, but also present challenges in some aspects of weed control.

“It provides a great environment for caneberries to grow,” Matthews says. “It helps keep the rain off and there are fewer weeds.

However, anchor rows are a problem. We can't run a Lilliston or other cultivators down the anchor row so we end up having to use a weed whacker or something else.”

“Tillage will work in the furrows,” Bolda says. “You can throw up some soil on the smaller weeds in the bed, but you don't have a lot of space to maneuver tractors.

“Cover crops are always helping us with weeds.”

Bold says a grower needs to make sure that the cover crop is not restricting the air flow within the hedgerow or keeping a lot of moisture in the canopy and inviting disease problems.”

A cover crop should be planted after harvest and taken down in early spring, Bolda says. Mulches are another option, but not one that works well.

“The problem with mulches is that we don't know where all the canes are coming in,” he says. “I have not seen many mulches in caneberry production that work well.”

Controlling primocanes with hand cutting is another option but very expensive. Propane or flame burning is a possibility.

“You have to time it correctly and do it frequently,” Matthews says. “It only works when primocanes are no larger than about 2 inches. They have the entire root system to draw from, so they have a lot of power behind them and they're hard to stop when they are larger.”

All caneberries are not equal, however. “Blackberries are really a quite different cropping system than raspberries,” Matthews says. “In raspberries, if we can eliminate all the primocanes we're fine.”

With blackberries, the new primocane is essential for the next year's crop. Also, the old wood doesn't harden off the way it does in raspberries so it is susceptible to damage from chemicals and flame burning.

“The new canes and the old canes are quite green,” Matthews says. “Generally, blackberries are grown for six or seven years, so it's more of a true perennial crop and we see a shift in the weed spectrum. Perennial weeds such as field bindweed are more of a problem.”

Weed control costs remain a substantial factor in all caneberry production. “Weed control runs about $550 an acre in fall crop raspberries when they're first planted and there are no metal stakes to contend with,” he says. “In the spring crop, it's about $200 an acre. However, the big cost in the spring crop is primocane control that can run up to $700 an acre. Blackberries present a big problem with perennial weeds and not many herbicides to control them. Weed control costs in blackberries can easily run $700 an acre.”