Cornell Researcher Looks at Weed Control Between Plastic Rows

2/1/2014 7:00 AM
By Chris Torres Regional Editor

NEW HOLLAND, Pa. — Growing vegetables under plastic mulch can extend the growing season and offer some cost-effective weed control on some farms. But producers still have to worry about the areas between the plastic rows, which can look more like a weedy jungle if left unchecked.

While herbicide applications can do the trick for many growers, it can also be expensive and harmful to other crops, according to Judd Reid of Cornell Cooperative Extension in Yates County, a presenter at the Jan. 20 New Holland Vegetable Day.

It’s one reason he’s looking at cover crops as an alternative to controlling weeds between plastic rows.

In 2012, Reid received a $15,000 Northeast Sustainable Agriculture Research & Education, or SARE, grant to look at ways of reducing the cost of controlling weeds and pests between plastic rows.

He wanted to compare a winter rye cover crop with a standard application of herbicide and hand cultivation to see which option offered the best weed control in onions and tomatoes grown in raised plastic beds.

The warm, early spring of 2012 allowed Reid to plant rye between established rows of plastic raised beds in early April.

The timing of getting rye into the ground can be critical, he said, since it can grow fast and prefers cooler conditions. But if left unchecked, rye can grow a seed head, Reid said, which makes it more difficult to cut down and more likely to succumb to summer disease.

Reid said he prefers a short rye crop, which can then be cut and used as a mat for weed control.

In the 2012 trials, rye provided good weed control in onions and tomatoes in comparison with herbicides and cultivation, Reid said.

But he also found that rye competed with onions for nutrients. and he ended up having to apply insecticide to control potato leaf hoppers.

The onions in the rye plot appeared taller than in the herbicide or cultivation plots, but Reid said that was because the crop was growing longer leaves to get more nutrients. This can also attract tiny thrips, which suck sap from the onion leaves.

Production was less in the rye plots, about 66 pounds per 10 linear feet of onions grown in plastic, compared with 83 pounds in the herbicide trials and 84 pounds in the cultivation trials.

When he pulled the plastic off in the rye trials, he failed to find rye roots under the onions.

“We’re still trying to figure out why this is happening,” Reid said. “I feel like rye is competing for nutrients. I just don’t know how it’s doing it.”

In tomatoes, Reid said he lost more than 10 pounds per acre in the rye trials. There was also a major armyworm infestation, which he had to use an insecticide to control.

“That wasn’t a very pretty picture,” he said of the rye trials.

In 2013, Reid received Extension funding to continue the trials, this time focusing on cover crop mixtures. He expanded the trial to include mixes of clover, rye and barley.

While clover is a good grass that can provide beneficial insects in a system, Reid said the challenge is getting it established. He found the mix of barley and clover to be a good one for weed control and not as competitive with crops as rye alone.

“The reason is barley ... seems to be less competitive with vegetables than rye. At the same time, it creates enough ground cover to establish clover,” he said, adding that the 2013 trials looked strictly at peppers at three different farms.

Another mix — rye and clover — also did well.

Reid said he’s happy he got some good results. Even though the 2013 trial focused on peppers, he believes the same success could be replicated in tomatoes, onions or other crops grown under plastic.

“I think it holds promise for those crops. There are some differences between these veggie crops, but I do see promise,” he said.

This coming season will be the third year for the study. Reid said he has applied for another $15,000 Northeast SARE grant to fund the work.

And while this research may not be for someone growing lots of one crop, Reid sees this as an option on farms growing several crops.

“The impact I see by doing this work is it may not be for everyone. But for farmers wanting to reduce herbicide use, it could do that. It’s also good for labor costs,” he said.

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