The last thing a grower wants in his or her rhubarb field or garden is a multilevel of different weed species. Typically, weeds don’t bother rhubarb too much because of the amount of mulches growers use in controlling them, according to the University of Tennessee.

Even so, growers must consider controlling weeds so they don’t out shade or take over the young rhubarb plant. They can pull weeds by hand if they like doing so, use a hoe if they don’t mind pounding in the possibly hard dirt or simply cultivate if the equipment is available. Whatever their weapon in the garden or open field, growers are encouraged to remove weeds out of fields when rhubarbs are smaller and just being established. This makes them easier to control than when they mature.

Weed concerns

According to Bernard Zandstra, a professor and Extension weed specialist at Michigan State University, weeds of concern in rhubarb include quackgrass, pigweed, nightshade and nutsedge. Let’s take a look at them.

Quackgrass

According to Penn State University, quackgrass is a cool-season, grassy-type of perennial weed.

The University of Vermont says this weed grows underground stems or rhizomes, which can spread rapidly. New shoots sprout from nodes on the rhizomes, making it difficult to control.

Quackgrass stems can stretch from 1 to 4 feet high, according to the University of Maine. The stems and upper leaves are hairy; however, the lower leaves are smooth. Besides by rhizomes, quackgrass is spread by seeds.

Pigweed

Pigweed is a summer annual that grows between 2 to 5 feet high and can produce more than 100,000 seeds, according to weed specialists at the University of Maryland. Its egg-shaped leaves are a green to red color.

Yellow nutsedge

Unfortunately, yellow nutsedge is one of those really difficult weeds to control, according to weed specialists at Purdue University. Yellow nutsedge is a perennial that can reproduce by underground tubers near the stems or rhizomes, and according to the university, one plant alone can produce hundreds of tubers. To identify yellow nutsedge, growers can look for a triangular-shaped stem. Its light green to yellow leaves appear in groups of three, and each shiny leaf grows to a long, pointed tip.

Nightshade

A summer annual, black nightshade is a perennial that can harbor diseases and insects, according to weed specialists at the University of California. Nightshade’s seed leaves are narrow and mostly egg-shaped with some tiny hairs. Eventually, the first true leaves grow to a spade shape, and lower leaves appear purplish. Egg-shaped leaves that appear later are bigger and a dark green with a purple tinge. Mostly white, showy flowers can grow to a star shape. Berries of this plant are a green to black color.

Fighting the weeds

To control quackgrass, Penn State University advises reducing patches of the weed in and outside of fields. Also, growers should clean rhizomes and seedheads from tillage and harvesting machinery once they finish. In addition, the university weed specialists advise maintaining adequate soil fertility, choosing high-yielding varieties and scouting fields regularly for insects.

For quackgrass, Zandstra suggests the use of Kerb. He advises applying it in the fall so Kerb will control quackgrass in the next crop. Spring application is possible but not as effective. Besides taking care of quackgrass, he indicates that Kerb can help control annual grasses.

Zandstra points out that rhubarb emerges early in the springtime, so applying herbicides is a struggle. He adds that some preemergence herbicides may burn rhubarb leaves if they are applied after the leaves stretch out; however, those leaves usually don’t cause too much harm.

Some preemergence herbicides for rhubarb may include Callisto, Dual Magnum, Lorox, Caparol and Sandea. Zandstra says:

  • Dual Magnum works well on annual grasses as well as pigweeds, nightshades and some different broadleaves.
  • Caparol and Lorox help to control annual grasses and broadleaves.
  • Callisto and Sandea works well on broadleaves as well as yellow nutsedge.

Unfortunately, Zandstra says none of the above herbicides provide year-long control. Rather, they last for about four to six weeks. They also do not control perennial weeds too much, so cultivation or hand weeding may be necessary.

Zandstra points out that Quinstar, a postemergence herbicide, helps control Canada thistle, field bindweed and a lot of annual broadleaves and grasses. For postemergence grass control, he recommends Poast and Select Max.

Before using any herbicides, read and follow the label correctly. If you have any questions, contact your local Cooperative Extension agent or specialist.

The University of Maryland advises to remove any pigweed plants before they flower so seeds won’t be produced.

Remember: The last thing you want in your garden or field is too many weeds. Learn to identify and control them so your rhubarb will make customers the best baked goods in the entire neighborhood.