Like an athlete who struggles against a tough competitor, weeds compete in strawberry fields, and often are victorious, much to the detriment of growers.
“Weed competition of course can damage strawberries, but due to the value of the crop, weeds aren’t left to compete,” said Steve Fennimore, a Cooperative Extension specialist in the Department of Plant Sciences at the University of California. “The damage is due to cost of hand weeding, not due to competition.”
For protection against weeds, he suggests growers can remove weeds from fields and practice crop rotation with vegetables such as lettuce, broccoli and celery. “Most California fields where strawberry is grown are not very weedy to begin with,” Fennimore said. “Organic fields are an exception, and weeds are more difficult to manage there. But black plastic is used to suppress weeds, and hand weeding is used to keep the planting holes clean.”
Weed seeds are a big concern. “Most of the weeds that infest strawberry are seed that survive fumigation like clovers and little mallow,” Fennimore said, “or the seed blows in after fumigation, like sowthistle, hairy fleabane and horseweed.”
He said herbicides such as GoalTender, Prowl H2O and Chateau provide good protection. He advises to apply one of them 30 days at pre-transplant. For grass control, he said Select Max works well.
Strawberries often fend off weeds in the field. Sometimes they win; other times they don’t. “The main problem is that strawberries are short and have very shallow root systems so they don’t compete well with weeds,” said Kathy Demchak, a berry specialist and senior Cooperative Extension associate at Penn State University. “They are a high value crop, so companies are concerned about liability issues should the crop be damaged by their product(s). This means that companies are often hesitant to label new herbicides for strawberries, so not many herbicides are available for use on strawberries. In addition, because of the plant’s shallow root systems, plants can be easily damaged when the soil is cultivated. This makes weed control in strawberries a challenge.”
Following are some other weeds that present a challenge, according to Demchak, Penn State Cooperative Extension publications, and the book, “Weeds of the Northeast” by Richard H. Uva, Joseph C. Neal and Joseph M. DiTomaso.
We know for sure, unfortunately, that common chickweed is not a popular chicken that happens to prefer weeds for food – it is much more profound and determined. Common chickweed can germinate in the fall under cool, shady and moist conditions. The common chickweed plant can produce more than 10,000 seeds and can survive in soil for more than 10 years.
This plant can flower and set seed in the spring and early summer and can germinate immediately. Common chickweed only needs five weeks to go from emergence to seed set. Normally, only one generation occurs, but two can happen.
Common chickweed hates drought conditions, so growers won’t need to worry as much about them growing if their crops go through a dry spell.
Shepherd’s purse seed grows in heart-shaped pods in late spring and early summer. A single plant can produce as great as 38,500 seeds. They can stay in the soil up to 35 years. This weed germinates in early fall, later in the summer or in early spring in the Northeast.
Henbit roots at its nodes. This weed germinates similar to common chickweed. One plant can produce 2,000 seeds, which can stay in the soil for 25 to 40 years. Growers can control henbit by tilling the land; however, growers must till at the right time to prevent seeds from germinating.
The seeds of field pansy germinate in late summer and early fall, and flowers appear in the springtime. Field pansy can produce 46,000 seeds.
Dandelion has windblown seeds and a large taproot, causing the plant to resprout many times. Growers will notice that the dandelion flowers will produce seeds even if they pull them off the plant.
Growers can control them by shallow-tilling the land; however, if they notice that dandelions are well established, neither tillage nor hand pulling help. Growers can mow or cut close to the ground before these weeds bloom and can apply 2, 4-D at spring dormancy, or Roundup with a wick applicator, making sure they are aware of the 14-day preharvest interval. Growers should not let the applicator touch any strawberry plants.
Canada thistle shoots emerge in the spring, flower and produce wind-blown seeds. Shoots come out in the fall and produce food for the wintertime. Their roots are vertical and horizontal, which gives the roots a better opportunity to spread.
Mowing or applying a burndown herbicide in the springtime works effectively. Additionally, growers can till the land frequently as plants resprout.
A flumioxazin such as Chateau is a pre-emergent herbicide growers can use when plants are dormant in the late fall or early spring. It also can be used with a hooded sprayer between strawberry rows. Growers can tank-mix it with 2,4-D or Gramoxone for better weed control. Chateau works well on all weeds mentioned already except Canada thistle.
Dacthal is a pre-emergent that works briefly on chickweed and henbit, but on none of the others mentioned. Growers can apply it in the spring before the weeds blooms; however, it won’t help when weeds emerge.
Devrinol, (napropamide) helps stop grass seeds from germinating in straw mulch. Growers are wise to apply it in the fall before applying mulch. They also can apply Devrinol in the spring before blooming, yet it is only effective on germinating seeds. This works well for chickweed and dandelion and is only fair for other weeds mentioned already.
Stinger, a clopyralid, works well against thistle and is a post-emergent. Yet, it is ineffective for other weeds mentioned.
A post-emergent herbicide for dandelion is Formula 40 or 2, 4-D. Applying in early spring as dandelions slowly emerge from straw mulch works best.
For emerging weeds on all those mentioned already, use Roundup or Touchdown, both glyphosates. Growers can apply them with a wick or sponge applicator, avoiding the strawberry plants themselves. Sinbar also is an option on strawberries.
Growers are wise to check with their local Cooperative Extension agent or specialist and follow their recommendations and herbicide label directions.