Labour Day: Critical Time to Control Problem Weeds

Labour Day is one last vacation day before the school year starts - right? Of course, but for strawberry growers, Labour Day should also be a reminder that weed challenges are moving into your berry fields. And at this time (around Labour Day in the late summer/early fall), we can do something about it.

Many of our problem weeds will be establishing in berry fields soon. Winter annuals like common chickweed, thyme-leaved sandwort, night-flowering catchfly, corn gromwell, and several members of the mustard family like garlic mustard, wormseed mustard, common peppergrass, and shepherd's purse are common problems. These weeds germinate now, and form a low-growing rosette to overwinter. Next spring, their flowers will appear, and they will be very difficult to control.

Some biennial and perennial weeds may also establish in the fall. Celery-leaved buttercup, yellow rocket, yellow wood sorrel (oxalis), common mallow, common mullein, toadflax, ox-eye daisy, and some fleabanes have been reported in growing in fields as small plants in the spring, likely germinating in the previous fall. Dandelions are also establishing in the fall, and are more susceptible to preemergence herbicides at this small stage.

Several annual weed problems in berries also get a toehold in our fields in the fall. Field violet is usually considered an annual weed, but may survive the winter to flower and seed again the next year, especially under mulch. Dwarf snapdragon and groundsel are also annual weeds, but are shedding seeds extensively through the fall.

So what's a grower to do at Labour Day? Applications of Sinbar and/or Devrinol at this time will be critical to prevent many of these weed seedlings from getting a toehold. Note that the registered rate of Sinbar at this time is 0.18 to 0.28 kg/ha. This is the lowest registered dose, so even sensitive cultivars may be tolerant to it. Remember that Devrinol may only be applied once per season, and that moisture will be required for incorporation, but if groundsel is your problem, this may be the critical time to use Devrinol.

Remember Labour Day as a window for weed control. Herbicide application at this timing can reduce many of these problem weeds next year.

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