Q: Can someone please identify these weeds growing in the new grass on our Orewa Croquet Club lawns? They appear in large patches and are quite new to us. We need the name of a weedkiller that will kill these weeds without harming the new browntop grass. Meanwhile we will have a go at hand weeding them, but the sheer volume could be beyond us.
Question from P. & J. Jones-Merredew, Orewa
A: It’s hard to tell for sure from your photo but these look like seedlings of one of the weeds in the brassica family, which includes such common weeds as wild turnip and several different species of cress. They are prolific seeders and given the chance take advantage of freshly cultivated soil by germinating quickly and growing strongly. The weed seeds were probably already in the soil when you sowed the new grass.
There are two items of good news. First, they are relatively easy to pull out by hand though that approach is labour-intensive and time-consuming. Second, after you control the first flush of these weed seedlings and start mowing the grass, regular cutting should keep the weeds under control as they are annual weeds and won’t tolerate being chopped down. If you want to have a go at controlling them with herbicide you need to use a selective herbicide, one that kills broadleaf weeds and does not harm grasses.
There are several you could choose from, all using much the same active ingredients, including Yates Turfix, Kiwicare Lawn Pro Turfclean and McGregor’s Lawn Weedout Spray. Make sure to follow the label instructions carefully especially regarding dilution rate and how much to use over the area to be sprayed. Also do not mow the lawn for at least seven days after spraying and do not use the grass clippings from the first few cuts after spraying to mulch other plants or put them in the compost. You also need to be careful to avoid any spray drift onto non-target plants. Some of these herbicides are available in ready-to-use form, requiring no mixing, which you could use to spot spray individual weeds rather than spray the whole lawn.
Good luck with your browntop grass; it’s a lot of work keeping a fine grass lawn in good condition in warm northern parts of the country.
Answer by Andrew Maloy (The Plant Doctor)