Do you mean "Common MALLOW" (not "mellow") is the plant?
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If you look at this
UC Davis report about the common mallows, it says there are no chemicals the homeowner can purchase that will control this plant.
Apparently planting things that will compete with it (in your area what would that be? Grass? Clover?) and before that, if you can, pull the plants before they have very many leaves. Tough on six acres. Maybe pay neighborhood kids with a bounty on the plant? (Do any kids in any neighborhoods want to work for money any more? But that's another topic. . . )
Quote:
MANAGEMENT
Mallow control in home gardens and landscapes is best accomplished by pulling out young plants. Because of the rapid development of the long tap root, this is best accomplished when the plant has four or fewer true leaves. The taproot gets woody as it matures and is very difficult to cut or pull out. Removing plants before they seed will help reduce the impact of the plant in coming years.
Mechanical Control
Mallows are best controlled mechanically by hoeing or pulling out young plants. Young mallow can also be killed by cutting them off at the crown, but older plants may resprout from the crown. If there are a large number of plants, shallow mechanical cultivation may be used when the plants are young. The cultivator should be set so that the blades or tines will pull the plants from the ground or cut the tap root below the soil level. Mowing is not an effective method of control because the plants have viable buds on the stems below the height of the mower blade. Common mallow tends to have a more prostrate growth habit so that species is even less affected by mowing.
Solarization is not effective for mallow control, nor is flaming.
Cultural Control
Cultural control can be done by planting competitive desirable plants in areas where mallow is a problem. The shade provided by these plants will reduce germination and growth of mallow seedlings. Mulches can also be effective. At least 3 inches of organic mulch, such as bark or wood chips, will make it physically difficult for the seedling to emerge and will screen out the amount of light that mallow requires to effectively sprout. However, the mulch must be maintained to ensure that it remains at the needed depth. Otherwise, the seedling can push through the mulch and become established.
I hope you find something here that will help.