John,

Purple deadnettle is a winter annual weed, so it typically germinates in the late-summer/fall, overwinters, and then flowers and produces seed before dying in the summer. Is this the life cycle your population is exhibiting? Sometimes we do get winter annuals that germinate in the spring...but this is not as common. If it is behaving in the typical manner, then physical methods of control in the late fall would be effective (e.g. tillage or hoeing). Preventing emergence in the late summer may also be possible using a mulch (e.g. straw of other). 

If you end up hand pulling or hoeing plants that are flowering it is important to remove that material from the garden as seeds can develop as the plant is drying down...you'll have less seeds that doing nothing but will still perpetuate the population.

During the spring and early summer when plants are growing there are no options to spray the plants that will not also cause harm to vegetable that are contacted. There are some organic (OMRI-approved) herbicides, such as those with the active ingredients pelargonic acid or ammonium nonanoate, that could be effective if you can protect the vegetables from contact.

Please let me know if you have more questions, I am happy to help. 


 

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