Got thistles?

Farm Forum

This topic is a bit after the fact, but as I drive around the area, it looks like I’m not the only one. A common saying when the topic of thistles comes up is that if you own land, you have thistles. If that saying isn’t true this year, it may never be! Another saying might be, if you own land and haven’t been busy spraying thistles this year, you’re not being a good neighbor, you know, like the good neighbors who control noxious weeds?

This spring has not only been a good one for growing thistles, but causing farmers and ranchers to get behind in their work. Wet weather has caused delays with planting, spraying and haying, among other activities. Once thistles bloom, i.e. you see purple, it will take 7-10 days for the seed to be viable. There has been “purple” showing for some time on many of the thistles, but if you have some late ones, there may still be some time to prevent seed production. Initiating control measures may avoid new plants in the future for both you and your neighbors. One producer recently mentioned hand pulling blooming heads from his 4-wheeler and then spraying them. Although effective in preventing seed production, that might be a little labor intensive for big operators.

For control recommendations, ask for the following factsheets at your Regional Extension Center or access them online: “2013 Weed Control – Noxious Weeds” ( or “2013 Weed Control – Pasture and Range” (

Sweet Clover Poisoning

In the recent column, “Develop a Grazing Plan for a “Sweet Clover Year”, a reader pointed out to me that I didn’t mention the benefits to the soil and grasslands that sweet clover provides. Although I’ve heard range managers curse the biennial plant, claiming that it can choke out desirable grasses, it certainly fixes nitrogen, adds diversity to the forage base and the roots help break up any compaction that might occur. Point well taken.

A real concern worth knowing about when sweet clover is harvested for hay is sweet clover poisoning. This was also not discussed in the recent column, nor the article by Dave Ollila that the column attempted to summarize (

Sweet clover poisoning is well explained in a 2012 iGrow article by Ken Olson, Extension Beef Specialist, “Using Sweet Clover Wisely” ( In essence, sweet clover contains a substance called coumarin, which is converted to dicoumarol by fungus in moldy hay. Dicoumarol is an anti-clotting agent that will cause animals that consume it to hemorrhage (bleed) severely. If dicoumarol sounds familiar, it may be because it is the main ingredient in most rat and mouse poisons.

This topic may also be “after the fact” as a good deal of sweet clover has already been put up for hay. Seeing the amount of sweet clover being harvested and knowing about sweet clover poisoning seemed justification to remind producers of the potential concern and the need to properly cure sweet clover before baling and to store it properly.