eXtension

Wild cucumber in hay/horse pasture

Asked April 17, 2020, 5:38 PM EDT

Hi, I talked with someone last year concerning "wild cucumber" in my hay/horse pasture. I lost my whole crop of hay last year. The farmer wouldn't cut and bale with the wild cucumber in it. He said it was poisonous even after it is dead? I did what the gentleman from OSU Extension Service told me to do: We cut it, sprayed the field with Weedmaster and let it sit over winter. I mowed again in fall after spraying. This spring it is BACK! I'm just sick. I have marked each plant with a tall stake, at least 50 stakes, and sprayed with Weedmaster. Most died, some probably didn't have enough leaves and they are still alive. I've staked new weeds and am spraying again this weekend. QUESTION: Some of the plants I sprayed with Weedmaster didn't die. I read where Roundup might work, knowing that I'd kill the grass around it? QUESTION: Once the weeds die, can I go pick up my stakes, cut the weeds and put in plastic bag, and let the farmer take crop and graze my horses? QUESTION: Will horses eat the new weeds that may come up or those that I missed or will it taste bitter to them? They don't eat tansy for instance. Thank you so much. I'm losing sleep over those darn weeds!!!

Clackamas County Oregon

3 Responses

Hello. I am sorry to hear that you are dealing with a poisonous plant that is being very difficult to kill. Depending on the stage of growth of the plant when the field was cut it might have spread seeds when it was mowed. The herbicide wouldn't have affected/killed the seeds thus potentially why you are having trouble this year.
The main thing with wild cucumber is that it is poisonous fresh and dried (such as in hay) and all parts of the plant are poisonous. I have read several articles about wild cucumber and it is very poisonous. Were the plants dry when you sprayed them?
Yes, Roundup would work, but yes, you would kill the surrounding grass.
The only question I would have about haying and grazing the field after you remove the weeds are...are you confident that all of the weeds have been removed? I can not honestly say whether the horses would eat the new weeds or not. A lot of that would depend on the grass stand/amount in the area. I don't know if it has a natural deterrent to the horses such as taste.
I will do some more research on wild cucumber and be in touch again.
I know weeds are horrible. I am dealing with poison hemlock right now.
Dawn

Thank you for your response. I appreciate that you are still researching whether or not I can let my horses graze on the good grass and if they will leave the wild cucumber alone, providing it will be bitter to them.

Also, which herbicide is the best? Roundup or Weedmaster? At this point I don't care if I kill some grass. I just want the weed to die.

And, am I doing the right thing to cut the weed once totally dead and bag and dispose of it so the seeds don't spread?
Thank you so much! Fighting weeds is not fun!

Hello,
I was able to do some more research regarding the wild cucumber. There is not a lot on the poisonous part of it other than it is poisonous. The compound that makes the plant poisonous is called curcurbitacin. This is the same compound that makes some eating cucumbers bitter. It is a natural compound for the cucumber to protect itself from insects and fungus. The stem and leaves contain the most curcurbitacin. I have attached a website that has some good information regarding using herbicides to kill/manage the wild cucumber.
https://pnwhandbooks.org/weed/problem-weeds/cucumber-wild-marah-oreganus
I would recommend removing the dead vines after the herbicide has done its job. If you can remove the tap root as well this will also help.
I hope this helps a bit more.
Dawn