Winter Weed Dangers 

January, 2022
Laura Bennett, UF/IFAS Extension Pasco Sumter & Hernando Counties

Poisonous weeds are present in varying degrees in most pasture. With Winter weather and short forage supply, problems can arise quickly. Forage-consuming livestock like cattle, goats, sheep and horses, have to consume large quantities of grass to keep their digestive systems operating correctly. When growth of our grass is slowed by lower temperatures and shortened day length, sufficient quantity and quality for livestock can become an issue. This is when animals will become more likely to eat weeds, including poisonous ones, to fill their forage need.

There are some weeds that are worse than others. Most of the time, animals must eat a percentage of their bodyweight (2-3% on a dry matter basis) to have an acute poisoning. However, at much lower levels, they can sustain chronic poisoning that damages the liver and may or may not cause the animal to show signs of being sick.

Here are some to watch out for:

Coffee Senna

Coffee Senna:  photo credit Doug Mayo

The seed pods on coffee senna are especially poisonous and once the plant has experienced a frost, animals tend to really consume it.


American Black Nightshade

American Black Nightshade: photo credit Brent Sellers

This weed will have small white flowers and black, smooth berries. It typically grows in fence lines.


Showy crotalaria

Showy crotalaria: photo credit Doug Mayo

This weed is also called rattle box because once the pods dry the seeds will shake around in the pods.

All of these weeds are known to have caused death and illness in livestock. While this is not an exhaustive list of poisonous weeds, these tend to be some of the more troublesome. Be aware of your forage supply and provide ample hay or lower your stocking rate when necessary. Also, scout pastures for weeds regularly. Weed seeds are very resilient. They can repopulate the area for many years.  The Weed Management Guide is a helpful resource for making a herbicide plan.



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