AIR OCTOBER 21, 1998

Thank you Mark and good morning everyone. More rain over the past weekend, guess that shouldn’t be a surprise to anyone! Now the first cold weather of the year is making its appearance and we may shoot right past frosts and into the freeze zone, the hard freeze zone.

While we may need that cold weather to freeze dry the milo to continue harvesting, the freezing weather should raise some red flags for grazing milo stalks, forage sorghum or sudangrass. For the most part I think nitrate problems should be minimal on sorghum crops this year. You can never take anything for granted because various stress factors can create nitrate problems, even late in the season and under low fertilization situations. The biggest concern right now is hydrogen cyanide poisoning or what is commonly called prussic acid. Prussic acid is commonly produced in plants in and closely related to the sorghums. When an animal eats plants containing prussic acid the prussic acid precursors are degraded by the animal to release hydrogen cyanide which we all know is very toxic. Our biggest problem is in smaller, lush regrowth following harvest of grain sorghum. When this regrowth, as well as the older growth in some cases, is subjected to a killing freeze it can quickly release very large quantities of cyanide. Unlike nitrate poisoning which occurs slowly enough to be treated, prussic acid poisoning is fast, often occurring in less than an hour. If caught in time animals can be treated by a vet and saved. But we don’t often know there’s a problem until we drive by the field in the morning and half the herd is already feet up. Fortunately the hydrogen cyanide dissipates quickly after a hard freeze. If you wait until after a hard freeze before turning cattle into a stalk field you should be okay. If there are cattle out there and a hard freeze is coming you need to pull them out. How long? Most sources recommend 4 days. We know that if the weather warms right back up the hydrogen cyanide can be gone in as little as 12 to 24 hours, but under cold conditions it will take longer, so play it safe and wait 4 days. To reduce the potential of prussic acid or nitrate poisoning always turn cattle into the field with a full stomach, make sure they have plenty of fresh, low nitrate water, and then watch them very closely and regularly for the first week or so. If you need further information I have several good bulletins at the extension office on both prussic acid and nitrate problems.

This is Chuck Otte, County Extension Agent, with Ag Outlook '98.

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