Spraying After A Frost
Will fall herbicide applications still provide control of perennial weeds? We had a moderate frost last week with temperatures below the freezing point for several hours. Many of the perennial weeds I’ve looked at since still have green foliage. Herbicide application on these weeds will likely be effective. I have looked at some Leafy Spurge, Canada Thistle, and Dandelions which remain mostly soft and supple.
Producers considering a fall application of Plateau on Leafy Spurge should scout carefully. If the stems still have the milky latex when broken the application should be effective. If the stems are dried and have no milky sap a herbicide application will have no effect.
Grazing After A Frost
Delaying grazing of alfalfa, sweet clover, millets, sorghums, and sudangrass for at least 5 to 7 days will decrease the chance of bloat or prussic acid poisoning. If you have areas of millets, sorghum, or sudangrass that did not completely freeze and begin to have regrowth you should avoid grazing those areas. New growth is very palatable but can have dangerous levels of cyanide.
Nitrate-accumulating crops include small grains, millet, brassicas, corn, sorghum and sudangrass. Rangeland or pasture weeds such as pigweed, Russian thistle, lambsquarter and kochia also are nitrate accumulators. Reduced growth in annuals during the fall may slow conversion of soil nitrogen to protein and amino acids in the plant, causing high levels of nitrate to accumulate.
Unlike prussic acid, nitrate levels do not decrease after a killing freeze. When plants die off, nitrogen uptake by roots will cease, but nitrate that is in the plant at that time will remain because no further photosynthesis will take place.
I can do a “Nitrate Quik Test” at the Burke County Extension Office to determine the presence or absence of nitrates. For baled hay, I can probe the bales and send them in for lab analysis at no charge to the producer. Contact us at 701-377-2927 or call my cell at 701-339-1133