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Deadlines/Dates
April 17: Deadline to submit a General CRP Offer; Deadline to apply for the Farmer’s Bridge Assistance (FBA) Program
April 30: Deadline to apply for SDRP Stage 1, SDRP Stage 1 Quality Loss, and SDRP Stage 2
May 14 - August 2: Primary Nesting Season 

Is it too early to do a prescribed burn on Prairie CRP?

by Greg Schmitt, DNR Private Lands Biologist

The cause and effects of the timing of spring burns on native vegetation, mostly CRP (Conservation Reserve Program) ground, are always a hot topic this time of year. The dog days of March, before spring field work really gets rolling, are a popular time to take care of that prescribed burn requirement of some CRP acres. But what are the consequences of burning before the soil temperature reaches 50 degrees Fahrenheit? Our requirements to the government are met, and we are free to move on to other projects. But what have we really done to the desirable vegetation that doesn’t start growing until the ground is warm? And what about the undesirable vegetation that we are constantly battling in Iowa? I’m referring mostly to Canada Thistle and volunteer trees. Could an early spring burn help the stuff we don’t want?

All sites are different, but we need to consider some generalities when it comes to native prairie vegetation and some unwanted species. Canada thistle and invasive Brome grass starts to grow when the soil temperature reaches 45 degrees Fahrenheit. Most warm season prairie vegetation doesn’t really kick in until the temperature 4 inches below the surface reaches 50 degrees Fahrenheit. All springs are different, this is Iowa after all. Soil temps can rise quickly, can rise slowly, and they can rise and fall. I’ve seen it jump to 50 degrees for a few days and then fall to 45 degrees for weeks before rising again. That was a very bad Canada Thistle year.

Trees store all of their energy in roots over the winter. Monitoring soil temps for trees isn’t as big of a deal because we can see when they start growing by their leaves. Burning before the tree leafs out does very little to affect an established tree. You are just giving it a haircut and reducing the competition it gets from native vegetation growth. The tree will resprout with a vengeance, using its built-up energy reserve to create new stems and leaves. However, if a prescribed back burn is conducted after the tree has leafed out, usually about early May, that individual tree is severely stressed because it doesn’t have enough energy below ground to produce more stems and leaves that it needs to conduct photosynthesis. The window is shorter to do an effective burn before the primary nesting season kicks in on the 15th of May. Required Management for CRP cannot be done between May 15 and August 1.

A later spring burn is believed to enhance the native grasses and set back flowers in a prairie stand. And this is true with a grass dominant seed mix. 30/10 is the technical term. The best way to prevent grass dominance is to plant a very diverse mix with equal amounts of grass and flower seeds to begin with. A 20/20 mix. Pollinator CRP mixes are 10 grass seeds and 30 flower seeds per square foot. It is very hard to make these stands grass dominant just by burning later in the spring.

So, a prescribed burn in March or early April might not be such a great idea. You need to know what type of prairie stand you have and what objective is achieved through burning. If you have trees and weeds present, an early May backburn is the way to go. If your CRP stand is surrounded by trees or has a history of Canada Thistles or cool season Brome encroachment, early May again is the time to light the match. Burning before the soil temperature is consistently above 50 degrees could open your stand up to thistle and tree invasion.