Sheep can Reduce Sawfly in Stubble Fields

Sheep can Reduce Sawfly in Stubble Fields

Reprinted from The Prairie Star

(July 1, 2012) Believe it or not, sheep could be part of a management program to control wheat stem sawfly populations. 

According to Patrick Hatfield, a professor from the Department of Animal and Range Sciences at Montana State University (MSU), sheep can be used to increase the morbidity of sawfly larva.

Hatfield presented the results of an ongoing study to those in attendance at the fifth International Wheat Stem Sawfly Conference in April. The conference was held at the MSU campus and brought in speakers from a variety of fields to share the latest research.

According to Hatfield, the act of grazing by sheep and its potential impact on over-wintering sawfly populations includes both consumption and hoof action. 

Those two combined, can destroy or disrupt the over-wintering process of sawflies. During the growing season, mature sawflies lay one single egg inside a green wheat stem. The egg hatches and the larva feeds on the inside of the stem. 

As winter approaches, the larva, still inside the stem, eats its way down the stem until it is close to the ground. 

Then the larva cuts a groove inside the stem, plugs it with body waste to form a winter chamber, and hibernates there until the following spring. When the weather warms, the larva pupates and emerges as a mature sawfly to start the cycle again.  

Hatfield said they conducted both fall and spring grazing in the Golden Triangle and around Columbus, Mont. 

They grazed the sheep in plots, over short time periods and discovered that grazing sheep in wheat stubble fields in the fall, or the spring, or both, can increase the mortality of sawfly larva.

“Our highest mortality rates were 75-percent mortality,” he said. That is better than the sawfly control gained through tillage or burning, which are the two most common methods being used by producers to reduce sawfly numbers. Sheep can do a better job with less input costs for fuel or labor, and less risk.

While 75-percent mortality is a lot of dead sawfly larva, Hatfield did note that even a small number of  sawfly can lay enough eggs to create a serious problem the following year.

When asked whether cattle could accomplish the same feat if turned out to graze wheat stubble, Hatfield said if a lot of the mortality is due to the hoof action, sheep would be better than cattle. 

Their hooves are formed differently and they seem to have a sharper action on the stubble. 

“Also, in this country you have some of these big farm fields with no fences up. You can go out into the fields with a band of 1,000 sheep and a single herder and you’re fine. You don’t have to put up a fence. You can’t do that with cattle,” he said.

Although 75-percent mortality is a promising number, Hatfield would like to see mortality figures in the high 90 percentile. He speculates that to extend the time on stubble fields may help increase larva mortality.

“Of course, we aren’t talking about wheat producers becoming sheep producers. We’re advocating partnerships,” said Hatfield. “You don’t need sheep 365 days a year, maybe just for two or three weeks so they can feed on the stubble,” he said.

That partnership can be beneficial to the farmer as the sheep kill the sawfly larva, and to the rancher as his sheep get to graze on wheat stubble and it reduces his feed costs. 

Hatfield said when grazing sheep on wheat stubble, producers need to keep in mind that wheat stubble is low in protein so sheep will need an additional source of protein. 

He also does not recommend grazing sheep on wheat stubble during later gestation or while lactating. 

“We started this up at the U.S. Sheep Experiment Station in Idaho back in the mid 90s,” he said. 

They shifted from shed lambing in April to range lambing beginning May 15. 
In the fall and winter the rangeland ewes graze on “everything from alfalfa aftermath, and small grain stubble fields, to weedy fields, whatever we could find. Those ewes were spending their early- to mid-gestation time on pretty marginal residues.”  To offset that, they did provide a good-quality protein supplementation. They then compared the rangeland ewes to those ewes being fed a diet of harvested feeds.

“We weren’t seeing any difference in production,” he commented.

Hatfield said only 30 to 40 percent of wheat stubble is digestible to the sheep. That means, if a sheep consumes 100 pounds of stubble, 60 to 70 pounds of that is going to be processed back out and put on the ground. But the manure even has its benefits for the field. 

“Sheep manure is not hot at all,” he said. It is mostly organic matter, made of undigested fibers with microbial cell fragments that can be worked easily into the soil.

“The manure is basically rich in fiber that sheep can’t digest,” he said. 

Sheep do not need to be trained to eat the stubble.  “Basically any rangeland ewe can be used in a wheat field,” he said, adding that sheep are being used to control everything from spurge and spotted knapweed to pests. “We have one student whose family is from California and they have hundreds of sheep in their vineyards to control weeds.”  

A new element of the MSU sheep research project is incorporating sheep into organic farming systems.  

A major concern for organic farmers is how to terminate a cover crop used in a rotational system to help nourish the soil.  

Preliminary work indicates that sheep grazing may be a good method for cover crop termination, plus providing a high-quality feed for sheep.  

Hatfield explained as input costs go up, there is more and more demand for integrated plant-animal systems that are beneficial to all sides. 

“These systems really do have an upside to them,” he said. And as pressure increases for producers to reduce their carbon footprint and amount of greenhouse gases, these integrated systems are becoming more important. 

“One of the issues with tilled farming systems is we get some release of green house gases when we’re tilling. No-till systems lock that carbon, methane and nitrogen in the soil which is good for the environment and plant growth.

“Sheep grazing has the same response as the no-till system, so there is some really positive potential there for the environment,” said Hatfield.

So far the studies show that sheep grazing increases sawfly mortality more than burning or tilling. It also allows carbon, methane and nitrogen to stay locked in the soil at levels equal to no-till; and sheep grazing returns valuable organic matter to the soil.

“Sheep can become part of an arsenal, another tool in the box, for people to employ for controlling sawfly,” Hatfield concluded.

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