- Author: Dan Macon
Smutgrass, in my experience, is a complicated, opportunistic weed, by which I mean there neither seems to be any single factor that contributes to its spread, nor any single management technique that leads to its eradication. Smutgrass seeds require bare ground, sunlight, and warm temperatures (68°F to 95°F) to germinate. Management practices (like pasture harrowing), or pests (like gophers) that lead to bare ground may provide a toehold for smutgrass establishment.
We have grazing exclosures established on several irrigated pastures on the eastern edge of the Sacramento Valley. The grazed portions of these pastures have significant smutgrass populations; the exclosures, where the forage grows all season without being removed, have little or none. To me, this suggests that getting the grazing right on our pastures may be part of the answer. If we can graze our pastures to 4-6" of stubble height, and then allow sufficient time for the desirable forage plants to regrow before we graze again, perhaps we can allow these "good" plants to outcompete smutgrass. On paper, this sounds easy; out in the pasture, it requires us to vary our graze periods and (more importantly) rest periods based on the growth rate of the pasture. Our rest period in June might be 25 days; in August it might be 40 days! Not every operation is set up to accommodate this variability.
We have noticed that dry ewes are more likely to graze smutgrass than lambs, particularly early in the season. Other producers have observed that goats will graze smutgrass. Davy et al. suggests that this may be related protein levels and digestibility. Clipping (or grazing) can maintain smutgrass in a more vegetative state, increasing palatability and nutritional value.
But even where we get the rest periods and graze periods right for the plants we want, we may still have smutgrass. Irrigation inefficiencies may favor smutgrass in some cases. Josh Davy and Betsy Karle found that smutgrass was significantly decreases on a pasture where irrigation was changed from a 14-day rotation to a 7-day rotation (with corresponding increases in more desirable grasses). I've noticed on the pastures that we irrigate for sheep that we seem to have more smutgrass in areas where shallower soils or lower water pressure results in less than optimal irrigation (in other words, we can't get enough water on these sites to maintain sufficient soil moisture in our 12-day irrigation rotation). And since our system is designed to run on 24-hour sets and 12-day rotations, we don't have a great deal of flexibility when in comes to addressing our smutgrass problem by adjusting our irrigation schedule.
Some producers in our region regularly clip their pastures to avoid eye problems and keep forage in a more vegetative condition. Research shows that repeated mowing can decrease the diameter of individual plants but increase the density of the stand. Mowing may also spread seed. On the other hand, mowing may maintain the nutritional quality of smutgrass further into the summer (which may improve its palatability for livestock).
Finally, glyphosate (RoundUp) may be a viable control option. A rotary wiper allows the operator to adjust the height of the wiper drum above the desirable pasture plants and "wipe" the herbicide directly on the smutgrass plants. This application should occur shortly after grazing (so that the desirable plants are lower than the smutgrass). According to Davy et al., "glyphosate should be applied after flowering when the plants are translocating sugars back to the roots or below-ground reproductive structures (generally late summer and early fall). Managing Smutgrass on Irrigated Pastures contains a helpful guide to using glyphosate with a rotary wiper. The Tahoe Cattlemen's Association has a wiper that is available for rent through Far West Rents and Ready Mix in Lincoln. If you'd like help learning to use the wiper, contact me at (530) 889-7385 or at email@example.com.
Weeds are often a symptom of a management problem, rather than the actual "disease" - if we don't address the underlying issue (in the case of smutgrass this may be grazing management, irrigation management, or other factors), the problem is likely to reoccur. And with a weed like smutgrass that seems to be so opportunistic, eradication may be especially difficult. Controlling it (rather than eradicating it) maybe the most cost-effective option.
- Author: Dan Macon
While it may be difficult to imagine with another atmospheric river storm bearing down on Northern California this evening, irrigation season is just around the corner. Most of the water districts in the foothills will begin delivering water around April 15 - and six months of moving water through irrigated pasture will begin for many of us! Here are a few tips to help make this coming irrigation season run smoothly!
First, we should schedule irrigation (or design our systems) to provide the right amount of water at the right time to meet plant needs. These obviously change as we go through the irrigation season - after this weekend's storm, we should have plenty of soil moisture for a week or more.
Plant and soil water demand, ideally, should determine the quantity of water applied and the frequency of irrigation. This will help improve forage quality, reduce runoff and increase water use efficiency. But how do we know what the plant and soil water demand is?
One of the easiest ways to determine this is simply to learn to assess soil moisture by feel. The Natural Resources Conservation Service has a great pamphlet entitled Estimating Soil Moisture by Feel and Appearance. If you'd rather have a hard copy of the pamphlet (it's even printed on waterproof paper), we have copies at the office!
Another way to determine soil and plant water demand is to use the California Irrigation Management Information System (CIMIS) to estimate evapo-transpiration (or ETo). ETo is the amount of water transpired by plants and lost through evaporation; CIMIS has weather stations throughout the state that provide regional estimates of ETo. The closest stations for our region include one near Auburn and one at the Sierra Foothill Research and Extension Center in Browns Valley. The CIMIS website provides data regarding daily (and even hourly) ETo, precipitation, air temperature, soil temperature, humidity, wind, and a variety of other parameters that can impact irrigation.
Finally, if you'd like to know exactly what's happening in your pastures, I can install a WaterMark moisture sensor. These sensors can help you track the effectiveness of your existing irrigation system and adjust the quantity of water applied and the frequency of application. Call the office if you'd like to schedule an appointment! You can reach me at firstname.lastname@example.org or (530) 889-7385.
In future weeks, look for additional blog posts about managing irrigated pasture! Also, mark your calendar for Saturday, May 19 - I'll be co-hosting an irrigated pasture workshop with the Nevada Irrigation District and the Nevada County Resource Conservation District in Penn Valley from 8 a.m. - 11:30 a.m. - stay tuned! In the mean time, enjoy the coming rain!