ISSUE 13 July 28, 2005
PERSIAN DARNELL - ANOTHER LOOMING WEED
Persian darnel is an introduced annual or winter annual grass that reproduces by seed. It is established in small grain fields in Montana, western North Dakota and the Canadian Prairies.
Traditionally, Persian darnel has been a weed of limited importance. However, during the last decade Persian darnel has become an increasingly troublesome weed where it can completely smother patches of wheat or barley and go unnoticed until harvest. This tendency is particularly true in reduced tillage or direct seeding systems that leave weed seeds close to the soil surface.
Persian darnel management presents three main challenges:
1. Unlike wild oat or kochia (Kochia scoparia L.), which grow above the crop canopy, Persian darnel is short in stature and difficult to see in maturing grain fields. Because of its short height, producers are usually unaware they have a Persian darnel infestation until harvest.
2. Persian darnel is often misidentified at the seedling stage. Achieve (tralkoxydim), Discover (clodinafop), and Silverado (mesosulfuron methyl) are selective post_emergence herbicides that effectively manage Persian darnel in small grains, but incorrect identification often leads to improper herbicide selection and unsatisfactory results.
3. Persian darnel biotypes have developed resistance to several acetyl-CoA carboxylase (ACCase) herbicides including Achieve, Discover and Hoelon. The first case of Persian darnel resistant to ACCase herbicides was reported in 1993, infesting wheat fields.
Seedlings Persian darnel seedlings are difficult to differentiate from downy brome and wild oat seedlings. The key to differentiating Persian darnel from other grass seedlings is its red culm (the base of the stem near the soil surface). It has dark green leaves which are narrow, very smooth, and shiny on the bottom. The ligule is truncate, much like wheat, while wild oats have a large, paper-like ligule.
To find additional information on Persian darnell, go to the Montana State University Ext publication web site at: http://www.montana.edu/publications
Go to agriculture weeds, look down the list under Persian Darnell and you will find a free online publication called Persian Darnell: Identification, biology and ecology. Publication #200411.
NDSU Extension Weed Specialist
DOWNY BROME - THE NEXT ND EPIDEMIC
Brome species have been problem weeds in the southwest areas of North Dakota for several years. Japanese brome and downy brome often are more common in cropland than other brome species. In the seedling stage, the two plants are very difficult to tell apart. The plants are more easily separated once the seed heads emerge because Japanese brome has a very wide, compact arrangement of seeds in the panicle compared with the very long, slender seed arrangement for downy brome.
These two weeds are spreading through North Dakota at an alarming rate. Downy brome especially is causing concerns and has been found across the southern one-third of the state. Japanese and downy bromes are winter annual grasses. They emerge in the fall or very early in the spring and often are reaching reproductive stage before spring crops are sprayed for weeds. Plants might emerge after preplant weed desiccation, but a cold period is required for seed production. Downy brome tends to mature earlier than Japanese brome, which makes downy brome more difficult to control.
Downy brome that emerges in the fall can produce a seed head by the end of May. Herbicides will have better activity on young plants, so herbicides applied in the fall or very early in spring are necessary when tillage is not an option. Glyphosate will control young plants, but plants with seed heads emerging are more tolerant. ACCase inhibitors, such as Puma, Discover, and Achieve, often give poor control of Japanese and downy bromes, but Assure II, Select, and Poast provide excellent control of non-stressed plants up to fully tillered.
ALS-inhibiting herbicides provide good to excellent control, depending to a large degree on precipitation as well as the specific herbicide. In wheat, Maverick and Olympus have activity on bromes, but one must consider the residual activity of these herbicides, which may prolong the intervals before seeding many crops in North Dakota. Everest and Beyond (Beyond can only be used on Clearfield wheat) also have good activity on these bromes, and the rotation intervals are much shorter. Beyond and Raptor are registered in several other crops but will only be effective on late emerging bromes in many crops because of the timing of herbicide use. In corn, herbicides with activity on bromes include Option and Basis.
It might be too late to significantly affect the brome population in your field this year. It is important to scout your fields to determine if you have Japanese or downy bromes. Then create your plan for getting after them this fall and next season.
NDSU Weed Scientist