ISSUE 1 May 3, 2001
WEED CONCENTRATIONS CONNECTED TO CONTROL STRATEGIES
In recent studies out of Kansas, Nebraska and Iowa, researchers found that site properties as well as previous weed control strategies dictate weed species abundance, but variation on the types of weeds that reappear and the total number of specific weeds may be more influenced by your immediate control measures. Indeed, you may have figured that all along, but the new research ("Weed Science" 48:567-575 and 48:576-587, 2000) was specifically run on fields of soybeans and corn as separate studies to see just what variables generate the next weed populations. In soybeans--the field was previously rotated from corn-and one significant parameter was found to correlate to weed species abundance and it was a link between soil texture and the presence of two of the four weeds the researchers were studying. Indeed, certain areas of the field were able to support the specific weed species growth and this largely determined the reoccurrence of the same weed species year after year. During years in corn, there was an association between herbicide activity and weed presence as well as the field topography and soil texture characteristics. Such site properties can influence weeds; however, annual variation is greatly influenced by agronomic and weed management practices as well as the temporal weather variations. Indeed, weed patchiness as seen in fields was greatly influenced by soil moisture availability that in turn influenced weed seed germination, emergence, and seedling growth. Pre-emerge herbicide concentrations across a field also contributed to weed control efficacy as did the variability of soil fertility that over the season affected weed and crop growth, reproduction and competitive abilities. In other words, concentrate on long-term weed control within every season so that weed seed bank reserves can be lessened in future field crop situations.
Dr. Denise McWilliams
NDSU/UM Extension Crop Production Specialist
PESTICIDE LABELS AND SPRAY VOLUMES
Most pesticide labels provided a spray volume per acre (water plus pesticide) to use in applying the pesticide. A typical spray volume range found on a herbicide label would be 10 to 20 gallons per acre for ground sprayers and 3 to 10 gallons per acre for aerial application. A few sprayer manufacturers have been promoting their ground sprayers by stating that herbicides can be applied with their sprayer at volumes of 5 gallons per acre or less and that weed control from the low volume treatments will be acceptable. Some aerial applicators would like to apply pesticide using a lesser spray volume than stated on certain labels as well. The question is, can applicators legally apply pesticides at a spray volume lower than stated on the pesticide label?
According to Gerry Thompson with the North Dakota Department of Agriculture, applicators that apply less than the minimum spray volume stated on the label are using the pesticide in a manner not consistent with the label. Therefore, applicators can be fined for use of a lower volume than is stated on the label. Spray volumes that are greater than stated on the label are acceptable and legal under an EPA ruling that allows application of spray solutions that are less concentrated than the concentration resulting from labeled spray volumes and pesticide rates. The low spray volumes are not allowed because the spray solution is more concentrated than the concentration resulting from labeled volumes and rates. Any change to allow use of spray volumes less than listed on the label would require a modification of EPA policy or their interpretation of policy.
The various chemical companies generally are not willing to remove the spray volume recommendation from their labels since excessively low spray volumes can result in increased risk of damage from spray drift and increased risk of poor pest control.
NDSU/UM Extension Sugarbeet Weed Specialist
ND SECTION 18 UPDATE
All Section 18 Emergency Labels that have been granted in North Dakota have been posted on the web and are up to date as of 5/1/2000.
All 24c Labels granted in North Dakota since 1999 have been posted on the web and are up to date as of 5/1/2000.
The URL is: http://www.ag.ndsu.nodak.edu/aginfo/pesticid/pesticid.htm
Look under "What's Hot" or click on the green button on the left side of the page entitled "Pesticide Label Search". All Labels are in PDF format and require Adobe Acrobat Reader software to view.
Summary of herbicide Section 18s cleared for ND in 2000:
Dry bean: Raptor and Reflex
Spartan on sunflower
Sonalan on safflower
Curtail M on flax
Roundup Ultra Max preharvest on flax
Sonalan on canola
Stinger on canola
Plateau on CRP to allow grazing and haying.
New Full Section 3 Federal Registrations:
Valor on soybean
Pursuit PPI on chick pea
Pursuit PPI on lentil
Select on sunflower
Select on potato
Muster on canola
Raptor on Clearfield canola
WEED ID AND WEED CONTROL WEB SITES
The following web sites are excellent sources of weed ID, weed control, and herbicide information.
Review of Top 10 "Weed Science" Sites:
1. Resistant weed web site:
The most complete reference site for all resistant weed in the U.S. and the world.
2. EPA - Office of Pesticide Program
Latest progress in registration of all pesticides.
3. USDA Plant Photo Library
Over 20,000 plant photos
4. IR-4 Web Site
Registration status of pesticide on minor crops through the IR-4 program
5. ND Weed Control Guide
Complete electronic version of the 2001 ND Weed Control Guide.
6. Pesticide Labels
A free web site with all current pesticide and adjuvant labels. Also contains state, 2ee, and supplemental labels.
Known in weed science circles as the "Green Bible" or "Blue Bible" contains all labels for most all pesticides currently labeled. Free service allows search and printing of all labels. Must have Adobe Acrobat Reader but can down the software from this site.
7. Oregon State University:
Over 90 links for weed ID and miscellaneous information.
8. Purdue Pest Survey and Information Site:
Alphabetic pest search guide.
9. Idaho Noxious Weed ID Site:
Good western noxious weed ID site with pictures and descriptions.
10. Federal Wildlife Service:
Noxious weeds and exotic and invasive plant management resources.
WEED ID WEB SITES OF INTEREST
UC Pest Management Guidelines & Photo Gallery:
University of Illionis Weed ID:
Common weed seedlings of Michigan:
Oregon Weed ID Site:
Weed Science Society of America Photo Herbarium: http://ext.agn.uiuc.edu/wssa/subpages/weed/herbarium0.html
NDSU Extension Weed Specialist