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ISSUE 12   July 19, 2001

 

DORMANT WEEDS RESIST HERBICIDE ACTIVITY

Weed control is limited simply by the huge number of dormant weed seeds that remain in fields. Some weed seeds can persist for decades in the soil and all are immune to herbicides. In fact, in the tilled layer of soil (the top six-inch plow layer) weed seeds often reach over 50 million seeds per acre or 10,000 per square yard. Each year, only 5 to 10% of these weeds germinate and emerge from the ground. The rest are left dormant, waiting for a future growing seasons or good, opportunist germination conditions.

Largely, herbicides affect only seeds that germinate. Most dormant seeds remain unharmed. In order to destroy existing, ungerminated weed seeds, growth must be initiated with costly chemicals (if they can be and the stimulant can remain active in the soil) or with soil sterilants that also can also kill beneficial organisms. A more profitable action is to use existing moist conditions through the spring or irrigation to stimulate germination and then to eliminate the weed seedlings with current herbicides.

Some nitrogen compounds, growth regulators, anesthetics and a few herbicides can stimulate weed seed germination. The most successful has been the growth regulator ethylene. Ethylene can even stimulate the germination of hard to germinate parasitic weeds such as witchweed, which normally requires a chemical release by the roots of other plants that serve as hosts. Unfortunately, ethylene is costly, difficult to apply (usually is kept captured in the soil with plastic tarps) and does affect beneficial organisms.

Stimulants for breaking weed seed dormancy should be able to break the dormancy in seeds that normally require light to germinate, too, among the many other diverse weed seed characteristics. The stimulant must be able to penetrate tough weed seed coats and should be volatile enough to distribute the product through the soil.

Unfortunately, no miracle product currently exists. However, this year environmental conditions have helped germinate more weed seedlings than normal due to the very wet spring and continuing, timely rains. Use this year to provide good weed control on your fields by controlling germinated weeds in order to limit the number of weeds that contribute to the weed seed bank. Remember now is often the time to mow or spray fence rows and edges of fields in order to limit weed seed introduction into your fields. The fewer weed seeds that remain in the soil will be less time and money spent on control in future years.

 

NOW IS THE TIME FOR FINALIZING WEED MAPPING

With the cropping season cutting back closer toward harvest, now is the perfect period to do some farm management strategy on weeds. Yes, even this late a date those rascally, rabid, railroading, ranging, rapacious, ravenous rascals called weeds must be revenged! Bring out your site-specific management skills--even if you aren't on GPS (global positioning system) you can set up a GIS (geographic information system) for your farm. Whether you are fleet of hand (via pencil drawings) or fleet on computer feats (via spatial analysis software), now is the time to map the remaining weed problems in your fields in order to plan your strategic maneuvers for next season.

Scout your fields and determine the remaining weed pockets in each field. Evaluate this information against the early season weed pressure to determine how well your management program worked this year. Do comparison shopping across your fields and across neighbors' fields where tillage or herbicide programs are known in order to evaluate what went well this year and what could be improved next year. Map out your current weed problems and any perceived trouble management areas. Specifically mark your maps with each weed culprit's name so that you have a list of weed species that you are gunning for this next year. Site down the specifics on each weed in your notes in order to get a clear shot at the weed for next year: whether it is a perennial, biennial or annual; whether it is a broadleaf or grass; whether it was poorly controlled with the strategy used this year or well controlled but still lingering within the field in small numbers; whether it was a late-germinator or came into the field early; or, if it was controlled early so you eliminated some of the problem or it produced seeds.

The utility of precision agriculture technology in integrated pest management (IPM) is improvement in 1.) mapping and relocating pest populations, 2.) applying control tactics selectively to pest populations that are above your established thresholds, and 3.) keeping records over time in order to determine the impact of both the location and timing of pest resurgence. Like a well-planned deer hunt, weed walloping requires the dexterity of a devious, diabolical hunter with a diligent dossier on each of the weed species wanted to trap, control and contain.

Mapping the weed locations will allow you to observe any yield in the areas where weeds are prevalent in order to determine if yield loss occurs (a combine equipped with a yield monitor will give you an excellent idea). The maps will also provide you with a way to relocate the weed problem areas next year so that you can hone your tillage and/or herbicide skills in on the pest problem. By applying additional knowledge of location and timing of weed emergence to your pest problem, you can compare tillage techniques or herbicide habitudes to determine if targeting trouble can selectively narrow down weed populations. This will save you chemical costs and long-term weed control efforts. By maintaining a record of the weed problems over the years, you can further refine your control strategy to get the most for your efforts against major weed problems. This will also, over time, give you a better idea (with harvests) just how much weed control is economic on your fields and will allow you to know where best to utilize field scouts in future monitoring programs.

Denise McWilliams
Crop Production Specialist

dmcwilli@ndsuext.nodak.edu

 

CONTAINER RECYCLING EFFORT SLATED AT 38 SITES

The ND Dept of Ag has announced the pesticide container recycling schedule for July and August. The details have been posted under "What's Hot" at the pesticide program home page. Go to:

http://ndsupesticide.org

 

EPA OKAYS DESICCANT FOR SEED PEAS

The U.S. Environmental Protection Agency has granted a specific exemption for GramoxoneŽ Max, allowing North Dakota producers to use the herbicide as a desiccant in peas grown for seed.

The exemption allows a single ground or aerial application at a rate of 0.83 to 1.25 pints of product per acre. No application may be made within seven days of harvest. Livestock may not graze on treated fields or be fed the crop byproduct.

Applicators must follow all instructions, precautions and warnings on the product label and have a copy of the exemption label in their possession during application. A maximum of 3,000 acres may be treated.

The exemption expires Nov. 30.

 

NEW GLYPHOSATE PRODUCTS REGISTERED

RT Master from Monsanto and GlyMix MT from Dow were recently registered for use in the U.S. These two products contain glyphosate and 2,4-D, are identical in composition, and are registered for use on cereal grains, corn, sorghum, pastures, CRP, rangeland, and soybean. It has been suggested that these products will be sold at a price below the glyphosate products sold in Canada. Thus, these new registrations have the potential to address one of the major price differential concerns for growers in the border states.

Products containing glyphosate + 2,4-D, such as Landmaster BW are already registered. Below is a chart comparing some of these products.

 

Salt

% ai

lb ai

lb ae

RT Master/ GlyMix MT

 

     

Glyphosate

isopropyl amine

41

4

3

2,4-D

isopropyl amine

4.2

0.4

0.32

Landmaster BW

 

 

 

 

Glyphosate

isopropyl amine

12.9

1.2

0.9

2,4-D

isopropyl amine

20.6

1.9

1.5

AI = active ingredient
AE = acid equivalent

Richard Zollinger
NDSU Extension Weed Specialist

rzolling@ndsuext.nodak.edu


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