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ISSUE 13   July 30, 1998

 

ND SLN LABEL FOR BANVEL PREHARVEST TO WHEAT ISSUED

    The North Dakota Department of Agriculture has issued a n EPA SLN (State Local Needs) label for application of a maximum of 1 pt/A Banvel SGF tankmixed 2,4-D amine or low-volatile ester at 0.5 to 1 qt/A as a preharvest application to control or suppress annual broadleaf weeds in wheat. The application must occur at least 14 days prior to harvest.

    All precautionary statements from the federal Section 3 label on drift and movement to sensitive crops must be observed. The user must posses the label at the time of application.

 

WEED CONTROL IN TREES

    We are receiving many calls about weed control in trees. Extension Circular W-1097, "Weed Control in Tree Plantings" is available from the extension service or through your county agent. The circular is a revised publication containing helpful information on weed control using various mechanical weed control methods, use of mulches, cover crops, and chemical weed control. A section was included containing instructions on calibrating hand-held sprayers. Description of several herbicides are listed for weed control prior to weed emergence, postemergence, and for postemergence directed applications. Tables are included showing the susceptibility of annual and perennial grass and broadleaf weed to herbicides labeled in shelterbelt and tree plantings.

    A detailed section has been developed listing herbicides that are labeled on many tree species grown in the Northern Great Plains.

    Contact your county agent for a copy or contact the NDSU Extension Distribution Center at (701) 231-7882.

 

COMMON MILKWEED CONTROL

    Common milkweed has become a problem weed in cultivated cropland due to an extensive root system, insulating winter snow, moist to wet summer conditions, tolerance to many commonly used herbicides, and lack of persistence in chemical, mechanical, and cultural control measures. Common milkweed appears tolerant to most all labeled herbicides currently registered. It cannot be controlled with one herbicide application of any herbicide except possibly patch spray with Tordon at very high rates like 1 to 2 gallons/A). Preventing common milkweed patches from spreading and establishment of new patches requires continuous scouting and persistent control efforts.

    Seeds readily germinate and new plants readily become established from seed in fields. Common milkweed becomes perennial (capable of reproducing from underground roots) approximately three weeks after seedling emergence. New shoot developing from established roots begin emerging in late April and grow more rapidly than spring seeded crops.

    Some reasons why herbicides are ineffective in controlling common milkweed are: large underground roots that can penetrate to more than 13 feet below the soil surface, shoots arising from as deep as three feet below the soil surface, waxy leaves which hinder herbicide uptake, and root buds near plant stems that are most tolerant to systemic herbicides. Increased control results from fall application of systemic herbicides due to greater movement to large buds that are closest to plant stems as they begin to develop. Greatest herbicide translocation extends out to the outer buds because they act as "sinks" as the buds develop. Ammonium sulfate stimulates root bud growth.

    Control recommendations in small grains: In 1990, researchers from University of Minnesota applied several small grain herbicides at the highest labeled rate. Herbicides included: 2,4-D ester, MCPA + Banvel, Bronate, Curtail, Stinger, Harmony Extra, and Starane (to be released in 1998). Most herbicides did not reduce milkweed plant mass, height, or stand. However, the best treatments were Harmony Extra at 0.5 oz 75DF/A, and Starane at 1.5 lb ai/A. None of the treatments decreased milkweed populations the year following application.

NDSU Research Data - applied June of 1988

Herbicide

Rate

Fall 88

Spring 89

 

pt/A

% control

2,4-D
Banvel
Banvel + 2, 4-D
Curtail
Tordon
Roundup

4
2
0.5+2
13
86
6

36
71
26
13
86
56

48
61
15
6
83
99

General recommendations:

    Apply when milkweed is in the late-bud to flowering stage and actively growing.

    CAUTION: The following treatments may cause significant crop injury and death if applied on cropland. Growers must determine the benefit from control against crop loss from excessive herbicide rates applied. In addition, Tordon will leave a residue for several years and may injure crops grown in successive years. However, applications made to small patches of milkweed may be justified because only a small percentage of the field will be applied.

    Roundup Ultra + Ammonium sulfate: (No residue)
        Patches: 3 to 4 qt/A
        Rope or Sponge Wick: 33% solution

    Tordon at 2 to 4 qt/A (Many years of residue)

 

PAY ATTENTION TO MALICIOUS MILKWEED

    Common milkweed blankets the state. Less tillage, insulating snow and ample spring moisture has caused infestations in epidemic proportions of this weed. Ignoring it will not make it go away. Because there are few viable chemical control options on cropland does not mean you should let it go and hope it goes away. It will not. It will only get worse. Consider the following factors in your decision to take action or not.

    1. Prevent seed production: Milkweeds seed are highly viable and will germinate readily under various conditions. Pappus on seeds allows long-distance travel and can contribute to small patches taking over complete fields. Seedlings become perennial within a few weeks after emergence. One shoot can soon become a large patch with ample subsoil moisture to feed underground roots. If herbicide application is not feasible then clip or cut the flowering parts.

    2. Milkweed control is expensive: Individual plants and small patches are easier and less expensive to treat than entire fields. Patch spraying covers only a fraction of the area of a broadcast application. Patch spraying allows use of higher herbicide rates which means getting milkweed under control sooner and with less expense than broadcast spraying. Research has shown good root kill the spring after application from Roundup and Tordon.

    Patch-spray Roundup Ultra at 3 to 4 qt/A (up to 5 qt/A is allowed). Apply at late bud to flowering. Add ammonium sulfate to Roundup at 12 to 17 lb/100 gallons of water. Do not apply after small grain is headed and only a maximum of 10% of the field can be treated. After heading the application is regarded as a preharvest application and maximum use rates are limited to 1 qt/A (See ND Weed Control Guide page 13).

   Patch-spray Tordon at 3 to 4 qt/A. Tordon residue will help prevent other shoots from emerging. CAUTION: Tordon residue will be present for several years after application.

    Patch-spraying is much less expensive than broadcast applications across entire fields.

    3. Patch spray now: Research shows that application at late-bud to flowering is effective. There is a lot of growing time left this year. By letting the patch increase in size will mean increasing the expense in control. Just as a comparison to show how fast one milkweed shoot can grow. One Canada thistle root was planted in the spring of 1995 in an above ground root box (2 ft wide by 16 ft long by 4 ft tall). By the end of that summer, that one shoot had produced 127 above ground shoots and had covered the entire space of the box. By harvest the next spring 310 above-ground and 223 below-ground shoots were counted. Common milkweed has the potential to equal Canada thistle.

    4. Herbicide Residue: Patch-spraying of Tordon will only leave residue in small patches. However, broadcast spraying Tordon across entire fields will restrict planting of any broadleaf crop for several years.

    5. Reducing Tillage: Reduced tillage has probably contributed as much as weather to the increase of milkweed. Tillage will add to chemical control methods for milkweed control but may not be viable in soil and moisture conservation practices.

    Common milkweed is continually getting worse each year. Control milkweed now before it becomes the leafy spurge of cropland.

Richard Zollinger
NDSU Extension Weed Scientist


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