Section 3 - Weed Management

Five Steps to Proper Sprayer Cleanout

Proper sprayer cleanout procedures are given on many herbicide labels, and the procedure on the label should be followed for specific herbicides. The following procedure illustrating a thorough sprayer cleanup procedure is effective for most herbicides:

Step 1. Drain tank and thoroughly rinse interior surfaces of tank with clean water. Spray rinse water through the spray boom. Sufficient rinse water should be used for 5 minutes or more of spraying through the boom.

Step 2. Fill the sprayer tank with clean water and add a cleaning solution (many labels provide recommended cleaning solutions). Fill the boom, hoses, and nozzles and allow the agitator to operate for 15 minutes.

Step 3. Allow the sprayer to sit for 8 hours while full of cleaning solution so the herbicide can be fully desorbed from the residues inside the sprayer.

Step 4. Spray the cleaning solution through the booms.

Step 5. Clean nozzles, screens, and filters. Rinse the sprayer to remove cleaning solution and spray rinsate through the booms.

Common types of cleaning solutions are chlorine bleach, ammonia, and commercially formulated tank cleaners. Chlorine lowers the pH of the solution, which speeds the degradation of some herbicides. Ammonia increases the pH of the solution, which increases the solubility of some herbicides. Commercially formulated tank cleaners generally raise pH and act as detergents to remove herbicides. Read herbicide label for recommended tank cleaning solutions and procedures. Never mix chlorine bleach and ammonia, as a dangerous and irritating gas will be released.

Sprayers should be cleaned as soon as possible after use to prevent the deposit of dried spray residues. A sprayer should not remain empty overnight without cleaning; fill the tank with water to prevent dried spray deposits from forming.

Questions to Ask If You Suspect Herbicide Resistance

• Was the correct herbicide rate and adjuvant added to the spray tank?

• Was application and spray coverage adequate?

• Was the environment favorable for herbicide performance (unstressed plants)?

• Did only one weed species escape control (weed escapes may be localized in patches)?

• Is the suspected resistant weed mixed in with other weeds of the same plant type that were controlled?

• Does the herbicide typically control the weed species that escaped control?

• Has the herbicide (or herbicides with the same mode of action) been used frequently in the past?

• Have other cases of resistance been confirmed in the area?

One may strongly suspect the presence of a herbicide-resistant weed with a yes answer to these questions. If possible, pull or till suspected herbicide-resistant weeds to restrict their spread. Rotate herbicides with different modes of action, apply herbicides in tank-mix/multiple modes of action, and rotate crops to help minimize herbicide resistance. See section on herbicide resistant weeds in NDSU Weed Guide: Go online to www.ag.ndsu.edu/weeds/w253/w253w.htm - scroll down to table of contents text (bottom half of page) and see information under ‘herbicide resistant weeds.’ Other online information sources for herbicide resistance management:

• www.weedscience.org

• www.resistancefighter. com

• www.weedresistance-management.com

• www.glyphosate weedscrops.org

Considerations in Preharvest Weed Control

Following are some factors to consider before applying a herbicide as a harvest aid:

The expectations for preharvest weed control usually exceed reality - it is not possible to kill or dry down a three-foot weed in the same manner as a three-inch weed. Lower portions of the weed may not be affected.

It requires time to dry down treated weeds - usually 7-10 days. It may require more time if wet and/or cool weather conditions occur after treatment. All herbicides labeled for preharvest application are systemic and slow acting, which requires a longer dry down period as compared to contact, fast acting herbicides.

Glyphosate is labeled as a harvest aid only in spring wheat and durum - not barley or oats. Glyphosate at 0.5 to 2 pt/A of a 3 lb ae/gal concentrate controls annual grass, broadleaf weeds, and quackgrass and suppresses Canada thistle in hard red spring wheat and durum. Do not apply to barley. Do not apply to wheat grown for seed, as a reduction in germination or vigor may occur.

Glyphosate should be applied after the hard dough stage (30% or less grain moisture ) of the wheat and at least 7 days prior to harvest by air or ground in 3 to 10 gpa spray volume. Applying glyphosate before physiological maturity can reduce yield, test weight and seed germination. See label for adjuvant use. Always add AMS at 8.5 to 17 lb/100 gallons of water. AMS increases control of annual and perennial weeds and especially control of weeds stressed by dry weather. AMS also eliminates antagonism from ions and carbonates in hard water. Do not use AMS in place of an NIS. Refer to label for addition of other adjuvants.

Herbicide Storage Temperatures

Herbicides may be exposed to freezing temperatures in storage. For specific temperature restrictions for various herbicides, refer to page 77 of the 2008 NDSU Weed Control Guide available online at www.ag.ndsu.edu/weeds/w253/w253-3a.htm.

Weed Info Online

North Dakota State University: www.ag.ndsu.edu/weeds (with links to weed I.D., 2008 ND Weed Control Guide, Section 18 status, herbicide label search)

South Dakota State University: http://plantsci.sdstate.edu/weeds

University of Minnesota: http://appliedweeds.cfans.umn.edu

North Central Weed Science Society web site with links to extension publications from most Midwest universities: www.ncwss.org - Click on “Publications” then “Midwest Web Extension Publications.” From there you can get a large variety of extension materials, including herbicide mode of action and pictures of herbicide symptomology.

Pesticide Labels: www.cdms.net/labelsmsds/lmdefault.aspx?+=

Greenbook: www.greenbook.net – Known in weed science circles as the ‘Green Bible’ that contains labels for most all pesticides currently labeled.

Take Advantage of Pesticide, Container Disposal Programs

The MN Dept of Ag Waste Pesticide Collection web site: www.mda.state.mn.us/chemicals/spills/wastepesticides/default.htm

Project Safe Send in N.D: www.agdepartment.com/Programs/Plant/PSS.html

S.D. container collection and recycling info: www.state.sd.us/doa/das/hp-pest.htm Also see www.acrecycle.org