MSMA, or Monosodium Methyl Arsonate, is a powerful herbicide often relied upon for controlling stubborn grassy and some broadleaf weeds. While highly effective, it's a restricted-use product with specific guidelines for application due to its active ingredient being an organic arsenical. Understanding how to use MSMA correctly is crucial for maximizing its benefits.
What is MSMA and What Does It Control?
MSMA is a selective, post-emergent herbicide, meaning it targets weeds that are already growing. It works by being absorbed through the foliage of the weeds, disrupting their growth processes, particularly photosynthesis. This leads to the plant's death, often with visible results within a few days to a couple of weeks.
MSMA is particularly effective against a range of challenging weeds, including:
- Crabgrass
- Dallisgrass
- Johnsongrass
- Nutsedge
- Goosegrass
- Chickweed
- Sandbur
- Puncturevine
- Pigweed
- Clover
- Foxtail
- Woodsorrel
Where Can MSMA Be Used?
- Cotton fields: For post-emergent weed control.
- Golf courses: Primarily for spot treatments (not exceeding 25% of total acreage annually) or one broadcast treatment on newly constructed courses. Avoid use on golf course greens or collars.
- Sod farms: Typically for one to two broadcast applications.
- Highway rights-of-way: Usually limited to two broadcast applications per season.
- Non-bearing fruit and nut trees (e.g., almonds, apples, cherries, peaches, pears, plums, walnuts), and citrus.
Important Note: Always check the specific product label and your local state regulations, as restrictions can vary (e.g., some states like Florida have specific limitations on MSMA use in certain areas or for certain applications).
How to Use MSMA: A Step-by-Step Guide
1. Read the Label Thoroughly: This is the most critical step. Every MSMA product will have specific instructions, rates, and safety precautions. The information provided here is general guidance and does not replace the detailed instructions on your product's label.
2. Determine Your Application Area and Rate:
- Measure the length and width of the area you intend to treat to calculate the square footage (Length x Width = Square Footage).
- For acreage, divide the square footage by 43,560 (Square Footage / 43,560 = Acres).
- Refer to your product label for the precise mix rate. A common general application rate is 1 to 2 fluid ounces of MSMA per gallon of water per 1,000 square feet. For larger areas, rates can range from 2.5 to 6 pints per 40 to 50 gallons of water per acre. Use higher rates for dense weed growth.
3. Prepare Your Spray Solution:
- MSMA products often include a surfactant, so adding an additional surfactant is usually unnecessary. Check your label to confirm.
- Fill your spray equipment reservoir about half full with water.
- Add the measured amount of MSMA to the water with agitation.
- Finish filling the tank with water, ensuring thorough mixing.
- Do not store spray solution in the tank for prolonged periods.
- DO NOT MIX msma with other herbicides or chemicals.
4. Prepare the Area (if applicable):
- For turf areas, it's often recommended to mow the grass to a height of 1 to 1.5 inches before application.
- Avoid mowing for at least two days before and after application.
5. Apply the Herbicide:
- Apply the MSMA solution to the target weeds with a low-pressure, fan-spray, or coarse spray setting for uniform coverage.
- Spray thoroughly to the point of wetness on the undesirable plants, but avoid excessive runoff.
- Apply on calm days when wind speeds are between 2 and 10 mph to minimize drift.
- Optimal application temperatures are generally between 65°F and 90°F (some labels suggest 70°F to 90°F). MSMA works best on young, actively growing weeds.
- Do not water the treated area for at least 24 hours after application.
6. Reapplication (if necessary):
- Weeds should show signs of dying within 2 to 4 days. If not, a second application may be needed after 7 to 10 days, particularly for stubborn weeds or perennial grasses like Johnsongrass and Nutsedge.
- Adhere strictly to the maximum number of applications and total active ingredient per season as stated on the product label.
7. Clean Equipment:
- After use, thoroughly clean your spray equipment by flushing it with water.
- Do not use galvanized or aluminum equipment as MSMA can be moderately corrosive.
Safety Precautions are Paramount!
MSMA contains organic arsenic and requires strict adherence to safety guidelines.
- Personal Protective Equipment (PPE): Always wear a long-sleeved shirt, long pants, chemical-resistant gloves (e.g., polyethylene or polyvinyl chloride), chemical-resistant footwear plus socks, and protective eyewear. For overhead exposure, chemical-resistant headgear may be required.
- Handling and Storage: Avoid contact with skin, eyes, and clothing. Avoid breathing spray mist. Wash hands thoroughly before eating, drinking, chewing gum, using tobacco, or using the toilet. Store away from feed or food products and out of reach of children and domestic animals.
- Environmental Hazards: Do not apply directly to water or to areas where surface water is present. Maintain required buffer zones around permanent water bodies (e.g., 25 feet for sod farms, 50 feet for cotton, 100 feet for highway rights-of-way). Do not contaminate water when cleaning equipment or disposing of washwaters.
- Re-entry Interval (REI): Follow the Restricted Entry Interval (REI) specified on the product label before allowing workers or others into treated areas.
- Disposal: Dispose of product and empty containers in accordance with local, state, and federal regulations.
By carefully following the product label and these guidelines, MSMA can be a valuable tool for effective weed control in approved settings. Always prioritize safety and environmental responsibility when working with any herbicide.