Jefferson City, MO 88° View Live Radar Sat H 97° L 77° Sun H 93° L 70° Mon H 81° L 63° Weather Sponsored By:

Ask a Master Gardener: Combating root rot, finding alternative herbicides

Ask a Master Gardener: Combating root rot, finding alternative herbicides

July 7th, 2019 by James Quinn, Field Specialist in Horticulture, MU Extension in Life & Entertainment

Q. What happened to my lovely dogwood tree (see photo)? Can I do anything about it now? Can I replace it with another next year?

A: I'm sorry to see your tree suddenly tanked. When a tree has relatively good foliage that all of a sudden wilts and dies, this indicates root rot. There really isn't anything you can do about it to save the tree. It's a goner.

We have a saying to never plant a tree of the same type back where one just died. This is especially true for root rots, that fungus is now in the soil, and there is no practical way to rid the soil of its presence. You could submit a sample of the tree to our plant diagnostic clinic to get the disease identified. That could allow you to make some judgment on what you might plant back there. Otherwise, choose a tree is not prone to root rot and (unfortunately) definitely not a dogwood.

Q. I have heard so much bad things about the herbicide glyphosate (aka Round Up), I was interested in using something else. I saw on Facebook some remedy of a natural mixture that would just as well. It was 1 gallon of household vinegar, 1 cup of salt and cup of dish soap. Does this really work as well?

A: This issue has been around for a while. A good article on it was written on it by North Dakota State University in 2014 in response to a similar claim of a "magical, natural, weed killing potion" with high "safety, effectiveness, and naturalness" and recommended as "an alternative to chemical weed killers" (see www.ag.ndsu.edu/cpr/weeds/homemade-herbicide-08-28-14 ).

Vinegar has been used as an organic herbicide for some time, with a stronger content often used (20 percent vs. household of 5 percent). Salt (sodium chloride) is a chemical that predates 2,4-D for use as a herbicide, and soap (detergent) is another name for "surfactants" that is applied with herbicides to stick spray droplets (retention) on leaf surfaces, reduce droplet surface tension (spread the droplet) and aid forming a herbicide deposit (close interface of the chemical active ingredients with the leaf surface). Soap when at a high level can 'burn' foliage, so the three ingredients are designed to burn back green growth.

This mix can kill many small annual weeds, but has significant limitations to the chemical glyphosate: Table vinegar contains only 4-5 percent acetic acid while industrial vinegar contains about 20 percent acetic acid. Table vinegar was not effective in any treatment while industrial vinegar gave greater results but still considered unacceptable weed control.

The article cited above also notes grasses were much more difficult to control than broadleaf weeds, and sunlight and temperature were very important, finding that when sunlight and temperature are less, so is the effectiveness. Complete coverage and spray volume are important to get a good kill. The burning action of vinegar and salt solution is not effective on perennial weeds. It will burn off the top growth of perennials (which may be desirable), but it will not provide long-term control.

The price of this 'home remedy' is just as expensive, if not more so, than glyphosate.

For complete discussion, see the full article.

Regarding safety, the combination of soap, vinegar and salt may seem harmless, but this would be horrible to get in one's eyes, and may be irritating to skin.

For a list of herbicide alternatives, see: content.ces.ncsu.edu/are-there-alternatives-to-glyphosate-for-weed-control-in-landscapes.

Finalsan Non-Selective Organic Weed Killer is an EPA labeled product that works much the same as this home garden remedy. The benefit is it has a label that describes how to use it, what to expect for results, and its limitations. This product is likely not carried by area retailers, so for more info check this companies info for pricing, etc.: greenearthagandturf.com/products/organic-weed-killers/finalsan/.

Q. I am ready to spray to control Japanese beetles. Should I wait until they arrive so I can get the spray right on them? And how often does one usually have to spray a plant?

A. While it is rather satisfying to spray them directly, it isn't necessary. For beetles, the insecticides are lethal if they consume leaves that have been sprayed. However, direct contact is also effective. By having a product on before they start munching, it prevents them from releasing a smell that attracts many others. This occurs when they eat a lot.

An insecticide that has been properly applied should last at least a week. To improve its effectiveness, include a spreader sticker with the spray solution and follow the label instructions. When pressure hasn't been high, I've seen two weeks of control. If a plant can handle some defoliation (e.g. grapes), I have gotten by with just one application, as once they started back in they never were that bad. For plants that don't readily grow additional leaves, like cherry trees, then a second application is likely needed.