Organic Dollar Spot Control

This morning Ruth emailed me the following question about how to deal with dollar spot fungus in a Northeastern lawn. Specifically she'd like to know about using corn meal to treat dollar spot.

Ruth asks:

I live in the Northeast and have noticed that after a week of rain I now have brown spots/dollar spots. I am trying to go organic this year. I was wondering if you are still using cornmeal to eradicate the fungus problem. I noticed in your article that you used cornmeal and a activator. Do I need to use the activator? Also am I putting the cornmeal on the whole lawn or just on the spots. I also need to fertilize. Do I fertilize before or after? If after, how much after? Thank you. 

Ruth, thank you for taking the time to ask your question and I hope I can help. When it comes to all plant diseases it's important to start treating before you see any signs of disease. I am exactly the type of person to say "I told you so" but because you might have just found my site I won't. :) Last month I posted an article that it was time to start treating for lawn diseases in the Northeast. You can enter your email address in the upper right form on my site to get notifications whenever I post new topics. Use the links above the email form to follow me on twitter as well because next time I will taunt you mercilessly. :)

I don't have a lot of direct experience with dollar spot so had to reference a few sources to refresh my memory which are linked below.

There are a couple other cultural controls that can avoid having to use any fungicides (organic or synthetic). First, make sure that you adequately fertilize your lawn in the early spring because low nitrogen levels makes the lawn more susceptible to dollar spot and other diseases. A good choice would be corn gluten meal which can also decrease the germination of annual weeds. If you can't find it locally, or like me just like the convenience of having it delivered to your door Amazon has a couple good choices at prices comparable to what I can find locally. There's Espoma Organic Weed Preventer and Jonathan Green Organic Weed Control Plus Fertilizer which are offered using the free 2-day Prime shipping if you have a Prime membership which I also recommend. If you don't they're probably still available with free shipping though a bit slower. The common guidance is to fertilize your lawn with CGM when forsythia begin to bloom.

Another factor that can contribute to dollar spot disease is dry soil but wet leaves. This can either be from morning dew or light sprinkling of rain that don't do much more than just get the blades of grass wet. Make sure your lawn gets about an inch of water a week depending on your conditions. Some golf courses will also run their sprinklers in the morning to wash off the dew. That seems counterintuitive but the water washes away the dew and any fungus spores that might be on the leaves.

Okay, that covers what you should be doing next year. Now let's get to dealing with your existing problem and directly answer your question.

The theory behind why cornmeal helps to control diseases is that it either has or helps promote the growth of trichoderma hazianum and possibly other beneficial microbes. Trichoderma is a predatory fungus that should already be in your soil and cornmeal, or any organic matter really, will help increase the population in your and soil. Trichoderma actively kills pathogenic fungus and in my article on treating lawn disease organically you can actually see a video of trichoderma killing sclerotinia in my earlier article on organic lawn disease control.

Anything that kills fungus needs to be registered by the EPA to be sold for that purpose so nobody can sell corn meal as a disease control. Sadly the researcher that was doing the work on cornmeal retired and nobody has picked up the ball. I've had a lot of success with corn meal and lawn diseases in the past and corn meal is a decent fertilizer that will add nitrogen to your soil. The added nitrogen will help boost the growth of your lawn and increase it's vigor.

What you're seeing in your lawn isn't necessarily the disease but rather the damage caused by the disease. Think of it like seeing a bunch of holes in your zucchini plant after it got hit by flea beetles. Spraying to kill the insects won't fix the holes. Feed your lawn to help promote growth and then mow away the diseased portions. Bag and throw away your clippings to help get some of the dollar spot spores from falling back into the soil and lawn.

Do you need to use an activator? Like I said, even though I've seen cornmeal work for me the resarch stalled and I'm the type of person that likes to guarantee that something is going to be in the application. Since you're already having a problem with dollar spot you might want to get one of the many products containing trichoderma that are now available. Another option labelled to control dollar spot is Serenade Garden which has bacillus subtilis, a bacteria that controls many plant diseases. At the very least the corn meal will help your lawn outgrow the disease. Sadly the product I mentioned in the previous article is no longer being produced and I haven't found a direct replacement. It had everything you'd want in it.

This year I've been lazy and have only been using Serenade and milk sprays to control disease. It's easier and cleaner to spray than it is to spread corn meal since it's too fine to put in a spreader.It's been working great for me.

One more thing to consider is finding grass cultivars that are more resistant to dollar spot. In the fall, and then for the next 2 or 3 falls, overseed with your lawn with the better grass seed to get a lawn that's more naturally resistant to disease.

Hope this helps.

References:
Wikipedia article on dollar spot
NCSU Turfiles Dollar Spot