Organic...still Grubs

sc77September 8, 2013

I have maintained an all natural organic lawn for the past 4 years. I follow all the rules, mow high, water deep (1inch) weekly, leave clippings, spray compost tea, top dress with compost, overseed in the fall, fertilize with Ringer brand organic fertilizer, sbm, and corn gluten meal.

Most areas are doing very well, but the last two years my lawn in the front yard has gone yellow in late July. I assumed it was dormant and would come back, but it never did. This year was worse and when I dethatched the lawn it literally just peeled off in sheets. Underneath I found grubs...lots of them. In a square ft. section I could could almost 20. I plan to treat with beneficial nematodes, Had anyone had success/experience with applying nematodes?

2 other questions:

1. Why is there a belief that organic lawns don't get grubs, or at least not in high enough volumes to destroy a lawn. Last year I didn't even inspect closely for grubs, because everything I read online suggested that is just an issue for synthetic lawns. I reseeded last fall and the this spring an early summer it was one of the best looking sections of my lawn, lush, thick, and green.

2. I also always hear that a healthy organic lawn won't need to be dethatched, but mine needs to be annually. I'm confident that my lawn is healthy, when removing the grubs the soil was a nice loan with many worms... yet I still have a thatch build up by the fall? thoughts?

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1) That myth is just that, a myth. You'll still get grubs. However, there are at least two organic methods of control--nematodes, which will happily eat the grubs and kill them, and Milky Spore, which will happily infect the grubs and kill them.

Nematodes take effect immediately, Milky Spore requires some time to build in the soil.

I had limited luck with either and use...non organic methodology...on that one single issue. Grubs are a real problem for me, and damage or widespread lawn death would happen if I didn't. I had more than a thousand square feet of lawn "float" a few years ago.

2) If you're dropping enough organic food to keep nitrogen levels at the top layer up, thatch will disappear. Most of us don't do that (including me this year), so we get some thatch. It's usually not nearly as bad as a synthetically-fed lawn, though.

You can safely ignore up to a quarter inch of thatch (in the lawn, when pulled out even a quarter inch looks like several inches). It won't do any harm, isn't thick enough to encourage insects, and does help to protect the crowns a little bit.

Amounts larger than that should be dethatched. Alternately, heavy use of soybean meal for a year or so will consume the thatch as the bacteria get more than ample nitrogen from the soybean and go after the thatch for carbon.

    Bookmark   September 8, 2013 at 9:45PM
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morpheuspa, really appreciate the reply. Yes, the grubs did a lot of damage this year, not 1000sq, but probably like 400 or so. I hand picked out like 200 today, as I am preparing the area for reseeding. The grubs should be dying soon anyways, so I will wait until next year to put down the nematodes.

I have heard that milky spores take a very long time to be effective, as much as a few years and that timing is critical. Did you apply the milky spores year over year and still have no improvement?

Your probably right about the thatch not being too thick, but seems like a lot when I pull it all up. The main reason I feel the need to do that is I need to overseed and if I don't remove the thatch, the seed will have a tough time making good contact with the soil.

I noticed a lot of birds feeding in that area of the yard. I thought they were eating my worms, but now think they were eating the grubs. Maybe I will look into attracting specific birds to the yard if the nematodes don't work. I have been temped to use chemicals for crabgrass, but refused and slowly strengthened my lawn organically...hopefully I can solve this naturally as well. If not, I'll just let it turn to dirt...haha.

    Bookmark   September 8, 2013 at 10:45PM
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Grubs don't actually die for winter, they go dormant and wait for spring. But at that point, they're quite large and tough to kill. Post-September, you'd have to pull out guns big enough that I wouldn't ever contemplate using them. Even now, the guns are bigger than they would have been in July.

Fortunately, spring grubs don't feed much (Japanese beetles, anyway). Then they turn into beetles and stop hassling the lawn and start hassling everything else. :-)

You can stop hand-picking them unless you enjoy doing it. You can't really make much dent in the population, I'm afraid. Fortunately, a flock of robins can whip through and pick out more than you could ever manage.

I did do the Milky Spore over several years at slightly above recommended rates. Zip. Nada. No dice. But others do report good effects from it, so perhaps I was just unlucky.

For overseeding purposes, I can understand dethatching, so no argument there at all. Although really, you shouldn't have to overseed every year, which may reflect on your care regimen.

Crabgrass definitely does reflect on it. I do get it in the gardens and my pots, but not one bit in the lawn. It gets choked out. But if you look at my blog (link included) you can kind of see why. There are photos down the list somewhere there from early September.

That's a Kentucky Bluegrass lawn, fed organically. My care regimen is kind of heavy:

early May: 15 pounds per thousand sq ft of soybean meal
August 1: 15 lbs/K of soybean meal
August 20: Milorganite at bag rate
September 10 (or so): 15 lbs/K of soybean meal
October 1 (or so): 15 lbs/K of soybean meal
October-ish: Mulch all fall leaves, import leaves if I have time
Growth stoppage, usually Thanksgiving-ish: Winterize

...for a total of around 6 pounds per thousand nitrogen equivalent per year. And this is a low year, I've been transforming my soil and adding organic material in previous years. My top flight year was over 1,200 pounds per thousand of organic material in the form of grains, leaves, and everything else I could scrounge including home-made compost. That's severe overkill, but sure did whip that soil into shape fast.

Here is a link that might be useful: My blog

    Bookmark   September 8, 2013 at 11:12PM
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I am not sure where you ever saw that organic lawns would not get these grubs but that is very incorrect information. Many people do not understand how Milky Spore, "Bacillus popilleae", Disease works so they will tell others that it does not. MSD is a passive pest control product, the grubs must ingest the spores, the spores do not go out in search of the grubs. MSD is also effective for only a fairly short time tin the grubs life, shortly after they hatch which means it should be applied so it is there when they hatch. Many people apply MSD in the spring hoping to control the grubs that are almost ready to pupate which is the wrong time since these grubs are not affected by the MSD.
There is also a genuine misunderstanding of what lawn thatch is, and the link below may be of some help understanding what it is. An accumulation of grass clippings is not that evil thatch although many people think it is. Some thatch is even beneficial.
You may well be putting too much Nitrogen on your lawn. The recycled grass clippings can provide up to 1/2 the N requirements of your lawn annually and that is about 2 pounds of N per 1,000 square feet. Compost, Compost Tea, The Ringer, Soybean Meal, and the corn gluten meal all provide N. Since N is quite volatile what is not used fairly quickly by the plants can be washed out into the ground water which causes that water to be polluted.
What does a good reliable soil test tell you about the soil you have?
How much Organic Matter is in that soil?
How well does that soil drain?
How well does that soil retain moisture?
Other then the grubs what kind of life is in that soil?

Here is a link that might be useful: About lawn thatch

    Bookmark   September 9, 2013 at 7:34AM
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Kimmsr, Thanks for the info. I have seen it mentioned that grubs don't typically occur in an organic lawn. Probably the main place I am recalling and quoting comes from

That website, while simple started me down the organic lawn care path. The author says:

"I have never had to personally deal with grubs. And I have yet to encounter an organic grower that has had to deal with them. But I have had many people write to me and ask how to deal with grubs organically. Nearly all of them have mentioned "Last year I sprayed toxic goo to get rid of the grubs and now they're back"

In terms of thatch I doubt I put down too much nitrogen, since I have lots of clover, which indicate a lawn is nitrogen deficient. I listed all the stuff I use, but sparingly due to cost. I haven't done a soil test in 3 years, I sent it to my extension office. I was more concerned with pH at the time and can't find the results now. The soil has a lot of worms. Drainage tested using the 1ft by 1ft hole, fill/drain, then fill drain again and found that it all drained very fast (about 1/2 hour).

Im no expert, just trying to maintain an acceptable lawn without chemicals.

    Bookmark   September 9, 2013 at 11:11PM
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None of us are experts although we are students trying to learn how to live and grow in our environment.
Although clover can be an indicator of low available Nitrogen in soil it will grow even in soils with ample amounts of N once established. Thatch and Nitrogen are only remotely connected, but thatch buildup is an indication that the Soil Food Web is not very active. Your drainage test indicates there is too little organic matter in the soil and that has an adverse affect on the Soil Food Web because they feed on organic matter. In addition to a soil test for soil pH, P, K, Ca, and Mg perhaps these simple soil tests may be of some help.
1) Soil test for organic matter. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drainsâ too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer your soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.

    Bookmark   September 10, 2013 at 7:52AM
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+above. You can get thatch buildup from heavy use of synthetic nitrogen due to the excessive growth. It leads to excessive sloughing of material that your food web may not be up to digesting fast enough--and hence, thatch buildup.

But the link between the two is kind of vague and indirect. Even heavily overfed lawns with good food webs can handle the thatch. Poor food webs may not be able to handle even normal thatch levels.

I have KBG, which is famously thatchy (not quite as bad as zoysia, though), but have very little to no thatch. I've encouraged the food web by increasing organic material and feeding organically.

    Bookmark   September 10, 2013 at 12:28PM
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dchall_san_antonio(8 San Antonio)

None of us are experts although we are students trying to learn how to live and grow in our environment.

Ahem. I'd like to introduce this forum to MorpheusPA. Morph, meet the forum. I consider myself to be fairly well read on organic lawn care, Kimmsr, too; but I consider Morph to be an expert. Sure we're all students, but Morph has been my teacher for the past few years. I realize Morph left this forum years ago, so the reintroduction may help people when trying to evaluate the advice they get. If there was a planetary award for lawn of the year, Morph would get it. Listen carefully to what he says.

Back to the grubs, I think we all jumped out of our chairs at the idea that organic lawns don't get them...or might even be less prone to getting them. Grubs come from the Japanese beetles and June bugs that flock to our porch lights in the late spring. I have heard it said that people usually don't get grubs two years in a row, so this might be a rare case.

I have used beneficial nematodes successfully and unsuccessfully. The key to success is to apply them to a saturated soil and then water them in. I tell people to apply them on day 3 of a 4-day rainstorm. So water an inch, apply bn, and continue to water another 1/4 to 1/2 inch.

In terms of thatch I doubt I put down too much nitrogen, since I have lots of clover, which indicate a lawn is nitrogen deficient.

There's another misconception. Clover loves fertilizer. So do most other plants. But clover is simply a plant that will tolerate worse soil than some other plants. It will not die out when you start fertilizing, and the presence of clover does not indicate much of anything. It can be very hard to get rid if organically because it drops so much seed. It rebounds easily.

I'm concerned about reseeding. It sound like you reseed every year. Is that right?

    Bookmark   September 13, 2013 at 6:18PM
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I have spent many hours reading about organic lawn care and feel like I understand all the concepts, but clearly am still having issues. I am going to submit another soil test, have not done one in about 3 years. In the meantime, I have starting working through some of the tests outlined by Kimmsr.
Here is what I have found so far:
1. About 6-8 worms in a shovel full of the lawn.
2. Tilth - tough to tell. Wouldn't hold together at all when slightly damp, adding a bit of water and hit held together too well...
3. Smells earthly, no foul odor
4. Just did the soil in jar test, I will review in 24hrs. I have done this in the past and couldn't make heads or tails of the different layers, hopefully this time it is more clear.

Dchall, thanks for the info on the nematodes, will be doing that next June. I will wait to see what the soil test says, but I interpret the clover as nitrogen deficiency because I go very light on the fertilizer due to cost. This year, as an example, I put down probably 20lbs of corn gluten meal in the early spring as a pre-emergent, and then again 6 weeks later, and that is about it. In the fall I usually would also apply ringer brand organic fertilizer at about the same rate. This year I have not, because I have been so busy re-seeding all of the damaged areas.
Yes, I overseed every year and seem to always have dead spots after the summer. This is probably because I cannot keep up with the 1inch per week that is needed. Water is just too expensive. As a result, my lawn goes dominant, but often I have many spots that just don't come back. Then in the fall I spend many hours using a detaching rake to pull out all the dead grass and overseed. Next spring, my lawn will look really good, thick and green, but by July it starts to suffer.
I had grubs in the same area last year, but didn't inspect closely as I assumed they were a small population. This year, they are Bad...

Other issues I have to deal with, are mature trees on surrounding properties that limit the amount of direct sun I get. Nothing I can do about that. Probably as a result, I have areas of my lawn that always get moss, although I may be able to improve that by adding amendments.

Thanks again for all the advise. I will keep you posted when I get my soil test results

    Bookmark   September 15, 2013 at 9:03PM
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Where we did do some digging this year we found here no grubs and I did not see any June Bugs or Japanese Beetles anywhere this year while I have heard from people that have been inundated with them. Last year we had many of both.
I think moss is more an indication is compacted soil. Common thought is that moss grows on compacted, moist, acidic soils in shady areas, while I find moss growing on my crushed dolomitic limestone covered driveway in full sun that only gets wet when it rains. I also find moss growing on the concrete blocks that are the foundation for the house, lime, little moisture, but on the north side so little sun. I also find moss growing on some loose sand, very well drained and in full sun.
Grasses need bright light, not necessarily direct sun, and there are species of grass that grow better in shadier areas then some other grasses, ie. Fescues rather than Blue Grass.

    Bookmark   September 16, 2013 at 7:32AM
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@Kimmsr/All -

Here are the results of my soil test done by Umass Extension Office. I was quite surprised that I have been able to increase my organic matter to > 11% in the last 5 years. The last time I had this test done I was also lower in Potassium and my pH was around 5.9.

Anything else that can be determined from these results? Actions to be taken?


    Bookmark   October 1, 2013 at 7:03PM
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