Southern Root Knot Nematodes. They invaded my garden about five years ago, coming in (I think) on a truck load of soil I had delivered while building new raised beds. They’ve gradually spread to other beds, probably from a combination of water drainage and hitchhiking on tiller tines, shovels and hoes during the time I didn’t know I had them. And I've been battling them ever since in about two thirds of the sixteen 4'x18' raised beds that make up the veggie garden.
They are microscopic worm-like organisms that invade plant roots, multiply and disrupt the flow of water from roots to upper plant. The result is stunted growth and little plant output. Plants look thirsty but watering doesn’t help too much; maybe just a temporary boost.
You can't kill them and can only hope to knock them back and suppress them with a combination of methods. Here's information on early symptoms I gleaned from some southern Extension Service websites and others:
Above ground symptoms of a root knot nematode infestation include wilting during the hottest part of the day even with adequate soil moisture. Damage is most serious in warm, irrigated, sandy soils. It’s easy to see the loss of vigor, yellowing leaves, and other symptoms similar to a lack of water or nutrients. And, of course, the knotted roots you find at the end when you've watered and watered, fertilized and the plants finally look bad enough that you pull them. Some cucumber roots:
Infested vegetable plants grow more slowly than neighboring, healthy plants, beginning in early to midseason. Plants produce fewer and smaller leaves and fruits, and ones heavily infested early in the season can die.
Things to do for suppression of nematode populations:
Plant nematode resistant veggies/flowers.
Plant as early as possible in spring and as late as possible in fall. I learned that in soil temps below 64, nematodes can’t function so it's best to plant resistant stuff as late in the fall as can be safely done and really early in the spring to get a jump on the nematodes. They don't infect older plants as hard as they do young ones. Because of that, it also pays to grow really large transplants if possible.
Get lots of organic matter into the soil because high water retention in soil helps fight nematode attacks. I mulch with leaves raked in the fall and till them in when the crop’s done.
One extension service suggested tilling the infected beds every ten days in the summer as the hot sun will kill eggs brought to the surface. While doing this, also keep the soil moist to induce egg hatch and keep weeds out so that any newly hatched nematodes have nothing to feed on. Starve ‘em! I did this faithfully the summer of ’16 and it seemed to reduce the ’17 population so I did it again last summer. This spring I’ll see if it helped.
Thickly planting French marigolds and mustard several times in one season and tilling them in disrupts the reproductive cycle and it did help a little. They have to be French marigolds (species Tagetes patula) as some other marigold species can attract more nematodes. I cheated by planting them along just the edges of one bed and although I’ve read where you have to plant the whole bed for it to be effective, what I did seemed to help a bit.
I've read where sowing mustard and then tilling it in several times in one season disrupts the reproductive cycle. It seemed to help a little and mustard seed is really cheap at the feed & seed store. The mustard’s volatile oils knock them back enough that the next year you can plant other stuff before having to repeat the process. Territorial Seed has in their Brassica Cover Crop section a ‘Mighty Mustard’ that has high levels of volatile oil to act as a natural soil fumigant. I haven’t tried it yet.
Plant winter cover crops (annual rye, rye or wheat) after several fall tillings. I sowed annual rye in four fallow beds this past fall and just now turned them under. It’s the first time trying that
Plant summer cover crops and till them in. In ‘16 I grew some sorghum in one bed just to starve the critters. No more of that as it was a mildew and aphid magnet. Late last spring I planted two beds with Sunn hemp which is supposed to have a somewhat nematocidal effect when chopped up and tilled in. We’ll see this year if it had any effect.
Good garden sanitation practices. Thoroughly clean all tools used in infected areas.
Since I have something growing in the garden all year long I have to pick and choose my battles. Beds that show big nematode damage get targeted for war. There hasn’t been any damage in the fall planted veggies due to the colder weather. I’ve read where RKN don’t bother corn, onions. So far that’s true.
There’s currently some research going on exploring the use of molasses, of all things, against nematodes. Something about a diluted spray. If I find any more about that I’ll post it. It's WAR, I tell ya!
Resources (in no particular order):
http://www.missouribotanicalgarden.o...nematodes.aspx
RNK in garlic:
http://www.gourmetgarlicgardens.com/...es--pests.html
http://www.clemson.edu/extension/hgi.../hgic2216.html
https://content.ces.ncsu.edu/control...getable-garden
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7489.html
There’s also one I had from U. Of Florida but I can’t find it right now.