Friday, August 2, 2013

Infestation Lessons from the Plant Pathologist

This morning I had an appointment at the County Department of Agriculture, Weights and Measures with the plant pathologist to look at my sickly heirloom tomato plants.  She was kind enough to actually let me come in with my plants and learn from her!  Thank you!  These are my notes from our appointment.

I had 2 terribly stunted samples form the North Bed, one moderately stunted and wilting sample from the West bed, and 2 larger and rapidly wilting samples from the Community Garden bed.  I made the appointment figuring that since not everything responded miraculously to my fish emulsion that the problem went deeper than nitrogen deficiency.  And oh how very deep the problem is!

From the North Bed:
Plants 1 + 2: Snow White Cherry + Orange Cherry
a) chewing damage along stems consistent with pill bugs, ear wigs, etc. (I knew this, but the problem seemed more extensive than this)
b) tomato russet mite - can decimate fields, but not that many were present
c) no evidence of fusarium wilt or parasitic nematodes but the sample tomatoes were so stunted that one really couldn't tell for sure.  Easier to diagnose in bigger plants.  These were tiny - like less than 4 inches tall despite being seedlings from the spring.

From the West Bed:
Plant 1: Mortgage Lifter
a) Root Knot Nematode (prominently!).  Easy to see the knotting, not uniformly tapering roots.  Parasitic worm in a gall, which is a reaction to her presence.  The pathologist shaved off the gall carefully with a scalpel under the microscrope and we could see the small gooey white looking balls that were the adult nematodes.
b) Fusarium Wilt - plenty.  Easy to see when we cut the plant's stem in cross section near the soil line.
c) Tomato Russet Mite - mild
d) no spider mites

From the Community Garden Bed:
Plant 1: Super Sweet White Cherry
a) Fusarium wilt - prominent
b) Root knot nematode - mild - it was harder for me to see in this specimen, but she saw it.
c) tomato russet mite - mild
d) spider mite - a few present, but not many at all
Plant 2: Yellow Pear
a) Fusarium wilt - plenty
b) tomato russet mite - some
c) aphid - present
d) no root knot nematode noted

Fusarium wilt is a soil born fungus.  "Basically there forever" due to spores.  When the stem is cut in cross section, it is easy to see the brown discolored ring in the plant's vasculature.  Further up the stem it becomes less obvious.  It is nightshade specific, thus the recommended rotation of nightshades, which can be very difficult to do in the home garden.  More practical to get VFN (Verticillium Wilt, Fusarium Wilt, Nematode) resistant tomato hybrid varieties.  If doing the rotation, rotate out at least 3 years and see if you can get one decent crop in before the fungus population rebounds significantly.

Root Knot Nematode - Parasitic nematode that lives in the soil, has a broad host range (including most vegetables and some weeds, etc), and is basically there forever according to her.  Some resistant varieties can be found (mostly tomatoes, though) and can solarize the soil as a last resort.  This involves a clear tarp on top of soil for 4-6 weeks in the heat of the summer.  Problem with this is that it kills everything, even beneficials in soil.

Also discussed powdery mildew on the squash - soap and water can help, but do not apply at hottest part of day.  Sulfer can work, too, but with the same caution.

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