MOFGA's Pest Alert - October 23, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist
Another Garlic Pest - Bulb mites (Rhizoglyphus spp) - It is garlic planting time and we thought we saved the most beautiful heads for our seed. But, when we broke open the heads we were shocked to see the amount of damage to many of the cloves. Again, this year has proved to be a very challenging growing season for a handful of crops. This time it is garlic. I have never before seen this level of damage by bulb mites. And now that my awareness has been raised, I am getting calls from other growers seeing this damage and wondering what it is.
The mite itself is nearly microscopic so it is not a surprise that growers cannot figure out the culprit. Of course, Becky can see the little critters, but I had to use my dissecting microscope. They live down in the tiny, tight space between the cloves or between a loosened wrapper and the clove. If you see damage similar to the picture below, carefully dissect the lower part of the head of garlic, especially down near where the roots and the bulb come together and look under layers of scales. With a hand lens you can identify the bulbous shaped mite. In addition to the mite, we also found thrips living under the scales of the garlic. I am not sure yet whether this thrips is contributing to the damage, or is a predatory thrips feeding on the mites. I will get samples to experts and figure it out soon, so stay tuned and be sure to come to MOFGA's day at this years Agricultural Trades Show (at the Augusta Civic Center, January 8 - 10) where I will again do a talk on pests of the 2012 season.
Garlic and onions plants are not only damaged from the direct feeding by bulb mites, but also by pathogens to enter through the wounds caused by the mites. My garlic that was wounded had Rhizopus (black bread mold) and Penicillium (blue mold) growing in some of the wounds.
This bulb mite has a wide range of hosts, including many flower bulbs. It sure loves garlic. These mites are shiny, creamy white. They have four pairs of legs that seem to be more forward than on most mites, making their rear end look bulbous. They survive the winter in crop debris and decaying vegetation in the field, and in heads of garlic. Hot water treatment of the bulbs is recommended in lots of literature. Contact me if you want the details. But, I would not recommend it after the stories I have heard this year with growers who hot water treated garlic to control the bloat nematode only to find they killed the garlic and it did not sprout.
Crop rotation, sanitation, and planting clean seed is the only recommendation I have at this time. And of course, at this time the seed you have is probably what you will plant, so at least plant the cleanest of it. Try not to plant the cloves infested with mites. Avoid planting in fields with lots of decaying vegetation, especially cole crops which can harbor very high populations of the mite. Fallow fields with completely decomposed organic matter would be best.