How to Recognize and Deal With Garlic Diseases and Pests
When things don't go right in the garlic garden you need someone you can turn to to find out what went wrong and how to correct it. Unfortunately, there are very few people who can discuss garlic pests and diseases with authority. There was Dr. Ron Voss at UC-Davis, but he has retired, leaving Dr. Fred Crowe of Oregon State U as the remaining active authority that I know of in this country and his time is limited by a rigorous schedule. The bottom line is that each grower of garlic has to learn to identify the cause of problems in their garlic and find out for themselves what to do about them. My job here is to provide a place where garlic lovers can find the information necessary to protect their garlic and gardens from excessive contamination.
There are several primary problems that can beset garlic; soil nutrient imbalances, irrigation variance, seasonal weather variation, insect pests, fungi and viruses. Most of these we can do a little something about. Prevention is usually the easiest way to deal with growing problems. By maintaining a good organic garden soil, most of these problems can be eliminated or minimized. When you don't get the growing results you had hoped for, how do you find out what you have and how it happened? That is what this page is all about. I'm not a microbiologist, entymologist or any other kind of ologist, but I try to summarize some of their findings here and link to a bunch of different kinds of ologists below (please pardon the weak attempt at applied humorology).
One of my chief concerns is garlic disease. Unfortunately, there are a lot of different garlic diseases running around in this country and they're all over the place. They are a lot more common than we would like to admit. I have heard that there are some growers in Northern California who have had to stop growing due to white rot infestation of their fields and have taken to contracting with other growers throughout the Northwest to grow for them and have the garlic trucked to Gilroy for processing. In Canada, they are having some similar problems. Growers are the only people who can do anything about the problem. I cannot in good conscience sell diseased garlic to the public knowing that they will plant it and infect their gardens with garlic diseases and/or pests. Therefore, we will not knowingly ship garlic that looks, feels or smells bad.
How Did All These Garlics Get Here? A few of the kinds of garlic now in America came in with Polish, German and Italian immigrants over the centuries, but most of them came in all at once in 1989. The USDA had been asking the Soviets for permission to go to the Caucasus region between the Black and the Caspian Seas to collect garlics but permission had always been refused because there were many missile bases in the area. Finally, as the Soviet Union was disintegrating in 1989, they suddenly invited the Americans in to collect the garlics. They went from village to village along the old Silk Road buying garlic from local markets and naming the cultivars after the town or village where they were purchased. When they got back to the US, they realized they had no gardens ready to plant the garlic in so they contracted out the growing to a few private growers on a share-the-garlic basis. There was no time for adequate phytosanitary precautions to be made so we don't really know what kinds of "hitchhikers" might have been brought in with them. After they crop was harvested and the USDA got their share, these growers began to trade with each and to sell some to friends and other garlic growers and that is how they came to be available now when they were not available 15 or 20 years ago.
This chapter is about identifying the diseases and pests that are harmful to garlic and trying to deal with them in a safe and effective manner. I do not know whether any of the things that are harmful to garlic are also harmful to people, but better to err on the side of caution and say that people should not eat diseased garlic or garlic that looks or smells bad or has soft cloves.
Insect Pests of Garlic - I used to think that garlic was iron-clad and bullet-proof and that it repelled insects and that nothing attacked garlic. Then I began to grow garlic and soon discovered how wrong those ideas were. When the grasshoppers ate my garlic to the ground and then went into the ground to eat the bulbs, I cleverly reasoned that I had erred in my thinking. This was confirmed the following year when grub worms (in our case, June bug larvae) ate into a lot of my large, otherwise beautiful bulbs and ruined them for market.
Airborne PestsWhile there are few bacteria, if any, that can live very close to garlic, garlic is subject to some viruses that may be airborne and some that come from insects. For example, the yellowstreak virus is carried by the Wheat Curl Mite which attacks garlic among other things. Wheat Curl mites are the worst pest problem I see in garlic I get from other growers.
Wheat Curl Mites and the Yellow Streak Virus - Did you ever find a garlic bulb that was a little soft and seemed dehydrated and when you open up a clove, you can see that it looks like it is drying out and has a white, powdery residue inside the clovecover and all over the shrinking clove? That white powdery residue is probably wheat curl mites. If you look at them through a small 30 power pocket microscope, you can see them moving around. If planted, the resulting plant will have stunted, knarled yellow streaked leaves. Those effects are caused by the Yellow Streak virus carried by the mites. UC-Davis has a good page on this (link below). Since they live everywhere, come in on the wind and are almost invisible, there's no way to exterminate them. You can protect against airborne infestation by evenly sprinkling a dusting of DE into the heart of each plant where the leaves emerge every couple of weeks as the new leaves emerge in the spring and as the plants mature in the late spring. The DE serves as lethal barricades to them entering the clove area of your plants.
If you plant garlic cloves that already have adult mites in them, tucked in between the clove and the clove covers, they will eat the surface layers of the cloves, they or their eggs will survive the winter and reproduce all spring long and your next years crop will perish. The best way I know of to deal with this problem is to soak the seperated cloves in water overnight to loosen up the clove covers and then soak the cloves for a few minutes in alcohol to kill the adult mites at planting time. I don't know if the alcohol soaking kills any eggs that may be present or not. In my experience, contaminated garlic soaked like this does much better than contaminated garlic not soaked.
Grasshoppers - The first time they came, they were a curiosity because while they jumped away trying to escape from you everywhere else, when they were on the garlic leaves, you could walk right up to them and pick they off by hand and kill them - they made no attempt to escape, it was as though they were drugged. The next year they again ran from us and then ate the field to the ground. The only way I could think of to protect against them is to put on floating row covers at the first sign of a real infestation. Physical separation between garlic and grasshopper will work until they learn to chew through it or find a way under it. Expensive, but cheaper than losing a crop. I don't know of any poison or anything else that is truly effective, although Nolo bait (a biological IPM control agent) seems to help. Physical separation is at least non toxic and helps retain needed moisture - and in Texas, its shade is appreciated. We have had to screen in our drying shed to screen them out - one grasshopper can chew into 10 or 12 bulbs a day, rendering them worthless.
Sometimes they come in such numbers they strip the trees, bushes and weeds and the ground is black with grasshopper dung. They just hang around and stare at you as if laughing or eyeing you for their next meal. It's freaky having bare trees in summer - downright surreal. In the end, their manure and dead bodies mixed into the soil become next years fertilizer. Then the cycle begins anew and we have a few years with only a handful of them. They never say anything, they just stare at you all the time, and eat and mate. There's lots of satisfying ways to carry out a war of attrition that borders on useless, such as soapy water and Diatomaceous earth, but they are broad and kill other things as well. Fly swatters and big, thick rubberbands work well to smack them with and give a certain personal satisfaction also.
Soilborne Pests Nematodes Nematodes are tiny worm or snake-like animals and there are thousands of kinds of them but only a few kinds of which bother garlic. Some, called pratylinchus sp., attack the roots while the Ditylynchus sp. attack the stems and bulbs.
You can tell if there are nematodes in your garlic cloves if you know the signs to look for. If there are tiny pimple-like spots on the bare naked cloves, those are the entrance holes from stem and bulb nematodes. If the area around the bottom of the clove, just above the root plate has a brownish discoloration and is dessicated, that is the entrance-signature of a different kind of stem and bulb nematode.
If there are nematodes in your garlic, a time-honored remedy is to soak the cloves in hot water (110 F - 112 F) for 10 to 12 minutes, in addition to any other pre-planting soakings, before planting and that will be hot enough to kill the nematodes but not the garlic and you can safely plant the cloves.
There are also some sustainable ways to treat the soil for nematode infestation without harming most other things in the soil. Horticultural cornmeal applied as a top dressing to the soil at the rate of one pound per 100 square feet is very helpful in reducing soilborne nematode populations, as is growing brassicas (mustard, cabbage, etc.) and tilling the green plants under. I strongly suspect you could also chop up brassicas from other gardens or from an organic grocery store and saturate the clippings with water and irrigate with the water to help keep both fungus and nematodes down in the soil. You can also purchase nematodes that kill other nematodes and add them to your soil to help keep the populations of harmful nematodes at bay.
More information on insect pests will be added later - stay tuned.
Fungal Diseases of Garlic - Garlics mostly seem to be subject to various fungi such as smut, penicillium mold and something that appears to be powdery mildew that can be soil-borne as well as white rot, Fusarium sp. and several forms of Botrytis. Even though crushed raw garlic has strong anti-fungal properties, living garlic is readily attacked since the allicin is not formed until and unless the seperate cells containing the enzyme, alliinase are breached and the chemical action started.
Almost all the diseases that garlic gets are fungi and almost all can be prevented or minimized inexpensively. Removing them from the beds where your garlic is grown involves fertilizing with corn meal as it is anti-nematodal and anti-fungal, so is corn gluten meal, which has other properties as well. Another thing you can do is to plant brassicas of all kinds and let them get of good size and then till them under - the chemicals released in their decomposition are toxic to fungus and nematodes. Another trick is to shread a bushel of brassica vegetables raw and let soak overnight, strain and dilute the liquid and irrigate the beds with the water and water in for a quick kill. Wild mustard is said to work quite well and I'm going to try it soon and let you know how well it works. All of these treatments are effective in reducing soil populations of the offending creatures to tolerable levels while being organically compatible.
Soak the garlic before planting to minimize fungus. - Since fungal diseases are so common, I think it is a good idea to assume all incoming garlic to be planted has a problem of some kind even if there is no evidence of it and soak it overnight the night before planting in a solution of one gallon of water, one tablespoon each of baking soda and liquid seaweed to give it an innoculation against diseases and an energy boost as well to get the growing process off to a good start (The seaweed stimulates root growth.) Be careful not to leave the garlic soaking too long - 16-18 hours is enough and if you leave it in much longer it will already start to grow roots and I have seen 1/4 " long roots on cloves after soaking 24 hours - not good as those roots break off during planting inviting pathogen invasion.
I then soak it in alcohol for a few minutes just before planting to try to kill any unseen hitchhikers, like mites, stowing away between the wrappers. One of the reasons to soal the garlic so long is to loosen the clove covers so that the alcohol can penetrate the clove covers and kill any mites lurking inside the clove covers.
These precautions may not get everything, but from my experiences and experiments, they help a lot. For a few years during the 90s, I tried various different preplanting soaking solutions and compared them to cloves from the same bulbs that had no special treatment, just planted. In every case, the treated cloves out-performed the untreated ones in that they were larger and healthier. The ones that did the best were the ones that had the most ingredients in the soakings. The ones that were best among the ones that receives only a single soaking were the ones soaked in alcohol. In another interesting observation, some cloves were completely peeled while others were left intact and they received the same soakings as the others and in almost every case, the bare naked cloves out performed the intact ones, from which I infer the presence of pathogens or pests in the clove covers - but who has time to peel all those cloves?
It would serve little purpose for me to try to reproduce here all the information that is in the links below or for me to try to diagnose everyone's problem, because I'm not an ologist (heh) of any kind. If you have a garlic problem, since you know best what your garlics symptoms are, I encourage you to check out the links and find out what your problem(s) are and then come back here and see what you can do, if anything, to deal with these diseases.
The individual grower with the problem garlic can better diagnose the disease if there are lots of pictures and descriptions to compare his problem garlic to. I have linked to a few websites that have a lot of information that will help you find out for yourself what is wrong and maybe some idea of what you can do about it. This is an ongoing project and we will be adding more to it on a regular-ish basis.
More information on fungal diseases will be added later - stay tuned.
General Precautions with Planting Stock - This is the beginning of a long term project to learn more about garlic diseases and pass that information on to those who want to know. In the coming months I will add a section on each of the major diseases and discuss them in detail. I will be adding more specific information in the page itself as well as more links to other sources of information of a similar nature as time goes by. That is the reason for the onion links below, some of the information also relates to garlic and some of the pictures and other information can help identify particular garlic diseases.