Last week Arash in Iran left the following comment:
Hello to all
I am a researcher in iran.I and my cooperator have collected 22 accessions from region of Tarom (one of areas of Zanjan province). We want to research taht how many genotypes are being farm in this area and also study resistance to puccinia alli. please gide me how I operate thate conclude best.
He actually doesn’t say it’s specifically on garlic, rather alliums in general, but since my original post was on garlic I assume that’s what he meant.
Does anyone have any information for him?
I can say that in the last few years since I’ve been making posts about garlic rust, I first read that it was present in on the US west coast, specifically in California in the region around Gilroy and a few isolated places in Oregon. I also knew it was present in northern Europe because it was in my garden and those of fellow gardeners in the UK, Denmark and Sweden.
In the years that followed I had reports from readers that it was present in the entire Willamette Valley area of Oregon, and later British Columbia in Canada and Los Angeles, in southern California. Two years ago someone reported it appeared in Ethiopia. I see mentioned on the Internet it’s also appeared this year on the east coast of the US in Maine. It seems to be spreading now, almost all over the world.
Following a suggestion from Søren, a fellow blogger in Denmark I’ve been experimenting with spraying dilute milk on my plants. I have not done this in any sort of scientific way, but my feeling is it’s of significant benefit. It seems to slow the rust down and manage it, to the extent it’s no longer a serious problem. I spray this on the plants about once a week or after rain, during the last 2-3 months or when I think rust infection is likely to occur. It’s benefit seems to be much greater if applied before the plants are infected. I use a ratio of 3-10 parts water to one part milk.
In the last several years I have grown more than 120 varieties of garlic in my garden, and a friend of mine more than 300. We have not really noticed significant signs of resistance to garlic rust on any of them, except a few of the more vigorous varieties like Susan Delafield and Estonian Red (a purple stripe type) seem to stand up a little longer to the rust probably because of the strength of the plants, and some silverskin varieties like Chilean Silver seemed to get infected a little later than the others.
The other thing a number of people observed was the application of high nitrogen fertilizer, in particular animal manure, caused the rust problem to become much worse.
I find the amount of rust varies drastically according to the season. This year, we’ve had a drought, and I’ve had no rust, and almost no white rot for that matter. A couple of bulbs were slightly affected and that was all.
A few years ago, we had an extremely wet season, and my maincrop garlic had it so badly the foliage died in mid-June. I still got a slightly reduced crop.
This season I only had garlic rust in a single cultivar, and very late. All in the row was affected, but none in neighbouring rows with different cultivars. Here the extremely wet season doesn’t seem to have diseased or decreased harvest noticeably.
My understanding and personal experience is rust infection occurs on warm days (25C or higher) when the humidity is high (about 70% or higher). Once infected, the rate of infection depends on other things, like the cultivar, stress from excessive available nitrogen or drought, etc.
I agree with Søren that the amount of rain is not directly related to rust problems. Even southern California, which has no summer rain but a humid sea climate, has garlic rust problems now. I’ve also frequently seen different cultivars growing side by side, some infected and others not. By the end of the season, every year, all my garlic is usually infected in the end.
My understanding is the conditions for infection (25C or warmer, 70% min humidity) must be maintained for at least 6 hours or so, and infection cannot take place when the humidity is over 100% (ie the plants are wet). For the small number of plants I have it’s not worth it, but in theory it should be possible to install sensors to detect when conditions are right for infection, and irrigate the plants every 6 hours to prevent infection. A little more research would need to be done to determine the exact conditions for infection, according to local climate and cultivars used.
I forgot the 25C! This summer we had very few hours at or above. Good for the garlic, not so good for my pale sun tan. And then the garlics have been soaked in rain most of the time anyway! Actually drowning has been more close to damaging my garlics than rust, but in the end, it was the leek moth (in my garden it should be renamed garlic moth) that gave me the only real problem. I watch my garlics for small holes in leaves and scapes, later especially in the angle where the leaf meet the scape. I seems I’ve prevented any moth from migrating into the cloves this year. I really don’t like them foraging there.