How should I deal with garlic rust after the harvest?

Question

I've grown garlic that got infected with garlic rust. I had some luck in that the infection started late in the spring so the bulbs are actually pretty big - around 60g, cleaned.

The garlic stems and leafs are heavily infected by now. I've found some resources that say the disease is air borne and it is okay to compost the foliage, others say the opposite. I am looking for an authoritative answer on whether or not I should compost them.

Also, can the harvested bulbs be used as seed next year? Does the disease spread to the cloves? Does it affect storage longevity? As with the previous question, I am getting some mixed search results so an authoritative answer is desired.

Thanks for helping me out!

Answer 1

Puccinia allii is dispersed by the wind but that's because it sporulates on the infected leaves spreading the infection. The spores persist on infected material and can reinfect your garlic the following year when the spores can be splashed back onto the new garlic leaves. That's why it's recommended that once you have an infection you should not grow garlic there again for some years. If you do need to grow garlic there, do it in containers with new potting mix, and cover the ground nearby with straw so that spores are stopped from being blown or splashed onto the new plant leaves.

Unless you have a hot compost heap, you can not be sure you'll kill every single spore. So, I would not chance it. I gathered all my infected leaves and put them into the trash.

As for whether you can use bulbs where the leaves have been infected, the answer appears to be yes. The infection is on the stem and leaves and doesn't get underground to reach the bulbs. One study showed that cloves taken from infected plants did not exhibit rust.

Koike, S. T., Smith, R. F., Davis, R. M., Nunez, J. J., and Voss, R. E. 2001. Characterization and control of garlic rust in California. Plant Dis. 85:585-591.

Answer 2

I would not intentionally compost any plant material with a fungal infection. Fungal spores stay dormant in the soil. Good horticultural practice says you'll plant your garlic elsewhere next year, so you'd reduce the risk of transmitting the rust, but you're asking for problems if you spread this material around in a year or two's time in your compost.

According to the RHS, leek rust (Puccinia porri, syn. Puccinia allii) can fulfil its entire lifecycle within the leek without producing resting (dormant) spores, but on other alliums it does produce resting spores. This might be why you're seeing conflicting advice, as it would indicate that it's ok to compost infected leek plant matter, which in theory would contain no spores. (Personally I would still not do this).

It also states thay the pathogen is confirmed as being seed borne, so along with the fact of its biotrophism and the garlic clove being living tissue from an infected plant, I would suggest that planting infected cloves will very likely result in infected plants.

As long as you can control the rust somewhat it shouldn't be a massive deal on garlic. It's more if a problem on alliums grown for the leaves (spring onions, leeks, chives) which it renders unappetising if not inedible.