Written in collaboration with KBFA Advisor, Andrew Bennett
Garlic growers got hammered by diseases this wet and cool spring, suffering dead plants and stunted bulbs. We can’t control the weather, but a few management fundamentals can help Allium aficionados reap the rewards of resilience and avoid the many possible root rots that garlic is susceptible to.
The solutions are rooted in the soil, so today we’ll look at ways local growers have achieved success in our region, despite the dank spring, using amendments, cover crops, rotations, and good stock.
SIGNS & SYMPTOMS
Garlic is on the menu for a motley crew of rots, rusts, and blights and, unless you’re an expert, we pretty much all instinctively gasp and ask, “Is it White Rot?” We’ll get to prevention, but first know that KBFA is here to help. If leaves are yellowing or look “off”, or bulbs are soft or discoloured, phone us, write us, send us photos, and we’ll get in touch with experts like Linda Gilkeson for their superb advice. If there’s any concern at all, we’ll help you get a sample off to the Provincial Lab where they’ll dissect your bulbs and tell us what’s up. (The same goes for any plant you grow commercially on your farm.) And don’t panic. Most of the time it’s not White Rot, but something like Fusarium (a fungus that rots the base), or another fungi (Penicillium, Mucor, Rhizopus, Uredinia, you name it), or maybe a fungus like Embellisia that is usually just a minor cosmetic issue. If you see worms or other decomposers, they’re probably not the problem, but just a symptom of the rot. We’ve got some details and links at the end of this blog, but better safe than sorry, don’t hesitate to use our resources at KBFA. Okay, so how do we avoid these problems in the first place? Simple management is the key.
Grow something completely unrelated to garlic for at least a couple years (3-4) before returning garlic to the same field or bed. Pathogens quickly build up in soils that grow garlic (or onions, leeks, and other Allium relatives) year over year. In a complex market garden, it’s easy to forget what got planted where two years ago. A basic sketch map for each season is a really helpful record. Some growers like to plant a pungent “biofumigant” cover crop, like certain mustard varieties, in the summer, and then mow that down and till it in before they plant their bulbs in the fall. At least one farm likes “Caliente” mustard bred specially for this purpose, whether for alliums, potatoes, or other blight sufferers (not for late blight!). We were thinking of a webinar, what do you think?
Healthy soil grows healthy crops, and a diverse soil ecosystem will keep diseases at bay. It’s the usual advice:
- Don’t go through the winter with bare soil, cover it with mulch or sow a cover crop in the fall.
- Build organic matter and pump up your soil life with composts and green manures.
- Make sure garlic wastes are composted in a good, active pile, or get chowed down by a pile of worms in a vermicompost (And apply it to non-garlic fields in the rotation.)
We’re looking for information on Fall Rye as a winter cover crop between garlic rotations. Fall Rye, often mixed with legumes like winter peas or red clover, makes one of the best winter covers in our region. But Fusarium is a pathogen of wheat, barley and several other cereals, so rye may harbour the fungus? We don’t yet have a solid answer. One tip from a farm that was hit by Fusarium this spring: they fed their garlic with regular foliar nutrients (fish and seaweed), and believe this fed their big, healthy bulbs even though many plants had severely weakened root systems. It’s food for thought…
Nothing beats good genes and healthy seed. Process the ugly stuff, sell the good stuff, and save your very best, unblemished garlic for seed. Store it somewhere cold, dry, and well-ventilated before planting. Or why not develop your own clean seed stock? Several growers in our area are experimenting with raising new garlic stock from bulbils. Growing garlic from bulbils is an economic alternative to buying expensive seed garlic and avoids borne diseases. Bubil size differ greatly across varieties. Rocambole varieties produce the largest bulbils, Purple Stripes are mid-size and Porcelain types are quite small. The size of the bulbil determines the number of years needed to harvest full size garlic. Let us know if you are interested to hear more about this!
ROGUE THE ROGUES
Walk the rows regularly, especially in the spring, and dig up the problematic “rogues” with some of the soil around the roots. You may want to burn these culls, or compost them along with other wastes that are destined for landscaping areas, rather than put potentially diseased soil on your precious farm fields.
Dang it! You did what you could, but you’re sure there’s a problem. Well, here are a few things it could be: For commercial growers, the first step should be to contact KBFA and contact the provincial Plant Health Lab to get a positive diagnosis because symptoms of these diseases can look pretty similar.
Fusarium: This fungus can live a long time in the soil. It rots the base of bulbs and stops the flow of water and nutrients. Rotting basal plates are pretty obvious, and dark brown or pink roots. If you cut open the bulb, it will be soft and brown or red.
Vegetable Rot: Usually a fungal mold (e.g. Penicillium, Mucor, Rhizopus) will grow on tissue damaged in transport or planting.
Garlic Rust: Spores of this orange, blister-like Uredinia fungus appear on leaves. Spores can be transported hundreds of kilometeres by wind and survive in crops over winter. It spreads faster in high density plantings, and possibly on plants grown with excessive nitrogen. Rust is now widespread throughout the region.
Embellisia: This fungus usually only causes cosmetic damage, such as blotches on bulbs’ outer skin. It is worst in wet weather.
White Rot: This extremely unfortunate fungus can live in the soil for 20 years. Yellow leaves and rotting bulbs should get your attention. If you suspect it, quarantine the area, wash and disinfect your tools and boots, prevent water runoff from leaving the area, and definitely reach out to KBFA for assistance and send samples to the provincial Plant Health Lab.
- Jim Capellini gave a KBFA workshop in 2018 and his website is like “garlic school”, including this dive into the main diseases:
- The BC Ministry of Agriculture offers many in-depth growing guides, including one for garlic:
- The BC Plant Health Lab is there to diagnose your samples: