Rust, Puccinnia allii

This allium rust affects garlic the most, compared to onions very little. Leeks and chives are in the middle. In my experience, the rust that affects leeks is not the same as the rust we suffer on garlic, but from what I can see the Latin name is very similar, Puccini porri.

Onions suffer little by comparison.

First signs are small and slightly raised spots or pustules on lower and older leaves. They are orange-brown, a similar colour to rust on metal.

In humid springtime conditions, rust can spread rapidly, and half-grown garlic plants can be quickly diseased – here in May, above all, and into early June. When you see the orange spots on lower leaves, it’s worth twisting, snapping or cutting them off, to reduce (although sadly not prevent) the spread.

Rust spores do not survive on old and dead leaves, which you can compost safely. Spores arrive on the wind, so you may suffer rust even when you have no obvious source in your plot or garden.

Every spring I notice far less rust on leaves of garlic in the polytunnel and greenhouse, compared to outdoor grown plants also planted mid-October. Consequently the under cover harvests in early June are bigger.

Currently I’m trying two new strategies:

1. Planting cloves on approximately 21st September, autumn equinox, so that more growth happens before rust arrives.
2. Sowing white mustard in late September, and plant garlic then or a little later among mustard seedlings. Mustard dies off in late winter, or we pull them. My hope and desire is for the mustard roots to improve the soil microbiome, and therefore for garlic to be more healthy and able to resist damage from rust spores.

By the end of December, after a frost of –9°C/16°F, the mustard was dying and we could see the garlic looking fine.

• Leaf removal and growing under cover are ways to slow the spread of rust.
• Start twisting off infected lower leaves of garlic in mid-spring, and of leeks in early autumn
• In dry weather, water in the morning rather than evening, so that leaves dry quickly.

Septoria

This is a widespread family of fungal diseases. Here are two examples, of which the apiicola causes most damage in temperate climates.

1. Septoria apiicola

This develops on the leaves of umbellifer vegetables in autumn’s damp weather, and it’s sometimes called ‘late blight of celery’. Worst damage is on leaves of celery, celeriac, parsley and coriander.

The first signs are brown spots with round edges, followed by rotting leaves, also brown stains on celery stems.  After a month or two and in wet weather, Septoria can enter bulbs of celeriac and cause them to rot.

Here, in the warmth of November 2022, this happened rapidly, and we needed to harvest earlier than I had thought, before the hypocotyls rotted from top down. (Celeriac is a swollen stem = hypocotyl.)

I find it’s hard to control here. Removal of infected leaves makes little difference, perhaps slowing the spread a little.

• You can put damaged leaves on the compost heap.
• Like late blight of tomatoes, the fungal spores are widespread in favourable conditions. I suffered this disease in my first year of a new garden on virgin soil, and see little merit in excessive hygiene such as removing all traces of infected material.
• There are varieties with some resistance, such as celery Granada F1, and celeriac Porthos. However they do not guarantee immunity and you may need to harvest earlier than you had expected or hoped, if your site and climate encourage this disease.

2. Septoria lycopersici

This affects solanums, mainly tomatoes. It needs temperatures in the low 20s°C / 70s°F, and wet leaves. Lesions are dark brown with a grey centre.

Verticillium wilt, Verticillium spp

Symptoms are similar to fusarium wilt. The main food plants susceptible are solanums and strawberries.

Most vegetable gardeners will not suffer this disease. It’s a serious problem if it happens, and beyond the remit of this lesson – best search the internet for details.

Viruses

Fortunately these are not common. I would inform yourself about viruses, without worrying too much. While viral infections are hard to cure, it’s pleasing that most soils and conditions grow plants without virus.

In contrast, I have noticed how horticulturalists with full training can be almost obsessed with this. Once I showed a very learned friend around my garden, where there was a lot of healthy abundance. Her main comments were expressions of worry about a very few plants which looked, to her, like they were infected by virus!

Viruses show as bright yellowing/curling/veining of leaves, and mottled fruits with light streaks and patches. They might affect celery, spinach, legumes, lettuce, cucurbits and solanums, plus many flowers. Virus is either seed- or aphid-borne and should not happen too often.

Yet virus is the main reason quoted for not replanting your own potatoes. Official advice is to buy new ‘seed potatoes’ every year. While my experience of several years is that you can use your own potatoes for seed, as long as the plants they come from were healthy.

Cucumber mosaic virus, CMV, Bromoviridae cucumovirus

This causes leaves to turn bright yellow, with dramatic mosaic patters. It also brings a ‘shoestring’ effect to new leaves, making them thin and deformed, resulting in plant growth stopping, and even the plants dying.

On cucumber plants you notice deformed fruits, and this virus affects many more vegetables than cucumbers, so the name is a little misleading. It’s thankfully rare in the UK, perhaps because the main agent of spreading it is cucumber beetles, and I’ve never seen one here.

However, I have suffered CMV badly on spinach in the last two years, possibly a result of mild autumn weather allowing aphids to continue breeding for longer. They transmit virus between plants, although I have not noticed many aphids. Suddenly you see spinach leaves that are bright yellow, and then the plants give up with new leaves deformed. In 2022 this was from October to November. It does not happen in all my autumn spinach, and spring sowings are so far unaffected.

CMV happens to some lettuce, while also there is Lettuce Mosaic Virus which is seed borne. It results in stunted growth of mixed colour with leaves mostly deformed.

Tobacco mosaic virus infects tomatoes, and again has similar symptoms. If you handle cigarettes, you may be spreading it!

• Positive identification is not straightforward because symptoms look like many other problems. Rapid yellowing of leaves and the mosaic pattern are the main symptoms.
• If you reckon that a plant or plants have virus, best remove them to the compost heap sooner rather than later, to reduce spreading by insects.
• My approach of adding virus-infected plants to the compost heap is not the ‘official advice’!

White rot, Stromatinia cepivora

This soil-living fungus is specific to allium plants. It shares the white rot name with beneficial fungi called Phanerochaete chrysosporium, which decompose both the lignin in wood, and many toxic chemicals (see Mycelium Running by Paul Stamets).

Stromatinia can exist in soil for 3–15 years, as dormant sclerotia. These spring to life in temperatures of about 15–20°C/60s°F, when they detect allium roots nearby. Their longevity means difficulties for us.

Signs of damage are onions and garlic falling over in early summer, sometimes with bright yellow leaves. Many roots are dying, fast. Leeks suffer too, but more in autumn than summer, because white rot goes dormant in soil when it’s above 20°C/68°F.

• Grow onions from seed not sets, because seeds cannot transmit white rot, nor do most sets, but they can.
• Save your own garlic for planting in autumn.
• Do not spread soil from infected areas, and wash tools where appropriate. No dig’s minimal soil interference therefore reduces the spread of white rot – see quote below.
• Leave a gap of 3-5 years before growing alliums in a bed where there is infected soil. When taking over an allotment, you may have to discover where there is white rot, by suffering it. Like clubroot, it can be prevalent in soil which has been poorly looked after.

• An observation from Jayne Arnold, market grower in central England at Oxtons Organics. She wrote in a mail on 20th November 2020, after their third year of no dig:

‘For the first time in 30+ years, we have not had a single leek with white rot. A disease we inherited, and which obliged us to practice eight year rotations to enable us to grow alliums.’