Did you know that there are over 500 types of rust that affect plants? Rust is a spore that usually begins as white spots on the leaves or stems of plants and becomes yellow or orange or sometimes black as it progresses. It is a fungal parasite that is spread by the wind or by watering and often lives in soil. The spore needs living plants to survive and spreads from infested leaves to healthy ones.
Vegies that can suffer from rust include asparagus, beans, celery and celeriac, corn, leeks and garlic, potatoes, tomatoes and spinach. Herbs include members of the mint family. Berries include raspberry (Raspberry yellow rust which starts as yellow spots and overwinters as black spots) blackberry (Blackberry orange rust) and strawberries (Common leaf spot). Flowers include roses, sunflowers and calendula among many others.
At the community garden, we are currently pulling out all the calendula plants from the gardens and pathways as a yellow/orange rust is ripping through the plants. This includes plants not yet visibly affected. All plants are being bagged and will not be composted. Last year we had significant rust on garlic leaves. This year we will plant garlic in a different spot and begin again with fresh heads. If we were to use heads from last year, we would soak cloves in a mix of 1L of water, 2 teaspoons of Seasol and a teaspoon of bicarb for 12 hours and then dunk them in vodka just before planting. Our raspberries, blackberries and strawberries also suffer from time to time and we remove all affected leaves and bag them. If the whole cane is badly infected we remove it.
Essential in controlling rust, is good garden hygiene, good air circulation around plants, only moderate amounts of nitrogen in the soil, appropriate watering, a spraying regime and the selection of rust resistant varieties of plants.
Good garden hygiene requires the removal, bagging and disposal of all infected plants (and often adjacent plants that are not yet affected as with calendula above), the removal of all dead leaves from the soil surface and covering that area with fresh soil, a 3 year crop rotation before replanting in the same bed, and making sure that your hands, clothes, tools and secateurs are clean before and after working with infected plants. The latter is sometimes overlooked. Never add plants with rust to your compost heap.
Good air circulation requires good spacing of plants, cutting out of overcrowded berry canes, thinning of dense bushes or trees and the avoidance of dense plantings of flowers that through touching each other cause plants with rust to readily infect healthy plants. In humid weather, this is particularly important.
Nitrogen rich manures such as poultry or NPK chemical fertilisers cause soft leaf growth which is susceptible to rust. This is to be avoided, especially spring application of nitrogen fertiliser.
Watering spreads rust by splashing it from leaf to leaf or soil to leaf. The best solution is dripline but if that is not possible, water with a soft spray directly onto soil and avoid getting water on the leaves.
- Organic sprays include Eco-fungicide, available from nurseries, or mix your own. These make the leaves alkaline which stops fungal spores germinating. You can use:
2L of water, a drop of vegie oil (to make it adhere), a drop of detergent, and 2 teaspoons of bicarb. This is safe for animals and insects but can build up alkaline salts in the soil so do not overuse or mix with a horticultural oil. Best used weekly in early spring to prevent outbreaks.
- Better than using baking soda is using potassium bicarbonate as the potassium benefits plants and does not leave a potentially toxic residue, or use Neem oil from the Neem tree. It is a natural fungicide and safe for living creatures.
- Sulphur must be applied before rust develops and is therefore a preventative and requires working out which plants are susceptible to rust. You can obtain it as a powder, liquid or as wettable sulphur. Check directions for both mixing and application for each type. Not to be used on pumpkins, cucumbers, zucchinis or some berries which are sensitive to sulphur.
Rust resistant varieties of many plants including raspberries, blackberries and strawberries and some vegetables are available.
See Sustainable Macleod’s YouTube video on preventing and treating rust on mint which will give you general tips on deterring rust.
Written by Robin Gale-Baker