Fight the blight: check your crops for signs of disease

This summer has been the perfect for storm for crops. A wet July and early August, coupled with the heatwave in September, has seen a rise in fungal diseases such as rusts, scabs and leaf spots – problems that can be even more damaging when plants are stressed, such as from drought.

Now, RHS Plant Health scientists are recommending that gardeners check their plants to look for signs of stress and poor health.

The RHS Gardening Advice Service have received over 7,500 enquiries about plant diseases so far in 2023, rising from 2022. Questions are wide-ranging, covering all kinds of bacteria, fungi and viruses that affect plants.

Some of the diseases that have become more prevalent following the wet weather are scabs, blights, leaf spots and downy mildews. Though many of these fungal diseases won’t kill off garden plants, they can weaken them, reduce flowering and look unsightly.

Blights, such as tomato blight and potato blight caused by Phytophthora infestans, can also ruin crops.

RHS scientists recommend keeping a close eye on plants for signs of disease so that these problems can be nipped in the bud. 

What can I do?

Maintaining good plant health in the garden is also especially important after the unusually wet summer. There are several things you can do to help prevent outbreak and spread of disease in your garden:

• Cut out any leaves or flowers showing signs of disease
• Collect fallen plant material
• Allow good air flow around plants and ensure plants are not stressed, for example by being too wet or too dry, or receiving insufficient light

Tomato blight

Hope for honey fungus

An RHS summer studentship project is also providing new hope for gardeners troubled by honey fungus, which attacks and kills the roots of many woody and

Perennials are plants that live for multiple years. They come in all shapes and sizes and fill our gardens with colourful flowers and ornamental foliage. Many are hardy and can survive outdoors all year round, while less hardy types need protection over winter. The term herbaceous perennial is used to describe long-lived plants without a permanent woody structure (they die back to ground level each autumn), distinguishing them from trees, shrubs and sub-shrubs.

Honey fungus mushrooms

• Find out more about keeping your garden healthy

Notes from the ground

RHS Chief Horticulturist Guy Barter shares his thoughts and suggestions for the rest of September in the garden, and what else you can do now for your crops.

• Downy mildews tend to spread dramatically after rainfall, so the rain forecast may see the demise of outdoor potatoes and tomatoes – a case of save what you can.
  This fungal disease causes dark, scabby marks on the fruit and leaves of apple trees and a few related ornamental trees and shrubs. It spreads by airborne or rain-splashed spores and survives the winter on fallen leaves and infected twigs

  Apple scab and rose blackspot are also prevalent, but all you can do now is gather and destroy fallen leaves and fruits.

• The weather will soon be too cool for diseases to develop, so drastic measures are seldom called for, but selective removal of infected material can be worthwhile.

• Numbers of less welcome insects have built up through August, and populations can increase rapidly now. These include caterpillars on cabbages, sporadic aphids, and vine weevil will also be laying eggs now, which will hatch into root-destroying larvae. Happily, beneficial insect populations are also high, which in many cases gives adequate control. Best practice is to monitor pest levels and only intervene if severe damage likely.  

• Slug populations are high after wet July and normal August rainfall. Most garden plants are too big to take much harm, but
  A seedling is a young plant grown from seed.

  seedlings of autumn salads and flowers sown now to overwinter will be vulnerable. Potatoes still in the ground can also be damaged. Prompt lifting and storage will save the crop. With luck, winter weather will suppress slugs during the critical period next spring and early summer.

• Gluts are common now, as plants are big and can exploit light levels to be very productive. It is worth picking even if produce has to be given away as maturing produce suppresses flowering, when with reasonable weather, cropping of courgettes, outdoor blight-resistant tomatoes and runner beans can continue into October.

• Many crops are maturing and the ground left vacant – it is good practice to sow cover crops to protect and improve the soil until spring. These quick-growing lush plants include clover, oats, ryegrass and trefoil, and are best sown now. Peas, field beans and vetches share diseases with common vegetables and are inadvisable in vegetable gardens.

• Leafy salads and greens, marche and mustard greens can still be planted for this year. However, much can be sown for early next year – annual flowers such as cornflowers, chard, lettuces, salad onions, spinach and wildflowers. Time to order onion, shallot and garlic sets and broad bean seed for October.

• It’s peak season for lawn care (aerating, scarifying, feeding and overseeding) and making new lawns from seed or from turf. ‘No-mow lawns’ can get their annual trim now to prevent tussocks and tree seedlings taking over. As ground is cleared, composting peak season is also imminent.

• Peak fruit harvest starts from mid-September. RHS gardens, gardeners and other non-commercial producers report light crops this year, but that means plenty of growth and fruit
  A bud is a small, undeveloped shoot that contains the potential for new growth. Buds are typically found on stems, where they can be apical (found at the tip) or axillary (found between leaf axils) and may develop into leaves, shoots or flowers.

  buds for next year, so it’ll be worth concentrating on winter and spring pruning to avoid excessive crops that may break boughs and lead to lighter crops in 2025.