Some gardeners grow the same crop in the same soils for several years, unaware that without crop rotation, pests and diseases build up in the soil, causing yields to reduce. It is better to alternate crops. In this way there will be less need to use sprays during the growing season.

Source: European Centre for Integrated Pest Management, Natural Resources Institute of the University of Greenwich

For the avid gardeners who lovingly maintain and take care of their gardens, there are few things worse than walking outside and finding the beauty and life of their plants slowly fading with some form of plant disease.

There are literally thousands of plant diseases and to list them all here would be of no value, but they can be broken down into two main categories: parasitic and non-parasitic diseases.

Parasitic diseases are contagious and can be spread from one plant to another through anything from tools to plants to insects. Non-parasitic diseases (also known as ‘disorders’) can be caused by a number of factors including:

  • air pollution
  • too little fertiliser
  • nutrient imbalances
  • incorrect temperature
  • harmful chemicals
  • incorrect levels of water

Over at Wilkinson we’ve been talking to industry experts who really know what they’re talking about when it comes to plant diseases, why they happen and how you could avoid them. We’d like to say a big thank you for all their help and advice!

With the treacherous snow recently covering the UK, we also thought we’d ask whether this had the potential to damage plant life.

Take a leaf out of the experts’ book this summer by following the advice below.

The Experts

Professor Bruce FittProfessor Bruce Fitt– Professor of Plant Pathology at the University of Hertfordshire

Bruce Fitt is Professor of Plant Pathology at the University of Hertfordshire and leads a Crop and Environmental Protection research group.  They work on how plant diseases spread and developing plant resistance against the pathogens that cause the diseases, focusing on diseases of agricultural crops like oilseed rape, wheat and barley. They also work to assess how climate change is affecting severity of crop disease epidemics in relation to global food security. Professor Fitt’s answers are a summary of a telephone conversation.

 

Jerry CooperJerry Cooper – Pest Management specialist and lecturer at the Natural Resources Institute of the University of Greenwich

Jerry Cooper has over 30 years’ experience in crop protection, particularly in the control of major vegetable crop pests. He delivers training on pest management and production of safe food using integrated pest management.

 

Professor Jon WestJon West – Senior Scientist at Rothamsted Research

Professor Jon West is a senior post-doctoral plant pathologist at Rothamsted Research, with extensive experience in applied multi-disciplinary crop protection projects. He is also a member of the British Society for Plant Pathology.

 

 

Professor Matthew DickinsonProfessor Matthew Dickinson – Professor of Plant Pathology at the University of Nottingham

Professor Matt Dickinson moved to the University of Nottingham as a lecturer in plant pathology and was awarded a personal chair in 2011. His research looks at molecular diagnostics of plant pathogens including work on cereal rust fungi, root-infecting pathogens of tomatoes and phytoplasma diseases of a range of plants. These diseases include coconut diseases in Sri Lanka and Ghana.

 

Professor Michael ShawProfessor Michael Shaw – Professor of Plant Disease Ecology at University of Reading

Professor Michael Shaw lectures on plant disease management and his research interests include plant disease epidemiology and ecology, especially the development of fungicide resistance and foliar disease forecasting.

 

 

Question 1: What is the most common plant disease in UK gardens?

Matthew Dickinson – Professor of Plant Pathology at the University of Nottingham

“The most obvious ones visually will be the powdery mildews and rusts, which occur on many different ornamental and vegetable crops. These are generally different species depending on which plant you have (even though the symptoms of all rusts look very similar) – for example, the rust that you get on leeks will not be the same species as the rust that you might get on roses – so if you see a rust or a mildew on a particular plant species, it is not going to spread to other plant species (apart from possibly to very closely related ones). Other common foliar diseases will be black spot on roses, and perhaps some Phytophthora species that often cause large black lesions on some plants.”

Bruce Fitt – Professor of Plant Pathology at the University of Hertfordshire

“For most gardens, the problem is with fungal rather than bacterial plant diseases. In UK gardens, late blight of potatoes and tomatoes is one of the most serious diseases that a gardener should look out for. It can completely destroy the crop, whereas other diseases may only decrease yield or cause blemishes. There are always new diseases to look out for, such as European pear rust, which has recently become much more common in UK gardens.”

Jerry Cooper – Pest Management specialist and lecturer at the Natural Resources Institute of the University of Greenwich

“There is a common leaf disease of tomatoes and potatoes called late blight, caused by Phytophthora infestans. The two crops are genetically very similar, and late blight can devastate both when conditions are wet. The disease is a type of organism that is slightly different from a typical fungal disease, being classed as a water mould because it needs wet conditions to infect plants. Plants soon develop dark blotchy patches on the leaves, particularly near the tips, and also on the plant stems. Sometimes white mould can be seen underneath leaves, and sometimes the whole plant collapses. Fruits on infected plants develop an unattractive grey appearance which may develop on the plant or after fruits are harvested green.”

Question 2:  What can cause plant diseases?

Jon West – Senior Scientist at Rothamsted Research

“There are many different plant pathogens that cause leaf diseases – most in the UK are fungi (rusts, powdery mildews, leaf blotches or leaf spots) or oomycetes (downy mildew or potato blight) , some are caused by viruses (e.g. mosaics or yellows) and a few are caused by bacteria (Xanthomonas) or phytoplasmas (aster yellows). Many of the virus and phytoplasma diseases are spread by insects such as aphids.”

Jerry Cooper

“Development of Phytophthora on growing plants is favoured by wet conditions around 15 to 25 degrees Celsius, when infection can devastate a crop in a short time. The wind can transport spores, but the most common source of infection is disease causing spores being spread by rain splashes.”

Michael Shaw  Professor at University of Reading

“Plants become diseased when a micro-organism – a fungus, bacteria or a virus – arrives on a susceptible plant at the same time as conditions suitable for the micro-organism to start growing and damaging a plant. As a rule, think of each disease of each species of plant as caused by a different infection. For example, rust on leeks is quite a different thing from rust of roses. The most important cause of disease is that a plant can’t fight off the micro-organism, because it doesn’t recognise the danger posed, because the plant is in poor condition, or because the weather is exceptionally favourable.”

Matthew Dickinson

“Mainly fungi and fungal-like organisms in the UK. These will generally be spread between plants in the form of spores, either blown in the wind or splashing onto the plant from the soil. There are some bacterial diseases that might also be splashed onto plants and some viral diseases, most of which are spread between plants by insect vectors carrying them from one plant to another.”

Question 3: Can plant diseases be cured?

Jon West

“Damaged leaf tissue doesn’t actually get better but if the weather changes and if the plant starts growing faster or the gardener changes other conditions (removing nearby dead plants that might be the source of infection, increasing ventilation or applying plant protection products), any new leaves produced by the plant can escape getting any disease so in time the damaged leaves are lost and the plant appears healthy again. For a crop plant, even if further disease is prevented, its yield will usually be reduced – fungal diseases reduce food yields by about 16% globally.”

Bruce Fitt

“The first thing is to assess if it is worthwhile to treat the plant. If the disease is going to destroy the crop (e.g. potato or tomato late blight), the gardener will get nothing without an appropriately timed fungicide treatment. It will work only if the disease is found and treated quickly. There is no general purpose fungicide that treats all forms of plant disease. Specific fungicides should be used which have been made to fight the actual plant disease that the plant has been affected with. It is also very important to remove and destroy infected plant material to decrease spread of the pathogen to other plants. Seeds of ‘blight resistant’ tomatoes can also be purchased; they have less of a chance of being afflicted with blight. However, although these vegetables can resist blight sometimes, they are by no means immune to it.”

Jerry Cooper

“The most common problem is disease causing spores being spread through rain splashes. One way to manage tomato blight is to provide some cover over the top of the crop to keep rain off. Other ways include putting mulch on the soil surface so that the rain does not splash spores on to the plant. Supporting the plants also helps, as the leaves are kept away from the soil. As with all plant diseases, the plant vigour is reduced and yields suffer when plants become infected with late blight. Chemical fungicides such as those containing copper can give a degree of control of late blight, but always check the label to make sure they are recommended for use on the crop, and follow label instructions. If growing tomatoes outdoors, it is better not to put them in soil following a previous crop of tomatoes or potatoes. Farmers have been using crop rotation for many years to reduce the accumulation of disease spores that can occur if the same crop is grown successively in an area. This general loss of productivity due to build-up of diseases in the soil happens with many crops.”

Q4. With the extreme snow that has hit the UK over the last two months, will this have had a positive or negative impact on leaf diseases?

Michael Shaw

“As most trees and perennials are dormant, the cold weather will have had little direct effect. Because they are flowering later – sometimes much later – than in the recent past, they may come in contact with a different range of bacteria from usual, or have altered susceptibility. As a rule, warm wet weather favours plants and diseases alike.”

Bruce Fitt

“Cold weather generally doesn’t increase or decrease the chances of plant disease but it may alter the balance between growth of the crop and the pathogen. Pathogens often infect plants only under specific weather conditions. At this time of the year, it is common for leek plants which have over-wintered to have some leek rust on them, however I have not seen any in my garden this year. This may have something to do with the abnormally cold weather we have had recently.”

Matthew Dickinson

“I suspect it won’t make much difference; it’s more the weather conditions once the spores start spreading that will be important. Most fungi prefer warm wet conditions, so if we get a warm and wet spring then diseases could be quite problematic, whereas if it is relatively dry, there might be fewer diseases; but then again, what would probably happen is other diseases would be more prevalent instead.”

Conclusion

When it comes to creating your own garden, knowledge is the key. The British climate always keeps us second guessing so it is wise to make use of the warm weather when it is available. Take time to get up close and personal with your garden so that you can detect any developing plant diseases. Quite often it is a positive to have insects crawling amongst your plants!

Many people think that plant pests and diseases can only be halted by applying insecticide or fungicide. In fact these are often ineffective and they can easily make things worse if used wrongly. There are a whole host of methods available that can be used to control these problems, of which some are explained above. But the best method varies with the disease problem. The most important thing is to grow plant varieties with good levels of resistance to the diseases which afflict the species, and avoid over- or under-fertilising.

Depending on the problem, the solution may require a bit of knowledge, effort, and patience alongside an application of garden health products including; Fungus Fighter Disease Control, lawn feed, insecticide smoke and phosphate plant food.  These  help to keep any unwanted pests and diseases under control or provide enough nutrients to enable plants to grow vigorously, enabling them to resist attack from  many common pests and diseases.

By giving your garden a healthy existence using compost and products such as Fish, Blood & Bone and other nutrients you are already going some way to ensuring that your soil will be healthy, and good yields should result.

Print this page