Effective disease management for pansy and viola

Careful management of environmental conditions is crucial to avoid serious disease outbreaks on your nursery. Find guidance on this page.

This information was last updated in 2014.

Disease management advice

• Ensure nursery employees are familiar with disease symptoms.
• Examine bought-in plant material and monitor growing crops to ensure early detection of any disease symptoms.
• Where unusual symptoms are found, act quickly to isolate affected plants and if necessary submit a sample to a diagnostic plant clinic for identification purposes.
• Dispose of any infected plant material into sealed bins or bags to prevent pathogen spread.
• Minimise leaf wetness by irrigating crops early in the day so that foliage dries before the onset of evening.
• Provide good air circulation within plant canopies by appropriate plant spacing and structure ventilation.
• Disinfect production areas on a regular basis to minimise any background pathogen pressure.
• Devise and use an effective disease control programme using both cultural and biological and/or chemical treatments, the latter ideally applied as protectants, to prevent disease development. Consider the risk of pathogen resistance and alternate products from different fungicide groups.
• Review the control programme annually to take account of changes to fungicide availability.

Cultural control

Careful management of environmental conditions is one of the key factors in avoiding serious disease outbreaks on the nursery and this is especially relevant in the case of foliar pathogens such as Peronospora (downy mildew), Ramularia and other leaf spot causing pathogens.

When coupled with other suitable cultural control methods, infection pressure should be reduced, minimising the need for intensive fungicide applications.

Quarantine:

• On arrival on the nursery, if possible, place all seedlings and other young plants in a temporary holding or quarantine area until they can be inspected and demonstrated to be disease-free.

Good hygiene and disinfection:

• Remove any weeds that may be growing under the benches as these can harbour pests and possibly pathogens.
• Maintain a high level of nursery hygiene during the production and marketing process.
• Thoroughly clean the relevant glasshouse area, including paths, benches and standing areas of crop debris and substrate dust before the arrival of any new plants.
• Where possible, use new plug trays, packs and pots, if exposed to dust, wash and disinfect them prior to use.
• Ensure raw materials (including water, substrate, pots, trays etc.) are correctly stored and covered to avoid dust contamination.
• Avoid standing plug trays on the glasshouse floor where there is contact with soil or other debris as this will significantly increase the risk of root infection.
• If foliar or root pathogens do occur in a crop, dispose of severely infected plants and associated substrate directly into bags to avoid pathogen dispersal throughout the remainder of the crop and the nursery.
• Ensure that there is a thorough clean-up once infection has been detected, disposing of all fallen leaves and other debris that may otherwise allow pathogen carry-over.

Plant and environment management:

• Keep the base of plug trays off bench tops and matting where possible as the root damage caused when they are prised off is likely to predispose the plants to root infection.
• Do not hold plants in plug trays for any longer than necessary.
• Monitor environmental conditions carefully – use ventilation, fans and, where necessary, pipe heat to reduce humidity within the crop to control downy mildew and other foliar pathogens.
• It is particularly important to reduce to a minimum the time when free water is present on the leaf surface as many pathogens require a period of leaf wetness for spore germination and infection to occur.
• Avoid overhead irrigation if possible, particularly in the evenings when prolonged leaf wetness can result.
• Check the growing structure for leaks, especially around the gutters, or other areas where condensation drips on to plants and rectify these as quickly as possible to avoid wet areas from where pathogens can subsequently be disseminated.
• Ensure crop watering is uniform, that substrate drainage is adequate, that substrate pH levels are around 6.0 and try to avoid high temperatures or rapid temperature fluctuations as such plant stress can exacerbate root diseases such as black root rot.

Monitoring and diagnosis:

• Check the foliage for leaf spot diseases and downy mildew remembering to look at the underside of the leaves for the latter pathogen.
• Remove a random selection of plants from the plug tray so that the roots can be examined carefully.
• Check for any orange-brown or black discoloration on the roots or stem base tissues which may indicate disease.
• If any foliar disease or root discoloration is found, either isolate the plants whilst a diagnosis is made and suitable treatment regime applied or reject the consignment altogether.
• As some pathogens may be latent in the early stages of infection, it is important to continue to monitor crops on a weekly basis for early disease detection.
• Use plant clinics for early diagnosis as necessary.

Chemical control

General disinfectant strategy

Careful use of disinfectants to routinely clean glasshouses, production areas, recycled plug trays, containers and trolleys, will reduce the incidence of pathogen infection in crops.

As the various disinfectant products tend to be inactivated rapidly in the presence of large quantities of organic matter, it is advisable to remove as much substrate and debris as possible by physical cleaning, using water with added detergent prior to the disinfectant treatment.

There is a known risk of infection from Thielaviopsis basicola from plug trays when they are re-used.

For more information read our pages on Use of chemical disinfectants in protected ornamental production.

General crop protection strategy

While a number of fungicides possess label recommendations for use on protected ornamental plants, there are a large number with Extensions of Authorisation for Minor Use (EAMUs) applicable to various ornamental crops and others which can still be used via the Long Term Arrangements for Extension of Use (LTAEU).

It is important to note that such EAMU and LTAEU product uses are entirely at the growers own risk.

1. The over-riding strategy in the use of fungicides should be to: 1. Only apply fungicides that are safe to the crop, spray operator, workers and the environment.
2. Use the minimum number of treatments to provide effective control, ideally alternating between multi-site protectant fungicides where available such as chlorothalonil, mancozeb or thiram in the early stages of crop development and site- specific eradicant products once a specific pathogen has been identified. (Note however that products containing only chlorothalonil or only mancozeb are no longer permitted for use under protection).
3. Devise a programme that does not encourage resistance development in the pathogen population, this usually means restricting the total number of applications of a particular active ingredient or group of active ingredients within the same fungicide group.

To achieve effective disease control it is recommended that:

• Crops are regularly inspected and monitored for diseases and other problems and spray programmes are adjusted as necessary according to the outcome of these crop inspections.
• Protectant fungicides are applied to avoid any build-up of disease, particularly where there is a history of disease outbreaks on the site.
• Full use is made of multi-site protectant fungicides, where available, as these are less prone to resistance development.
• Eradicant fungicides are applied at the very early stages of disease development to provide more effective control and minimise the risk of resistance development. It is important not to allow the pathogen to build up within the crop making disease control more difficult.
• Spray programmes are devised alternating products based on their fungicide groups.
• The method of application, spray pressure and water volume are adjusted in order to treat the lower as well as the upper leaf surface whilst trying to avoid spray run-off into the substrate.
• The approved dose rate, either from the manufacturers label or the Extension of Authorisation for Minor Use (EAMU) document, is followed.
• The risk of crop damage from the intended fungicide treatments is assessed prior to use.

It is generally suggested that:

• Before using a new product a few plants are test treated first to check for potential phytotoxicity as some species/ varieties are likely to be more sensitive than others.
• To minimise leaf scorch, any spray application is not undertaken in hot, sunny conditions.
• As appropriate, a copy of the product label or the EAMU document is obtained and complied with.