Quick video of disease check on Parlsey
Botrytis infection on Paeonies'
High Risk periods
Damp, humid, wet-weather. Periods of prolonged plant-wetness.
Young plants usually begin to rot at soil level when they are 12-20 cm in height. Stems appear water-soaked, and the infection can be mistaken for a bacterial issue. Shoots wilt and fall over in a short period of time. Just above soil level, the stalk will be covered with a greyish fungal growth where conidia (fungal spores) are produced. Conidia are transported by wind, insects (attracted by rotting material), water splash and physical contact by staff to other leaves and buds. This causes further in leaf spotting and bud dieback. Small buds turn black and die. Larger buds turn brown and fail to produce a flower. If a plant is infected, most of the buds will more than likely fail.
Biology and lifecycle
Botrytis spp. are saprophytic (living on dead/decaying plant material) and parasitic (feeding off living material). First signs appear on the base of the stalks and the fungus over-winters on fallen plant debris. In the spring, as temperature increases ( Late March- early April) conidia form and spread to young, soft plant tissues. As the disease progresses, a gray-mold develops. The gray mold is made up of spores that are either wind-blown, splashed or transported by insects or touch by hands or tools onto new plants.
Prevent infection: Plant debris should be removed often destroyed, not composted. Wash hands after contact with infection. Spray tools periodically with a weak bleach solution (2%) or 70% ethanol solution. (Shop-bought bleaches are usually 5% in strength (check label), so dilute 1:2.5 i.e. 1 liter 5% sodium hypochlorite plus 1.5 liters water = 2.5 liters of 2% sodium hypochlorite)
Soil drainage: Peonies in well-drained soil have a reduced risk of botrytis formation. Do not overwater.
Location: Increased air circulation reduces disease risk. Space plants as widely as possible (2-3 feet is optimal but may not be practical in some situations). If possible, remove aging leaves from plants.
Use disease-free roots: If propagating, only take divisions only from healthy, disease-free plants.
Fungicide: Stem and bud Botrytis is the main disease issue and a programme for control will have to be implemented from emergence in the spring. The programme should be maintained throughout the growing season through harvest and should extend out to early Autumn. Rovral WG and Switch are systemic fungicides which have full label recommendations and can be used in a programme with protectants such as Amistar and Signum which have off label approval. Fungicides must be applied in advance of the disease as a protectant.
The European Commission have published the latest update of host plants susceptible to the bacterium Xylella fastidiosa in the union territory (16/1/2017 https://ec.europa.eu/food/sites/food/files/plant/docs/ph_biosec_legis_emergency_db-host-plants_update08.pdf) .
There are now over 300 known host species susceptible to the bacterium, though not all of these species develop disease, and not all species are affected by all Xylella subspecies (pauca,multiplex,fastidiosa,sandyi ) .
The list of host plants includes many common trees and ornamentals relevant to the Irish horticulture industry including Acer, Aesculus, Brassica, carex, Cornus florida, Fuchsia magellanica, Ginkgo biloba, Hedera helix, Hemerocallis, Hydrangea paniculata, Liquidambar styraciflua, Liriodendron tulipifera, Magnolia grandiflora, Olea europaea, Platanus, Prunus, Quercus, Rosmarinus officinalis, Rubus, Salix, Veronica, Vinca. The full list of susceptible plants is available here: http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32015D0789&from=EN .
X.fastidiosa was first regulated at EU level as a harmful organism with quarantine status in 1992 (Directive 2000/29/EC) but was not confirmed in Europe until 21st October 2013 when an outbreak of X.fastidiosa subsp. pauca was detected on olive trees in the Apulia region of Italy.
Reaction from the EU commission was swift with emergency measures published on 13th February 2014 which aimed to prevent the spread of X.fastidiosa within the union (Decision 2014/87/EU). This was quickly followed in July 2014 by the publication of more detailed measures to prevent disease introduction and spread within the EU.
Despite the introduction of these emergency measures, further outbreaks were reported in the neighbouring Italian province of Brindisi on the 9th of March 2015, Corsica on the 27th July 2015 (on Polygala myrtifolia) ,and the French mainland in the region of Provence-Alpes-Cote d’azur on 18th September 2015.
Detection and spread
Sap-sucking insects are important potential disease vectors once disease becomes established in an area. The primary risk comes from movement of infected material which means Irish plant importers will have to be vigilant in the sourcing and subsequent monitoring of imported host plant material.
Symptoms on plant material include dieback, stunting and leaf scorch, all of which are symptoms of many other plant pathogens and environmental factors such as frost damage. This makes a laboratory diagnosis necessary and involves identification of the disease at the molecular level by DNA extraction from infected material.
The ability of X.fastidiosa to ‘hide’ within asymptomatic plant material adds an extra layer of complication to its detection and control.
Suspected cases of this disease should be reported to the Plant Health Division of the Department of Agriculture Food and the Marine (DAFM). DAFM can be contacted as follows:
Horticulture and Plant Health Division,
Department of Agriculture, Food and the Marine,
Backweston Administration Building,