Factsheet 02/07 Horticultural Bradbourne House Development East Malling Cane fruit Council Kent ME19 6DZ T: 01732 848383 F: 01732 848498 E: [email protected]

Phytophthora root rot of and other cane fruits

by Scott Raffle and Janet Allen, ADAS

This factsheet provides information on the biology of fragariae var. rubi and the effect it has on raspberry and other cane fruit crops. It summarises techniques that should be employed both to avoid and contain infection and offers the currently approved control measures.

Background being Phytophthora fragariae var. rubi uncommon for plantations to die out (P. fragariae var. rubi). The disease was completely within three years of initial Phytophthora root rot of raspberry and first reported in raspberry plantations in infection occurring. The disease led other cane fruit crops brings about in 1937. Further reports were to significant reductions in total yields root death, leading to die back of both made in in the 1950’s being produced by raspberry planta- the floricanes (fruiting canes) and pri- and 1960’s, but it wasn’t until the mid tions in Scotland in the 1980’s and mocanes. The root rot can be caused 1970’s that serious outbreaks began to 1990’s, and made a significant con- by a number of species of the soil- occur in the , leading tribution to the rapid decline of rasp- borne fungi Phytophthora. The most to significant loss of plantations in berry production in Scotland during important is now recognised as both Scotland and England. It is not that period (Figure 1). Photo supplied by SCRI

1 Phytophthora root rot has led to rapid die-back of raspberry plantations and a corresponding decline in raspberry production in Scotland Symptoms be found to possess very few, if any red/brown in colour, with a distinct mar- root hairs. If the epidermis is scraped gin at the interface between diseased Symptoms generally first appear on away from surviving main roots using and healthy tissue. Dead root tissue single plants or isolated groups of a pen knife, the underlying cortical tis- can sometimes be found as far back as canes within a plantation (Figure 2). sue is usually found to be necrotic and the crown region of plants. As the disease develops, it spreads to the roots of other canes, very often along the length of the crop row. Symptoms can develop on both primocanes and floricanes. Where plants are affected, fewer numbers of primocanes may emerge in the spring months compared to healthy plants and those that do may be weak. Infected primocanes may exhibit signs of wilting and die back shortly after emergence. The tips of the primo- canes often wilt first, producing a characteristic ‘shepherd’s crook’ effect (Figure 3). Affected primocanes may initially develop water-soaked lesions on one side, which run upwards from

their base. These later turn dark purple Photo supplied by SCRI or brown in colour as the canes wilt 3 Affected spawn exhibiting the classic 4 Water soaked lesions develop at the base and die (Figure 4). Where the die back ‘shepherd’s crook’ effect of spawn, which may later turn dark purple or of primocanes is slower, the leaves brown in colour gradually turn chlorotic, wilt and then die during the summer months. In some instances, primocanes may be infected but survive and remain symp- tomless until the following season, when they become floricanes. Affected floricanes produce weak fruiting laterals that tend to wilt or turn yellow and necrotic either around the leaf margin or between the leaf veins. Severely affected floricanes wilt and usually die before harvest begins. Affected plants or stools often have weak and poorly developed root sys- tems when compared to healthy plants

(Figures 5 & 6). When the roots of in- Photo supplied by SCRI fected plants are examined, they will 5 Illustration of poorly developed and dying root systems (three roots on left) compared to healthy roots (on far right) Photo supplied by SCRI

2 Symptoms first appear on single plants or 6 Declining root volume in module raised plants caused by increasing levels of Phytophthora infection isolated groups of canes Infection and spread production of sporangia and discharge when soils begin to drain and dry out, of zoospores are favoured by moist and normally in the summer months. Initial infection and spread can be wet soils (Figure 7). Optimum discharge Early infections are often (but not brought about by several means: of zoospores occurs when soils are always) located in areas of a plantation • By planting infected plant material on saturated with water and at soil temper- where the drainage is impeded. They clean land or into soil less substrate atures of between 4–25oC. The most can also be found in areas where the soil common period of infection therefore has a clay texture or in low lying areas • The movement of contaminated soil occurs during periods of prolonged of the field to which soil water drains. or run-off water from infested to wet weather. In the United Kingdom, Extended periods of wet weather can clean sites such conditions most commonly occur spread the infection along the length between autumn and spring. The dis- of a row or to other low lying areas of • Use of contaminated irrigation water charge of the zoospores is impeded the plantation.

The movement of contaminated soil on plants, farm machinery, footwear or clothing can rapidly lead to the spread of this disease around an individual or several farms.

Conditions that favour spread

The spread of the fungus P. fragariae var. rubi is dependent upon the pres- ence of high levels of soil moisture. The most common form of inoculum is the zoospore stage. These zoospores are contained within sporangia. The 7 Waterlogging and poor drainage can lead to root death and Phytophthora infection

Life cycle and a passive phase when the fungus soil from dead or dying root tissue. remains inactive in the soil (Diagram 1). These oospores can remain viable for The life cycle of P. fragariae var. rubi The fungus survives during this pas- many years in the absence of a host consists of two phases – an active phase sive phase in the form of dormant and are relatively insensitive to environ- when infection of occurs oospores, which are released into the mental extremes and fungicides

Diagram 1 Life cycle of the fungus Phytophthora fragariae var. rubi

•• •• •• • • • • Infected nursery plants •• • Sporangium High soil • • • •• • • • • • or symptomless plants • • •• moisture carrying the fungus Zoospores

Active Phase

Root infection Zoospore germination Mycelium in • •• and penetration of root • • • •• • • •• living tissue • • • • • • Oospore germinates

Passive Phase

Secondary infections within new roots

• • • • •• • Movement of infested soil • • • • •• •• • • • (on clothing, machinery) • • • Oospore Overwinters as oospores • •• • or irrigation water • in soil or rotting plant • • contained in ••• •• an oogonium debris (including roots) applied to the soil. They can be moved In the active phase, sporangia are sections of roots being asphyxiated to new sites either on rotting roots or produced which release zoospores or root cracking. This in turn leads to plant debris, in soil, on clothing, during periods of wet soil conditions. an increased release of root exudates, machinery or in irrigation water. In the These move through soil water and to which zoospores are chemically presence of new host plants, the attack raspberry root tissue, setting attracted. The fungus can persist for oospores can germinate, giving rise up new infection. Prolonged periods some time as mycelium, within the to the active phase. of soil water logging can also lead to living plant tissue.

Cultural control during the growing season. It must be material, infected soils or irrigation emphasised that no health scheme can water. Although peat and most other measures guarantee freedom from disease, but soil-less substrates cannot be they can help to reduce the risk. considered to be sterile, if manufac- Propagation tured, handled, stored and decanted into pots, bags or troughs correctly, Raspberry propagators must be partic- Site, soil and substrate at the point of planting they should not ularly vigilant to the risk that visitors selection contain P. fragariae var. rubi spores. pose to their units, who may have come To produce conditions that are not con- from infected premises. To reduce Selecting virgin land, which has never ducive to the development or spread the risk of cross contamination, when produced raspberries or cane fruit of this fungus, substrates should be visitors arrive on their premises, prop- crops before is the best way of avoiding chosen that have a high level of air agators should: infection, although the availability of filled porosity (preferably 15% or more), • always insist that clean protective such land is often scarce in the main to allow free drainage and promote footwear is worn that is fit for the fruit growing areas. Phytophthora healthy root development. purpose infection has become so common in raspberries in the UK, that sites that • always insist clean coveralls are worn have grown raspberries before should Organic matter and soil be considered to have a high risk of additives • only allow the propagation site containing the fungus. To completely vehicles to be used for transport avoid any risk of infection, it is better Before planting, some growers incor- around the property to plant raspberries and cane fruit crops porate organic matter such as well on virgin sites or in soil-less substrates rotted farm yard manure or composted than to use previously cropped soils. green waste. When used in heavy or Healthy planting material Where the only option is to plant in clay based soils, this helps to improve soil that has previously been used for soil texture, structure and drainage. In Healthy planting material is an essential raspberries, consideration should very free draining sandy soils, it not only starting point for a healthy crop. Plants be given to the health status of the improves soil texture and structure, should be purchased from a recognised previous crop and where necessary, but also reduces the risk of water run- certification scheme. Both SEERAD thought can be given to the various off and the possibility of soil erosion and Defra, through its Plant Health control measures that may need to be during periods of heavy rainfall. In

Propagation Scheme (PHPS), offer such employed to control this disease. theory, the use of organic matter will a service to the industry. Such schemes Field sites with heavy soil (clay) and help to reduce the frequency and aim to provide a reliable source of poor drainage should be avoided degree of water logging or the move- healthy plant material, which is propa- wherever possible. If site availability is ment of water down crop rows, thus gated according to strict protocols. limited, then the installation of tile drains reducing the risk of infection and rapid Plants grown within the PHPS have will help to reduce the risk of water spread of this disease. a known history regarding the health logging. Ensuring that ditches are free Some growers also lay mulches status of parent material. They are flowing will further help to reduce the of straw, composted green waste grown on sites which are isolated from build up of soil water in wet conditions. (Figure 8) or other well rotted organic fruiting plantations. Sites are chosen The action of sub-soiling during material onto the soil surface in the that have either practiced long crop periods when soils are dry will provide crop row. This maintains or improves rotations between cane fruit crops or new channels in the soil profile to the organic matter content of the soil that have never previously grown cane further improve drainage. However, and thereby promotes the growth of fruit. Defra Plant Health Inspectors even if such remedial action is followed, new fibrous roots close to the surface, routinely examine and test the plants the risk of spread on infected sites thereby counteracting the loss of roots during their propagation, checking will still be high on such soils during to the disease, deeper in the soil. for the presence of pests and diseases wet conditions. In the case of the straw, it is allowed including Phytophthora. Cane fruit crops grown in soil-less to rot down into the soil during the Growers intending to purchase plants substrates should carry no fungal winter months. However, there is evi- are advised to visit plant propagators disease, unless they have been contam- dence that the straw can also produce to inspect both their facilities and plants inated on site by diseased planting anaerobic conditions in the surface of the soil as it decays, which can actually Growing systems yard where infection has been known exacerbate the spread of Phytophthora to exist in the past. rather than reduce it. Research and P. fragariae var. rubi zoospores are very Where containerised plants are pro- commercial experience in dependent on soil moisture to spread tected throughout the year, it should be and has demonstrated that and infect new roots. It is therefore possible to maintain more control over to create conditions less conducive to important to employ systems that will the moisture content of the substrate. the development and spread of Phy- reduce the risk of infection by avoiding However in this situation, the nutrient tophthora, it is safer and more effective waterlogged conditions in the root zone. status of the substrate and volume to use composted green waste. Planting into raised beds or ridges of nutrients being applied should be However, this treatment cannot be can help to prevent a proportion of the carefully monitored. The build up of guaranteed to work. root system from being waterlogged high salt levels and subsequent high (Figure 10 – overleaf). This is particu- EC should be avoided to obviate the larly important on heavy soils or those need to flush out the substrate with Site preparation which are inherently slow to drain. high volumes of water. This practice Although soil-less substrates are can create ideal conditions for Well in advance of planting cane fruit generally devoid of any existing Phytophthora. In autumn and winter, crops in a field soil, a careful assess- P. fragariae var. rubi spores, should when the crop is outside the main ment of the site should be carried out, infection occur, the risk of rapid growing period, low levels of moisture by digging several pits at various points disease development and spread is can be maintained and this will reduce across the field and examining the soil high due to the constant levels of the spread of Phytophthora. This is in profile. The soil should be checked for moisture at certain times of the year. contrast to field soil grown crops, signs of compaction, poor drainage Care should always be taken to avoid where there is very little opportunity to and regular water logging of the soil the contamination of substrates with control soil moisture levels at this time in or immediately below the expected P. fragariae var. rubi spores. This can of year, so crops are at higher risk of rooting zone (Figure 9). Where neces- sometimes occur when substrates are infection because of the likelihood sary, subsoiling should be carried out stored prior to use on soil or areas of of waterlogging. before planting when conditions are dry, to break through any layers of compac- tion, thereby improving both the drain- age of the soil and plant root growth. When planning to establish a crop through polythene mulched raised beds, it is important to create a deep, well structured soil tilth to a depth of 250 mm within and 250 mm below the actual base of each bed. This will allow planting of either bare rooted canes or module raised plants to the optimum depth, ensuring rapid establishment and healthy root and cane growth. The fact that the soil in and below the beds is well drained will help to reduce the chance of infection occurring later, during periods of wet weather. 8 Composted green waste can be used as a mulch on the soil surface to improve the organic matter content of the soil and to promote the growth of new fibrous roots close to the surface

Planting and establishment

Rapid root growth immediately after planting is vital to ensure that a healthy and balanced plant develops. Such plants may be better able to tolerate any fungal spores, which may already be present in the soil. Plant roots must not be allowed to dry out before plant- ing takes place. To avoid this, the plants should not be laid out in the field ahead of planting, but instead kept moist by covering them with damp sacking or polythene sheeting.

9 Examination of the soil profile can sometimes reveal signs of compaction and poor drainage Container grown crops that are avoided, especially on heavier soils. Varietal resistance situated in the field but not protected This will increase the risk of water- during the dormant season must be logging and subsequent risk of Phy- Although varieties can vary greatly as able to drain freely at all times. This is tophthora infection and spread. regards their level of susceptibility or particularly important where pots or tolerance to infection by Phytophthora containers are laid on the tops of raised root rot, all varieties that are currently beds or ridges, which are covered Nutrition and soil pH of commercial value in the UK can with polythene sheeting. To prevent succumb to this disease. Although them from becoming waterlogged, Years of observation by pathologists it was previously believed that adequate drainage holes should exist and consultants suggest that plants blackberries were not affected by in the bases of the pots or troughs and which are grown in soils with a neutral Phytophthora, it should be noted that also in the polythene mulch covering pH value appear to be less susceptible some cultivars of blackberry have the surface of the bed or ridge. Beds to Phytophthora infection. Although recently been found to be susceptible and ridges should be formed with a raspberries and other cane fruit crops to Phytophthora, as are some profile which will allow excess water can tolerate a low pH, their vigour and raspberry x blackberry hybrids, such to run away from the containers, thus uptake of some nutrients at this level as . avoiding the base of the containers and may be impaired and this may partly A Horticulture LINK project that basal roots from sitting down in water. explain why they are less susceptible is part funded by HDC (SF 63) and Sitting the containers on wooden to Phytophthora at a neutral pH value. conducted at the Scottish Crop batons (Figure 11) or commercially However, care should be taken not to Research Institute has been under- available products such as ‘Draineasi’ raise the pH to such an extent that the taken to identify genes in resistant (Figure 12) will further help to remove raspberry crop becomes subject to raspberry varieties that confer a both rainfall and drainage water from deficiencies of certain micronutrients resistance trait to Phytophthora root the base of these containers. Their use at high pH values, including iron rot. Having identified these genes, it will also help to maintain a physical and manganese. should be possible in future raspberry barrier between the roots and the surface of the soil, which may contain P. fragariae var. rubi spores. Some trough systems employ poly- thene sheets, which are laid along the length of the rows so that the surplus drainage water is channelled to the end of the row via a drainage pipe. Such systems can increase the risk of Phy- tophthora spread along the rows as the zoospores move in the water as it passes to the end of the row. Although to date, nutrient film tech- niques or hydroponics have not been used for commercial raspberry production, they have been exper- imented with in other soft fruit crops such as . Although they have produced satisfactory crops, 10 Planting into raised beds or ridges can help to prevent a proportion of the root system from being the risk of Phytophthora spread by waterlogged the recirculation of water is very high. In the case of strawberry, in some instances infection by red core (caused by the related fungus Phytophthora fragariae) has been rampant, resulting in the loss of the whole crop.

Irrigation management

Careful irrigation of field or container grown raspberries is important throughout the life of the crop. Irrigation is important in the crop establishment phase to ensure rapid growth. However, excessive application of irrigation at 11 Use of batons beneath containers helps to 12 Use of commercial products such as Drai- any stage of the plant life should be improve removal of drainage water neasi helps to improve removal of drainage water breeding programmes to screen new Hygiene from site to site. Where crops are seedling selections for their presence protected by permanent structures or absence. This will reduce the The scrupulous removal of soil from all year round, the routine dipping time currently taken in the selection machinery, hand tools, footwear of footwear in a bath containing a process when screening new material, and clothing after working on suitable disinfectant at the entrance thus speeding up the process of infected sites and before moving to individual houses, can help to releasing new resistant varieties to to healthy plantations will help to maintain freedom from Phytophthora. the industry. reduce the spread of Phytophthora

Chemical control reduce the numbers of spores in the rates of use and other details are listed soil, their effectiveness is limited both in Table 1. measures by the depth of treatment and the soil Significant numbers of growers conditions at the time of treatment. currently grow cane fruit crops in field The use of chemical control options is soils on raised beds or ridges through an important component in the control a polythene mulch. Irrigation is applied of Phytophthora. However, due its Fungicide drench through a trickle irrigation line that limited effectiveness and the persistent treatments is laid beneath the polythene mulch. nature of P. fragariae var. rubi spores, The presence of the mulch restricts it is essential that chemical control For crops that are planted in field soils access to fungicide drenches, should measures be used as part of an inte- or soil-less substrates, there are Phytophthora infection occur. Some grated disease management strategy. currently specific off-label approvals growers have attempted to apply the Such action will then enable chemical available that permit the use of fungicide by passing it through the treatments to be more effective. fungicide drenches to penetrate the irrigation line during irrigation cycles, root zone. These must be applied as but this has consistently failed to pro- directed sprays onto the soil or com- vide adequate control. Should infection Soil fumigation post surface, around the bases of the occur, it is best to remove the polythene canes. If applied in the recommended mulch to allow the fungicide drench to Of all the soil fumigants currently avail- volumes of water, these fungicides adequately penetrate the root zone. able to commercial raspberry growers, should come into contact with a high steam is the only one that is likely to proportion of the plant roots in the top provide good control of Phytophthora. soil, particularly those just below the However at present, this is only a soil surface, and protect them against feasible option for glasshouse growers attack by the fungal zoospores. and is only as good as the depth of There are currently two active ingre- soil to which it penetrates. Although dients (fluazinam and metalaxyl-M) that chemical fumigants such as metham have specific off-label approvals for sodium and dazomet can all help to use on cane fruit crops. Their numbers,

Table 1 Summary of the fungicides with specific off-label approvals currently available for use in controlling Phytophthora root rot in cane fruit crops

Active Product Approval Application/Use Rate of Use Volume of Ingredient names water

fluazinam Shirlan SOLAs Applied as a drenching spray to the soil/ Field – 1.5 Field – 1250 Shirlan 2168/03 compost around base of canes to penetrate litres/ha litres/ha programme 2080/03 root zone. 2 applications permitted/year. Pot – 1.5 ml Pot – 500ml Latest application made before end of March per litre per 5 litres of in year of harvest. Permitted on outdoor and compost protected crops. Permitted for use on rasp- berry, black and hybridberry. metalaxyl-M SL 567A SOLA Applied as a drenching spray to the soil/ 1.3 litres/ha 1000 litres/ha 1515/05 compost around base of canes to penetrate root zone. Can be applied as a split dose of two applications of 1.3 litres of product per hectare each, in October and March. Permit- ted only on outdoor raspberry crops. Action points for • Consider planting on a raised bed • Where raspberries are grown in or ridge system to reduce the risk containers, be sure to sit these on growers of waterlogging and improve plant batons or alternative materials to rooting depth. improve drainage and avoid direct • Before planting a raspberry crop in contact with soils. a field soil, consider the previous • Install field drainage to further reduce history of the site and avoid those the risk of waterlogging. • Where infection occurs on polythene known to be infected with mulched ridges, remove the Phytophthora. • Purchase certified healthy plant polythene to improve access for material and satisfy yourself that all fungicidal drenches. • Choose field soils which are reasonable procedures have been free-draining and devoid of low followed to avoid infection occurring lying areas. before you take delivery of the plants.

Further information Names and addresses of UK raspberry Scottish Nuclear Stock and cane fruit suppliers offering Association Ltd Names and addresses of plant plants with a SEERAD or Defra plant Buchal Farmhouse diagnostic laboratories: health certificate: Alyth, Blairgowrie PH11 8JS ADAS Pest Evaluation Services Darby Plants Ltd Tel. (01575) 560349 ADAS High Mowthorpe Broad Fen Farm, Severalls Road Duggleby Methwold Hythe, Thetford IP26 4QU Thomas Thomson (Blairgowrie) Ltd Malton Tel. (01366) 727229 Bramblebank Works North Yorkshire YO17 8BP Blairgowrie PH10 7HY Tel. (01944) 738434 Hargreaves Plants Ltd Tel. (01250) 872266 www.adas.co.uk Cowpers Gate, Long Sutton Spalding, Lincs PE12 9BS Edward Vinson Plants Ltd Central Science Laboratory Tel. (01406) 366300 4 Ewell Barn, Graveney Road Sand Hutton Faversham, Kent ME13 8UP York YO41 1LZ Haygrove Plants Tel. (01795) 537500 Tel. (01904) 462000 Redbank Farm, Little Marcle www.csl.gov.uk Ledbury, Herefordshire HR8 2JL R W Walpole (Strawberry Tel. (01531) 633659 Plants) Ltd The Plant Clinic Ivy Farm, Tuxhill Road East Malling Research Highland Fruit Stocks Terrington St. Clement, Kings Lynn, East Malling Mains of Murthly, Aberfeldy PH15 2EA Norfolk PE34 4PX Kent ME19 6BJ Tel. (01887) 829899 Tel. (01553) 828829 Tel. (01732) 843833 www.emr.ac.uk Messrs David McIntyre J M Watson Fruit Growers Ltd Cruachan, Wester Essendy Mill of Montague Scottish Crop Research Institute Blairgowrie PH10 6RA Balbeggie, Perth PH2 7PR Invergowrie Tel. (01250) 884212 Tel. (01821) 640271 Dundee DD2 5DA Tel. (01382) 562731 Messrs J McIntyre & Sons Welsh Fruit Stocks www.fruithealth.co.uk Moyness Nurseries, Coupar Angus Bryngwyn, Powys Road, Blairgowrie PH10 6UT Via Kington, Hereford HR5 3QZ Stockbridge Technology Centre Ltd Tel. (01250) 873135 Tel. (01497) 851209 Cawood Selby T J Moore Woods Nurseries Plants Ltd North Yorkshire YO8 3TZ 20 Bilney Road, Gressenhall Tarry Hill, Swineshead Tel. (01757) 268275 Dereham, Norfolk NR20 4EG Boston, Lincs PE20 3LL www.stc-nyorks.co.uk Tel. (01362) 861091 Tel. (01205) 821155

Whilst publications issued under the auspices © 2007 Horticultural Development Council. of the HDC are prepared from the best available No part of this publication may be reproduced in information, neither the authors or the HDC can any form or by any means without prior permis- accept any responsibility for inaccuracy or sion of the Horticultural Development Council. liability for loss, damage or injury from the appli- February 2007 cation of any concept or procedure discussed. Design and production: HDR Visual Communication