Blossom wilt (Monilinia laxa f.sp. mali)
Wilting blossoms on a branch
Blossom wilt is an occasional disease of dessert and culinary apples but where it occurs on very susceptible varieties such as James Grieve, Cox and Lord Derby it can cause significant losses. The disease is much more prevalent on cider apples where most commercially-grown varieties appear to be susceptible and control measures are more difficult to implement.
Grey pustules of mycelium and spores develop on the affected flower parts.
The fungus progresses from infected flowers into the spur to form distinct cankers which bear grey sporing pustules in spring.
Monitor orchards of susceptible varieties for symptoms. During winter check trees for cankers with grey pustules and after blossom look for wilting dying blossoms.
In dessert and culinary apples, routine treatments are not required every season but in cider apples routine treatments may be required each season where the disease has become established.
- In dessert and culinary orchards, cut out affected blossoms, cankers and spurs during early summer when they are easily visible.
- In the following season or following two seasons after detection apply a spray of fenbuconazole (Indar) or pyraclostrobin + boscalid (Bellis) or cyprodonil + fludioxonil (Switch) or pyrimethanil (Scala) at first flower and repeat 7-10 days later.
- In cider orchards pruning out infected blossoms is not possible. Where the disease is present or on very susceptible varieties (e.g. Somerset Redstreak) apply a spray of fenbuconazole (Indar) or pyraclostrobin + boscalid (Bellis) or cyprodonil + fludioxonil (Switch) or pyrimethanil (Scala) at first flower and repeat 7-10 days later.
- Where the disease is present at high incidence, a four spray programme, using different fungicide products, may be needed, starting at pink bud.
Fungicides approved for use on apple which offer some incidental control of blossom wilt when applied to control other diseases – efficacy factors
|Typh Safety||Other Diseases
|boscalid + pyraclostrobin||Bellis||strobylurine (QoI + anilide||safe||Scab, mildew, storage rots, canker|
|cyprodinil + fludioxonil||Switch||anilinopyrimidine + cyanopyrrol||safe||Scab, storage rots, canker|
|fenbuconazole||Indar||triazole (DMI)||safe||Scab, reduces mildew|
Fungicides approved for use on apple which offer some incidental control of blossom wilt when applied to control other diseases – safety factors
|Human||Fish aquatic life||Bees||Width
|boscalid + pyraclostrobin||h||d||u||7||4||40|
|cyprodinil + fludioxonil||a, c||d||u||3||3||30|
|fenbuconazole||ir||t||u||28||10 (when applied at 1.4 l/ha)||sm|
d = dangerous; h = harmful; ir = irritating, a = may cause allergic reaction, t = toxic
PH = post harvest; Pre bb = pre-bud burst, sm=statutory minimum of 5 m for broadcast air assisted sprayers
u=uncategorised/unclassified/unspecified, c=closed cab required for air assisted sprayers
Control in organic orchards
- There are no fungicides approved for use in organic systems which are effective against blossom wilt.
- Cultural methods of control are the only option at present.
- In organic production, pruning out affected blossoms and cankers is the only effective control measure.
- Where possible avoid the use of susceptible varieties in organic production.