Botrytis Rots of Pome and Stone Fruit

Botrytis cinerea is a common fungus that can cause fruit rot problems in the field and post-harvest in both stone and pome fruit. It is considered to be a minor problem in the field, but can contribute to post-harvest losses in the packinghouse.

Green Fruit Rot

Botrytis can cause a green fruit rot of immature cherries. Symptoms include blossom blight and smooth brown lesions on cherry fruit. The disease is favoured by wet weather during the blossom period. It has occurred in the Okanagan, but is not common.

Botrytis rot on cherry at the immature green fruit stage.

Botrytis Rot of Mature Cherry Fruit

Botrytis rot of mature cherry fruit occasionally occurs in the Okanagan, and can be mistaken for brown rot. Fruit develop a brown decay and become covered with a growth of light brown or grey spores. Infected fruit becomes soft and watery.  Brown rot tends to be worse on varieties which develop tight clusters of fruit.  Botrytis will grow on aborted fruit and trapped leaf debris within the clusters, which then spreads to adjacent fruit. Fungicide coverage within tight clusters can also be difficult. 

	Early and advanced symptoms of Botrytis rot on 'Lapins' cherry
	Botrytis rot developing in a cluster of 'Rainier' cherry.  Note trapped leaf debris.

Botrytis and brown rot look very similar on infected cherry fruit. Brown rot tends to sporulate in a more tufted pattern.  Laboratory examination may be required to distinguish between brown rot and botrytis. They are easily distinguished under the microscope.

Botrytis on cherry fruit	Brown rot on cherry fruit

Dry Eye Rot in Apple

Botrytis cinerea can cause a disease in apple known as dry eye rot, or blossom end rot. This is not common, but has occurred in the Okanagan in wet years, with infection occurring during the blossom period. Initial symptoms include a reddish discoloration at the calyx end. A soft, water soaked lesion forms which expands to several mm and dries out forming a sunken brown lesion. Fruit may drop prematurely. If infected fruit are harvested, they will have a greatly increased incidence of botrytis rot in storage.

Dry eye rot symptoms on 'MacIntosh' apple, caused by Botrytis cinerea	Dry eye rot symptoms on 'MacIntosh' and 'Ambrosia' apple, caused by Botrytis cinerea

Post-harvest Botrytis Rot

Botrytis is an important cause of post-harvest losses in the packinghouse for both stone and pome fruit. It can develop at cold temperatures, and has the ability to spread in storage.

On pome fruit, Botrytis causes a soft, spongy rot with a sweet, cider-like odour. As the rot progresses, the fungus produces masses of gray spores on the surface of affected fruits.  The infection may spread from fruit to fruit during storage, producing "nests" or "pockets" of decayed fruit. Small black resting bodies (sclerotia) may eventually form on infected fruit.

Control:

Stone Fruit:

There are no fungicides currently registered to control botrytis rot on stone fruit. Many fungicides used for brown rot, such as Rovral, Pristine, Lance, Elevate, Vangard and captan, also have good activity against Botrytis. (Note - Vangard is not registered on cherries; Elevate is not registered on apricots or plums).

On cherries, when pruning remove excessive branches to allow for increased air flow and shorten current season’s growth to reduce fruit cluster formation.

Apple:

On apple, thin out fruit showing symptoms of dry eye rot. Infected fruit will not hold up well in storage. 

There are no fungicides currently registered specifically for botrytis on apples. Fungicides used for apple scab at the bloom to petal fall stage may help to reduce the incidence of dry eye rot.

Post harvest decay in the packinghouse may be managed using a post-harvest fungicide treatment and good sanitation practices.  Currently Mertect (thiabendazole) is the only post-harvest fungicide registered for use on apple and pear fruit in Canada.  Newer products are undergoing registration.

Pre-harvest fungicide sprays registered for pin point scab and bull's eye rot may also help to reduce post-harvest losses from Botrytis, and may be recommended by fieldmen for certain blocks. The fungicides captan and ziram have short pre-harvest intervals of 7 and 1 days respectively. Senator (thiophanate-methyl) is also registered on apple for scab and powdery mildew with a 1 day pre-harvest interval. Trials have shown Senator reduces botrytis storage rot when applied close to harvest. Note, Senator is not recommended for apple scab control in areas with past resistance problems to Benlate and Easout.

An emergency registration was obtained for Scala (pyrimethanil) for control of post-harvest rots on apple, valid Aug-Dec. 2006 in BC. An emergency registration will be requested again for the harvest period of 2007. Check for current label before using Scala after the blossom stage.

January 2007