FLORICULTURE EL NINO PREPAREDNESS - Botrytis Best Practices.

The Kenya Meteorological Department has warned of heavy downpours from the months of October to November 2023 likely to have the El Ni?o conditions.

With this prediction, it is imperative that not only growers, but everyone in the cut flower supply chain begins to take necessary precautions to prevent, manage and audit potential post-harvest losses.

BOTRYTIS:

This is a fungal infection responsible for considerable post-harvest losses during and after transit or storage. The disease is caused by the pathogen Botrytis Cinerea and is often called grey mold or “the disease of bad management” simply because with cultural management, this infection can be reduced considerably.

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BOTRYTIS HOSTS :

The fungi has a broad host range, causing disease in more than 400 plant species. This, coupled with its fast life cycle, makes its management difficult in the case of an epidemic.

Young and senescing tissues are the most susceptible to botrytis. This makes sending old flowers (that have stayed in the farm’s cold room for more than 72 hours) , a big red flag in the supply chain. Only fresh flowers should be shipped to the market during botrytis weather seasons.

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SYMPTOMS OF BOTRYTIS:

In young seedlings, it causes damping off while on a mature crop; symptoms can be seen on the flower bud, stem, leaves and even roots.

Flower bud symptoms: it starts as red/pink spots on the petals. As the disease matures, these spots become necrotic and coalesce to form brown lesions with older flowers rotting quicker owing to their heightened susceptibility. ?These flowers fail to open and the petals may fall off.

Stem symptoms: botrytis appears as stem cankers as seen as sunken, grayish-black spots that may continue from the base of the infected lower all the way down the cane.

Leaf symptoms: as infected petals fall off, hyphae proliferate onto the leaves causing spots and eventual browning of the entire leaf.

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ENVIRONMENTAL FACTORS:

Botrytis is often present in the greenhouses in it’s latent or rather dormant phase. This may not present visible symptoms unless the disease triangle is completed by a conducive environment since the other two requirements are constant (ie. Roses are a susceptible host and the virulent pathogen is almost always available). ?

Botrytis requires low temperatures, wet and high humidity conditions for a disease episode to occur.

All farm post harvest procedures must adhere to a strict cool chain protocol paying attention to temperatures below 8 degrees and when handled outside this set limit, time must be kept on the minimum.

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BOTRYTIS MANAGEMENT:

Since B.cinerea can persist in the greenhouse all year round in infested soils and on living and dead tissues, management of the pathogen requires a multi-faceted approach needs to be adopted.

Chemical control: At the field level, both protectant (contact) and eradicant (systemic) fungicides need to be incorporated into the spray program. It is important to note that the over use of systemic anti-botrytis chemicals can lead to resistance.

Cultural control: Avoid damaging the plant as this provides an entry point to the pathogen.

Secondly, infected plants should be removed as soon as possible since they serve as an inoculum.

Sanitation is a key check point in post harvest audits as it informs on likelihood of botrytis spreading, therefore, Organic matter from leaves, petals and open flowers, should not be left within the greenhouse .

Watering must be done carefully to prevent splashing on the plant surfaces because this creates a favourable spot for the pathogen to germinate. Canopy wetness should be maintained below 4 hours.

The greenhouse climate must be closely monitored to prevent humidity build up. It is important therefore to vent the greenhouse to allow proper aeration and humidity regulation.

Now is the time to go slow on nitrogenous fertilizers to prevent overgrowth of foliage which creates a microclimate conducive for the pathogen. The young growing parts are also more susceptible. Instead, more calcium fertilizers should be applied to boost the cell wall integrity.

Post harvest control: rots can be reduced by

Practicing 100% post harvest protectant fungicide dips. These kill the existing spores and an effective option is DIPNOY which has not only the contact fungicide but other patented components that prevent further contact with airborne botrytis spores.

Irradiation is one of the newer technologies in use here in Kenya where flowers are passed through some UV rays to kill existing spores.

Controlled temperature storage is applicable where there is a dedicated cold room that ranges strictly at 2degrees for short term holding of flowers for targeted peaks. The use of an operational cold room with fluctuating temperatures does not work in this case.

Controlled Atmosphere storage is currently being used both in storage and sea freight, low oxygen levels (from 21% atmospheric oxygen to 5-7%) deters botrytis from thriving. On the other hand, high carbon dioxide levels (from 0.03% atmospheric levels to 7-10%) have anti-fungal properties. This is attained passively once flowers are packed in the polinoy bags that have elective permeability to certain gases.

CONCLUSION:

In conclusion, as we anticipate the heavy rains in the coming months, we need to stay ahead of the potential challenges that the rains might bring which the biggest one being botrytis. I hope this article helps a grower be better prepared to face this disease head on, armed with information.

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