The control of Botrytis in grapes

by | Oct 1, 2020 | Wineland

Botrytis, a fungus commonly referred to as grey mould, affects many plant species of which grapes are one of its most notable hosts. If not treated, this disease can result in great losses in grape yields.

Botrytis is a necrotrophic pathogen that induces cell death of its host and lives on dead plant material. Infection occurs in one of two ways: The pathogen enters the plant tissue through wounds e.g. hail, bird or insect damage, or the pathogen can be latent in the grape plant and will develop once conditions are favourable. The disease can cause bunch rot close to harvest resulting in production losses pre- and post-harvest. In wine grapes Botrytis produce enzymes that reduce flavour, colour and storage quality of wine. In table grapes shelf life is reduced and sorting and packaging costs are increased.

Gray mould.

Strands of the fungus (mycelium) produce hard structures called sclerotia which will survive on the vine and on decaying matter in the soil. The mycelium and sclerotia can survive for up to 20 months under favourable conditions and can also survive on various other vegetative growth in or near the vineyard. Therefore, weed control for example, can also form part of disease control. Both these structures can produce spores for new infections. Spores can be transported by wind or water to infect vines and the pathogen can germinate in as little as one hour.

Prolonged wet periods combined with cooler weather in spring give cause to development of Botrytis. Although temperatures around 20 ˚C favour development, the pathogen can survive in a temperature range as wide as 1-30 ˚C. One of the factors that aggravates disease development, is dense canopies. Some varieties are also more susceptible due to thinner skin and dense bunch formation which will retain moisture. The most susceptible stage is the flowering period. Control during flowering is critical and once the pathogen penetrates the berry, control becomes difficult. Luna® Privilege offers ideal control during the flowering stage. This should ideally be applied in a programme with Teldor® and the new Biological fungicide Serenade® which supports the efficacy of traditional fungicides

When infection has taken place, typical symptoms include a greyish mould on the grapes, hence the common name grey mould. Leaf symptoms start as dull green spots turning necrotic. One of the ways in which to detect early symptoms on darker coloured grapes, is to lightly press on the light brown discolouration of skin. When Botrytis is present the skin will simply “slip off”. Later symptoms are the conidia spores visible on the grapes. As the disease spread it can form a “nest” within the bunches.

Certain preventative actions can minimise the Botrytis risk. These include plant establishment, positioning the row direction to optimise airflow through the vineyard, the spacing of plants to improve airflow and the use of trellising to improve airflow and irrigation selection. As Botrytis is a weak pathogen, a healthy plant is more tolerant to infection. Sanitation practices such as weed control and the removal of old plant debris can also minimise the risk of spreading Botrytis. In terms of crop protection methods, Luna® Privilege can be applied during the flowering stage to control Botrytis at several stages of its life cycle, including during spore germination, germ tube elongation, mycelial growth and sporulation. Teldor® can also be used together with the biological fungicide Serenade®. It has a short withholding period and inhibits germ tube elongation.

Botrytis is genetically highly adaptive and is known to develop resistance by means of its genetic mutations and various modes of action is needed to effectively control the pathogen. Optimal timing for application and the correct product for that growth stage is critical to obtain the most benefit from your chemicals. For the effective control of Botrytis in your vineyards, carefully follow the instructions and guidelines on the product labels.

Contact Bayer (Pty) Ltd on 011 921 5002 | www.cropscience.bayer.co.za | www.bayer.co.za

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