Corteva Agriscience™ was founded in 1803 and was built on the rich heritages of Dow, DuPont, and Pioneer.
Corteva Agriscience is a pure-play agriculture company dedicated to helping farmers get the most out of every hectare, season after season. We deliver value to the farmer in the seed, through digital and targeted breeding and biotech, on the seed, through seed applied technology, and on the farm through Crop Protection, and through digital and overall agronomic solutions. We are not just in the business of selling products, but of improving the farmer’s overall productivity, profitability, and environmental outcomes.
Corteva’s Crop Protection products offers an innovative range of insecticides, fungicides, and herbicides to ensure grape crops are protected against fungal diseases like powdery and downy mildew, and insects like mealybug to ensure ‘n healthy, high-yielding, and profitable crop.
Powdery mildew
Powdery mildew, also called oidium, is caused by the fungus Uncinula necator. It is regarded as the most serious grapevine fungal disease that occurs on the leaves, shoots, and grape bunches.
It is important to detect and protect the vine against this fungus as can influence the flavour and quality of the wine.
Symptoms
Faint green spots on the leaves are the first indication of the presence of powdery mildew. If an infected leaf is held up against light, grey-white hairs are visible on the spots. On young vine shoots, the grey-white spots turn black over time. The bunches show a grey-white fungus growth on the grape skins and stalks.
The spores of powdery mildew remain dormant within the bud but as soon as the bud breaks at the start of the growing season, the spores are released.
Treatment
The vine should be treated early in the season and should be sprayed at two, four and six weeks after bud break and when the shoots are between 2 cm and 5 cm long. I The intervals between sprays must not be extended. The powdery mildew should be treated along with the mealybugs, as the latter can spread the fungus.
Powdery mildew is controlled with contact or systemic fungicides, but the disease quickly becomes resistant when only one type of fungicide is used. Vigorous growers like the cultivars Chardonnay, Chenin Blanc, Riesling, Sémillon, Pinotage, Sultana and Muscadel, are more susceptible than others.
Vineyard management
To limit fungal growth, good canopy management should be applied, and weeds must be controlled. Reduce nitrogen fertilization to curb vigorous growth, and irrigate when the vineyard is already moist, like in the morning. Trellising, row direction and the location of the vineyard can help that the leaves dry quicker.
Corteva treatment for Powdery Mildew
Karathane™ STAR 350 EC (Reg No. L8640) is an emulsifiable concentrate fungicide for the control of powdery mildew in table and wine grapes.
Talendo® (Reg No. L8116) is an emulsifiable concentrate systemic preventive and residual fungicide for the control of powdery mildew (Uncinula necator = Oidium tuckeri) in grapes.
Associate® 240 EC (Reg. No L10358) is an emulsifiable concentrate systemic preventive and residual fungicide for the control of powdery mildew (Uncinula necator = Oidium tuckeri) in table grapes.
Downy Mildew
Downy mildew is caused by the fungus Plasmopara viticola.
Symptoms
The presence of the fungus is recognized by yellow ‘oil spots’ on the leaves. Fluffy white fungi develop on the undersides of the leaves. The spores, that develop under the oily spots, are spread by rain and wind.
Spores germinate and penetrate the leaf through the stoma at the bottom of the leaf. Oil spots appear five to fifteen days after infection. Young grape bunches become brown and oily and eventually dry out and fall off.
In humid conditions, the white downy fungus growth is visible on the grape bunches. Infected grapes stop growing, turn brown, shrivel, and fall off.
The fungus lies dormant in the residues of the contaminated plant on the ground. It is critical to control downy mildew early in the season. Young green shoots can also be infected, and the vines must be monitored for the appearance of the oil spots three to four weeks after bud break.
Treatment
To prevent contamination, spray with a preventive programme with contact fungicides. Spray before infection and follow up with twice weekly spraying during wet weather.
Good coverage is required but it will not protect new growth automatically. Rain lowers the fungicide residue levels on leaves. Spray with systemic fungicides directly after infection and before oil spots appear. If oil spots appear, spray with systemic fungicides directly after a warm wet night.
Corteva treatment for Downy Mildew
Equation® PRO (Reg. No L6677) is a preventive and curative fungicide (water dispersible granule) for the control of downy mildew (Plasmopara viticola) in wine and table grapes.
Curzate® 600 WG (Reg. No L10150) is a water dispersable granule fungicide, which is locally systemic and offers both preventative and curative control of downy mildew (Plasmopara viticola) on table and wine grapes.
Mealybugs
Grapevine mealybugs and ants are usually found together on the grapevine and the one may indicate the presence of the other. The ants that feed on the honeydew secreted by the mealybugs can spread them.
Symptoms
The female grapevine mealybug secretes waxy threads that form the ovisac or egg-containing capsule. In the larval stage, the larvae move from the leaf to the grape bunches. Black sooty mould that grows on the secreted honeydew is visible on infected vines. The mealybugs can also spread the viral grapevine leafroll disease.
Vineyard management
Although the main purpose of control is to prevent grapevine mealybugs from infecting the grape clusters or spreading to other grapevines, management of ants is the first step in mealybug control.
The plastic placed over the berm can in some cases provide the ideal environment for the nesting of ants and large numbers of active ants under the plastic must be removed as soon as possible.
Tall weeds that can provide a pathway for the ants to get to the vines should be removed during the growing season. A cover crop system can help control weeds. This will also provide a habitat for ladybirds whose larvae feeds on mealybugs, and their wasps that attack adult females. In addition, pheromone traps can be used to catch the males.
Treatment
Mealybug infested vines must be marked during the growing season so that they can be treated with a suitable chemical agent during the winter and before budding.
Adjacent vineyards must also be treated. The vines must be thoroughly wetted because the mealybugs hide under dead bark and in the roots during winter. Use a soil-administered systemic insecticide for heavy mealybug infestations.
Placing sticky insect barriers or barriers treated with a chemical pesticide around the trunk and trellising wires will help control the ants.
Corteva treatment for Mealybug
Closer™ 240 SC (Reg. No L9694) is a suspension concentrate contact and systemic insecticide, for the control of mealybugs on grapes.
More information
To find out more about these Crop Protection innovations from Corteva, please visit our website at https://www.corteva.co.za
Source references
Vinpro (2023) Grape Fungal Disease – Mildew: Wine Grape Growing in South Africa. South Africa Online
https://southafrica.co.za/grape-fungal-disease-mildew.html
Louw, M. (2023) Grape Pests – Ants and Grapevine Mealybugs: Wine Grape Growing in South Africa. South Africa Online
https://southafrica.co.za/grape-pests-ants-and-grapevine-mealybugs.html
