Vineyard Diseases & Fungi:

Planning for the Season and Effective Control Strategies

By: Alyssa L. Ochs 

No vineyard is immune to diseases and fungi, and the effects can be devastating if these organisms aren’t controlled proactively and on an as-needed basis. Fortunately, there are many different ways that vineyards can protect themselves against these risks and set themselves up for success for the year. It is beneficial to understand the common diseases and fungi that affect vineyards and what to do to keep vines safe and healthy.

Types of Diseases and Fungi in Vineyards

  Vineyard owners encounter both viral and bacterial diseases on grapevines that affect the plants in various ways. Red blotch and leafroll are common viral diseases spread through infected cuttings that pose risks to wine grapes. Anna-Liisa Fabritius, Ph.D., Plant Pathologist, University of California-Riverside, told The Grapevine Magazine that both viruses affect berry chemistry and cause delays in ripening of the fruit and color, which translates to poor wine quality. In 2009, Dr. Fabritius and Lana Dubrovsky started AL&L Crop Solutions, a plant pathology laboratory that provides disease diagnostic services to the agricultural industry.

  Meanwhile, crown gall is a common bacterial disease that affects grapes. Dr. Fabritius said that at least two different Agrobacterium species are causal agents of crown gall – one affecting grapevines only, while the other causes crown gall in several other plant species. Ultimately, large galls strangle the vine and restrict the water and nutrient uptake, which leads to reduced vine vigor and yield.

  Dr. Fabritius said that, like viruses, the distribution of the bacteria throughout the plant could be erratic. Bacteria may also be present at very low levels. A bio-PCR method, where the pathogen is first amplified on laboratory media, is often needed to diagnose low bacteria levels. PCR analysis is necessary to distinguish the tumor-inducing strains from non-pathogenic strains.

  Fungi can move between vines along intermingled roots and spread due to human activity, vineyard tools, plant debris in soil and even water splashing from rain or irrigation. Fabritius said that the most common fungal diseases are canker diseases caused by Botryosphaeria and Eutypa.

  “They cause big economic losses in vineyards throughout the world,” she said. “Vine decline disease is best noticed in spring or early summer when the new growth picks up. The shoot growth in vines infected with these fungi is poor compared to healthy vines.”

  Garrett Gilcrease, agronomic service representative of Central California for Syngenta, told The Grapevine Magazine that the main pathogens on everyone’s minds are powdery mildew and botrytis. These two pathogens are the most widespread, cause the most economic damage and can take an entire crop out in what feels like an instant.

  “With powdery mildew, we have the advantage of scouting now and combining that with the pressure we had last year to get a gauge of how aggressive we need to get in 2021,” Gilcrease said. “While scouting now during the dormant time and early spring, a telltale sign of a previous infection would be dark-brown-to-reddish diffuse patches along the canes and dormant buds. The patches are leftover infections from the previous season and contain dormant reproductive bodies which are sources of inoculum for the upcoming season.”

  Gilcrease said that the main issue here is the buds covered in dormant infections. During budbreak and rapid shoot growth, those shoots emerging from those buds carry that inoculum with it as it emerges from the bud.

  “This spreads the inoculum out over a larger area that becomes a large reservoir for infection once conditions are right,” Gilcrease said.” It’s sort of like placing an army throughout an area, building numbers, and then they all attack in a very coordinated way. This is one of the ways infections ‘explode’ over a very short period of time and cover vast acreages.”

  Meanwhile, he said that botrytis isn’t something that leaves behind visible references in such numbers compared to powdery mildew.

  “Most don’t know that botrytis infections, both early season and later season, are linked to some degree,” Gilcrease said. “The early infections around budbreak and into bloom are early and need to be treated when conditions permit, but all of that bloom tissue and initial inoculum essentially go dormant soon after spring & into the summer.”

  He advised that conditions are not the best for infection during that time, but things change later in summer and into the early fall. At that time, there is a large canopy, increased humidity and grapes are beginning the senescence process with veraison occurring and sugars increasing.

Effective Methods for Disease and Fungi Control

  Among the many control methods used in vineyards are solarization, soil fumigation, dormant sprays, scheduled fungicide application, using protectants for early season control and pruning and burning to eliminated diseased plant parts. Dr. Fabritius said that for controlling canker diseases, such as Botryosphaeria and Eutypa, pruning wound protection is important.

  “Pruning cuts are open surfaces for fungal spores to land and enter the vine,” she said. “Canker disease control can be accomplished by avoiding pruning during rainy weather, and by application of protecting fungicides onto the wounds.”

She said that controlling viral diseases can be achieved by planting virus-free vines and frequent monitoring of the vineyard.

  “Virus-free planting stock is essential for good productivity of the vineyard,” Dr. Fabritius said. “If starting with the clean material, only the viruses that are spread by vectors, such as insects or nematodes, can change the health status of the vineyard. To avoid introducing viruses, it is recommended to test your budwood for viruses. Most of the nurseries require this to be done anyway since they do not want to accept virus-containing material into their production. Virus containing budwood may not be an issue on rooted vines, but most of the rootstock varieties are very sensitive to the viruses.”

  Dr. Fabritius told The Grapevine Magazine that control of bacterial diseases, such as Agrobacterium, requires starting with clean budwood and cultural control to keep the disease in check.

  “This includes removal of infected wood and prevention of cold injuries,” she said. “When grapes are acclimatized to the cold, they can be better protected, and gall-formation is prevented.”

Recent Innovations for Disease and Fungi Control

  Syngenta Crop Protection offers various products to address these issues, including Miravis Prime and Aprovia Top. Gilcrease predicts that these products will play a significant role in all grape types due to the spectrum and technology enhancements compared to current product offerings and the products’ FRAC group composition.

  Aprovia Top contains Solatenol, one of the two new Carboximide actives brought to grapes in 2020. Solatenol reflects a change in Carboximide chemistry research and brings exceptional activity on powdery mildew on its own. 

  “Aprovia Top should be looked at as a powdery mildew specialist product that can be positioned at the early-to-middle timing of mildew infection,” Gilcrease said. “This will provide a good anchor for your powdery mildew program and increase the ROI for the grower, all while being very export-friendly with a clean MRL profile.”

  Meanwhile, Miravis Prime contains a breakthrough with Carboximide research with the active ingredient Adepidyn.

  “We, oftentimes, have ingredients that are very good at some pests but not others, or have great efficacy but don’t last very long,” Gilcrease said. “In Adepidyn, we created a molecule that has a wide pest control range because it targets both powdery mildew and botrytis on its own, very long residual control and very high intrinsic activity, meaning we can control pests with fractional amounts of Adepidyn compared to others on the market.”

  “In positioning Miravis Prime, it can be used early when both powdery and botrytis are active in the spring, thus anchoring your mildew program mid-season in rotation with other chemistries or later in the summer when botrytis and mildew again are active,” Gilcrease said.

  While dormant applications of various fungicides are effective, many of them, such as lime sulfur, can be corrosive to equipment, hard on beneficials, tough to clean and hazardous. In response to this issue, BioSafe Systems has developed a broad-spectrum, foliar fungicide for application during dormancy. Taylor Vadon, technical sales representative for BioSafe Systems, told The Grapevine Magazine that is why BioSafe brought PerCarb to the market. This product is an ideal alternative to many fungicides applied during dormancy because of its broad spectrum and contact mode of action with five to seven days of residual.

  “PerCarb is a soluble granular that, when put into solution, releases 27% hydrogen peroxide by weight and can be applied at a rate of four pounds per 100 gallons of water,” Vadon said. “The high concentration of hydrogen peroxide is very effective at killing and reducing overwintering structures of Phomopsis, black rot, anthracnose and, most notably, powdery mildew, thus reducing the inoculum going into the growing season.”

  Vadon noted that as with any dormancy-applied fungicide, it is important to use enough water to get the solution into the crevasses of the bark of the canes, cordon and trunk to saturate the overwintering structures and effectively kill them. He said that application timing is critical because if temperatures are warm, the solution could dry out too fast, thereby not allowing the contact time needed to kill the overwintering structures.

Environmental Sustainability with Disease and Fungi Control

  Although diseases and pests must be dealt with quickly and effectively, many vineyards want to do so as eco-friendly as possible. BioSafe Systems creates environmentally sustainable products to protect crops, water and people.

  Vadon said part of sustainability is keeping effective pest management products viable for many years because fungicide resistance is an issue facing vineyards across the country. Ways to address this include rotating mode of actions in fungicide FRAC groups and using a broad-spectrum contact fungicide. For example, BioSafe’s OxiDate 5.0 utilizes peroxyacetic acid to oxidize a pathogens’ cell structures at all developmental stages. Killing the organism through oxidation on contact dramatically reduces the chances of developing mutational resistance.

  “OxiDate 5.0 can be tank-mixed with many organic and conventional fungicides that are susceptible to developing resistance,” Vadon said. “This tank mix with Oxidate 5.0, in every compatible spray, will not only help fight fungicide resistance but will also lower inoculum in the vineyard. OxiDate 5.0 leaves no harmful residues and breaks down into hydrogen and carbon, making it an environmentally sustainable chemistry.”

Tips and Advice for Preventing Diseases and Fungi

  Prevention is the best strategy for staying on top of plant diseases and fungi before they strike. Fabritius said vineyards should be visually monitored throughout the growing season for symptomatic vines. Lab testing could confirm a viruses’ presence, and then virus-infected vines should be moved.

  “Vector monitoring is essential for the diseases that are spread by insects,” Fabritius said. “These can include visual monitoring for the presence of mealybugs, ant populations and use of pheromone traps. It is also a good idea to test your soils for the presence of nematodes.”

  Gilcrease said lime sulfur treatment during the dormant period has been shown to help knock back and limit mildew pressure throughout the vineyard. He also said vineyards should use sulfur to the highest degree and begin early.

  “Sulfur is one of those products that isn’t flashy but works great to break things up rotation-wise,” he said. “There are some restrictions on when and how late in the season you can use them based on your buyer, so make sure you fall within those regulations before you pull the trigger.”

  Finally, vineyards must think about coverage, regardless of what crop protection material they choose.

  “I think of large acreage and wanting to cover a lot of ground at once makes many think of aerial application,” Gilcrease said. “In the early season, this is okay as the canopy is not very dense and penetration from above is much easier. But as the season goes on, canes begin to really get dense and create a sort of umbrella over the clusters. At this point, an aerial application is nearly useless no matter how many acres can be covered in a short period of time. Long story short, aerial apps should be used when they can but not looked at as solution to rapid need such as putting a mildew fire out.”

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