Developing a Vineyard Disease Management Strategy
A vineyard disease management strategy takes into account all the aspects of a vineyard that could have an effect on disease development. Disease management should be planned on a block-by-block basis. This allows for tailoring of a fungicide program to the problems present in each block.
The best time to develop a disease management strategy is the year prior to implementing it. Growers are advised to take the time to collect all the information needed to make an informed decision and the thought needed to fully understand what is to be changed in the current fungicide program and why.
The following information will assist in the development of a vineyard disease management strategy:
Maps of each block
Assessing Disease Potential
Disease potential should be assessed on a block-by-block basis. Just as one would not put drainage tile into all vineyards because one site held water throughout the year, so one should not assume that all blocks have the same potential for disease. Following are some of the major factors involved in assessing vineyard disease potential each year:
- Variety of grape planted
- Past disease pressure
- Overwintering disease inoculum
- Training system
- Previous disease management strategy
- Growth stage and current weather conditions
Varieties vary widely in their susceptibility to fungal diseases. Table 2, (69k pdf file) "Relative Disease Susceptibility Among Grape Varieties," lists the relative disease susceptibility of many of the grape varieties grown in the Northeast. It is generally understood that Concord and Niagara are highly susceptible to a much smaller complex of diseases than are most Vinifera and French hybrid varieties. Due to their differences in disease resistance, it should be no surprise that the fungicide programs for American varieties are generally less intensive than those for the Vinifera or French hybrid varieties.
Past Disease Pressure
When assessing disease potential one of the first things to determine is the level of disease that was present in a vineyard just prior to harvest during the last growing season. It is also important to have knowledge of the complete disease history of a vineyard. Knowing a vineyard's disease history, not just what happened last year, gives a better overall picture throughout a variety of weather conditions.
The training system is particularly important for those who are considering conversion to minimally pruned or hedged systems. Minimal pruning leaves more canes in a canopy and does not remove weak, dead, or severely infected canes unless hand follow-up is done. A minimal fungicide program that has worked well in the past may need to be replaced with a more intensive program to help manage the increase in disease potential if the minimal pruning systems are used.
Previous Management Strategies
One of the most obvious questions is: why change a program if it is currently working? The new disease management strategies address many of the problems that are seen with increasing regularity in northeastern vineyards. Development of powdery mildew populations that are resistant to the SI class of fungicides (Bayleton, Nova, and Rubigan) is becoming more common. Benlate-resistant strains of powdery mildew developed quickly and eliminated a previously important management tool. By linking the disease management strategies to infection periods of black rot and powdery mildew, fungicides are applied only when needed. Field tests have shown good disease management with fewer fungicide applications in years in which weather conditions did not favor disease development. In years that favored disease development, fungicide applications that were timed using infection periods provided disease management similar to a protectant strategy in Concord vineyards.
Growth Stage and Current Weather Conditions
Current weather conditions and growth stage - combined with the biology or life cycle of the disease in question and the susceptibility of the cultivar - are the cornerstones of the new disease management programs. Knowing when primary inoculum of a disease is present allows the matching of available fungicides to the growth stages and the disease. There are three major growth stages or events that dictate the timing of the new disease management protocols: bud break, bloom, and veraison. This is due to the fact that primary inoculum of both black rot and powdery mildew is present at or shortly after bud break and is expended shortly after bloom in most years. With this background information, an assessment of disease potential for a vineyard can be made.