Alert Notes About Alerts You will notice that Disease Alerts are provided for the last seven days and not for future dates. The reason future predictive Alerts are not provided is that GrapeCast disease modeling requires detailed, site specific data in order to provide accurate Disease Alerts. Currently there are no statewide weather forecasts available that offer forecast conditions with the required specific accuracy. Trying to incorporate non-specific forecast data would result in high numbers of false positive and false negative Alerts. So until better forecasts become available, familiarize yourself with how GrapeCast Disease Alerts are triggered by reading the notes below. Acquire an understanding of how the various diseases affect your grapevine varieties (a brief overview is offered here). This will enable you to better evaluate the current disease pressure on your vines and how to prepare for any future adverse weather events. Leaf Wetness Most grapevine diseases thrive in high levels of moisture (leaf wetness). The leaf wetness values used here are calculated values, based on an algorithm that uses temperature, wind speed and humidity. More can be seen (and tested) here. Powdery Mildew If conditons are favorable for secondary (conidial spore) infections an alert is issued. If there are at least 6 consecutive hours with temps between 70 and 85, 20 points are added to the disease index. If not, 10 pts are subtracted. 10 pts are also subtracted if the temp gets above 95. POWDERY ALERT LEVELS: - None (green): risk factor = 0 - Low (yellow): risk factor >0 & <30 - Moderate (orange): risk factor >=0.5 & <1.0 - High (red): risk factor >1.0 Downy Mildew Primary infection (Downy 1) only requires 0.2" of rainfall in a 24 hr period. A secondary downy infection (Downy 2) requires a minimum of 97% humidity & a temp of 55°F or greater for 4 hours in complete darkness. PRIMARY DOWNY MILDEW ALERT LEVELS: None (green): Rainfall < 0.2" High (red): Rainfall >= 0.2" SECONDARY DOWNY MILDEW ALERT LEVELS: None (green): Low overnight Humidity High (red): Humidity >=97% in darkeness for 4 consecutive hours Black Rot If the humidity is over 89% for a 1 hr period, a risk factor is given based on the temperature: >=50 & <55 - risk factor = .04   -   >=55 & <60 - risk factor = .08 >=60 & <65 - risk factor = .11   -   >=65 & <70 - risk factor = .13 >=70 & <80 - risk factor = .14   -   >=80 & <84 - risk factor = .17 >=84 & <90 - risk factor = .11   -   Greater than 90 - risk factor = .08 The risk factor is added until there is a period of 9 hrs of no leaf wetness. At that point the risk factor is reset to zero. BLACK ROT ALERT LEVELS: None (green): risk factor = 0 Low (yellow): risk factor between 0 & .5 Moderate (orange): risk factor between .5 & 1.0 High (red): risk factor 1.0 or higher Phomopsis Phomopsis is quite sensitive to both temperature and humidity. The higher the average temperature goes, the lower the humidity needs to be. PHOMOPSIS ALERT LEVELS: Ave temp >=46 & <50 and 12+ hours of leaf wetness (LW) Ave temp >=50 & <54, LW >11   -   >=54 & <55, LW >10 Ave temp >=55 & <59, LW >9   -   >=59 & <61, LW >8 Ave temp >=61 & <64, LW >7   -   >=64 & <68, LW >6 Ave temp >=68 & <70, LW >5   -   >=70 & <81, LW >4 Ave temp >=81 & <86, LW >5   -   >=86 & <87, LW >7 Botrytis Infection calculations are only run during episodes of leaf wetness and temperatures below 104°F. Temperatures below 54°F are adjusted to 54°F and temperatures > 90F & < 104F are adjusted to 90F. The following formula is used: Infection index = (0.061601 * # of wet hours * temp) - (0.001511 * # of wet hours * pow ((temp), 2)) - (0.374927 * # of wet hours) - 2.647866 BOTRYTIS ALERT LEVELS: - None (green): risk factor = 0 - Low (yellow): risk factor between 0 & .5 - Moderate (orange): risk factor between .5 & 1.0 - High (red): risk factor 1.0 or higher Ripe Rot Leaf wetness and warm temperatures increase the risk for ripe rot. Also, as grapevines grow throuhout the season, so too does their susceptibilty. There are four lines of Alerts for ripe rot, each one corresponding with a stage of grapevine growth. One needs to determine stage of growth on order to evaluate the risk of infection. Read about how the Ripe Rot Model came to be came to be RIPE ROT ALERT LEVELS: - None (green): risk factor < 0.45 - High (red): risk factor >= 0.45 Other Notes Weather conditions greatly affect grapvines, both positively and adversely. And while the saying 'Sunshine Into Wine' has merit, wine would not be possible without rainfal too. But rainfall can also create conditions favorable to disease. Some diseases target only berries while most also can also affect foiliage as well. To complicate matters, disease susceptibilty is dependent on the variety of grapevine, and also on the stage of growth. All these factors need to be considered when deciding both risk of infection and appropriate control measures.