Growers and PCAs can now access powdery mildew index maps online at www.westernfarmpress.com to obtain information on the likelihood of disease pressure developing in localized areas.

The maps are based on a powdery mildew model developed by University of California Cooperative Extension researchers. The powdery mildew index is an indication of climatic conditions that may favor development of the disease.

The online service is sponsored by Procure fungicide from Chemtura Corp.

The maps are generated by Precision Agri Lab, a division of Western Farm Service. “It’s a tool that can be used to alert a PCA about areas where a problem may likely occur,” says Michael Larkin with Precision Agri Lab. “It doesn’t replace walking the field and assessing the situation first-hand, but it can serve as a forewarning.”

The maps are updated daily. The telemetry and computer processing involved in the data generation provide almost instantaneous results. Although the maps may not be indicative of every microclimate in every field, they are a fairly accurate representation of the overall picture within a given area.

“We have 2,500 stations that are placed directly in growers’ fields,” says Jeff Diebert with Precision Agri Lab. “Our data is site-specific. It’s not simply based on weather data from the local airport.”

The powdery mildew index uses a point system derived from a number of climatic and environmental factors to assign risk. Reviewing data on a daily basis can help a PCA or grower visualize what could happen in the field in a week to two weeks in advance therefore simplifying treatment decisions.

Conditions appraisal

“I think the maps are a valuable tool simply because they give you a general idea of the environmental conditions in a field and how that might affect the probability of developing powdery mildew,” says Steve Quashnick, PCA with Western Farm Service in Stockton, Calif. “Powdery mildew is much easier to prevent than it is to eradicate. If you know up front that conditions are conducive for disease, you’re more attuned to that possibility when you’re walking the field and making recommendations. I wouldn’t necessarily say that the maps reduce the number of treatments that are actually applied during a season, but I would say that the applications are probably better timed and more effective because of that information.”

While sulfur has often been the backbone of powdery mildew management programs, some of the newer materials such as Procure, a sterol inhibitor, offer greater efficacy and longer intervals between application. Procure offers both protectant and eradicant activity. It is locally systemic translocating rapidly through plant tissue after application and is rainfast within one to two hours. Procure is an ideal partner in a resistance management program particularly in rotation with strobilurin fungicides.

Given the severity of the powdery mildew problem in California and the ever-ominous potential for resistance, improved timing of application is a significant advantage in a management program. “So far this has been a bad year for powdery mildew,” Quashnick says. “We need every tool we have to fight it.”

Currently, the maps cover six growing areas including Delano, Greenfield, Lodi, Madera, Paso Robles and Santa Maria.