There are many pesky concerns for Wisconsin vegetable growers every year—weather, growth problems, pests, water, market demand—but one pest problem, collectively known as foliar or leaf blights, is especially challenging. You have all battled these in your home gardens since they attack crops such as tomatoes, potatoes, carrots and cucumbers. These are the diseases that cause perfectly green plants to break out in brown spots, turn yellow and die prematurely in mid-season just when you are anticipating a delicious harvest. When the leaves begin to yellow and the brown spots appear, many home gardeners run to the garden center seeking a remedy to stave off the impending loss of their carefully nurtured plants only to find that once the disease starts to progress, there is no stopping it.
The vegetable growers that we rely on for our food also face the same threat from foliar blights every year. They have worked closely with University of Wisconsin researchers for decades to understand every facet of what makes these blights tick and have developed innovative disease management strategies to both avoid and combat the problems.
The first step is often to simply reduce the threat of infection. Blights are caused by the fungal spores and most can survive over winter in soil on decaying vegetation. Growers take great care to move their crops away from the previous year’s crops and plant them in disease-free areas, thus avoiding the threat of early season infection from overwintered spores. Growers are also careful to avoid moving fungal spores from field to field by washing and sanitizing equipment when moving between fields. They also cut down the up-front risk of loss by using disease-resistant varieties; plant breeders select varieties with the ability to resist various diseases for many years (seed catalogs often include disease resistance in their descriptions of varieties).
However, nature has a way to thwart their disease-free plans, and despite their best efforts to reduce the impact of foliar blights, growers know that sooner or later, spores will be carried on the winds to susceptible vegetables and control will be needed. The trick now is early detection of the spores to keep the controls to a minimum without sacrificing crop yields; again, this is achieved by knowing everything possible about the specific fungal spores.
To determine when the spores will reach the fields, all crops are carefully inspected weekly; growers are now on the verge of using cutting edge DNA assays to identify individual spores before they can even begin to infect plants! Researchers can assess the precise needs of the foliar blight spore for water and temperature and then develop sophisticated prediction models that allow growers to deploy precise control measures.
So far, the results have been spectacular. No longer do growers depend on the old-time, calendar-based control. They now use precisely-timed treatments that are only applied when needed, often resulting in a 50% reduction in controls over the season. When combined with the additional 15-30% gained when resistant varieties are used, the benefits really add up—not only does the consumer have access to a dependable and nutritious crop at affordable prices, but the environment benefits because fewer controls are used. Although battling these foliar blights is an ever-evolving process that requires a continuing investment by the growers and researchers, the security of our food supply in key production areas such as Wisconsin’s Central Sands is too valuable a resource to be placed at risk.