Honing the health within

The health of greenhouse plants is in constant competition with the desire to make those plants appealing to the commercial market. Unfortunately, meeting the demand for aesthetics and ability to keep sometimes weakens plants’ natural defense mechanisms, says Michael P. Parrella, Ph.D., Department of Entomology at University of California, Davis.

In a presentation at the 2013 Society of American Florists’ Pest & Production Management Conference titled “Improving Plant Health to Combat Pests in the Greenhouse,” Dr. Parrella detailed how far we’ve come with eliminating chemical pesticides in the greenhouse and field. He also stressed the need for further pesticide reduction, perhaps by increasing plant health using “bottom-up” strategies that can help improve disease and insect resistance within.

In the United States where government regulations abound, we can point to several factors that have helped to reduce the use and abuse of chemical pesticides in the industry, including the following:

• The advent of third-party certification organizations that ultimately lead to pesticide reduction and a wiser choice of pesticides;
• The greater use of screening in many greenhouses;
• The ever-increasing rules and regulations focusing on groundwater and farm worker health and safety;
• The greater acceptance of thresholds, where some insects can be tolerated on a crop before a pesticide is applied;
• Greater use of monitoring with light traps, pheromone traps and yellow/blue sticky cards;
• Increased frequency of spot spraying to control early pest infestations without treating the entire greenhouse;
• The advent of effective ‘reduced risk’ materials that can replace traditional chemistry;
• A new generation of growers who have grown up under the concept of going green;
• A consuming public that has a greater acceptance of organic production and an increasing negative perspective of pesticides; and
• Widespread use of biological control agents – namely, insect pathogens, parasitoids and predators.

Source: “Reducing Pesticide Use (Further) In Floriculture By Growing a Healthier Crop,” M. Parrella, C. Casey, M. Murdock & D Klittich, UC Davis, 2012.

According to Dr. Parrella, there appears to be an actual increase in pesticide usage in the last few years — or at the very least, we’ve reached a plateau in pesticide reduction. Dr. Parrella says this is due in part to the fact that most beneficial insects that are used in greenhouses have been discovered and/or approved for use by the USDA.

“What you see is what you get,” he says in regard to any new biological controls becoming available to growers. USDA regulations are in place to limit what parasitic insects you can use and especially how and where they can be shipped. The only new parasites that may come available, according to Dr. Parrella, would be native ones.

Data from California
From 2006 to 2009, overall use of pesticides in the Golden State dipped, according to Dr. Parrella and colleagues. However, from 2009 to 2010, overall pesticide use increased by 9.5 percent (15 million pounds active ingredient). In 2010, California used more than 173 million pounds of pesticide Active Ingredient. Despite an increase in pesticide use across all of California crops in 2010, however, pesticide use in greenhouse cut flowers continued to decline. In 2001, cut flowers ranked 49th among all agricultural commodities in terms of total pesticide use. By 2010, this ranked had dropped to 82nd. A corresponding reduction in accidents involving workers and pesticides was also noted during that time period, Dr. Parrella says.

“Despite an increase in pesticide use across all of California crops in 2010, pesticide use in greenhouse cut flowers continues to decline. For some, this decline in pesticide use was not fast enough, but it is still a positive, and the cut flower industry needs to be recognized for this,” Dr. Parrella says.

Bottom-up strategies
Integrated pest management methods that employ top-down strategies continue to garner wide acceptance in reducing chemical pesticide usage. Dr. Parrella detailed what can be achieved with bottom-up strategies that ultimately strengthen a plant’s natural defenses against disease and pests in his talk, which was based on years of research and corresponding testing in greenhouses at UC Davis and commercial greenhouses in California.

What a plant feeds on truly forms the basis for good plant health. Using sterile soil is a given, but are there nonchemical additives that can improve plant health? Dr. Parrella says he thinks so.

Successful top-down pest management practices occur when natural enemies and organic and inorganic pesticides keep pests in check. Dr. Parrella and others say they have preliminary evidence that suggests bottom-up strategies can contribute to plant health by slowing the development of pests, which will in turn enable natural enemies and pesticides to work more efficiently. “If we can just slow down aphids a little bit (for instance) we can allow biocontrols to work more effectively,” he says.

There are two bottom-up strategies that are currently being employed in greenhouses, according to Dr. Parrella: adding inorganic material silica and/or microbial inoculants to the soil or soilless mixes.

He points to the research his team has done at UC Davis that has shown silica to be useful in reducing Liriomyza leafminer populations. This is a product that can be obtained from a company called Dyna-Gro. The team has also been working with EM-1 from TeraGanix.

This product contains liquid microbial inoculants containing lactic bacteria (Lactobacillus casei), yeast (Saccharomyces cerevisiae) and phototrophic bacteria (Rhodopseudomonas palustris).

Dr. Parrella says these bottom-up strategies can — and are — being used very effectively in greenhouse operations. “We have worked with growers, they’ve seen it, they like what they’ve seen and are actually ahead of us; these are real live growers,” says Dr. Parrella. “They know what is going to work and immediately know what isn’t. I think they’re growing better plants … I think every grower in the country should be doing this.”

Neil Moran is a horticulturist and contributor to Greenhouse Management magazine. Visit his website at www.neilmoran.com.