by Melissa Piper Nelson

New cultivars, pesticide treatments and beneficial insects are proving to be invaluable tools for commercial vegetable growers, but best management practices, both in the field and in the greenhouse/high tunnel, remain a producer’s strong defense system against plant diseases.

Penn State vegetable disease specialists speaking at a Jan. 10 regional meeting in cooperation with the Cumberland Valley Produce Auction, Shippensburg, PA, emphasized the important role of scouting, sanitation, crop rotation, clean equipment and weed management, among other practices, as key components of keeping diseases at bay.

“I tell producers to farm like they always have the potential of plant diseases,” said Dr. Beth Gugino, associate professor of vegetable pathology. Discussing bacterial diseases in tomatoes, Dr. Gugino cautioned that spot, speck, canker and necrosis problems seem to be getting worse each year.

Often spread by splashing water sources and finding their way into plant wounds, bacterial diseases cut directly into commercial growers’ profits by damaging tomatoes with both external and internal blemishes and rot.

Cautioning producers to guard against infected seeds, the pathology researcher discussed seed treatments including new hot water-heat treatments that can best penetrate seed layers and kill bacteria before planting.

Keeping growing areas “hospital clean” is imperative, according to Dr. Gugino, who also emphasizes strict weed control and isolating and treating transplants, as additional defense systems.

With new vegetable cultivars on the market each year, she encouraged producers to keep good field notes on the different varieties they plant and note disease problems that may become associated with each.

Identifying used tomato stakes as a primary potential bacteria source, Dr. Gugino told producers that chemical or deep penetrating heat treatments are essential if stakes will be re-used in the production cycle.

While new defense systems, which can boost a plant’s viability, are coming on the market, Dr. Gugino said that some of these preparations can also divert a plant’s energy and may cause growth to lag behind. Scouting, crop rotations, clean environments and vigilance still are the primary defenses in successfully growing disease-free vegetable crops, according to the vegetable pathologist.

Dr. Carla Burkle, Penn State extension educator for vegetable and small fruit crops, brought her expertise in commercial production to the regional meeting with a discussion on thrips. Dr. Burkle has a strong background and experience in insect pest management having worked with strawberries, blueberries and vegetable crops. Discussing onion and western flower thrips, Dr. Burkle cautioned that thrips are not easy to manage, having a wide host range and can transmit diseases to onion, cabbage, cauliflower and other plants.

Thrips have a biology that makes them tough for commercial vegetable growers. To reduce the insect populations, she advises using less susceptible cultivars, beneficial insects such as pirate bugs and nematodes, and some chemical treatments, although thrips can hide deep within plant’s leaves. Some new methods for curtailing the pesky bugs is to utilize reflective mulches, straw mulches and if necessary, even reducing nitrogen as thrips thrive on fleshy, succulent plant growth. Treatments demand high spray volume and penetrating surfactants as the tiny insects can efficiently hide in plant material.

Discussing rot diseases in commercial ventures, Dr. Burkle spelled out best management practices including keeping fields well drained, not moving soils between fields, planting cover crops in low-lying areas and breaking up hardpan soils. One mistake she wants producers to avoid is dumping culls in the field where diseases can spread to other plants. “Weeds can act as alternative hosts for diseases so management and control are essential,” she added.

The increase in greenhouse/high tunnel produced vegetables is dramatic, according to Tom Ford, Penn State extension educator. Noting food safety issues and quality control, Ford told the producers that consumers are concerned with where and how food, especially produce, is grown.

Producing for peak periods when demand is high for vegetables such as cucumbers, tomatoes, peppers, lettuces, herbs and even watercress, Ford said most traditional growers are only receiving about 20 percent of the retail value of their crop as opposed to European growers who garner much more profit per square foot in covered growing spaces.

“Vegetable imports into the United States are up by as much as 85 percent from Canada, Mexico, Spain and the Dominican Republic,” he said. To cover all-year access to vegetables many of these crops are now grown under cover.

Ford compared the advantages of soil-less and soil-culture crops noting that soil-less and hydroponic crops offer some ease of handling and better sanitation practices over soil-culture crops, but equipment, plant testing and the steeper production learning curve can be a disadvantage as are start-up costs.

Soil-culture crops must be managed for diseases and soluble salt issues, according to Ford, who is concerned that many producers face water quality issues leading to plant disease and cultivation problems.

The educator told producers that scouting and vigilance in seeing what is happening in any growing condition is extremely important. “Things can happen quickly and you need to be aware of what is going on with your crops at all times,” he said.