For many vegetable crops, drip irrigation lines have essentially become umbilical cords, providing crops with water, fertilizer, insecticides and fungicides. Now even preplant fumigants are being applied through drip irrigation lines. And field trials conducted in melons in Arizona are showing dramatic results.

Five years ago, University of Arizona Extension Agent Dr. Mohammed Zerkoune, of Yuma, Ariz., first conducted a trial in cantaloupes using various fumigants. “At one time, desert growers were having problems with nematodes,” he says. “But in looking for trial sites, we were unable to find a significant population of nematodes. Instead, we planted into a site loaded with diseases.”

That trial took place on the fall crop, which is planted in the intense summer heat and thought to be more susceptible to diseases than the spring crop. From 2000 to 2003, the trial was repeated on three subsequent fall crops and one spring crop. Four fumigants were compared: chloropicrin EC, metam sodium, Telone EC soil fumigant and InLine soil fumigant. Metam sodium, Telone EC and InLine (a combination of Telone and chloropicirin) were applied via drip irrigation lines.

“The first year, we didn't even know what diseases we were dealing with,” Zerkoune says. “We just knew that the InLine treatment resulted in an incredible increase in biomass and fruit yield compared to the other treatments and the untreated check.” Zerkoune's data showed that high rates of InLine nearly doubled fruit yields that first year.

Primary diseases

By the third year of the trial, soil sampling determined that the two primary diseases in the soil were Monosporascus cannonballus (vine decline) and Pythium.

“Throughout the West, melons have a lot of problems with soil-borne diseases,” Zerkoune says. “It's a devastating situation for growers. A crop can be part way through a season, then all of a sudden plants start collapsing. At certain times of the year, it is very important to keep the vegetation going to provide cover for the fruit. When the vines start dying, the fruit stops growing, too.”

In the past, soil fumigation has been an option for management of soil-borne diseases. Methyl bromide, Telone and metam sodium are all registered for use in melons. Those fumigants would traditionally be shanked into the soil. In Zerkoune's trials, fumigants were applied via drip irrigation lines.

“Applying fumigants through drip irrigation lines turns out to be even more effective on diseases than applying those same fumigants with a shank,” says Dow AgroSciences Product Technology Specialist Jesse Richardson, who cooperated in the trials.

“With shank fumigation, fumigants are applied as liquids, then evaporate underground and move through the soil in the vapor phase to control pests. With drip fumigation, fumigants stay in the liquid phase and move with the water to control pests. Wherever the water moves, that's where the fumigant goes. It's a method that has proven itself — in terms of pest control — in crops like strawberries, peppers and tomatoes.

In the Arizona trials specifically, drip fumigation with InLine reduced pathogen populations of both diseases and provided a significant reduction in weed populations.”

With most production ag trials, the ultimate measure of success is yields. Not only did drip fumigation increase yields compared to the untreated check, marketable yields were higher.

Higher packout

“Regardless of the treatment, unmarketable yields stayed about the same,” Richardson says. “What really changed was the marketable portion. This means a higher packout for growers, but also translates to higher harvesting efficiency because a greater percentage of what's in the field is harvestable. Harvesting crews can pass by fewer rejects during the harvest.”

Zerkoune's drip fumigation trials were conducted for five years. “We got the same results over and over,” he says. “Whether it was the fall or spring melon crop, drip-applied fumigants led to more vigorous vegetation, increased biomass and higher yields.

“We used cantaloupes in our trials because they are a good indicator crop for other cucurbits. Drip fumigation will also be a good fit in the pest control programs of high-value cucurbits like watermelons, zucchini and other specialty melons.”