As growers who’ve faced the threat to their vines from the vine mealybug can attest, this invasive mealybug, Planococcus ficus, is the most difficult to control of the five species of mealybugs that can attack California vineyards.
Like the others – the native grape mealybug and the invasive Gill’s mealybug, long-tailed mealybug and obscure mealybug – the vine mealybug feeds on the roots, trunk, cane, leaves and fruit clusters of the vine where it excretes sticky honeydew.
That substance can encourage development of sooty mold and bunch rot. Also, like the others, the vine mealybug can transmit at least some of the viruses (GLRaVs) associated with grapevine leafroll disease.
What sets this particular species apart from the others, though, is its prolificacy – it produces more generations and larger populations in a season – and can be found throughout the year in every life stage (from egg to adult) feeding almost anywhere on the vines. All this adds up to a bigger, more challenging job of limiting the damage it can inflict in the vineyard.
Still, while the ability of the latest generation of insecticides to control this pest has never been better, some growers have more success than others in using these materials. That’s left some growers as well as University of California Cooperative Extension personnel scratching their heads, wondering why. One of them is Kent Daane, UCCE Specialist based at the Kearney Agricultural Research and Extension Center, Parlier, Calif.
“Most of the materials we have now, certainly all the contact insecticides and most systemics, do quite well killing vine mealybugs on leaves or where they are exposed. But, a small amount of the population remains untreated underneath the bark. Growers see these populations and wonder if we’re getting some resistance to these products, are they breaking down after application or is something else going on?”
To find some answers to these and other questions about the effectiveness of current practices for controlling this pest, Daane has worked with growers in Napa County, Lodi-Woodbridge wine grape region and Fresno County to investigate possible reasons for significant vine mealybug damage to their vineyards in 2016, despite their use of insecticides to control the pest. One table grape grower lost 20 percent or more of his crop that year to the vine mealybug.
His findings led him to conclude that while breakdown of an insecticide might seem to be the reason for higher populations, the real cause could very well be misapplication of the material. For example, Movento is one of the best materials. But, as a systemic insecticide it has to be properly applied. In some cases, he found growers used the wrong surfactant or amount of water when applying it.
“With Movento you need a penetrator type of surfactant, not a spreader, because the product has to move into the leaves to be effective,” Daane says,
Another example: Shortly after spraying the vines with Movento, one of the growers removed leaves before the product could move upward and downward within the vine as its meant to be used for controlling the vine mealybug.
Another grower didn’t apply Movento until he started seeing vine mealybugs in his vineyard in late July – much too late in the season for effective control, Daane notes.
Meanwhile, Daane’s lab research is revealing other aspects of application methodology that may be important with systemic insecticides, such as Movento. This work involves the use of an “HPLC” (commonly used to determine components in wine) to determine how spirotetramat, the active ingredient in Movento, and it’s enol form, the chemical compound that actually kills the various stages of the pest, are translocated within the vine.
Valeria Hochman Adler, a researcher working in the Daane lab, found that the rate at which spirotetramat is taken up, converted to enol and moves throughout the vine can vary among the studied vineyards.
“We don’t know why,” Daane says. “Sometimes, we’ve found that as much as 95 percent of spirotetramat was converted to enol. Other times, we found that five months after Movento was applied only 70 percent of the spirotetramat had converted to enol. Perhaps there’s something about the physiology of the vine that affects this conversion process, and this is our main focus of study with the HPLC.”
Proper application and timing is critical to making the most of Movento’s ability to control the vine mealybug, Daane stresses.
“When properly applied, the conversion of Movento to its enol occurs at a high rate and it moves relatively quickly throughout vine, especially to the leaves where it remains for quite a long time,” he says. “In fact, we’ve found the enol in vines up to a year after Movento was applied. It might take longer to get to the roots, and growers have to be patient, because mealybug kill on these parts of the vine is dependent on the pest’s age, location on the vine and date of treatment with the insecticide.”
Proper application includes proper timing, he adds.
“You want to get enough Movento on the vines when the leaf surfaces are large enough to take up all the material,” Daane says. “And, you want to apply it early enough that Movento can move throughout the leaf canopy and into the canes before the vine mealybug gets to them.”
The window for proper timing of the spray is fairly wide as opposed to worrying about treating at a specific date, he notes. April or May is usually appropriate in the San Joaquin Valley, depending on location and probably later for Central Coast and North Coast vineyards. While July and August is too late for this season’s control efforts, it may help for next season.
When using Movento, Daane advises adopting a proactive approach, as opposed to a reactive one, to control this pest.
“Once you know that you have vine mealybugs in your vineyard, you can start planning your control program to stay ahead of the problem, rather than reacting after it becomes a bigger problem.
“If you’re facing higher vine mealybug pressure, one option might be to apply Movento in a timely manner and then, later in the season, come back with a contact material such as an insect growth regulator. Neonicotinoids are still a good option for some farms, but they have been used for a long time and PCAs must always consider resistant management as part of a long-term strategy. In some cases, you might also include CheckMate for mating disruption.
“Or, if you’re finding only a few vine mealybugs but want to be proactive, you could apply Movento as a single, well-timed spray for that season.”
The recently introduced sprayable version of the CheckMate synthetic sex pheromone product (CheckMate VMB-F), which had been available only as a dispenser-based product (CheckMate VMB-XL), provides growers another option for vine mealybug control.
Daane has conducted field trials of the sprayable version in Fresno County and results were similar to those done last year in Kern County by David Haviland, the county’s UCCE entomology farm advisor.
“In my area we had very good results in reducing trap counts of males using the sprayable product to disrupt vine mealybug mating whether used alone or in combination with an insecticide program” Daane says.
Unlike the dispenser-based product, which releases the synthetic pheromone at a fixed rate, the sprayable from can be used to adjust the application rate as needed based on how often the sprays are made.
“If you want to control mating for the full season, you might spray five or six different times,” he says. “Or, if you decide to disrupt mating for a shorter period, you’d make fewer sprays. In fact, we’re now looking at different timing of applications to see if we can achieve the desired amount of mating disruption using fewer sprays.”