It could be shaping up to be a challenging lygus management year in California’s San Joaquin Valley.
“History tells us a wet winter and spring means a bad lygus year,” says University of California IPM Advisor Pete Goodell.
“When water is not a constraining resource, it means spring growth in the foothills and uncultivated areas provided increased habitiat for lygus and that tends to make pressure a little worse. A lot of rainfall late also often creates above average lygus pressure, ” says the veteran entomologist, a widely respected expert on lygus management who developed a valley- wide annual monitoring network to assess where the pest are developing.
Goodell also has established valuable Integrated Pest Management strategies that include strip-cutting alfalfa to mitigate lygus migration to cotton, and has developed models to predict the movement of lygus from safflower, a major host.
There are many lygus hosts, including tarweed, California burclover, chickweed, common groundsel, curly dock, filaree, lambsquarter, cheeseweed, lupine, milk thistle and some mustards.
Tarweed has become Goodell’s harbinger for potential lygus problems in the valley, because it is a early summer annual plant.
“When tarweed comes out in the latter part of April or early May in the I-5 corridor on the West Side of the San Joaquin Valley, it gives us an idea of the lygus populations early in the season,” he says.
The confounding issue in 2011 is that with above normal rainfall, distributed over five months and cooler temperatures, one would expect more green cover in the western foothills. However the early heavy rain allowed for excellent grass emergence which not only limits the emergence of broadleaf plants but grasses are not a great host for Lygus population buildup. The effect of the early heavy grass can be seen in the eastern foothills as well with fewer wildflowers than in past years.
Lygus control early in the season sets the stage for insect pest management for the entire year. The use of broad-spectrum insecticides early in the year upsets the balance of other pests such as aphids, spider mites and foliage-feeding worms. It is critical that any early season lygus control products be target-specific to lygus, says Goodell.
Crop diversity in the San Joaquin Valley is also a key element in lygus IPM. Crops like tomatoes, garlic, safflower, forage alfalfa, seed alfalfa and cotton provide habitat or support reproduction, even if lygus does not damage the crop.
“While not all of these crops are good hosts, associated weeds in these crops provide protective habitat or support reproduction,” Goodell says. One season he evaluated a 34-square mile area of the West side of Fresno County and found 10 different such crops. He urges farmers and PCAs to be alert to the crops which surround cotton fields out to a distance of one mile in all directions.
The migratory nature of lygus offers challenges to the cotton industry, which seeks to increase its biological reliance on IPM. During the growing season, it is not difficult to find cotton fields where pests are initially under biological control, but within days of a lygus migration require insecticide intervention to protect the yield.
There will be more cotton in the valley this year, perhaps as much as 500,000 acres — more than double just two years ago. This will challenge lygus management.
“There are a lot of growers who have been out of cotton for a few years, but given the price of cotton, they may be more conservative than they need to be,” Goodell says. “The high price now adds a new dimension to the lygus control equation. With $1 cotton, are there different parameters for protecting the investment.” He adds, “however we have excellent decision support tools for lygus management including plant based monitoring and frequent field visits, weekly or twice weekly during critical fruit formation. Everyone needs to be familiar with these tools and understand how much fruit the plant can realistic retain.“
There are widespread reports that there will be more new cotton producers this season — the price makes it a very attractive cropping option. Many dairymen are growing cotton for the first time to generate income for their economically floundering dairy operations.
Finally, the cool spring has delayed cotton planting and has put many other crops behind schedule, which can only compound the challenge of pest management.
“It could push cotton squaring back five to six weeks and open more windows of lygus susceptibility in crops like tomatoes or safflower that were planted on time,” Goodell says.
He expects a busy summer of what he calls “grower tailgate meetings” in what he expects to be one of the most challenging lygus management years in a while.