It never fails. When you are running behind, the door bell rings with unwanted visitors.
That is the way the pest season is unfolding for the 2003 San Joaquin Valley cotton season. To no one's surprise, late rains that delayed the planting season for a month also are providing plenty of habitat for lygus bugs, according to Pete Goodell, University of California Cooperative Extension IPM advisor based at the Kearney Agricultural Center in Parlier, Calif.
Whether those unwanted guests stay to dine on cotton squares remains to be seen, but Goodell leaves little doubt from his lygus survey that it could be a matter of not who is coming for dinner, but how many.
Goodell said farmers need to look no farther than their neighborhoods to find numerous lygus hosts. The foothills, he said, will not likely be the source of lygus this year because there are no hosts there. The hosts are on the roadsides and abandoned fields throughout the valley.
The late 2003 start is drawing comparisons to 1995 and 1998 when yield loss to lygus was the highest during the 1990s. There are similarities, but there is a unique difference.
“In 2003 we found (host) plants blooming with mature seed loads. These hosts will provide lygus with good habitat and the sufficient rainfall in April and May may ensure that hosts will be available through May,” said Goodell.
Many hosts available
There is a wide variety of lygus hosts widely distributed this year. “Especially abundant were shortpod mustard along the roadsides and London rocket on acreage that remains uncultivated. Tumbleweed is germinating and will develop on ground that has been disturbed,” he said.
Lygus, said Goodell, were “abundant in the interior of the valley as well as on the rim. The population tended to be concentrated along roadsides on the rim of the valley, but distributed in field-size locations throughout the interior.
“Lygus are more abundant and widespread in 2003 than it has been for many years,” he said.
Goodell has little doubt lygus will move from weeds to crops. When is the question.
“If cotton is not susceptible in the pre-squaring stage with limited row coverage, lygus will settle into other crops. If movement is timed during early squaring, square loss could be high,” warned Goodell.
The most susceptible fields will be those adjacent to weedy areas.
The season has been shortened and growers and pest control advisers will be tempted to treat early to protect the crop. Goodell cautioned PCAs and growers to treat based on field sampling, crop stage, yield potential and severity of the threat.
“Visiting fields frequently during the early fruiting cycle is the best investment that can be made,” he said. If treatment is warranted, Goodell suggested a “measured response” to the situation.
“This will result the level of control required for the situation while potentially conserving natural enemies if there is a fit for a more selective insecticide,” he said.
Preserving natural enemies could prove handy later. Goodell warns that a late crop not only exposes it to lygus damage, but aphids and whitefly as well.
“Aphids are greater problems when planting dates are spread over time and late-planted fields will have lint exposed longer to honeydew,” he explained.
Whitefly is also a threat to late-planted cotton.
“A balanced and integrated approach to cotton lygus pest management will assure fewer secondary problems from mites, worms, aphids and whiteflies,” Goodell concluded.