Navel Orangeworm Control Critical

Orchard Sanitation is Critical This Season To Lower NOW Numbers

By Patrick Cavanaugh, Farm News Director

Emily Symmes is the area Integrated Pest Management farm advisor for the Sacramento Valley in the statewide IPM program. She recently spoke to California Ag Today about the high level of Navel Orangeworm (NOW) damage in nut orchards throughout California this past season.

“We had a lot of unique circumstances. The amount of rainfall we got in late 2016 into 2017 was pretty unprecedented and really led us into a really bad navel orangeworm year because we couldn’t get out and sanitize our nut crops,” she said.

Emily Symmes

“NOW is ubiquitous, and there is an increased nut crop footprint in California, with more than one million acres of almonds, plus pistachios and walnuts,” Symmes explained. “All play host to NOW, as well as a host of natural plants. This thing isn’t going anywhere. And it was pretty bad in 2017 in terms of harvest damage.”

One of the key factors for higher navel orangeworm damage was not being able to get into the fields because of the standing water.

“There were a couple of other factors as well. Typically, rainfall and moist conditions can help NOW mortality in the winter. We tend to think that it can help rot the nuts and do us some favors, but we have to be able to get out and get the nuts shaken or get pulling crews in and get those things on the ground. And then them being on the ground is not always a sure thing. Sanitation was huge in terms of NOW problems this year,” Symmes said.

Heat units also played a part in the development of more NOW pressure. There were a lot of moths flying around longer and laying eggs.

“It got hot in mid to late June, and it seemed to just not let up. What that meant was, in terms of our degree-day models or the heat unit that drive insect development, it ended up getting pretty far out ahead of what is typical, if there is anything such as typical. But certainly ahead of the last couple of years,” Symmes explained.

By September, we were about two weeks ahead in degree-days and that means that the moths were out earlier. They’re flying around. They’re laying eggs on the nuts when they’re still on the trees.

Symmes stressed that the importance of sanitation is to minimize the site where the NOWs mature.

“It’s really important to remember that sanitation efforts aren’t just directly killing any worms that are over-wintering in your orchard. Yes, it does that. But it also minimizes those sites where your first and second generations are going to develop next year,” she said.

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Steve Koike on Resistant Cultivars

The Search for Resistant Cultivars

By Emily McKay Johnson, Associate Editor

In the second part of our series with Steve Koike, plant pathology farm advisor for UC Division of Agriculture and Natural Resources, Cooperative Extension in Monterey County, the focus is on the critically needed research on resistant cultivars. Koike, who has focused his research since 1989 primarily on the understanding of disease systems and the investigation of new methods of disease control, said, “The role or the need for resistant cultivars is tremendous.”

“Some good case studies of resistant cultivar research address soil-born problems on lettuce,” Koike explained. “For example, Fusarium wilt and Verticillium wilt on lettuce could be managed lightly; but in order to overcome those diseases, resistant lettuce varieties need to be in place.”

Steve Koike, UC Cooperative Extension, Monterey County.
Steve Koike, UC Cooperative Extension, Monterey County.

“First discovered in 1995 on the Central Coast,” said Koike, “Verticillium wilt has the potential to infect and damage numerous different crops. And although Fusarium wilt was typically unseen in the San Joaquin Valley, it has recently begun to appear on the Central Coast.”

Continued improvement of management techniques upon discovering initial disease symptoms is necessary, according to Koike. “Symptoms of the disease usually appear on the lower leaves of plants, around the edges, and the areas between the veins can turn a yellowish-brown.”

“Strawberries currently have three really important disease pressures state-wide: Verticillium wilt, Macrophomina (charcoal rot) and Fusarium wilt,” Koike commented. “Even the fumigation tools we have are not cleaning them up 100 percent, so we have problems.”

“We will continue to have problems,” Koike elaborated, “until there are truly resistant strawberry varieties to those pathogens. Plant breeders understand that IPM management of these diseases is so dependent on developing resistant varieties,” he said, “but we’re not there yet. We do not yet have truly resistant lettuce or strawberry varieties out in the field,” Koike said.

_______________________________

Koike and his fellow researchers discovered a new race of the downey mildew pathogen in spinach that has been designated race 16. While there are some varieties that are supposedly resistant to race 16, Koike noted that there is still more research to be done.

To read the first part of our series on Downey Mildew, click here.

 

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