California Agriculture: What A Difference A Year Makes For Insect And Disease Control

Lake Oroville

Lake Oroville is a central piece of California’s government-run water delivery network, supplying water for agriculture in the Central Valley.


“We finally got the rain,” David Haviland, Entomology and Pest Management Farm Advisor with the University of California Cooperative Extension, says. “We’re extremely grateful for it.”

It’s that message that supersedes any of the negative issues relating to pests or disease. Maybe this state can finally catch a glimpse of recovery, after four years of historic water shortages that cost agricultural players $247 million in crop revenue losses in 2016 alone, according to an economic analysis by researchers at the University of California, Davis.

The reality is that there are still significant water issues in California, and it will take more rainy years to get fully back to where it was. While the recent rains have brought a reprieve in a larger sense, crop diseases have emerged in full force, as could be expected.

“Almond growers that haven’t sprayed a fungicide in bloom in four to five years have sprayed everything this year at least once and sometimes twice,” says Haviland. Concerns about disease are high for peach, stone fruit, and cherry growers as well. “Rainfall ties to disease particularly during bloom in tree crops. Fungicide demand has been very high.”

Rick Ekins, FMC Portfolio Manager, Fungicides and Insecticides, told CropLife® magazine in an interview at Commodity Classic the company is experiencing unusually heavy demand for insecticides and fungicides in California.

One of those is Rhyme (flutriafol), a fungicide it acquired in its purchase of Cheminova, which controls powdery mildew and black rot in grapes. It is also now registered on a wide range of specialty crops in California including: almonds, walnuts, tomatoes, strawberries, melons, stone fruits, brassicas and leafy vegetables.

Fracture, another fungicide key to its portfolio for specialty crops, contains a novel mode of action for prevention and management of powdery mildew, botrytis, and brown rot blossom blight. “We are building fungicides around these specialty crops that have multiple modes of action,” Ekins says, as more frequent production cycles with fruits and vegetables mean resistance management is that much more essential.

Pam Marrone, CEO of Davis, CA-based Marrone Bio Innovations, agrees it’s going to be a good fungicide year, “no question.”
This year, California growers have faced an unfamiliar dilemma: standing water in fields that has prevented them from getting into the fields for spraying in bloom, or even dormant sprays. California Department of Pesticide Regulation granted an emergency exemption in February allowing for aerial applications of certain fungicides to flooded orchards.

When DPR neglected mentioning biologicals, Marrone sent an alert to growers. “We reminded people that biologicals have such flexible labels because of the safety and risk profile that our (biofungicide) product Regalia could be applied by air. People forget that.”

Marrone adds: “Certainly water allocations to farmers are going to be a lot better than they were in many years. Groundwater has recharged a lot. University of California, Davis is saying that it’s amazing how much has recharged — it was really badly needed, because obviously it’s been pumped out. Up here (in northern California) we’re at double what is normal this time. We are very fortunate. It’s a godsend, really.”

Insect Concerns

According to Haviland, one concern is that insect pressure will be above normal later in the season, because there are certain pests that build in the rangeland, such as flower thrips, beet leafhopper — the vector for curly top disease in sugarbeets and tomatoes — and Lygus bugs, which can affect cotton later in the year. Their populations in May and June are dependent on how much vegetation is in the hills right now — and there’s a lot, Haviland says.

Lygus pratensis

Lygus pratensis

“Anyone that’s concerned about those particular pests is probably gearing up for a big pest year when all the green vegetation in the hills starts drying down, and all of those bugs move into agricultural areas,” Haviland says.

On the other hand, surplus rain can suppress insect populations, such as that of naval orangeworm, a major pest of almond crops. The pest overwinters as larvae inside mummy nuts on the tree hatch, but extra rain will cause mummy nuts to rot and disintegrate so worms can’t survive.

Of course, insect populations overall will be more determined by temperature than anything.

Eric Natwick, Entomology Advisor with the University of California Cooperative Extension in Imperial County, says that in southeastern California, “We are beginning to plant melons, watermelon and squash; there is always a concern about sweet potato whitefly and several aphid species and myriad viruses they transmit that cause disease in melons, watermelon, and squash.

“Also starting in April, we become concerned about onion thrips, the vector of Iris yellow spot virus (IYSV). There are several other aphid and whitefly transmitted viruses that cause diseases of concern to pepper and tomato vegetable growers and to sugarbeet growers such as the Beet curly top virus complex (BCTV).”

Natwick says southeastern California’s greatest pest concern, however, is the sugarcane aphid, which reached the state and Arizona in 2016 and has the potential to destroy the region’s sudangrass industry. “The prognosis is pretty bad,” he says for sudangrass, which is sold primarily to Japanese dairy cattle as feed and livestock feed. “It’s important to us because not a lot of things can grow in the Imperial Valley in the summer — that’s the main crop.” Bayer CropScience’s Sivanto remains the only product that can control sugarcane aphid effectively, but its high cost limits use.

Natwick is currently conducting a field test of sugarcane aphid on eight different crops in the region including wheat, barley, and Giant King Grass. He is trying to determine the potential of the pest to yet again switch hosts and find a possible replacement crop for sudangrass.

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