Combating California Red Scale

Tacy Callies California Corner, Pests

red scale
California red scale
Photo by Lyle Buss, University of Florida

California red scale (CRS) is one of the key pests for growers in the San Joaquin Valley, home to 75% of the state’s citrus production. CRS is a sap-sucking insect that attacks all parts of citrus trees. It causes dieback of branches, yield loss and downgrading of fruit.

According to Sandipa Gautam, University of California assistant research entomologist at the Kearney Agricultural Research and Extension Center, CRS has become more problematic over the past 10 years.

“There are several factors that have contributed to creating this perfect storm for red scale population explosion,” Gautam said during a recent Citrus Research Board webinar. Warm winters have allowed scales to develop at all times, making it difficult to target a particular life stage. Overwintering mortality rates have also declined. Drought conditions are stressing citrus trees, making them more vulnerable. In addition, warmer overall temperatures are accelerating the accumulation of degree days, leading to an additional generation that growers are having to address.

Keeping up with CRS populations is proving difficult. Gautam said there is no insecticide treatment available that can control all five generations. “They usually last about one generation, forcing our growers to treat more often,” she said.

Gautam discussed the management choices available to growers. After many years of research, Sevin, Esteem, Centaur, Movento, oils and Aphytis parasitic wasps have all illustrated varying levels of efficacy.

“All these are rated as moderately effective because none of these choices are super toxic to red scale. They all have issues,” Gautam explained. Some materials have issues of resistance, while others require very precise timing.  

One of Gautam’s management recommendations is to attack the first and second generations when populations are more uniform. “There are overlapping insect populations in the third and fourth generation, and any method you choose may not effectively control all the red scale,” she said.

Addressing stages that are the most sensitive will achieve the highest kill percentage with a given treatment. Driving slowly and getting good coverage of applied materials is critical for management, Gautam advised.

“In the groves that may have chronic red scale problems, use the pheromone disruption in combination with insecticide and Aphytis,” said Gautam. “Don’t let Aphytis release overlap with your insecticide applications, especially that of the broad-spectrum insecticides.”

Source: Brian German, AgNet West

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