What is in this article?:
- Citricola scale valleyâ€™s No. 1 citrus pest
- Lorsban resistance
- Citricola scale is the No. 1 citrus pest in the San Joaquin Valley.
- Citricola scale is a voracious pest that in high numbers can dramatically reduce yield.
- The only effective control method in the valley: insecticide treatments.
Beth Grafton-Cardwell, University of California citrus IPM specialist and research entomologist, helps Paramount Citrus’ Jim Hatakeda identify citricola scale on a citrus leaf.
Understanding the timing of the life cycle of the pest is critical to controlling it, Grafton-Cardwell says. If a grower thinks he will control citricola scale in the spring with his red scale spray, he is mistaken, she says.
In the spring, the egg-laying female is protecting her eggs under her body then and pesticides will not kill adults; therefore her 1,000-egg brood is not affected by the pesticide.
There is a wide array of products available for use against citricola scale, but the scale has developed resistance to one of the most popular and effective ones, Lorsban. Grafton-Cardwell says 40 percent of the valley’s citricola scale is resistant to Lorsban.
Regardless of the product selected, she says use the top label rate recommended in plenty of water to get good coverage, even as much as 750 to 1,000 gallons of water per acre if necessary to penetrate thick foliage. And slow down for best coverage.
She is evaluating new products that will be on the market over the next two years.
Oil will control citricola scale for organic growers, but it may take two applications per season.
There is a list of registered foliar and systemic compounds on the UC IPM website.
“You can make any (registered) chemistry work, if you work at it,” she says.
The first step in controlling citricola scale is to find them.
UC has developed two sampling techniques.
Sample in the northeast corner of the grove.
With a presence/absence technique, UC recommends walking down a row taking one to two fully expanded, shady leaves from the northeast corner of 25 trees (25 leaves).
Count the number of leaves with one or more live citricola scale. Ignore the dead ones.
Repeat this in three evenly spaces rows in the block.
If any of the rows have 13 or more infested leaves, treat the whole block with an insecticide this fall. If all rows are in the one to four-leaf range, wait until next season. If some rows have “consider treating” ratings, Grafton-Cardwell says “it would be wise to treat.
Another sampling method is to take one leaf from 100 trees in the northeast corner and count all live nymphs. If the number is greater than 0.5 per leaf, treat.
The females lay eggs on twigs from March to April. From May to July, the nymphs are “pretty easy to see on the twigs,” says Grafton-Cardwell. By mid-October through November the citricola scale moves back into the interior of the tree.
Grafton-Cardwell said it is relatively easy to distinguish between live and dead scale. Using a hand lens, live scale are more plump and a little more yellow than the dead scale, which are more flat than live scale.
Citricola scale is found in California and Arizona.