Citricola Scale Insecticide Trial, 2017

Citricola scale causes loss of tree vigor, yield reduction, and downgrading of fruit in the packing house due to sooty mold growth on honeydew deposited by the insect. A field trial was conducted in a 28-yr-old ‘Old line’ navel orange orchard at the Lindcove Research and Extension Center, Exeter, California to compare various timings and rates of insecticides for efficacy against citricola scale. Insecticides were applied diluted in 500 gpa to eight trees per treatment using a 100-gal high-pressure D30 diaphragm pump sprayer with mechanical agitation and a hand wand with a D6 nozzle and using 250 psi. Treatments were assigned in an RCB design with blocking based on 11 Apr 2017 pretreatment counts of mature female citricola found on five twigs (approximately 40 cm in length) randomly selected from around each sample tree. Omni 6E oil and both applications of Sivanto Prime were applied with 1.0% oil, whereas the Actara treatment was applied using a 0.5% oil rate. One treatment of Sivanto Prime was applied during petal fall on 21 Apr when the population consisted primarily of females infesting twigs. The remaining treatments were applied on 21 Jul when the population consisted of first-instar nymphs infesting leaves. Post-treatment sampling consisted of counts of first-instar citricola nymphs infesting five leaves collected from the NE corner of each sample tree during Jul through Oct 2017. An additional sample of mature female citricola on 5 twigs per tree was collected on 12 Apr 2018. Mean numbers of scales per twig or leaf were compared among treatments using ANOVA and the means were separated according to Fisher’s LSD (P = 0.05) after log₁₀ (x + 1) transformation of numbers.

In Aug and Sep samples, all treatments significantly reduced the number of nymphs per leaf; however, only the Sivanto and Actara treatments reduced the number of nymphs below the economic threshold of 0.5 nymphs per leaf (Table 1). In Apr 2018, all treatments reduced the citricola scale adults below the untreated control; however, only Sivanto applied in Jul and Actara had significantly reduced the population of adult females per twig below the threshold of one adult per leaf. Sivanto treatment of nymphs (Jul) was more effective than treatment of adults (Apr).

This research was supported by the California Citrus Research Board and industry gifts of pesticides and funding.