Description of the Pest
There are two generations of white apple leafhopper per year. Eggs of this species overwinter in the apple trees and hatch shortly after bloom. Adults of the first generation appear in the last part of May to early June. Nymphs of the second generation develop in July and August.
Rose leafhoppers do not overwinter in apple trees; instead they overwinter on plants of the rose family such as blackberries. In spring, the first generation develops on the overwintering host; adults then migrate to other hosts, including apples. The second generation and apparently a third generation may be spent on apples. This species often reaches great abundance near to or after apple harvest.
The adults of both species are white, about 0.12 inch long and cannot be readily distinguished from one another. Rose leafhopper populations can be identified by the presence of black spots at the base of thoracic setae on older nymphs; these spots are not found on nymphs of the white apple leafhoppers.
Leafhoppers feed by sucking on leaf tissue. Their feeding causes a white stippling on leaves. In heavy infestations, fruit may be reduced in size and buds may be weakened. Excrement dropped by leafhoppers will appear as black specks on apples. These specks are easily removed by washing. Leafhoppers also produce honeydew, which forms into sticky droplets around the calyx end after rainfall or overhead sprinkling, and is not easily removed.
White apple leafhopper has become an increasing problem in the past decade because it has developed resistance to organophosphate insecticides. Start monitoring at petal fall to determine need for treatment.
Parasites of the white apple or rose leafhopper have not been studied in California apple orchards. In other areas, parasitization of eggs may be significant in holding populations in check.
Monitoring and Treatment Decisions
Insecticides are most effective when applied during the first four nymphal instars of the first generation, especially in the fourth instar. These stages occur between petal fall and the first codling moth spray. Start monitoring for this leafhopper at petal fall. At weekly intervals sample four leaves per tree from 25 trees dispersed throughout the orchard. Peak nymphal emergence typically occurs 3 to 4 weeks after the first nymphs are found. Treatment is warranted when populations exceed an average of 0.5 nymphs per leaf or when 30% of the leaves are infested. Rose leafhopper is a concern when high populations of nymphs exist near harvest; treatment of nymphs may be warranted at this time.
|Common name||Amount per acre**||REI‡||PHI‡|
|(Example trade name)||(conc.)||(dilute)||(hours)||(days)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.|
|(Admire Pro)||1.4–2.8 fl oz||12||7|
|MODE-OF-ACTION GROUP NUMBER1: 4A|
|COMMENTS: Allow 10 days between applications. Repeat applications of any neonicotinoid insecticide (acetamiprid-Assail and imidacloprid- Admire Pro) can lead to resistance to all neonicotinoids. Alternate neonicotinoids with an insecticide that has a different mode of action to help delay the development of resistance. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.|
|(Assail 70 WP)||1.1–1.7 fl oz||0.275–0.425 fl oz||12||7|
|MODE-OF-ACTION GROUP NUMBER1: 4A|
|COMMENTS: Repeat applications of any neonicotinoid insecticide (acetamiprid-Assail and imidacloprid- Admire Pro) can lead to resistance to all neonicotinoids. Alternate neonicotinoids with an insecticide that has a different mode of action to help delay the development of resistance. Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.|
|(Avaunt)||5–6 fl oz||12||14|
|MODE-OF-ACTION GROUP NUMBER1: 22A|
|COMMENTS: Must be timed for leafhoppers and not other pests to be effective. Do not apply dilute applications of more than 200 gal water/acre. For best results, use 50-150 gal water/acre. Minimum interval between treatments is 7 days. Make no more than 4 applications per season or 3 applications before hand-thinning. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.|
|(Diazinon 50W)||3–4 lb||1 lb||96 (4 days)||21|
|MODE-OF-ACTION GROUP NUMBER1: 1B|
|COMMENTS: Apply when nymphal stages are present. Applications made during the foliage season are very disruptive of beneficials. Avoid drift and tailwater runoff into surface waters. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.|
|**||For dilute application, rate is per 100 gal water to be applied in 300 to 500 gal water/acre, according to label; for concentrate applications, use 80 to 100 gal water/acre or lower if the label allows.|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.|
|*||Permit required from county agricultural commissioner for purchase or use.|
|1||Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode-of-action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee).|