How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

The grape leafhopper is a pest of grapes north of the Tehachapi Mountains, especially in the San Joaquin, Sacramento, and North Coast valleys. It is also a problem in warmer, interior Central Coastal valleys. The variegated leafhopper is the major pest of grapes in southern California and in the Central Valley as far north as San Joaquin County.

Leafhoppers overwinter as adults and are found in spring on basal grape leaves and weeds. The adult grape leafhopper is about 0.12 inch (3 mm) long and light to pale yellow with distinct dark brown and reddish markings. Eggs of the first brood are laid in epidermal tissue on the underside of the leaves in April and May and appear as a bean-shaped, blisterlike protuberance that is slightly less than 0.04 inch (1 mm) long. Although similar in size to the grape leafhopper, the variegated leafhopper is darker in color and distinctly mottled brown, green, and white with a reddish tinge. The nymphs are almost transparent when first emerged, becoming orange-brown to yellow-brown, in contrast to the white nymphs of the grape leafhopper. Eggs are similar in appearance to the grape leafhopper but laid deeper within the leaf tissue. This latter characteristic reduces the effectiveness of the egg parasite against variegated leafhopper.

DAMAGE

Nymphs and adults of both species remove the contents of leaf cells, leaving behind empty cells that appear as pale yellow spots or stippling. If populations are high, the entire leaf may be pale yellow or white. Loss of leaf efficiency and leaf drop can occur when leafhopper densities are extremely high. This can result in fruit sunburn and may delay fruit ripening, especially in young vines. If there is a significant reduction in the overall photosynthetic capacity of the vine, young or stressed vines may have less shoot growth the following season.

The accumulation of small droplets of excrement on berries and the associated growth of sooty mold results in berry spotting that is a concern in table grapes. Adult leafhoppers are also a nuisance to workers when populations are high at harvest time. Their excrement appears as minute, sticky clumps that darken with age.

MANAGEMENT

Although leafhoppers infest most vineyards in California, they may not require chemical treatment because vines can tolerate fairly high populations without harm, and predators and parasites may be able to maintain leafhopper populations below tolerance levels. In coastal regions and the Central Valley, however, grape leafhopper populations may occasionally reach damaging levels and require treatment. If chemical control of leafhopper is necessary, wait until the second (summer) generation, whenever possible, before treating.

Biological Control
Many natural enemies help to provide control of leafhopper.Egg parasites, including Anagrus epos and other Anagrus spp., are commonly found in vineyards during part of the season. These parasites may be more abundant in vineyards that are adjacent to prune, plum and almond orchards, and riparian areas where other leafhoppers that overwinter in the egg stage reside. Anagrus spp. can parasitize these eggs and survive the winter. After a leafhopper egg is parasitized it becomes visibly red. Unfortunately, this parasite is not as effective on variegated leafhopper eggs as it is on those of the grape leafhopper. Sulfur sprays applied for fungal control are very toxic to Anagrus spp.

General predators of grape leafhoppers include spiders, green lacewings (Chrysopa spp.), minute pirate bugs (Orius spp.), lady beetles (Hippodamia spp.), and predaceous mites. The predaceous mite, Anystis agilis, is an important predator of first instar nymphs especially in the North Coast. Although many growers have experimented with releases of lacewings for leafhoppers, control of economic populations has not been achieved in university field trials.

Cultural Control
Removing basal leaves or lateral shoots during berry set and the 2-week period following (before adult leafhoppers emerge), as recommended for Botrytis bunch rot management, will normally reduce peak leafhopper populations during the season by 30-50%. This coupled with Anagrus activity may preclude the need for insecticide treatment even when leafhoppers exceed the thresholds below. Time leaf removal to coincide with first generation nymphal development up to and including the 5th instar but just before adults are present. Also, leaf removal will improve coverage and efficacy of pesticides. In warmer growing areas, be careful not to remove excessive numbers of leaves, which can lead to sunburned fruit. Preventing overly vigorous vine growth will also help suppress leafhoppers.

If the vineyard is accessible before budbreak and erosion is not a risk, remove weeds in vineyards and surrounding areas before vines start to grow in spring to reduce adult leafhopper populations that might disperse to new grape foliage.

Organically Acceptable Methods
Biological and cultural control methods, including basal leaf removal, assist in control. Narrow range oils, insecticidal soaps, or kaolin clay may give partial control when nymphs are small. Soaps may spot table grapes and should only be used before bloom on this crop.

Monitoring and Treatment Decisions
About 4 weeks after budbreak, or whenever nymphs first appear, begin sampling for leafhoppers. Randomly select 20 vines in each block of the vineyard, each at least a few vines in from the end of the row.

How to monitor:

• First generation nymphs—On each vine, choose one leaf at the 3rd or 4th node up from the basal node.
  Second and third generation nymphs—Choose young but fully expanded leaves in middle of canes.
• Count nymphs on underside of each leaf. Note whether they are grape leafhopper nymphs, variegated leafhopper nymphs, or both.
• Check the leaves for red, parasitized eggs or eggs with emergence holes.
• Record observations on a monitoring form (example form—149 KB, PDF)

Continue monitoring weekly until harvest. Starting at bloom, combine leafhopper monitoring with monitoring for spider mites and mealybugs see MONITORING INSECTS AND SPIDER MITES.

Treatment thresholds. Treatment thresholds vary according to leafhopper generation; whether grapes are being grown for table, wine, or raisin use; canopy size; region; and degree of parasitization. A level of 10-30% parasitism on eggs of the first generation may result in economic control of the grape leafhopper during the second and third generations. However, if the leafhopper population is made up primarily of the variegated leafhopper, economic control by this parasite is less likely, although a combination of parasite and predator activity can be effective. Use the general guidelines below to help determine treatment needs. If treatment is necessary, removing basal leaves will allow better spray coverage and thus improve pesticide efficacy.

Wine and raisin Thompson Seedless grapes. For the first generation, treatment is not necessary if 20 or fewer nymphs per leaf are found. If Anagrus is active on eggs of the first generation, it is best not to treat unless leafhopper numbers are well above 20 per leaf. Also helpful is the removal of basal leaves before adults of the first generation appear, as described under CULTURAL CONTROL, to allow better spray coverage and thus improve efficacy of the pesticide. If you have to treat, wait until more than half the nymphs are in the third instar; this allows sufficient time for most eggs to have hatched.

For the second or third generation on wine and raisin Thompson Seedless grapes, the treatment threshold is 15 to 20 nymphs per leaf. Generally lower populations do not need treatment. However, coastal wine grapes with a low incidence of parasitism and small canopies may have a threshold of 10 to 20 nymphs per leaf. Vigorously growing vines can support higher populations.

Table grapes. Treatment level is lower for table grapes because they need better fruit protection. For the first generation, treat if more than 15 leafhopper nymphs per leaf are found. In the second and third generations, early varieties (Flame Seedless) should not exceed 10 nymphs per leaf; midseason varieties (Thompson) 5 to 10 nymphs per leaf; and late varieties (Emperor) 5 to 8 nymphs per leaf. Large populations of adult leafhoppers in the fall are very annoying to workers who are hand harvesting grapes. A treatment just before harvest may be warranted if adult populations are high.

• Summary of Important Links

Common name		Amount/Acre**	R.E.I.+	P.H.I.+
(trade name)			(hours)	(days)
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies and honey bees. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
A.	IMIDACLOPRID
	(Provado Solupak) 75WP	0.75–1 oz	12	0
	MODE OF ACTION GROUP NUMBER1: 4A
	COMMENTS: Foliar application: allow at least 14 days between applications. Do not exceed 0.5 lb a.i. of imidacloprid/acre/year.
	. . . or . . .
	(Admire Pro)	7–14 fl oz	12	30
	COMMENTS: Apply a total of 7-14 fl oz/acre in one or two drip irrigation applications. Two applications 21–45 days apart are recommended on coarse soils or where the longest periods of protection are required. Make first application between budbreak and pea-berry stage. A total of 14 fl oz/acre is recommended where vigorous vine growth is expected or in warmer growing areas such as the Coachella, San Joaquin, or Sacramento valleys. Soil moisture is important for effective soil application; follow label instructions carefully.
B.	BUPROFEZIN
	(Applaud) 70WP	9–12 oz	12	30
	MODE OF ACTION GROUP NUMBER1: 16
	COMMENTS: An insect growth regulator; kills predatory beetles. Good coverage is essential. Apply no more than 2 applications/season. Allow at least 14 days between applications. Use allowed under FIFRA section 2(ee) recommendation.
C.	ACETAMIPRID
	(Assail) 70WP	1.1 oz	12	7
	MODE OF ACTION GROUP NUMBER1: 4A
D.	PYRETHRIN/ PIPERONYL BUTOXIDE
	(Pyrenone Crop Spray)	Label rate	12	0
	MODE OF ACTION GROUP NUMBER1: 3 and 27A
	COMMENTS: Spray containers with 1 pt/150 gal water and as needed. Apply alone or in combination with a narrow range oil. Use in combination with a narrow range oil when treating the first generation leafhoppers, except on table grapes. Do not use oil on later generations.
E.	ENDOSULFAN*
	(Thionex) 50W	2–3 lb	2 days	0
	MODE OF ACTION GROUP NUMBER1: 2A
F.	INSECTICIDAL SOAPS/NARROW RANGE OIL#	Label rates	12	0
	MODE OF ACTION: Contact insecticides with smothering and barrier effects.
	COMMENTS: Partially effective on low leafhopper populations if applied when nymphs are small. Research indicates soap works better in combination with low rate of oil. Care must be taken as both products can spot the waxy bloom on the berry. Do not apply sulfur within 10 days of a sulfur spray.
I.	DIMETHOATE 25WP	6–8 lb	2 days	28
	MODE OF ACTION GROUP NUMBER1: 1B
	COMMENTS: To avoid visible deposits on grapes, do not apply after berries reach 0.25 inch diameter. May not be effective in all areas due to resistance. Disruptive to natural enemies.
J.	KAOLIN CLAY#
	(Surround) WP	12.5–37.5	4	14
	MODE OF ACTION: Unknown. An inorganic insecticide.
	COMMENTS: An organically acceptable alternative for wine grapes.
**	Apply with enough water to provide complete coverage.
+	Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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.
#	Acceptable for use on organically grown produce.
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). For additional information, see their Web site at http://www.irac-online.org/.

IMPORTANT LINKS

• Insect and spider mite monitoring form (149 KB, PDF)
• Photos of Leafhoppers

PUBLICATION

UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Research Center, Parlier
L. G. Varela, UC IPM Program, Sonoma County
F. G. Zalom, Entomology, UC Davis
R. J. Smith, UC Cooperative Extension, Sonoma County
A. H. Purcell, Environmental Science, Policy and Management, UC Berkeley
P. A. Phillips, UC IPM Program, Ventura County
D. R. Haviland, UC IPM Program, Kern County
K. M. Daane, Kearney Agricultural Research Center, Parlier
M. C. Battany, UC Cooperative Extension, San Luis Obispo County
Acknowledgment for contributions to Insects and Mites:
J. Granett, Entomology, UC Davis

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