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 (View photos of natural enemies.)
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 5^th 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 bud break 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 (View photos.)
About 4 weeks after bud break, 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.

• 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 the presence (+) or absence (-) for each leaf on a monitoring form (100KB, PDF).

Continue monitoring weekly until harvest. Starting at bloom, combine leafhopper monitoring with monitoring for spider mites (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. An alternative to pesticide application is 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.

Common name		Amount/Acre**	P.H.I.+
(trade name)			(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.
A.	IMIDACLOPRID
	(Provado Solupak) 75WP	0.75–1 oz	0
	MODE OF ACTION: A neonicotinoid (Group 4A)1 insecticide.
	COMMENTS: Restricted entry interval: 12 hours. Foliar application: allow at least 14 days between applications. Do not exceed 0.5 lb a.i. of imidacloprid/acre/year. Repeat applications of any neonicotinoid insecticide (acetamiprid-Assail; imidacloprid-Admire, Provado) 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.
...OR...
	(Admire Pro)	7–14 fl oz	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. Repeat applications of any neonicotinoid insecticide (acetamiprid-Assail; imidacloprid-Admire, Provado) 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.
B.	BUPROFEZIN
	(Applaud) 70WP	9–12 oz	30
	MODE OF ACTION: A thiadiazine (Group 16)1 insecticide.
	COMMENTS: Restricted entry interval: 12 hours. 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	7
	MODE OF ACTION: A neonicotinoid (Group 4A)1 insecticide.
	COMMENTS: Restricted Entry interval: 12 hours. Repeat applications of any neonicotinoid insecticide (acetamiprid-Assail; imidacloprid-Admire, Provado) 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.
D.	PYRETHRIN/ PIPERONYL BUTOXIDE
	(Pyrenone Crop Spray)	Label rate	0
	MODE OF ACTION: A botanical (Group 3)1 insecticide and a synergist.
	COMMENTS: Restricted entry interval: 12 hours. 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	7
	MODE OF ACTION: An organochlorine (Group 2A)1 insecticide.
	COMMENTS: Restricted entry interval: 2 days. Dilute application only at 1 lb/100 gal water. Do not apply to Concord varieties as injury is likely to occur. Cannot be applied in any situation where run-off may occur; check with county agricultural commissioner. May not be effective in all areas because of resistance.
F.	INSECTICIDAL SOAPS	Label rates	0
	and NARROW RANGE OIL#
	MODE OF ACTION: Contact insecticides with smothering and barrier effects.
	COMMENTS: Restricted entry interval: 12 hours. 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.
G.	METHOMYL*
	(Lannate LV)	0.75–1.5 qt	Raisin/Table: 1
	(Lannate) 90SP	0.5–1 lb	Wine: 14
	MODE OF ACTION: A carbamate (Group 1A)1 insecticide.
	COMMENTS: Restricted entry interval: Check with county agricultural commissioner. Do not feed treated grapes to livestock. Disruptive to predators of mites and parasites of leafhoppers.
H.	FENPROPATHRIN*
	(Danitol)	5.33–10.66 fl oz	21
	MODE OF ACTION: A pyrethroid (Group 3)1 insecticide.
	COMMENTS: Restricted entry interval: 24 hours. Not recommended for the San Joaquin Valley because of problems with mite outbreaks. See label for additional requirements regarding hand labor.
I.	DIMETHOATE 25WP	6–8 lb	28
	MODE OF ACTION: An organophosphate (Group 1B)1 insecticide.
	COMMENTS: Restricted entry interval: 2 days. 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	14
	MODE OF ACTION: Unknown. An inorganic insecticide.
	COMMENTS: Restricted entry interval: 4 hours. An organically acceptable alternative for wine grapes.
	**  Apply with enough water to provide complete coverage. + Preharvest interval. Do not apply within this many days of harvest. * Permit required from county agricultural commissioner for purchase or use. # Acceptable for use on organically grown produce. 1 Modes of action are important in preventing the development of resistance to pesticides. 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. 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 is assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

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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 the insects and mites section:
J. Granett, Entomology, UC Davis

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