How to Manage Pests
UC Pest Management Guidelines
Fuller Rose Beetle
Scientific Name: Naupactus (Asynonychus) godmani
(Reviewed 9/08, updated 6/12)
In this Guideline:
DESCRIPTION OF THE PEST
Adult Fuller rose beetles are brown, flightless snout beetles and are all females that reproduce without mating. They can be distinguished from two other snout beetles that occur in California citrus groves but do not cause damage: viewed from the top the Fuller rose beetle head and bulging eyes are different than the cribrate weevil, which has a teardrop-shaped head with closely spaced eyes, and viewed from the side, the Fuller rose beetle's snout is less sharply pointed to the ground than that of the vegetable weevil.
The Fuller rose beetle has one generation a year. Eggs are laid in a mass of several dozen on fruit, especially underneath the button, or in cracks and crevices in the tree. When eggs hatch, larvae drop to the ground and live in the soil where they feed on roots of citrus for 6 to 10 months. They pupate in the soil and the adults emerge 1.5 to 2 months later. Peak emergence is July through September, but adults emerge from the soil year-round (in the San Joaquin Valley, roughly 4.3% emerge in June, 14.5% in July, 53% in August, 17.3% in September, 3.7% in October, 2.6% in November, 2.8% in December, and 1.9% for the combined months of January through May). Adults are flightless and reach the canopy by climbing up the trunk or branches that touch the ground or vegetation.
The beetle itself does not generally cause economic damage in citrus but the presence of viable eggs on fruit exported to other countries such as Korea can be a quarantine concern. Since Fuller rose beetle has been found in Japanese citrus groves, it is no longer a concern for fruit exported to Japan.
Fuller rose beetle adults feed along the margins of citrus leaves, creating notches and leaving a characteristic sharp, ragged appearance. Normally, they are not a concern except on topworked trees where the beetles will feed on new buds or if a young tree is planted in a mature grove and beetles concentrate their feeding on the new growth of that tree.
If management of Fuller rose beetles is necessary because it has become a quarantine concern there are two management strategies explained in Monitoring and Treatment Decisions below that incorporate cultural and chemical control methods: season-long local suppression and treatments to prevent egglaying close to harvest.
The internal egg parasite, Fidiobia citri, can parasitize up to 50% of each egg mass. Parasitized eggs are a dark gold color during the parasite's larval stage and a few may persist long after unparasitized eggs have hatched. Once the parasite pupates, the egg appears dark black for several days prior to wasp emergence. While parasites assist with control, they do not reduce Fuller rose beetle numbers enough to enable fruit to be exported to quarantine countries.
If Fuller rose beetle has been a problem in your orchard in the past, one strategy is to prevent the flightless adults from reaching the canopy by using skirt pruning combined with trunk treatments. Skirt pruning by itself is somewhat effective in reducing the number of beetles that will produce eggs several weeks after feeding on citrus foliage. Skirt prune trees 24 to 30 inches above the ground to prevent adults from reaching the canopy and apply a sticky material to the trunk. Sticky material can be expected to last 2 to 10 months, depending on wash-off by sprinklers and the amount of dirt and leaf contamination. Sticky material will also control ants, and if it contains tribasic copper sulfate, it is effective against brown garden snail as well.
Some concern has been expressed regarding the application of sticky polybutene materials directly to the trunk of citrus trees, especially if multiple applications are applied to the same area of the trunk. The sticky material can be applied on top of a tree wrap but this is both laborious and expensive. Trials to date have failed to show serious phytotoxicity (minor bark cracking has been seen in a very small number of cases) except in situations where damage is associated with sunburn—that is where the banded area is exposed to direct sunlight. This is especially a concern on topworked trees or on young trees that have a very thin cambium layer and are more susceptible to damage. On young or topworked trees, apply sticky materials only on top of a tree wrap to protect the tree from sunburn.
Organically Acceptable Methods
Biological and cultural controls, including the application of sticky materials are acceptable organic methods.
Monitoring and Treatment Decisions
Calculate degree-days for fuller rose beetle in your location.
Learn to use degree-days to time insecticide applications.
If fruit may be exported to countries prohibiting fruit with unhatched Fuller rose beetle eggs, sample the orchard starting in June. Previous-year damage to foliage low and inside the tree canopy provides past evidence of Fuller rose beetle. Current-year numbers can be monitored from a minimum of 20 trees per 10 acre block by shaking or beating branches to knock adult beetles onto a sheet or tray. The next step is to conduct either season-long local suppression or treatments to prevent egglaying close to harvest.
Season-long local supression: the goal is to reduce the population by (1) skirt pruning, (2) trunk treatments with sticky materials, and (3) season-long suppression with foliar insecticide sprays applied every 30 to 60 days during June through October. Continue to sample the orchard on a monthly basis for adults to determine if the control methods have been successful and sample fruit near harvest to make sure they are free of viable eggs. A substantial reduction in beetle numbers may take several years. It is helpful to combine skirt pruning with one or more of the other strategies (trunk treatment and/or foliar insecticide sprays) to improve effectiveness, as skirt pruning alone only reduces Fuller rose beetle numbers by roughly 30%.
Treatments to prevent egglaying close to harvest: apply 1 to 2 foliar insecticide applications 600degree-days (accumulated above the 51°F lower threshold) before harvest to kill adults that would lay viable eggs at harvest.
Typical degree-days per month above the Fuller rose beetle egg development lower threshold of 51°F. Modified from Morse, J.G. and K.R. Lakin 1987 (A degree-day model for Fuller rose beetle, Citrograph 72(11): O-P).
Weather data were obtained from UC IPM Online (UC Statewide IPM Program) at http://www.ipm.ucdavis.edu/WEATHER/index.html. The above data are EXPECTED degree-days each month of the year for the indicated location based on average weather data over the past 30 years.
* For Lindcove and Porterville, data were based on average weather data for two nearby weather stations for a total of 25 and 29 years respectively.
With this treatment strategy, only unhatched eggs (eggs deposited before the 600 degree-days point in time) are present at harvest. For example, if harvest was at the end of January, insecticide applications to prevent adults from laying eggs that would be viable at that time would need to start in early to mid-November in Riverside and Ventura counties, and in early October in Kern and Tulare counties. The eggs laid prior to these treatments would have 600 degree-days to complete their development and hatch before harvest.
Skirt pruning and trunk treatments would improve the efficacy of these treatments by lowering the overall population. Examine eggs on fruit to determine if these treatments were successful in eliminating the presence of unhatched eggs.
Just before harvest, sample fruit for egg masses, especially in the areas where adults were found during branch shaking or feeding damage was observed.
For fruit to be shipped to a country that requires fruit free of unhatched Fuller rose beetle eggs, infestation levels should be less than one fruit infested with a viable, unhatched egg per 500 fruit sampled at harvest.
UC IPM Pest Management Guidelines:
Insects, Mites, and Snails
Acknowledgments for contributions to Insect, Mites, and Snails: