Fuller Rose Beetle

Adult Fuller rose beetles are brown, flightless snout beetles and are all females that reproduce without mating (parthenogenetically). 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 or longer. They pupate in the soil and the adults emerge 1.5 to 2 months later.

In the San Joaquin Valley, peak emergence is July through September (highest emergence in August), 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). In Southern California, emergence is delayed about a month from that in the San Joaquin Valley and is a bit more spread out with peak months being July through November (very high August through October). Adults are flightless and reach the canopy by climbing up the trunk or branches that touch the ground or vegetation.

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.

The beetle itself does not generally cause economic damage in citrus. However, Korea the presence of viable eggs on fruit exported to Korea is quarantine concern

Fuller rose beetle management is necessary if the fruit may be exported to Korea.

Countries that do not have the pest enforce quarantine regulations to prevent its entry, requiring minimal or negligible pest numbers on incoming fruit. As of October 2025, Korea is the only quarantine country for Fuller rose beetle, and it was formerly a quarantine pest for Japan.

There are two management strategies explained in Monitoring and Treatment Decisions below that incorporate cultural and chemical control methods: Season-Long, Local Suppression and Insecticide Application to Prevent Egg Laying 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 previous seasons, an important component of the strategy to prevent the flightless adults from reaching the canopy is using skirt pruning. Organic growers may want to combine skirt pruning with a sticky trunk barrier.

Skirt pruning by itself is about 30% 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 and apply a sticky material to the trunk to prevent adults from reaching the canopy.

Sticky material or spray 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 on mature trees 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, as with topworked trees. Young trees 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.

Use biological and cultural controls, including skirt pruning and the application of sticky materials in certified organic crops.

Adult Monitoring

If fruit may be destined for countries prohibiting fruit with unhatched Fuller rose beetle eggs, sample the orchard starting in June. Previous-year’s damage to foliage low and inside the tree canopy provides 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. If low Fuller rose beetle numbers are found in a grove, and it is likely fruit will go to Korea, apply insecticides two to three times per year (discussed in Season-Long, Local Suppression) to suppress Fuller rose beetle numbers.

Season-Long, Local Suppression

The goal is to reduce the beetle numbers by skirt pruning combined with one or more bifenthrin ground (soil) or trunk sprays, or foliar insecticide sprays applied while adults might lay eggs that will be viable at harvest. Ground sprays are most effective against adults as they emerge from the soil. Foliar applications are useful for targeting adults that survived ground sprays, or if no ground sprays were applied.

In the San Joaquin Valley, August is a key month for control because more than 50% of the beetles emerge during that month. Apply a ground or trunk bifenthrin spray before peak emergence (June 1 to July 15). Foliar sprays are more important to apply August through October after peak emergence, because the eggs deposited earlier in the season hatch before harvest.

When practicing season-long suppression, follow these guidelines in the San Joaquin Valley (in Southern California, a similar strategy should be used but applications should be applied one month later):

• If three insecticide applications are planned, they should be applied in June or July (soil), late August to September (foliar), and October (foliar).
• If two insecticide applications are planned, then apply a ground (soil) or foliar spray in August and a foliar spray in October.

In recent years, researchers and growers have observed that the Fuller rose beetle population in the San Joaquin Valley is at a historically low level, particularly in orchards that follow the Fuller rose beetle management program for multiple seasons. Because Fuller rose beetle is flightless and only has one generation per year, the likelihood of population outbreak is low.

Growers who ship fruit to Korea now have the option to incorporate grove sampling in their program and, if no beetles are found, they can skip one or both foliar applications (see Voluntary Sampling Program for Fuller Rose Beetle). A substantial reduction in beetle numbers will likely take several years with two to three applications per year. It is essential to combine skirt pruning with one or more of the other strategies (ground sprays, trunk sprays, foliar insecticide sprays, or a combination of these) to improve effectiveness.

Voluntary Sampling Program for Fuller Rose Beetle

Protocols have been established for growers to export fruit free of Fuller rose beetle eggs. For information on current protocols see the California Citrus Quality Council (CCQC) website. (Contact the California Citrus Quality Council to receive the password to access the pages.) Be sure to read over all conditions and recommendations as protocol is revised annually.

Starting in the 2025/26 season, growers can choose from the three options below. Options 1 and 2 allow for fewer insecticide treatments when the treatment threshold is not reached, (three or fewer trees with Fuller rose beetle present when following the recommended sampling protocol).

• Make one ground application with bifenthrin between June 1 and July 15, in combination with the sampling protocol (new option). If the treatment threshold is not reached, the grower can skip two foliar applications for that season.
• Sample, and if the treatment threshold is not reached, make only one foliar application by October 31 (skip the first foliar application).
• If no sampling is done, make two foliar applications, first by September 7 and the second by October 31.
• If the treatment threshold is reached, two foliar applications are required.

Fuller Rose Beetle Sampling Protocol

Conduct sampling between August 7 and August 31, coinciding with the peak period of adult emergence. To accurately assess Fuller rose beetle infestation levels, follow the sampling procedure:

• Divide each block into 4 quadrants. Randomly select and sample 18 trees in each quadrant, totaling 72 trees per block (regardless of block size).
• Examine suckers inside each tree for signs of Fuller rose beetle leaf chewing. Record any beetles found. If no beetles are found internally, shake two large exterior branches over a light-colored cloth and inspect. Any presence indicates infestation.
• Maintain records of the block ID, inspection date, name of inspector, and number of infested trees out of 72 sampled.

Stop sampling as soon as thee or more trees with Fuller rose beetle infestation are found. Once the treatment threshold is reached, growers must follow Option 3 which requires two foliar applications.

Skirt Pruning and Ground (Soil) or Trunk Sprays

To reduce egg laying on fruit, skirt prune trees to a height of a 24 inches or more by late May and apply bifenthrin ground or trunk sprays starting in early June (San Joaquin Valley) or July (Southern California). Monitor the orchard every 4 to 6 weeks and remove weeds growing upward or branches and suckers bending downward that beetles can use to access the tree.

Apply bifenthrin to the ground using low pressure so the spray does not splash on fruit. Cover the entire area under the tree canopy from the trunk to the drip line. Consult the insecticide label for details. Apply ground or trunk sprays in a way that prevents spray from reaching fruit:

• Use low pump pressure and a shielded sprayer so the insecticide does not splash onto the foliage or fruit.
• Do a test application with water only to determine the amount of solution that is needed per acre for thorough coverage of the soil under the tree or trunk and to make sure the spray does not contact foliage or fruit.
• Keep the solution thoroughly mixed during application.

Insecticide Application to Prevent Egg Laying Close to Harvest

Fuller rose beetle eggs require approximately 600 degree-days (above 51°F) after being laid to hatch. (Degree-days are a measurement of the number of heat units that have accumulated above a threshold and are used to predict insect development.)

Any eggs deposited more than 600 degree-days before harvest will have enough time to hatch prior to harvest, which is relevant because egg shells do not require quarantine, only viable eggs. In contrast, eggs laid within 600 degree-days of harvest will not hatch before harvest, and will remain viable on the fruit.

If skirt pruning and ground or trunk sprays have not been effective, and the treatment threshold is reached, apply one or two foliar insecticide sprays during the period 600 degree-days before harvest. These sprays are to kill adult beetles and prevent them from laying eggs that are viable (unhatched) 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 insecticide applications would have had the required 600 degree-days to complete their development and hatch before 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.)

To learn more about how to use degree-days to time insecticide applications, see Using Degree-Days to Time Insecticide Applications in Fruit and Nut Orchards. For assistance in calculating degree-days for Fuller rose beetle in your location, see Pest and Plant Models for Fuller Rose Beetle in Citrus.

Examine eggs on fruit to determine if these insecticide applications were successful in eliminating the presence of unhatched eggs.

Egg Monitoring

Just before harvest, sample fruit for egg masses, especially in the areas where adults were found during branch shaking or feeding damage was observed. Sample a minimum of 500 fruit in a 10-acre block (5 fruit per tree from 10 trees per acre).

• Select fruit at chest height from a different quadrant of the canopy.
• Clip the stem 2 inches from the fruit, then hold the stem and twist off the button.
• Look for egg masses on the underside of the button and on the fruit where it was covered by the button.

For fruit to be shipped to a country that requires fruit be 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.

• Degree-day calculator
• Degree-day table
• Using degree-days to time insecticide applications