How to Manage Pests
UC Pest Management Guidelines
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 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 (very high 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.
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 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 the past, an important component of the strategy to prevent the flightless adults from reaching the canopy is using skirt pruning combined with a 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.
Organically Acceptable Methods
Biological and cultural controls, including skirt pruning and the application of sticky materials are acceptable organic methods.
Monitoring and Treatment Decisions
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 season-long insecticide suppression to prevent egg laying close to harvest.
Season-Long Local Suppression
The goal is to reduce the population by skirt pruning combined with one or more bifenthrin ground (soil) or trunk sprays,or foliar insecticide sprays applied during the period of time when adults might lay eggs that remain viable at harvest. In the San Joaquin Valley, more than 50% of the beetles emerge from the soil in August so that is a key month for control. Apply a ground or trunk bifenthrin spray before peak emergence (June or July). 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):
A substantial reduction in beetle numbers will likely take several years with two to three treatments 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.
Skirt Pruning and Ground (Soil) or Trunk Sprays
To reduce egg laying on fruit, skirt prune trees to a height of 24 inches or more by late May and apply repeated 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 with a weed or other sprayer 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 trunk sprays with a shielded sprayer or with a home-built U-shaped hand wand.
Treatments to Prevent Egg Laying Close to Harvest
If skirt pruning and ground or trunk sprays have not been fully effective (adults are laying eggs under the button of the fruit) also apply one or two foliar insecticides during the period 600 degree-days (accumulated above the 51°F lower threshold) before harvest to kill adults that would lay eggs that would be viable (unhatched) at harvest.
Typical degree-days per month above the Fuller rose beetle egg development lower threshold of 51°F.
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.
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. Sample a minimum of 500 fruit in a 10 acre block (5 fruit per tree from 10 trees per acre).
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
E. E. Grafton-Cardwell, Entomology, UC Riverside and Kearney Agricultural Center, Parlier
Acknowledgments for contributions to Insect, Mites, and Snails:J. Barcinas, E.S.I., Corona, CA
R. Dunn, Badger Farming Co., Exeter, CA
J. Gorden, Pest Management Associates, Exeter, CA
H. Griffiths, E.S.I., Corona, CA
D. Machlitt, Consulting Entomology Services, Moorpark, CA
C. Musgrove, retired entomologist, Riverside, CA
K. Olsen, S & J Ranch, Pinedale, CA
T. Roberts, E.S.I., Corona, CA
T. Shea, UC Cooperative Extension, Riverside County
J. Stewart, Pest Management Associates, Exeter, CA
P. Washburn, Washburn & Sons Citrus Pest Control, Riverside, CA