[From the August 2016 issue of the UC IPM Green Bulletin]
A new psyllid pest that causes a distinctive, tight, typically complete rolling of leaves (Figure 1), has been found on Ficus microcarpa (Chinese banyan, Indian laurel fig) in Los Angeles, Orange, San Bernardino, Ventura, San Diego, and Riverside counties. This species of Ficus is one of our most common, useful, and widespread ornamental landscape trees. Incidentally, it has also long been a target for numerous exotic pests.
The psyllid, identified as Trioza brevigenae and tentatively named the Ficus Leaf-Rolling Psyllid (FLRP), was discovered in February 2016 south of Los Angeles in Carson, California and appears to have spread rapidly among the six counties listed above. It has only been observed on Ficus microcarpa (sometimes incorrectly called F. nitida or F. retusa).
Damage
Rolled leaves, though brittle, remain green throughout, although other pests, such as Josephiella microcarpae (the leaf gall wasp) and various mealybug species, might be present and may discolor or further deform them.
The rolled leaves could be mistaken initially for damage from Gynaikothrips ficorum (the Cuban laurel thrips), which creates a gall by folding the leaf blade adaxially (upper surface) along the rachis. However, careful observation will quickly show the distinct difference between the rolled leaf (caused by the FLRP) and folded leaf (caused by Cuban laurel thrips).
Description and Identification
Peeling back the rolled leaf blades typically reveals various developmental stages of FLRP nymphs (Figure 4). Early instars are 1–2.5 mm long, oblong, dark grayish-tan initially, changing to brownish and then brownish-green.
Advanced nymphal instars have skirts of long, white, waxy filaments at cranial and caudal parts of their bodies (Figure 5). Wing pads are typically visible in later developmental stages.
Cast skins of the final instar FLRP nymphs from which the adults have emerged are often seen attached to the leaves. Also, small, oval, mostly orange-colored nymphs embedded in leaf tissue on the outside of the roll and observable to the naked eye are likely very early instars of the FLRP, although we have not confirmed this possibility.
The FLRP exhibits two peculiar behaviors. In one (the more common of the two observed), an individual psyllid sits on a leaf blade or perches on the margin of a rolled leaf, raises its abdomen until it is at about a 45-degree angle (Figure 8), and then moves it from side to side like a dog wagging its tail. In another, it extends one wing until it is at a right angle to the body, then waves it back and forth while walking.
Management
One management strategy likely warranting evaluation includes vigilant scouting followed by judicious and immediate removal, bagging, and disposal of shoot tips with infested leaves.
Frequent, periodic pruning, as is done for hedges and topiary, might also be an effective management technique by constantly removing infested leaves. Such regularly pruned Ficus specimens have frequently been observed with less damage from foliar pests such as the leaf gall wasp, Indian laurel thrips, and the FLRP. Timing of such pruning, though, might be critical; if possible and practical, time pruning so that resulting new growth appears at a time when FLRP activity is low, typically during the cooler months.
The practices listed above could be combined with insecticidal treatment for noteworthy and valuable tree specimens, although no pesticides have yet been tested specifically for FLRP. In these special cases, soil applications of imidacloprid or similar materials applied to the soil might be beneficial.
—Gevork Arakelian, Entomologist, Los Angeles County Agricultural Commissioner/Weights & Measures, garakelian@acwm.lacounty.gov
—Linda M. Ohara, Biology Sciences Lab Technician, El Camino College, lohara@elcamino.edu
—Cheryl Wilen Wilen, Area IPM Advisor, UCCE San Diego, Orange, and Los Angeles counties, cawilen@ucanr.edu
—Surendra K. Dara, Affiliated IPM Advisor and Strawberry and Vegetable Crops Advisor for UCCE, Ventura, Santa Barbara, and San Luis Obispo counties, skdara@ucanr.edu
Read the full article, originally published in the eJournal PalmArbor at http://ucanr.edu/sites/HodelPalmsTrees/files/242336.pdf.
/h3>/h3>/h3>/span>[From the April-May 2016 issue of the UC IPM Green Bulletin]
A downy mildew caused by the fungus Peronospora mesembryanthemi has recently been confirmed by the USDA-APHIS from a red apple ice plant (Aptenia cordifolia) sample collected in San Diego. Since this first finding in San Diego County in summer 2015, the disease has spread to Orange, San Bernardino, and Ventura counties and is now found in the Goleta area in Santa Barbara County.
Peronospora mesembryanthemi was first reported from South Africa and later in the United Kingdom and New Zealand, but has never before been reported in North America. The host range of P. mesembryanthemi is thought to be limited to ice plants, and in California it is currently found infecting the red apple ice plant, trailing ice plant or pink carpet (Delosperma [= Mesembryanthemum] cooperi), and Lampranthus spp. These ice plant species are all native to southern Africa.
Pathogen
Downy mildew appears as a mat of grey, blue, or brown fungal growth on the undersides or sometimes on both sides of leaves and other infected plant parts. Fungal growth consists of the asexual fruiting structures known as sporangia that are produced on sporangiophores, which are specialized hyphae.
Downy mildew fungi cause systemic infection and grow internally in all plant parts. Infection rapidly spreads under cool and wet conditions. Windblown rain or sprinkler splashing help disperse sporangia and aid in the disease spread. Downy mildew fungi are obligate parasites of plants and most of them have a narrow host range of one or just a few hosts.
Damage
Management
There are relatively few fungicides effective against oomycetous fungi, and control can be very difficult. Since most of the fungicides available inhibit rather than kill the fungal growth, treatments against P. mesembryanthemi only suppress the fungus; systemic infections cannot be cured.
Downy mildew fungi evolve very quickly to form new races and can rapidly develop fungicide resistance. Good cultural practices and sanitation can prevent or minimize downy mildew of ice plants.
Prune plants regularly and remove weeds to improve air circulation and reduce fungal growth.
- Avoid overhead irrigation during cool weather.
- Consider watering in the morning hours so that plants dry during the day.
- Do not over- or under-fertilize as it may increase the chances of infection.
- Monitor highly susceptible species like the red apple ice plant and remove and destroy plants with symptoms of infection.
- Consider other non-host plants as ground covers when replacing diseased ice plants.
—Heather Scheck, Santa Barbara Agriculture
Commissioner's Office, hscheck@agcommissioner.com
—John Chitambar, California Department of Food
and Agriculture, jchitamb@cdfa.ca.gov
—Surendra K. Dara, UCCE Santa Barbara, San Luis
Obispo, and Ventura counties, skdara@ucanr.edu
This article was modified from the original at ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=20558