Posts Tagged: fungal
Time to Treat for Peach Leaf Curl
Peach leaf curl is a disease that affects peach and nectarine trees. Although you may not...
It's Time to Prune Apricot & Cherry Trees
Although most fruit trees are pruned during the dormant season, in areas with wet winters, apricots...
Septoria fruit spot is common this year
How to Manage PestsUC Pest Management Guidelines
I have had a number of requests to identify fruit spotting on lemons. It turns out to be Septoria fungus which can show up on leaves, stems and fruit. The key to this is to make sure there is a fungicide on the tree in the fall before the wet weather kicks in
CitrusSeptoria SpotPathogen: Septoria citri(Reviewed 9/08, updated 9/08) In this Guideline: SymptomsEarly symptoms of Septoria spot appear as small, light tan to reddish brown pits on fruit, 0.04 to 0.08 inch (1 to 2 mm) in diameter, which usually do not extend beyond the oil-bearing tissue. Advanced lesions are blackish, sunken, extend into the albedo (white spongy inner part of rind), and are up to 0.8 to 1.2 inch (20 to 30 mm) in diameter. Dark brown to black fruiting bodies often develop in these lesions, which usually do not extend beyond the oil-bearing tissue. The spots are much more conspicuous after the fruit has changed from green to yellow or orange. Small spots may develop into large, brown blotches during storage or long-distance transportation. Septoria citri may also cause similar spotting on leaves or twigs that are weakened by frost or pests. Comments on the DiseaseThe Septoria fungus causes spotting of Valencia oranges, late-season navel oranges, and occasionally of lemons and grapefruit. It occurs in the San Joaquin Valley and interior districts of southern California during cool, moist weather. Infections begin when Septoria conidia are transported throughout the tree by rainfall. The spores germinate with additional moisture from rain or dews and commonly infect cold-injured fruit tissue and mechanical injuries. The damage to the rind lowers the grade of the fruit and results in culling. Septoria spot may be confused with copper injury and other abiotic and biotic agents. ManagementApply a preventive copper spray in late fall or early winter, just before or after the first rain. In years with heavy rainfall, additional applications may be necessary. For California oranges (Navels and Valencias) shipped to Korea:
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septoria
KARE and USDA collaborators visit Israel to learn more about the Polyphagous Shot Hole Borer.
In 2003, the Polyphagous Shot Hole Borer (PSHB) was observed in Southern California. This beetle has a Fusarium sp. symbiont that causes susceptible host tree damage. The PSHB appears to be established in Los Angeles, Orange, and Riverside Counties. In the Los Angeles area, PSHB has attacked over 200 species of native, ornamental and horticultural trees, including the native Coast Live Oak, California sycamore, and about 57% of the commonly used street trees in the area. Avocado trees are susceptible; the beetle and fungus have been found in several backyard avocado trees as well as some commercial avocado orchards in Los Angeles and Orange counties. The PSHB has caused severe damage to commercial avocado orchards in Israel, and is a threat to California’s avocado crop which is worth about $460.6 million and accounts for about 87% of the US production.
To better understand the biology of and potential management strategies for the PSHB Fusarium complex threatening California’s avocado trees, Mary Lu Arpaia, Subtropical Horticulture Extension Specialist in the UC Riverside Botany and Plant Sciences Department and Kearney Agricultural Research and Extension Center, and David Obenland, Plant Physiologist, at USDA-ARS in Parlier, California, visited Israel in March, 2013. The PSHB is an invasive pest in Israel and was found in Israel’s commercial avocado orchards in 2009. The PSHB in Israel is causing serious damage, and Israeli research may help us develop detection and management strategies in California.
Biology and Behavior: A visit with Drs. Zvi Mendel and Stanley Freeman, Israel’s lead PSHB researchers provided insight into research on the biology and behavior of the PSHB Fusarium complex. Drs. Mendel and Freeman contend that even though the beetle uses several tree species as hosts, it is monophagous, only feeding on the Fusarium symbiont. According to their research, the beetle’s reproductive cycle in susceptible trees is: the adult pregnant female beetle bores through a tree’s bark, creates galleries under the bark, infests the galleries with a Fusarium fungal symbiont carried in the adult beetle’s mycangium (a specialized structure at the back of the jaw), and lays eggs in the galleries. Larvae are mostly female. While the larvae develop, the Fusarium sporulates. The developing larvae eat the fungus, develop into adults in about a month, and mate while in the gallery. The pregnant females exit the gallery through exit holes in the bark. To survive, the emerged pregnant female has about 48 hours to find a suitable host location and continue the life cycle.
Hygiene: The geographic area where the beetle is found in Israel appears to be expanding, even though the infested avocado trees in the primary infested area were destroyed. The PSHB is thought to have been transported in bins originating from the infested area. A best practice for California growers and packers will be to use clean bins and ensure that there is no vegetative matter in the bins prior to transport. This practice will also help reduce the spread of avocado thrips and persea mite.
Chemical control of the beetle or the fungus: There has been limited success in controlled lab situations, but field applications are not effective. So far, no effective chemical control technologies have been developed for the beetle.
Infestation: A mature orchard that was infested approximately 5 to 6 years ago became heavily infested within 2 to 3 years, and will be bulldozed. Infestations may require bulldozing orchards.
Detection: Mature avocado orchards with heavy infestation have severe limb dieback, many broken branches littering the orchard floor, dropped mature fruit, abnormally small mature fruit, and sugar exudates caused by the bore holes. A 2-year-old infested orchard did not exhibit very much limb dieback; when infestation of young trees is observed, it is usually on the base of the trunk (found in either the rootstock or the scion wood).
Spread to native and landscape hosts: Israel has seen the spread of the beetle to native oaks and the box elder. California will need to educate the public to help safeguard our native and landscape trees from the spread of the PSHB and Fusarium complex. Native and landscape tree infestations may make it difficult to control the spread of infestations into commercial avocado orchards.
California outlook: California must be diligent in looking for tree infestation. The avocado industry is working with the landscape industry and forestry service in California to understand the rate of infestation and range of susceptible hosts. Funding for surveys; understanding the beetle and fungal biology; developing control strategies, technologies and practices; and basic work on the origin of the beetle is essential. California researchers should collaborate with and learn from their Israeli colleagues.
Avocado tree in Israel with limb breakage and branch dieback due to PSHB infestation and its Fusarium symbiont (photo by M. L. Arpaia).
External symptoms of PSHB infestation, including sugar exudate, bark darkening, and wood staining due to Fusarium infection of the woody tissue (photo by M. L. Arpaia).
PHSB infested avocado branch in later stages of decline. The white larvae are termites that infested the branch after dieback started. Note the staining of the wood and evidence of the PHSB galleries. (photo by M.L. Arpaia)
Fall Treatment for Peach Leaf Curl
Last spring, I noticed that some of the new leaves on my peach tree were distorted. The leaves puckered and curled, then died and fell off. A second set of leaves replaced the fallen leaves and the tree appeared OK. The tree had peach leaf curl (Taphrina deformans). That means that this fall I need to treat the tree so it does not come back in the spring. We did a treatment two years ago and the leaves were OK but I forgot to do it again last fall. Once you have peach leaf curl, it is best to do it every year.
Peach leaf curl is a fungal disease that only affects peach and nectarine trees. Now I need to treat the tree with a fungicide in late fall to prevent leaf curl next spring. Choose a copper-based fungicide, such as tribasic copper sulfate or cupric hydroxide are easiest to use and are most effective if applied with oil. There are several products on the market. Be sure to wait and treat the tree after all the leaves have fallen. When you spray a fungicide, thoroughly cover all branches and twigs so all spores are killed. You may also want to do another treatment in the early spring before any leaves or buds appear. Treatment in the spring after symptoms appear will not be effective.
As with all fungicide applications, be very careful. Wear protective clothing and follow the label directions careful.