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Peacock Spot Update - By Paul Vossen UCCE - 4/04/2004 Timing Sprays for Control Peacock Spot and Olive Knot Disease from Olive News University of California Cooperative Extension Glenn County Nov 4, 2003 Preventing Olive Leaf Spot and Olive Knot Disease

Peacock Spot Update - By Paul Vossen UCCE - 4/04/2004

I have been visiting a lot of orchards this spring with severe leaf yellowing and leaf drop caused by Peacock Spot. The culprit is an organism called Spilocaea oleaginea. This is a fungus disease that just happened to love our frequent rains last November and December. Now we are seeing the symptoms of yellow leaves, spotting, and leaf drop - see the photo below. It normally causes dark spotting with a halo around each spot, but sometimes the leaves just turn yellow and fall off too. Another leaf defoliating organism called Cercospora cladosporioides (Mycocentrospora cladosporioides) is also a fungus that has been isolated from orchards on the north coast of California. Cercospora causes black sooty-mold-like symptoms on the undersides of the leaves, yellowing, and leaf drop, but no spots. The two diseases develop under very similar conditions. The only orchards that I have seen without yellow leaves this spring are those that had been sprayed with copper early.

These diseases are particularly important since they cause leaf drop and partial defoliation of branches, which weakens the trees and reduces crop set. Olive trees store most of their energy in their leaves. Defoliation will result in less shoot growth, decreased fruit set, and poor flower bud formation for the following year. With the high level of inoculum in the orchards from these infections, the likelihood of more disease is increased if we get early fall rains that will spread it to this year’s new shoot growth. The more it rains the more peacock spot and leaf drop you will see, if it does not rain, you won't see it. Another wet winter means big trouble, unless it is controlled.

You can’t do anything to control it in the summer, but an application of fixed copper fungicide as early as possible after harvest and hopefully before most of the fall rains, is essential for good control. Complete coverage is necessary too. That means using a power sprayer with high pressure to cover the leaves on both sides, especially in the interior of the tree.

Infection occurs in the fall with temperatures between 35F and 80F, but its optimum temperature is 58F to 75F. All it needs is about 48 hours of free moisture for the germinating spores to infect the leaf and cause significant disease. The warmer the temperature, up to about 75F, the shorter the time necessary for infection to occur and it can be as little as 14 hours. Both old and young leaves are susceptible and most varieties are susceptible, yet there are some differences. Winter and spring infections can occur too if there is continued rainfall, so in wet areas or when disease pressure is high, a second preventive application should go on about late February.

This disease is not significantly affected by tree nutrition and the only control we know for sure that works is covering the leaves with fixed copper sprays as a protectant. Compost tea does not work. The sprays should be applied before major fall and winter rains have a chance to spread the spores to the new leaves. The catch is that fixed coppers must not be applied to the fruit near harvest. It is difficult to wash off; in fact it is designed to not wash off. You absolutely do not want to get any copper residue into the oil.

Since the fall rains usually come prior to harvest this leaves orchards open to infection. Oil olives that are harvested late (November to January) may get rained on several times before they can be protected. The best that can be done is to get the application of fixed copper on immediately after harvest. If the orchard is non bearing, it can be sprayed any time. Fixed coppers come in various formulations of cupric hydroxide, copper oxychloride, tribasic copper sulfate, and copper oxide. Some are legally classified as organic minerals.

The key to controlling this disease is to never let it get out of control. There may be those years when we get a lot of rainy weather prior to or during harvest – that is when you will wish you had very little of this disease to spread around and get worse. Maintaining a low inoculum level should be your primary concern. inoculate

Timing Sprays for Control Peacock Spot and Olive Knot Disease from Olive News University of California Cooperative Extension Glenn County Nov 4, 2003

Timing Sprays for Control Peacock Spot and Olive Knot Disease Copper fungicides are recommended for control of olive leaf spot (peacock spot) and olive knot disease. To be most effective for control of peacock spot, copper sprays must be applied before significant rains occur in the fall, while research has shown that the greatest amount of olive knot infection occurs in the spring coinciding with natural leaf drop and that spring sprays (March-April) are more efficacious for control of olive knot than fall sprays. Therefore, two sprays are recommended, fall for leaf spot and spring for peacock spot. If, under the current economic conditions, you feel that you can only afford one spray, then I recommend that you decide which disease is more problematic in your orchard and then time your spray accordingly. Of our common table varieties, Mission is by far the most susceptibleto leaf spot followed by Manzanillo and then Sevillano, Ascolano and Barouni. If left uncontrolled in Mission trees, leaf spot can build up and increase disease pressure on nearby Manzanillos and Sevillanos. Manzanillo is by far the most susceptible to olive knot, followed by Sevillano then Mission, Ascolano and Barouni. Delay pruning varieties which are susceptible to freeze injury and olive knot (Manzanillo and Sevillano) until the spring after the threat of freezing temperatures and rain is diminished. Pruning opens tree canopies and makes them more susceptible to freeze injury. Pruning wounds are susceptible to olive knot infection for up to 14 days.

Olive Leaf Spot, also known as Peacock Spot, is caused by the fungus Spilocaea oleaginea. Wind and rain move spores from holdover lesions to new infection sites. Symptoms, dark green to black spots sometimes surrounded by a yellow halo, defoliation and twig death, develop in the spring. Of the common varieties in the Sacramento Valley, Mission is the most susceptible. Olive leaf spot is controlled by the application of copper fungicide before heavy rains begin in the fall. Research by UC Researchers Beth Teviotdale and Steve Sibbett during the eighties and early nineties showed the following. All of the fungicides tested (Bordeaux, Kocide, Nordox, Microcop and Copper Count N) performed equally. In any one year one copper treatment applied prior to winter rains (Nov.) was as effective as two sprays (Nov. and Jan.).However, where the double spray was used consistently year after year, long term disease infection was suppressed. Treatment differences were still apparent three years after all of the trees were returned to the same treatment indicating the role of consistent control programs in disease suppression.

Olive Knot disease is caused by Pseudomonas savastonoi bacteria which are spread about by wind and rain and get into trees through openings such as leaf scars, pruning wounds and frost cracks. The “knots” which are disorganized tissue, which can girdle and kill twigs and branches, develop in the spring. Of the varieties commonly grown here, Manzanillo is the most susceptible. Research that UC Plant Pathologist Beth Teviotdale and I have been conducting the last several years has shown the following. Copper resistance by the bacteria is limited. The majority of infection occurs in the spring, coinciding with the period of natural leaf drop. Efficacy of fall-applied copper treatments declines by March or April. Multiple treatments are more effective than single treatments. In our studies, two sprays were more effective than one and three were more effective than two.