PNW Plant Disease Management

09/26/2024

Question: Landowner with one mature aspen in their yard. It took some damage and was weakened by last year's ice storm but has otherwise been healthy. A few days ago, they started finding these unique looking leaves on the ground. The leaves are crisp. The only thing that seemed close was Bronze leaf disease, is it?

09/10/2024

With rain in the forecast and active bunch rot in the vineyard, we went ahead and sprayed for Botrytis. A little early to see symptoms but that was due to the last big rain event we had. This fungus likes it wet. Key times to spray are bloom, bunch close, verasion and preharvest. But you should pay more attention to the weather and make applications prior to rain events.

See: Grape ( Vitis spp.) Relative Disease Susceptibility and Sensitivity to Sulfur Cause This disease is common on the west side of the Cascade...

09/06/2024

Question: Client is asking about Asian pear fruit (hosui) cracking. Images they show us indicate the leaves have symptoms of pear trellis rust. Fruit does not show typical rust spots but is coincidental with arrival of rust. Another tree, 20th century, does not show cracking. Have other people observed cracking on Asian pears with trellis rust?

08/21/2024

Question: I have a small vineyard and we are observing a few of our Pinot Noir plants with deformation of the leaves, much like you would expect from pesticides. However, we have not used pesticides. Have you seen this deformity before and is there more evidence of this in Oregon?

08/19/2024

Question: I’ve had a lot of canes die back in my raspberry bed. Almost all of my fall raspberry canes have been affected. I planted these 3 years ago. I have June bearing and fall bearing varieties. I have 2 beds. One bed I cut to the ground last winter and the canes regrew nicely. These are the berries that seem to be most affected. The other bed I cut canes below where they produced berries last year. This bed is affected but not nearly as much.

The top of the canes are dying back and there is healthy growth below where the canes have died. It looks like the cane has a swollen spot but I have not seen any larvae. Is this cane borer?

08/19/2024

Drippy dieback of Alder is something you might see this summer. Not sure what is causing it. This problem has been observed in the Willamette Valley, mostly near Corvallis, OR since the mid-2000s on a few urban landscape trees. Although symptoms are noticed after summer heat stress, dripping cankers occur prior to those events. Diseased tissue is negative for Phytophthora organisms. Many different secondary fungi have been isolated including a Phomopsis sp. The bacteria Lonsdalea sp. has also been isolated from branch cankers.

08/16/2024

Overall, beech diseases are not an important issue in the PNW. The disease known as Beech Leaf Disease, caused by a foliar nematode Litylenchus crenatae ssp. mccannii, found in eastern North America has not been found in the PNW. Beech Leaf Disease symptoms include characteristic banding patterns on the leaves as well as thickening leaves that eventually shrivel and fall off the tree prematurely.

08/05/2024

Visited a vineyard with Esca to see lovely (to a pathologist) red leaves. Chop into the trunk and see the decay and discoloration in the wood. Black gumming in the vascular system were present. Black or amber streaks in the vascular elements are deposits of phenolic compounds in response to wounding, a general plant defense mechanism. These symptoms however can resemble other important diseases of grape including uneven wood maturity as in Pierce's disease, virus-induced incompatibility, and some nutrient deficiencies.

Cause Many fungi have been associated with these diseases, although the cause of esca continues to be disputed. Esca (black measles) is considered a...

07/24/2024

X-disease (Candidatus Phytoplasma pruni) can hit several different stone fruits including peach. Leaves tend to roll; infected tissue becomes necrotic and ultimately drops out in a rather ragged or shothole pattern. Fruit is smaller, lacks flavor, and may shrivel prematurely. Trees typically die in 4 to 8 years. Easily confused with the pear decline phytoplasma which causes peach yellow leaf roll.

07/17/2024

Looks almost like fall with all the fallen leaves blowing around. It is somewhat normal for trees to shed leaves in the summer but a lot came down after the 100+ degree weather. These are usually the leaves that are diseased, stressed, heavily shaded, sunburned, etc..... These leaves are not very efficient and have a cost to the tree. Better to keep the productive ones overall. Shedding too many leaves might indicate a more extensive problem.

Cause Blumeriella jaapii (formerly Coccomyces hiemalis ), a fungus. The disease is particularly severe on sour cherries, but also attacks sweet cherries in western...

07/15/2024

Question: I purchased a twisted version of Larix deciduous pondula from a local nursery. It is still potted in the original nursery pot, I believe about 5 gallon. About two weeks after I purchased, small areas of needles began turning brown, eventually spreading to more areas of the tree. It started in the lower branches and is continuing to move up the tree. I have treated it (sprayed) with copper fungicide twice, and Dr. Jimz Tree Secret fertilizer. I’ve also sprayed it with a seaweed spray to encourage greening, and am thoroughly watering twice a week. I am assuming a fungal disease based on research I have done. At this point, the crown of the tree is mostly green but whatever is wrong continues to spread up the tree. Can this tree be saved and do u have any suggestions for care?

07/10/2024

High temps can mean smog and ozone damage to plants.
Ozone at certain concentrations for certain periods of time can injure sensitive plants. All areas of Oregon currently meet the federal air quality standard for ozone. These levels, however, are based on human health. Sensitive plants can have problems when the ozone concentration is between 50–120 ppb for extended time periods. The most sensitive plants include alder, begonia, blackberry, currant, dahlia, fuchsia, grape, lilac, milkweed, ninebark, Oregon ash, Oregon oak, petunia, poplar (including aspen), radish, sequoia, snowberry, sycamore, tomato, and tulip poplar. For dicots exposed to high concentrations, symptoms may include bleaching, flecking, stippling, and interveinal necrosis. Less severe symptoms can include bronzing, chlorosis, and premature senescence of various plant parts.

Jay W. Pscheidt, Extension Plant Pathology Specialist, OSU There is great interest in air quality all over the Western United States when smoke from...

07/09/2024

Preventing sunburn is best as there is no remedial action that can be taken once leaves are scorched by the sun. Sun or heat related stress will occur primarily on the south side of plants. Lack of water, cankers, excessive salt (fertilizer), and root rot are possible causes. Several days of >100 F weather is likely these days. The bacterium Xylella fastidiosa has been associated with these symptoms in red maple, elm, oak, and sycamore but has never been found in the PNW.

See: Maple ( Acer spp.) - Bigleaf Maple Decline (Bigleaf Maple Dieback) Cause Drought or heat stress may cause leaf scorch. In general, there...

07/08/2024

Hard to keep up with watering in this 100+ degree weather. Even low water users may have trouble depending on how you irrigate. Marginal burning of leaf margins or tips can indicate sun burn or scorch. Wilting is obvious but plants can recover quickly if you catch it in time. Nothing will bring back dead plant parts.

See: Maple ( Acer spp.) - Leaf Scorch Dogwood ( Cornus spp.) - Anthracnose Cause Leaf scorch and leaf roll result from stress. Drought,...