Things to watch for during March
From our experience of samples we have received during March in previous years in the OSU Plant Clinic, this page will highlight some problems that may occur this month. The mild winter this year means we are again ahead in terms of plant growth and it may be useful to review this page as well as the April Highlights page.
The cold snap we had during last November is showing its effect now. For example we are seeing blueberries with dying and browning cambium along the length of stems, and darkened buds that do not expand. Secondary pathogens may invade the dead tissue and appear as dark necrotic lesions along stems.
Nutrient management is an important part of growing healthy plants and regular soil testing can identify problems that may be corrected. This article shows how to interpret your soil test results, and also some of the problems that arise when nutrients are out of balance. Requirements for specific crops are available through the OSU Extension Catalog.
GENERAL NOTE: Taking action this month near bud break for many crops (such as lilac, rose, peaches, and hazelnut) with timely disease and pest management programs will reduce the need to watch for things next month and this summer.
Black leg outbreaks continue on crucifer crops growing in the Willamette Valley. It is occurring in canola, specialty crucifer seed crops, and fresh market crucifers fields that have not employed a strict black leg management program starting in the fall. Ascospores are still being released from infected crop residues examined at the end of February. Brassica and radish plantings within several miles (download) of a site with infected crop residues from 2014 or 2015 are at risk for continued windblown ascospore pressure until the weather turns drier. OSU has observed 12 weeks of black leg infections on trap plants, seed fields planted last fall that did not receive at least several applications of effective black leg fungicides are now showing high disease incidence levels. Seed crops with no tolerance for black leg in the seed are at high risk for upper leaf infections once flowering commences; protect the upper leaf canopy with labeled fungicides if possible. Otherwise, remove infected leaves, rogue infected plants, or destroy highly infected fields. Destroy infected fields by multiple flailings, working with a high speed disk, or other method that breaks up the lower stems and upper root portion. Work crop debris into the soil (shallow tillage may suffice when fungicide programs are utilized for future crops), or otherwise remove infected debris from fields, or promote rapid decomposition to minimize presence infected crop residues and protect Brassica crops next fall.
Light leaf spot is re-appearing in a wide range of Brassica crops in the Willamette Valley, including canola and vegetable seeds crops as well as Brassica vegetable fields. Infections began last autumn but plants are asymptotic through the fall as disease remains cryptic till late winter. Disease symptoms are now starting to show on leaves as well as plant stunting. Infections of flowers can prevent seed production so seed crops should be protected from rain-splashed infections on the upper leaves. Vegetable crops that are affected, especially turnip greens, should not be stored long before use; disease symptoms will increase in storage and can become much more severe within a week.
light leaf spot
White leaf spot has shown up in turnip crops and other crucifer seed fields. Management of other leaf spot diseases in crucifers will aid in management of white leaf spot.
Look out for purple blotch on blackberry, caused by a fungus that produces red margined, purple lesions on canes. These lesions can develop into cankers that can girdle and kill the canes during spring. Now is good time to scout for these before leaves come out and hide the lesions.
Anthracnose and perennial canker on apple can be watched for now, especially while pruning. Anthracnose appears on smaller branches, or trunks of young trees, as small brown spots that develop into cankers. Perennial canker, caused by a different species of the same fungus that causes anthracnose, appears as overlapping concentric rings of woody tissue encircling a central wound. Perennial canker is often associated with the presence of woolly apple aphids, low temperature injury, and pruning wounds. Both diseases produce the bull's eye rot symptoms on fruit.
apple perennial canker with woolly aphids (in the cracked bark)
Since temperatures have been so warm recently, aphid populations will be developing higher numbers sooner this season. Grass seed fields scheduled for aphicide applications to control barley yellow dwarf virus should look at earlier timing this season. Past years aphid trapping showed peak populations were reached during May or June, but peak spring populations may occur during March or April of this year. Symptoms of Fall infection of Barley Yellow Dwarf Virus (BYDV) on fescue, rye, wheat and many other cultivated and wild grasses may first appear in the spring as yellowish leaf tips (reddish in oats).
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In greenhouses watch for Impatiens Necrotic Spot Virus, we have had recent samples of Diascia and Lobelia with this virus. Transmitted by thrips, this virus causes discolored, distorted leaves with necrotic spots, as well as stunting.
Greenhouse nurseries should be advised to be on the alert for crown gall (Agrobacterium) during transplanting, and also leafy gall (Rhodococcus). See our resource pages for symptoms of these pathogens on different hosts and host lists.
Damage caused by species of Pseudomonas including Pseudomonas syringae, on woody ornamentals are typically seen at this time of year. Note that Jay Pscheidt says this year he has not seen much Pseudomonas. These bacteria overwinter in diseased twigs or as epiphytes on healthy wood. Tissues that have suffered injury from frost, as well as from pruning, unsuitable soil pH, poor nutrition, or infection by other pathogens, are predisposed to Pseudomonas diseases and exhibit a variety of symptoms.
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see also "The Plant Clinic Year"