David Doll7 CommentsMarch 17, 2017Diseases

Bacterial Canker and Blast

Over the past few weeks, there have been a high frequency of problems reported with bacterial canker and blast. Bacterial blast results in blighted blossoms and causes crop loss. Interestingly, when there is a high frequency of blast, the very similar disease of bacterial canker appears a few weeks later in young trees(we are starting to get reports of canker now). Both of these problems are complicated. They involve the bacterium Pseudomonas syringae, plant stress which is often mediated by nematodes, and the weather. P. syringae is an interesting bacteria. It lives naturally on plant surfaces as an epiphyte – meaning that it generally does not cause problems. During wet winters which create a favorable environment, bacterial populations increase and spread through the tree and orchard. At some point the population becomes large enough that it begins to invade plant tissues – starting with buds (bud drop), then flowers (blast), and finally bud scars and other openings which leads to bacterial canker. Tree health has a lot to do with the susceptibility to P. syringae infection. Generally, if the tree is healthy, infections rarely occur. Weak, young trees- usually three years or less- are susceptible to bacterial canker which can cause the loss of tree scaffolds or death. Mature orchards usually don’t exhibit bacterial canker symptoms, but rather have blast and bud drop problems. Orchards with severe problems are typically planted in sandy soils, which often tend to be acidic, hold less water and nutrients as well as being more conducive to plant parasitic nematodes. All of these factors, if managed improperly, can increase tree stress, increasing susceptibility. Some micronutrient deficiencies, notably iron, have been found to increase susceptibility, while balanced, proper major nutrient fertilization has been shown to reduce occurrence.  Severe water stress can also increase occurrence, and is thought to be due

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David Doll12 CommentsApril 25, 2015Diseases

Managing Phytophthora within Almond Orchards

I have been in several orchards this year which have been determined to have Phytophthora Crown Rot. This disease is aggressive and can cause rapid decline of any aged tree. Conditions that favor disease include excessive periods of saturated soils and cooler temperatures, which are common in the late winter and early spring. An infected tree can be identified by a rapid collapse of the canopy and the observation of a canker extending from the soil. Often, when soil from around the crown is removed, the canker can be observed. The occurrence of Phytophthora has becoming more common over the past few years. Reviewing my records over the past 7 years, farm visits regarding Phytophthora disease diagnosis and management were around 3 per year. Over the past two years, I have seen a 133% increase in annual visits. My notes suggest that this is due to lower quality of soils in which orchards are planted, poor selection of rootstocks for these soils, and mismatched irrigation scheduling for the soil type and tree size. In managing this problem, the industry has relied on several cultural and chemical control methods. Below are a few of the cultural practices, chemical management, and problems/concerns regarding Phytophthora root and crown rot. More information can be found at the UC IPM website. Rootstock selection. More peach-almond hybrid rootstocks are being planted in new orchards. These rootstocks are more vigorous and tolerant of toxic salts, but are susceptible to Phytophthora. In general, plum parentage rootstocks (e.g. Marianna-2624) are the most tolerant. Peach rootstocks, which include Nemguard and Lovell are moderately tolerant, while other complex hybrids (Viking and Atlas) have demonstrated some tolerance in greenhouse tests. Peach-almond hybrids (e.g. Hansen 536) are the most susceptible. Newer rootstocks remain untested (e.g. Krymsk-86, Empyrean-1, etc). In some cases, varieties are being planted on different

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Joe Connell2 CommentsNovember 20, 2011Horticulture

Observations of Krymsk-86 Rootstock

Written By Joe Connell, UCCE Farm Advisor, Butte County Krymsk 86 is a peach-plum hybrid rootstock (Prunus persica x P. cerasifera) that originated in the Krasnodar region of Russia. As such, this hybrid rootstock is different than any other rootstock in use in the California almond industry. Now that it is planted in commercial orchards under many different conditions we are learning more about how it behaves when grafted to almond. When grafted to peach, plum, or apricot it is thought to be tolerant of cold temperatures, drought, water logging, resistant to phytophthora, and somewhat resistant to lesion nematodes. It was observed to be precocious, productive, and appeared to increase fruit size. Now that it is grafted to almond in California we are discovering that trees behave differently than almond grafted on peach rootstocks and differently than almond grafted on Marianna 2624 plum. In fact, it behaves uniquely like almond grafted on Krymsk 86. The first trial in Butte County including this rootstock was planted in 2003. Just completing their ninth growing season, the Nonpareil trees on Krymsk 86 are larger than adjacent trees on Lovell peach. What we know so far is that Krymsk 86 appears to be compatible with almond and it has a vigorous root system with good anchorage as a young tree. Krymsk 86 roots are susceptible to root knot nematodes and this will limit its usefulness in the San Joaquin Valley and on light textured soils where root knot can be a problem. In sandy soils in Stanislaus County, trees on Krymsk 86 are less vigorous than trees on peach roots. In spring 2011, soils were wet and cold for an extended period causing trees to get a slow start. Several young orchards had yellow trees showing up on Krymsk 86. Trees were yellow for

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Roger Duncan2 CommentsNovember 30, 2010Horticulture

Rootstocks for California Almond Orchards

Roger Duncan, University of California Cooperative Extension in Stanislaus County Joe Connell, UC Cooperative Extension in Butte County John Edstrom, UC Cooperative Extension in Colusa County Nemaguard has been the main rootstock of the California almond industry for many decades.  It is well adapted to the well-drained, non-calcareous loam and sandy loam soils common throughout the San Joaquin Valley.  Nemaguard is vigorous, immune to rootknot nematode, compatible with all almond varieties, doesn’t sucker much, has decent anchorage, and is easy to grow at the nursery.  Never-the-less, there are many situations in which nemaguard struggles.  Nemaguard, as with most peach rootstocks, is prone to lime induced chlorosis (yellowing / iron deficiency) in high pH soils.   It is also susceptible to salt toxicity (sodium, chloride & boron), “wet feet”, Phytophthora root rot, oak root fungus, crown gall and “heart rot”.  Despite the name “nemaguard”, this rootstock is susceptible to ring and root lesion nematodes.  The susceptibility to ring nematode leads to the danger of bacterial canker in orchards replanted into sandy soil.  Since 1998, UC Cooperative Extension farm advisors in Kern, Stanislaus, San Joaquin, Colusa and Butte Counties have researched several alternative rootstocks for California almond growers.  These include most of the common, commercially available rootstocks in California along with many newly available rootstocks from other countries.  While there is no such thing as the perfect rootstock, there are better choices than nemaguard where many chemical or physical soil problems exist.  Below are some suggestions for specific challenging situations. Heavy soil / poor drainage.  Nemaguard is not adapted to poorly drained soils and can become yellow, stunted or even die from lack of oxygen.  Lovell, another peach seedling rootstock, is not much better.  As a group, plum rootstocks are pretty tolerant to heavy soil.  Marianna 2624 has traditionally been the rootstock of

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