David Doll0 commentsAugust 23, 2013Diseases

Almond Replant Problems: Fumigation Trial Results

BACKGROUND Collaborative trials. More than 10 almond replant trials were established under sponsorship of the USDA-ARS  Pacific Area-Wide Program for Integrated Methyl Bromide Alternatives (PAW-MBA).  The trials were made possible through collaboration and in-kind support from USDA-ARS, UC, UCCE, the Almond Board of California (ABC), TriCal Inc., Cal DPR, growers and many others.  For almonds, initial focus of the PAW-MBA was on fumigant alternatives to MB, which are highlighted in this summary.  More recently, with ABC support, the PAW-MBA program has focused on non-fumigant alternatives, which will be featured (along with fumigant alternatives) in an upcoming issue of the journal California Agriculture (Browne et al.).  

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David Doll2 CommentsDecember 7, 2012Diseases

Lasting Effects of Soil Fumigation on Nematodes?

I am often asked about the duration of control that pre-plant soil fumigation has on parasitic nematodes. My typical response is “Probably about 3-4 years, or once the roots move outside of the treated area.” This generalization appears to be true in many orchards as symptoms of nematode parasitism, which include stunting, bacterial canker, and bud drop, often do not develop until the fourth or fifth year. This past fall, we performed our annual nematode sampling of all of our research plots. One of the plots was our almond replant plot located near Ballico. This orchard is located on a sandy soil with a history of almond trees and nematodes. In the fall of 2010, it was fumigated with four fumigant treatments, including methyl bromide row-strip, C35 row-strip, Telone II rowstrip, and Telone II broadcast, a control plot, and a spot steam treatment. In the spring of 2011, the trees were planted.

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David Doll4 CommentsDecember 15, 2009Diseases

Inquiries about Bacterial Canker on Almond

This week I have had a few questions regarding post harvest treatments for Bacterial Canker of almond. I thought it would be a good idea to use these questions as the theme for this weeks post. What is bacterial canker?Bacterial canker is commonly found on Prunus species (Peach, cherry, apricot, plum, almond, etc.). Caused by Pseudomonas syringe, a common surface inhabiting bacteria, the disease is often observed in the spring. Symptoms include limb dieback with rough, irregular cankers (Figure 1). Cankers do not extend into the soil and a very unique smell is present. In some cases, cankers do not form, but a “sour sap” stage occurs. This stage is characterized by brown inner bark with a distinctive fermentive, sour smell – hence the name. Generally, almond trees in the 2nd through 5th leaf are affected. Figure 1: Almond tree killed by bacterial canker. Note that the canker has an irregular shape and does not extend into the soil. How does bacterial canker spread?Pseudomonas syringe survives on plant surfaces and is spread by splashing rain. The bacteria is found throughout the entire orchard and is impossible to eradicate. The disease commonly occurs in the spring during periods of mild temperatures and high humidity. It does not spread like other diseases, but is common on trees that are stressed. Therefore, soils that have poor water/nutrient holding capacity (i.e. sand), have been replanted with several generations of Prunus sp. orchards, and have the presence of ring nematode are prone to this disease. Figure 2: Photo of an almond with a scaffold infected with bacterial canker. Note the irregular margin of the canker.What can I do to prevent the problem?In soils that have exhibited the disease, pre-plant fumigation with Telone or Methyl Bromide (if it is still available) provides the ability for the

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David Doll0 commentsAugust 24, 2009Diseases

Nematodes and Tree Growth

A grower made a request for a visit to his orchard due to poor growth by his replanted first leaf trees. The trees were replacing trees that were lost to heavy winds from the previous summer. Within the orchard, there were several different pollinators, and all of the trees were planted on Lovell rootstock. This orchard was located in a sand/loamy sand soil series, irrigated with solid-set sprinklers, with trees ranging from 1rst-15th leaf throughout the block. Often with replanted trees in an established orchard, it is very difficult to obtain vigorous growth. The trees usually are partially shaded out, receive either too much or too little water and fertilizer, and generally struggle with soil problems involved with replanting. The replants throughout the orchard were showing signs of low vigor, which include poor shoot growth, thinned canopy, and a general weak appearance (Pictures 1 and 2). The trees showed no other signs of disease on the scaffolds or trunk. Upon root excavation, a poorly developed root system was observed. There were no signs of fungal root infection or any other aggressive pathogens, vertebrate pests, or insects. Picture 1: A first leaf almond tree severely stunted by high nematode populations. Picture 2: A first leaf almond tree moderately stunted by high nematode populations. At this point, I decided to sample for plant parasitic nematodes. Sampling for nematodes is relatively easy: Remove the top 6″ of soil from the sampling locations, and use a soil sampling tube* to remove soil from the depth of 6″-18″ and place the soil in a bucket. Do this from 4-5 locations and mix the soil thoroughly within the bucket. Pull out 2-3 pounds of soil, place it in a labeled plastic bag, and place in a cooler or refrigerator until the sample can be sent to

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