David Doll1 CommentFebruary 29, 2016Diseases

Almond Fungicide Considerations for Upcoming Rain Event

Rain is predicted for later this coming week (Sat through early the following week). This looks to be a multiple day storm with rain potentially falling for 3-4 days. Temperatures will be between 40-60F. These conditions are favorable for a number of post bloom/petal fall diseases, including brown rot, shot-hole, jacket rot (or green fruit rot), anthracnose, and bacterial spot. The almond fungicide efficacy table should be consulted to help with fungicide selection. An updated 2015 Fungicides, Bactericides, and Biologicals for Deciduous Tree Fruit, Nut, Strawberry, and Vine Crops can be found here. Scroll to page 31 to find the efficacy of many common fungicides. Please not that not all fungicides are listed due to the inability to test all trade names. If a fungicide isn’t listed, check to see if the active ingredient is provided, and if not, check the efficacy of the FRAC group. The table on page 32 provides treatment timings which indicate susceptibility of almond to diseases at various growth stages. Finally, page 33 highlights various fungicides that are effective on diseases at specific growth stages and can be used to help determine a rotation. A fungicide product should provide coverage for the above diseases. Products used in earlier fungicide sprays should be rotated to another mode of action (or FRAC group). This should still be considered even if the FRAC number was one part of a combination product.  Rotation helps to preserve fungicide efficacy, which leads to a longer product life (and eventually cheaper prices). Some interesting points to keep in mind when reviewing the tables: FRAC 3 fungicides are not very effective on jacket/green fruit rot; Bacterial spot control will require the use of copper, Manzate Pro-Stick, or combinations of the two products. Keep in mind that almond trees are sensitive to copper. More

Read More
David Doll0 commentsSeptember 3, 2015Diseases

Rhizopus and Kernel Issues

Rhizopus stolonifer, also known as the bread mold fungi, is a ubiquitous fungi. Within almonds, we often think of it as the Hull Rot pathogen, which can kill limbs through the movement of a produced toxin. Over the past harvest period, however, there have been some interesting kernel symptoms observed that have been found to be caused by this fungus as identified through isolations. The increased occurrence of these infections is thought to be due to the increased humidity experienced during the July, which most likely favored fungal growth. The first set of symptoms observed was the white fungal growth on the surface of the kernel (figure 1). The initial infection begins as a light, white fuzz that grows, and if left long enough in suitable conditions, begins to develop black spores. When these lesions were submitted for isolation, they came back as Rhizopus stolonifer. This type of kernel infection rarely becomes a concern because as the kernel dries to a suitable percentage for storage (~6% moisture), the fungal growth usually dries out and is not visible. It does not create a food safety issue. The second set of symptoms observed was a black or dark lesion that occurs on ‘Sonora’ kernels. These lesion tends to follow the “veins” of the kernel skin. The severity of kernel discoloring can vary, with most of the discolored kernels not providing an issue at processing. If, however, the infected areas are large enough, the kernels could get kicked out by the color sorters at the processors. When these kernels were submitted for isolation, we found both Rhizopus stolonifer and Aspergillus niger. Both of these fungi are common opportunistic fungi, and outside of the staining, the infected kernels do not pose a food safety concern. Thankfully, opportunistic fungi infecting kernels does not always occur. This

Read More
David Doll0 commentsAugust 22, 2015Diseases, Irrigation

Irrigation Rates and Hull Rot

Written by Andrew Ray, Staff Research Associate for Univ of CA Cooperative Extension, Merced County Our water production function (WPF) project within almond has given us an opportunity to look at how irrigation rates can impact the amount of hull rot that develops.  The goal of the WPF is to be able to calculate the impact that water applied has on yield.  This plot is replicated in three different places across the Central Valley. In the Merced WPF plot, there are five different treatments of water applied at the rates of 110%, 100%, 90%, 80% and 70% of the evapotranspiration rate (ETc).  There are 3 blocks of these treatments within an 80 acre orchard.  Irrigation rates stayed constant with their established relationship to ET through hull split, and reduced deficit irrigation was not applied. During mid August hull rot occurrence was estimated in the Merced WPF plot on two trees in each treatment within each block.  Twenty five branches were counted on each quarter of the tree, totaling 100 branches per tree, and the number of incidents of hull rot was recorded. There were two ratings performed by two different people and the estimated percentages were averaged. Table 1 shows the averages by treatment of all the trees rated.  Included in the table is the average stem water potential (SWP) for each tree and leaf nitrogen percentage.  The SWP measurements were taken with a pressure chamber on three separate occasions during hull split in early July.  Baseline SWP during that time was -9 bars.  Leaf tissue samples were taken in mid July and the average percentage of nitrogen for each treatment. Table 1: Average hull rot percentage observed in each irrigation treatment, along with average SWP during hull split, and leaf tissue nitrogen percentage. %ET % Hull Rot SWP (bars) %N

Read More
David Doll0 commentsAugust 14, 2015Diseases, Irrigation, Salinity

Poor Nut Removal: Causes

There have been a lot of reports of poor removal of ‘Nonpareil’ almonds. This issue may be caused by a few different issues, all which require a different management plan. The potential causes as well as some thoughts on management are provided below: 1. Uneven ripening. Uneven ripening can be caused by several different things. A long, protracted bloom can create a delay in ripening due to the length of time between the first and last fruit that was pollinated and fertilized. Also, vigorous growing conditions can delay the ripening process. These include more than adequate water and nitrogen through the entire growing season. Often, this is observed in younger orchards as they are being “pushed” along with increased water and nutrients. Not much can be done about the long bloom period, but properly timed irrigation and nitrogen applications in the spring (especially early spring) can help reduce excessive vigor. 2. Hull rot. Once a hull is infected by Rhizopus or Monilinia, a toxin is secreted which leads to the death of fruit wood. As this toxin kills tissues, it can cause them to gum – especially at the peduncle, effectively gluing the nuts to the spur. These nuts are very difficult to remove and hull rot management practices should be utilized to help reduce the occurrence of this disease. In years were humidity is high at the onset of hull split, cultural management practices appear to be less effective. 3. Boron Toxicity. Becoming a bit more common with the expansion of trees onto lower quality land or irrigation from low quality water. Boron toxicity is identified as die back of this year’s shoots, gummy deposits that form at wounds or other plant openings (bud scars, lenticels, etc.), and corky areas on the midrib on the lower side ofleaves. The gum that is exuded

Read More
David Doll1 CommentJuly 25, 2015Diseases

2015: Lower Limb Dieback Returns

I have received several calls and comments regarding the severity of lower limb dieback (LLDB) in almonds this year. This topic has been discussed to a greater extent here, but I thought I would highlight a few points and some updates to keep in mind if you are observing these symptoms in your orchard. LLDB is used to describe branch death that occurs in the lower half of the canopy. The limbs tend to start the year off normally, but at some point – usually after a hot spell- the leaves on the affected limbs begin to yellow, and eventually the whole branch collapses. Observation of symptoms usually occurs between late May through late July, with symptoms delayed in years with mild springs. LLDB is very common on the ‘Padre’ variety. So what causes LLDB? The “jury” is still out, but there are a few hypothesis. The current thought is that over-irrigation in the spring followed by under-irrigation during the summer months can worsen or cause LLDB. Over-application of water often occurs in the spring time due to the variable weather conditions (e.g. unexpected cool spells and rain). When it cools off, it is easy to over-apply water especially if the irrigation scheduling is based on the 30 year average. A good example was this past May, in which we experienced an estimated 5.68″ of almond water use (ETc) and had rainfall events that dropped as much as 0.25-1.0 inches of rain in Merced. The 30 year average estimates that we would need to apply 6.44″ of water to match ETc, and if followed, over-irrigation with an inch or more water may have occurred. Furthermore, many orchard operators tend to begin too early with the first fertigation, often beginning before transpiration levels of the tree draw down soil moisture, which keeps the soil

Read More
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

Read More
David Doll0 commentsFebruary 25, 2015Diseases

Tank Mixing v/s Pre-Mixed Fungicides

There have been several questions asked by farmers developing their fungicide spray programs for 2015. A repeated question has been: “Is it possible to mix two generic or single mode of action fungicides to create a product similar to the bottle mixed multi-mode of action products?” The short answer: Yes, and often times it is cost-effective because one or both products may be generic. There are, however, more points to consider when determining which strategy is best for the farm operation. Tank-mixing of single mode of action fungicides: Pros: The use of one or two generics in creating the tank mix may help reduce the cost of the overall fungicide application. This, of course, is dependent on the price of both fungicides and the pre-mixed fungicide. Tank-mixed fungicides are usually just as effective as pre-mixed fungicides. A study by Brent Holtz in San Joaquin County has shown that 20 fl oz of Fontelis (FRAC 7) mixed with either 8 fl. oz of propiconazole (FRAC 3) or tebuconazole (FRAC 3) was just as effective in controlling scab as 6.0 fl oz of Luna Experience (FRAC 3/7), 6.0 fl oz of Luna Sensation (FRAC 7/11), or 6.5 fl oz of Merivon (FRAC 7/11). Trials in Colusa County by Dr. Jim Adaskaveg, UC Riverside, showed similar results with 14 fl oz of Fontelis mixed with 8.0 oz of tebuconazole as with 6.0 fl oz of Luna Experience, 5.0 fl oz of Luna Sensation, or 6.5 fl oz of Merivon for controlling almond scab. Selecting multiple single mode of action fungicides provides the flexibility to choose chemistries that work for the disease complex present within the orchard. This may be of more importance in areas that have resistant populations of Scab or Alternaria leaf spot or when trying to manage other diseases that may not be

Read More
David Doll4 CommentsFebruary 7, 2015Diseases

Almond Bloom 2015

Bloom is around the corner. After receiving adequate chill units through December (almonds need ~400-500), almonds switch from ‘chill accumulation’ mode to ‘heat accumulation mode.’ Although less is known about this stage for many crops, it is known that a certain amount of heat is needed in order for bloom to begin. This heat requirement keeps the plant from blooming too early, reducing the risk for the impacts of frost events. The warmer weather over the past few weeks, however, has provided conditions that have met the heat requirement for most areas of CA. This suggests that if the weather stays warm through the next week, bloom will begin for more areas within California. Below are some considerations to have in mind for bloom: Fungicide sprays. Due to the sensitivity of almond flowers to disease and conditions during bloom that are conducive for disease, most people will spray a fungicide during this period. In wet conditions, multiple sprays may be needed, while in dry years a single or no spray may suffice. Conditions that favor disease formation include wet weather, warmer temperatures for Brown Rot, Anthracnose, Bacterial Spot, and Shot-hole, cool weather for Botrytis, and heavy dew. Fungicide selection should provide coverage for the diseases of concern (Please see this link and scroll to ‘Almonds’). Bloom sprays should be applied before rain events to provide protection for flowers, flower parts, and emerging leaf tissue. Coverage from a fungicide spray will last around two weeks, unless significant rainfall occurs.  If applying prior to a rain event, applications will need a few hours to dry to prevent “run-off.” In rainy weather, follow-up sprays will be needed every 7-10 days. Some varieties – such as ‘Butte’ and ‘Carmel’- are more susceptible to disease and may require a spray even in dry weather, while others – such as

Read More
Roger Duncan0 commentsJanuary 24, 2015Diseases

Dormant Sprays Not Reducing Lower Limb Dieback

Lower limb dieback (LLDB) continues to be a problem in some area almond orchards, especially in the Padre and Butte varieties.  Beginning in late April or early May, leaves on affected lower limbs begin to yellow and then turn brown.  Eventually, entire limbs die and by late summer, significant death of lower canopy wood can occur. Early studies indicated that species of Botryosphaeria and Phomopsis fungi played a significant role in this problem, but later efforts indicated that LLDB may not be a disease at all.  Multiple spring fungicide applications did not reduce limb death.  The bottom line is that LLDB is still not well understood although a compromised root system, especially from overly wet soils in the spring, may contribute to the problem. 

Read More
David Doll3 CommentsJanuary 1, 2015Diseases

Bacterial Spot of Almond in California: Update on the Disease and Management

written by Dr. Jim Adaskaveg (UC Riverside), Brent Holtz (UCCE San Joaquin), Roger Duncan (UCCE Stanislaus), and David Doll (UCCE Merced).   In the spring of 2013, we reported a high incidence of bacterial spot in some Sacramento and northern San Joaquin Valley almond orchards, especially on the ‘Fritz’ variety.  It was also found on ‘Nonpareil’, ‘Butte’, ‘Carmel’, ‘Monterey,’ and ‘Price’ but at much lower levels.  The disease has not been found in orchards in the southern San Joaquin valley. Bacterial spot is caused by Xanthomonas arboricola pv. pruni and has also been referred to as bacteriosis, bacterial leaf spot, or bacterial shot hole. Bacterial spot occurs on leaves, twigs, and fruit of almost all Prunus spp.  The pathogen commonly causes bacterial spot of peach in the eastern United States and is one of the major foliar diseases in high rainfall years. On almonds, it is a significant problem in Australia because of mid-season rain events.  In 2014, we verified the presence of the disease at previous and additional locations in California, although at levels much lower than in 2013.

Read More