David Doll1 CommentFebruary 15, 2010Diseases

Brown Rot: A disease problem during bloom

Almond orchards are treated at least once during bloom for fungal disease brown rot. Rightfully so, as the brown rot fungi (Monilinia laxa) can kill the flower, fruiting spurs, and shoots. Flowers are susceptible from pink bud to petal fall, and are most susceptible when flowers are fully open. The fungus is able to infect all parts of the flower: anthers, pistils, petals, and stigmas (Figure 1). Upon killing the flower, it can move into and kill woodier tissues of the tree. Once in the woodier tissue, it forms a canker (Figure 2). This canker can enlarge to kill the branch and also serves as the survival structure for the fungus. These cankers are the reason why it takes many years to “clean up” an orchard after a severe brown rot infection. Brown rot can also infect the jacket of the almond and kill the young fruit as well. This is called jacket rot. Figure 1: Blossom blight of almond caused by the brown rot fungus Monilinia laxa.All varieties are susceptible to brown rot, but they vary in their degree of susceptibility. Butte is the most susceptible variety followed by Carmel. Ne Plus Ultra and Mission are moderately susceptible, while Nonpareil and Peerless are the least susceptible to brown rot. Brown Rot Blossom blight is usually controlled with a pink bud and full bloom treatment. Many of Brent Holtz’s (UCCE San Joaquin) trials suggest that the full bloom treatment may be the most important. A third petal fall spray may be necessary in years favorable to disease (rain). If bloom is strung out and the weather is wet and rainy, no more than ten days should elapse between treatments. A few growers have told me that they do not spray for brown rot. This may be okay if good conditions

Read More
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

Read More
David Doll3 CommentsNovember 30, 2009Diseases

Pruning Wound Cankers Found in Almond Trees

Making pruning cuts on almond trees is risky business. Every cut provides the opportunity for fungal/bacterial pathogens to enter the tree (Think: a cut on you hand can allow bacteria to enter). Once the pathogens enter the tree and successfully colonize, poor tree performance and shortened orchard life can be expected. Figure 1: Fungal canker associated with a pruning wound on a young tree. Upon bark removal, canker growth and damage is evident. Fungi are the most commonly found pathogens invading tree wounds. In figure 1, a large pruning cut was made on a super-vigorous first leaf almond. The pruning wound became infected with the fungi Eutypa which grew through the tree causing a large canker. This canker did not become noticeable until the third leaf. Upon bark removal, it is clear that the canker grows outward from the point of origin. As the canker continues to grow, it has the ability to kill branches by girdling (Figure 2), weaken scaffolds which then break (Figure 3), and/or killing the tree by girdling the trunk (Figure 4). Botryosphaeria is another fungi that may cause this problem. Figure 2: Scaffold killed by fungal canker girdling the vascular tissues of the branch. Figure 3: Scaffold split caused by weakening of crotch angle by invading fungi. Figure 4: Tree killed by wood fungal canker girdling the vascular tissue of the tree trunk. Bark removal shows the advancement of the canker. Irregardless of the possible infection by fungi, trees need to be pruned to shape (young trees), remove unwanted branches, and remove dead/diseased tissue. Knowing this, how can we prune the tree and reduce the chance of fungal infection? Most fungi require moisture/high humidity/rain event to produce spores. These spores are usually transferred by wind-blown rain. The “window of opportunity” for these fungi to infect

Read More
David Doll1 CommentSeptember 28, 2009Diseases

Phytophthora Root and Crown Rot of Walnut and Almond

Root and crown rot of fruit and nut trees have caused major losses within orchards around the world. First reported in California in 1912, Phytophthora, which means “Plant Destroyer” in latin, causes root and crown rot throughout the San Joaquin and Sacramento valley. The problem tends to be more severe in areas of clay to clay-loam series soils, which can be attributed to the higher water holding capacity and poor drainage of these soils in comparison to sandier soils. The effect of Phytophthora spp. on root systems is often not noticed until the above ground parts of the tree show symptoms. Symptoms of Phytophthora damage are usually observed by poor tree vigor, loss of scaffold branches, and gumming or bleeding found around the tree trunk. Orchards affected by Phytophthora crown rot can suffer tree loss quickly, especially during the spring when winter-infected trees collapse during the first hot spell and during periods of high heat in which over-irrigation easily occurs. This is in contrast to tree loss that is attributed to root rot. In this case, by the time most growers recognize the symptoms, several trees are in a declining state due to a long period of infection (several years). Careful observance of the orchard can reveal problems and warrant remediation before the manifestation of severe orchard losses. Figure 1: Overall view of a walnut tree with Phytophthora. Note the collapse of the tree from top to bottom. As the disease infects the roots or crown, flow of water to the highest branches is compromised, with upper branch dieback being the first above ground symptom. In the orchard, symptoms of crown rot usually include cankers that are centered at the crown or lower part of the trunk. Removal of bark in affected areas will reveal brown or black sap-wood that

Read More
David Doll3 CommentsAugust 17, 2009Diseases

Armillaria Root Rot (Aka Oak Root Fungus) of Almond

A call last week revealed a disease issue in which there are very few solutions. A grower called with concerns of several trees recently collapsing from the heat. The decline has been relatively gradual until a week or go, in which the trees suddenly turned brown and are now dead (Picture 1). This problem has been ongoing for several years in which he would replant the trees after a tree site fumigation. The orchard was a 10th leaf Nonpareil, Fritz, and Aldrich orchard, planted on Nemaguard. Picture 1: Overview of an almond tree affected by a root disease. The orchard was in a clay-loam soil series, flood irrigated with district water once every 10-13 days, and appeared to be in good shape outside of the affected areas. Affected trees were usually surrounded by younger, replanted trees confirming the replanting that the grower has done in the area (Picture 2). Furthermore, the affected trees appeared to be in groups, and this was confirmed by a Google Earth image once I returned back to the office (Picture 3). All this suggests a biotic agent causing disease, and seeing a total collapse of the tree, I began to investigate the root system. Picture 2: “Hotspot” of area infected by Armillaria root rot. Picture 3: Google Earth Aerial Image of the orchard affected by Armillaria Root Rot. Please note the large holes within the orchard canopy indicating missing or dead trees. Upon root excavation, the tell-tale signs of Oak Root Fungus or Armillaria Root Rot became relevant. Hitting a surface root and scraping back the bark, the white mycelial fans became evident (Picture 4). Furthermore, the roots possessed a smell similar to what we would expect from mushrooms – similar to the smell of mushrooms in the grocery store. Further bark removal and scraping

Read More
Brent Holtz10 CommentsJune 30, 2009Diseases

Hull Split Part 2: Hull Rot of Almond

As almond trees approach harvest, at about mid hull split, clusters of dry leaves begin to appear scattered through the tree canopy. Individual spurs, small shoots or entire small branches may collapse due to hull rot infections (Photo 1). The loss of fruiting wood, especially in the lower parts of the tree, can negatively affect yield for years to come. Nonpareil is usually the most severely affected cultivar though Sonora and Kapareil can also sustain extensive damage. Hull rot is caused by either of two fungi, Monilinia fructicola or Rhizopus stolonifer. Monilinia fructicola is best known as one of the brown rot fungi and R. stolonifer is often called the bread mold fungus, and will turn bread left out black and moldy. Photograph 1: Hullrot of almond caused by Rhizopus stolonifer. In the southern San Joaquin Valley I believe that Rhizopus is the primary pathogen responsible for hull rot while Monilinia may be more important in the Sacramento Valley. These two organisms are very different but can cause similar disease symptoms on almond. As the name implies, a lesion or dryish rotted area develops on the hull, and dense masses of Rhizopus spores produce a powdery dark gray to black growth between the hull and the shell (Photo 2). Monilinia spores are buff-colored and can be seen on inner and outer hull surfaces. The nut meat is not damaged, but a toxin produced in the infected hull moves from the hull into the neighboring leaves and shoots causing death of these tissues. Neither Monilinia nor Rhizopus are able to invade the healthy outer hull surface. Only after hull split begins can spores gain access to the inside of the hull and initiate infections. Once hull split starts, trees are at risk of becoming infected. One or both pathogens may be

Read More
David Doll8 CommentsJune 16, 2009Diseases

Foamy Canker in Almond

This is one of the most visually moving diseases found in almond. Once upon the location of the problem, not only is the disease obvious by looking at the trees, but the air is also filled with a fermented-like smell reminding one a bar when entering for happy hour. Overall Orchard Information: The orchard I was called out to visit was described as a complete loss to foamy canker. To me this came as a bit of a surprise as foamy canker typically comes later in the season. By time I have arrived, the grower was in the process of removing the orchard. The entire orchard was exhibiting symptoms of foamy canker (Picture 1), poor growth and dieing trees. Photo 1: Overview of the almond variety Fritz with foamy canker The orchard was a Nonpareil-Fritz-Monterrey on Lovell planted on clay/clay loam soil. The trees were in their 4th Leaf trees with average growth. Nut set of the trees was decent, but not great. Speaking with the grower, he mentioned that the orchard has a high water table, found at about 7 feet with subbing up to 4-5 feet. Quality of the water was unknown. The site is also high in boron within its soil, and has a history of verticillium wilt (old tomato and melon ground). Overall, the discussion yielded that there were many issues from the start with the orchard – over 30% of the Fritz variety planted in the first year did not survive and needed to be replanted. Irrigation of the trees tends to be minimal due to the high water table. The grower does not irrigate often – only 8 inches last year through double line drip. Nitrogen usage is minimum, but tree vigor is high due to being the first generation orchard on old row

Read More
David Doll0 commentsJune 4, 2009Diseases

Ceratocystis of Almond

Ceratocystis or “mallet wound canker” has been found on almond throughout California for almost 50 years. This fungal canker, caused by Ceratocystis fimbriata, can develop on areas of the trunk or branches that have been damaged by tractors, hedgers, and harvesting equipment. Pruning wounds are also susceptible. Cultivars that are most susceptible include Nonpareil, Mission, and Ne Plus Ultra. Ceratocystis cankers appear as either water soaked or dry cankers. Amber-colored gum is found at the canker margins. Infected tissue turns brown and the area eventually becomes sunken. Unlike Phytophthora infections, Ceratocystis remains active during the summer months in which rapid canker growth can occur. Cankers can girdle limbs, scaffolds, and tree trunks.Limbs 4-6 inches in diameter have been observed to be girdled in 3-4 years, while smaller branches are killed more quickly. Ceratocystis cankers appear as either water soaked or dry cankers. Amber-colored gum is found at the canker margins. Infected tissue turns brown and the area eventually becomes sunken. Unlike Phytophthora infections, Ceratocystis remains active during the summer months in which rapid canker growth can occur. Cankers can girdle limbs, scaffolds, and tree trunks.Limbs 4-6 inches in diameter have been observed to be girdled in 3-4 years, while smaller branches are killed more quickly. Several species of sap-feeding beetles and fruit flies spread Ceratocystis. These insects feed on the fungus, ingesting and coming into bodily contact with the spores. The spores are then transported to other trees and deposited on the bark by the insects. Rains and sprinkler irrigations can wash the spores into fresh pruning wounds or other injuries. Once the fungus infects the cambium, it will begin to invade the healthy bark and xylem tissues of the tree. Dark stains may permeate into the heartwood of the tree, but rarely is the fungus found in these tissues.

Read More