1- Phytophthora Root and Crown Rot

Causal organism Phytophthora spp.

SYMPTOMS

Symptom expression depends upon how much of the root or crown tissues are affected and how quickly they are destroyed. Generally, crown rots advance rapidly and trees collapse and die soon after the first warm weather of spring. Leaves of such trees wilt, dry, and remain attached to the tree. Chronic infections, usually of the roots, cause reduction in growth and early senescence and leaf fall. These trees may be unthrifty for several years before succumbing to the disease. Phytophthora infections typically kill young trees because their root systems and crown areas are small compared to those of mature trees.


DISEASE CYCLE

Periods of 24 hours or more of saturated soil favor Phytophthora infections. Conversely, good soil drainage and more frequent but shorter irrigations reduce the risk of root and crown rot. Surface water from irrigation districts is mostly contaminated with Phytophthora species. Rootstocks vary in susceptibility to the different Phytophthora species; none are resistant to all pathogenic species of the fungus. Thus, the success of a rootstock may depend in part upon the species of Phytophthora present in the orchard. In general, plum rootstocks are more resistant than are peach or apricot. Of the plum rootstocks, Marianna 2624 is the most tolerant to Phytophthora.

CONTROL

Proper water management is the most important aspect in controlling root and crown rot.

Do not allow water to accumulate or stand around crowns of trees.

The bud union mast be height about 20-25 cm from the soil level.


2- Rust

causal organism Tranzchelia discolor

SYMPTOMS

Rust appears as small, yellow spots on the upper surface of leaves. On the lower surface of the leaf these spots take on a rusty red appearance when the rust-colored spores produced in the lesions erupt through the surface. These spores are spread by air movement and infect other leaves to continue the disease cycle. Young twigs may be infected, but twig lesions are seldom seen on almond.


DISEASE CYCLE

Rust occurs sporadically throughout almond-growing areas in California. It is most likely to become serious in orchards near rivers or streams or other locations where humidity is relatively high in spring and summer. The disease causes leaves to fall prematurely and will weaken trees if not controlled.

The development of rust is favored by humid conditions, and the disease becomes worse when rain occurs in late spring and summer. Trees can be defoliated quickly when rust becomes severe. The rust fungus survives from one season to the next in infected leaves and possibly also in infected twigs.

CONTROL

To prevent the rust inoculum from increasing in late fall; apply zinc sulfate (KELKAT ZINC)

OR             COBOX               250g/100L.W
OR             BELLIS               30G/100L.W
OR             AMISTAR           40cm/100L.W     

3-Verticillium Wilt

Causal organism Verticillium dahliae

SYMPTOMS

Leaves on one or more branches, often on only one side of the tree, will turn yellow and/or wilt early in the growing season. The symptoms progress until the infected shoots die and dry up later in the season. When shoot, branch, or trunk tissue of infected trees is cut in cross section, the vascular ring and often much of the heartwood will display dark discoloration. Foliar symptoms usually appear only on young trees (first to fifth or sixth leaf). Older trees do not normally exhibit symptoms of Verticillium wilt.

DISEASE CYCLE

the causal fungus survives from season to season in soil, debris of previous, susceptible crops, and probably in roots and the lower trunk of infected trees. Often, the fungus can be isolated from living portions of infected tissue year around in the Central Valley. Research has shown that tree yields can be reduced by verticillium even when foliar symptoms are not readily apparent. Specific rootstock/scion varieties may vary in susceptibility.

CONTROL

Avoid interplanting young orchards with susceptible cover plants, such as cotton, tomatoes, melons, etc. When replanting in an area where susceptible perennials were previously grown, try to remove as many roots of the previous crop as possible.

Orchards may also be fumigated before trees are planted.


4- Shot Hole

Causal organism Wilsonomyces carpophilus

SYMPTOMS

Spots occur on leaves, fruit, twigs, and flowers; however, flower and twig lesions are relatively scarce or difficult to find. Leaf lesions begin as tiny reddish specks that enlarge by several millimeters into spots having tan centers and purplish margins. When the fungus sporulates, the fruiting structure appears as a small dark speck (the sporodochium and spores) in the center of the spot; this is a diagnostic characteristic of shot hole disease. Spots on young leaves usually fall out, leaving a whole (the shot hole); older leaves retain their lesions. Fruit spots are small with purplish margins, slightly corky, and raised. Spots are found on the upper surface of fruit with respect to the way it hangs on trees.      Heavy infection of young fruit may cause fruit drop or distortion and gumming of fruit.

DISEASE CYCLE

the fungus survives on infected twigs and as spores in healthy buds. Spores are moved by water to new sites; prolonged periods of wetness, either due to rain or sprinkler irrigation, are required for the disease to develop. Shot hole can cause losses in yield, defoliation, and weakened trees.

CONTROL

          COBOX               250g/100L.W (after fruit set)
OR    AMISTAR           40cm/100L.W (after fruit set)

5- Green Fruit Rot

Causal organisms Botrytis cinerea, Sclerotinia sclerotiorum, Monilinia laxa
                 
SYMPTOMS

Green fruit rot begins during the latter part of the bloom period when the fungus infects senescing petals and anthers. Infected petals develop water-soaked brown spots. Some infected petals may fall onto leaves causing secondary infections. Anther infections can spread to floral tubes or flower jackets causing them to wither and stick to developing fruit. As fruit sets and starts to grow, a brown spot develops where the jacket sticks to it. Frequently this leads to rot of the entire fruit.

DISEASE CYCLE

this disease is of little importance in many years, but when conditions are cool and conditions wet during bloom, it can cause severe losses. One or more of several pathogens may be involved.

CONTROL

When bloom is extended and moisture is abundant, apply a fungicide at full bloom to prevent green fruit rot

             BELLIS               30g/100L.W       

6- Powdery Mildew

Causal organism Podosphaera Tridactyla var tridoctyla

Symptoms

Powdery mildews first appear as superficial, white, powdery patches on the leaves, young stems, buds, flowers, and even the fruits.

These patches may enlarge until they cover the whole leaf on one or both sides. The white powdery growth is composed of mycelium of the fungus and chains of colorless spores (conidia) borne on upright stalks (conidiophores) arising from the white mycelium on the surface of the host plant. Later in the season, these patches may become mealy or felt-like, turn gray to tan in color, and become dotted with minute, dark brown-to-black cleistothecia. A stunting or dwarfing, curling of leaves, chlorosis, premature leaf drop, and deformation of flower buds frequently follow mildew infection. Many powdery mildews, especially those that attack trees and shrubs, are much more unsightly than harmful.

Disease Cycle

The powdery mildew fungi commonly over winter as mycelial mats in rudimentary leaves within dormant buds, especially on woody plants.

Infected buds break open in the spring and may develop into systemically infected shoots. The fungi sporulate on these shoots, producing large numbers of barrel-shaped conidia that are carried by the wind, splashing water, or other means to healthy plant tissue _ where they infect the upper and lower leaf surfaces, thus initiating a new disease cycle. Another means of winter survival for powdery mildew fungi in the Midwest is as cleistothecia embedded in the mealy or felt-like mildew growth on plant stems and fallen leaves. The minute cleistothecia are formed within the mycelial mat as the host tissues mature. During warm and humid weather in the spring, a cleistothecium absorbs water and cracks open to discharge one or more asci, depending on the fungus species involved. Each ascus usually contains eight ascospores. The microscopic ascospores are carried by the wind or splashing raindrops to healthy plant tissue where they germinate and may cause infection. A mycelial mat is formed and chains of conidia are evident within a few days, completing the disease cycle.

Control

USE                    
BELLIS               30g/100L.W
AMISTAR           40cm/100L.W

7- dieback

Causal organism Eutypa Lata

Symptoms

Eutypa canker and dieback of almonds was first recorded in commercial plantations in Greece in mid-1980 and confirmed as due to the ascomycetous fungus Eutypa lata. The disease manifests itself by the formation of cankers at the point of the junction of the branches and the trunk and is associated with pruning wounds made by the growers in order to confront the‘non-infectious bud failure’disorder or to remove unwanted limbs close to the crotch
Control

COBOX               250g/100L.W