MULBERRY PESTS AND DISEASES
Mulberries are generally pest free and affected by few diseases. For a list of the few that may occur, we have created this short post on mulberry diseases.
STEM CANKER
Lasiodiplodia theobromae/ Botryodiplodia theobromae
Symptoms of stem canker generally are most evident in cuttings that appeared to take and then subsequently died. The new shoots suddenly shrivel and die. When the cuttings are removed from the soil it is apparent that the bark is rotting and peeling away below the soil. Black mycelial threads may be seen under peeling bark. In commercial applications cuttings are most often taken dormant and pre-treated with carbendazim to prevent infection.
LEAF RUST
Cerotelium fici, Aecidium mori
Symptoms of leaf rust include small brown irregular shaped red or rust-colored spots appearing on older leaves underside. The leaves subsequently turn yellow and wither prematurely. Otherwise it may not harm the tree. Often exacerbated by lack of air flow between plants; planting out further apart reduces spreading. The problem may subside on its own. In commercial culture plants are sprayed with carbendazim.
LEAF SPOT
Cercospora moricola
Symptoms of leaf spot begin as circular spots on leaves that become larger and irregular in shape and eventually coalesce and form shot holes in the leaves. Severely affected leaves yellow and drop prematurely. Most common commercial control of leaf spot is through the use of carbendazim.
POWDERY MILDEW
Phyllactinia corylea
Powdery mildew is an ectophytic (lives outside of, and on the surface of its host) fungus that appears first as a powdery white (mycelial) film in spots on the undersides of leaves that spreads until it covers the entire leaf. The leaf will then begin to thin, curl, yellow, then brown and drop off.
Disease is most common in the low desert after spring rains where the humidity is greater than 70%, the temperatures are hovering between 75-80° F degrees, there is limited air circulation, and a low pH on the leaf surface. Thrives in shadier environments, such as on the north side of a building or under the canopy of another tree.
Commercial chemical control includes the use of carbendazim and other fungicides. Cultural control measures include ensuring more air circulation between plants, thin trees to increase sun exposure. Some commercial varieties grown for silk production have been tested for resistance. Home treatments include sprays that raise surface pH to levels that the mycelium cannot survive: common home remedies include milk sprays or baking soda sprays. Lady bugs will also feed on mildew fungus.
FALSE MILDEW
Mycosphaerella mori
False mildew is similar to powdery mildew. It appears as a web-like film on the mulberry leaves. To eradicate this disease, spray trees with a fungicide at the first appearance of the fungus. Again, simple surface pH treatments may prove effective. Remove leaf litter to prevent reinfection.
BACTERIAL BLIGHT
Psuedomonas syringae
This particular bacteria plays some fascinating roles in the environment. While it is a bacteria that can be highly pathogenic, in most healthy environments it causes little to no issue. It is highly hydrophilic and nucleizes ice crystals in warmer than freezing temperatures in the atmosphere creating rain clouds.
As a pathogen however it can cause serious damage. Infection manifests as black spots on the leaves and large brown spots on the fruit. Flowers, fruits, catkins, and branches may shrivel and die. Leaf veins may take on an unnatural dark color. At mature stages of infection cankers can appear on the branches and trunk. Infected areas may ooze moisture in wetter environments. This bacteria becomes problematic in areas where foliage is regularly damp or moist and there is poor air circulation. It is most commonly seen after rain with prolonged periods without dry-out.
Because the bacteria takes different forms and some are more pathogenic than others, Infected branches, leaves, and fruits should be removed and burned or bagged and discarded in municipal waste. If the trunk does develop cankers it should be removed before allowed to fully die. This will ensure that the bacteria does not end up contaminating the soil in populations that are more difficult to manage.
This bacteria needs to feed inside damaged plant tissues in order to propagate. One strategy it has for survival is to raise the freezing temperature on the leaf surface allowing freeze damage to occur at temperatures as high as 46° F! While the bacteria exists on every continent in the world, it has highest concentrations in tropical regions. Management of the disease is done by thinning and improving air circulation in the canopy of the tree. Limit moisture on leaves as much as possible.
Pseudomonas mori
Symptoms of bacterial blight caused by Pseudomonas mori appear as irregular patches on the undersides of the leaf that appear soaked. Leaves curl, turn brown to black, and rot. Black lesions appear running lengthwise down new shoots. Leaves turn yellow and drop prematurely. Unfortunately, this species of bacteria is a little more malign than P. syringae and the best management practice is uprooting and burning the plant, and exposing the soil to air circulation. Commercial treatment includes the use of the chemical Streptomycin or Streptocycline.
ROOT KNOT NEMATODES
Meloidogyne incognita
Root knot nematode infestation is not usually immediately apparent. The plant grows slower and stunted, and leaves may appear smaller. Leaves turn yellowish and the edges begin to dry up and turn brown. The entire plant may wilt, and flower and fruit production is severely affected. The plant’s failure to thrive may be attributed to several other things by observation before an accurate diagnosis is achieved through root examination.
The roots of a tree infected with root knot nematodes are quite another story. They exhibit characteristic galls, knots, and twisting. Roots may be stunted as well and show areas where the root is split open like a baked potato.
Root knot nematode is common in sandy soils with a good loam humus that remains a little on the dry side. Commercial control is often done by deep ploughing in summer and applying Carbofuran 3G. Other control measures include amending the soil with neem cake, or applying beneficial predatory nematodes on a regular basis. This is the preferred organic treatment. Evidence of success with this method is apparent when comparing initial infestation with root knot nematode population 3 years later.
ROOT ROT
Macrophomina phaseolina
Symptoms of root rot include sudden wilting and withering of leaves. Plants affected by root rot fail to sprout after pruning and subsequently dry up. Both the primary and secondary roots rot, resulting in plants that can be uprooted easily. Roots turn black and root bark is decaying. Control measures primarily consist of uprooting and burning the entire plant and its roots. Allow churned soil to fully dehydrate. Apply neem cake and Bacillus subtilis at recommended doses. In isolated pot culture where mycorrhizae will not be encouraged application of Trichoderma viride will also provide substantial benefit. Commercial treatment includes a soil drench of carbendazim at recommended doses.
MULBERRY LEAF SPOT
Cercospora moricola
Symptoms of mulberry leaf spot include yellowing foliage accompanied by dark spots. Most often seen on the fruitless male selection available at most nurseries. Trees will generally survive without a fungicide treatment, however prevention is entirely possible by thoroughly cleaning up all fallen leaves.
TEXAS ROOT ROT/ COTTON ROOT ROT
Phymatotrichum omnivorum/ Phymatotrichopsis omnivora
Texas Root Rot, or Cotton Root Rot, which is commonly seen in the Southern United States, is a very serious condition. Most flowering trees are susceptible to this disease to some degree or another. Monocots such as dates and bananas are immune, and trees that excrete powerful root exudates such as pecans, pomegranates, citrus, and guavas are often observably more protected. Desert native trees are highly resistant.
It is most often observed in Summer when leaves of many species will wilt and dry on the tree in a matter of days. By the time it is observable the fungus has already spread throughout the entire plant’s vascular system. Uncommonly, the tree may live for a year. Mulberries appear to be less susceptible than some other species, though still affected.
The infecting fungus prefers tight clay soils of a high pH, that remain moist for long periods of time. The disease is spread as new roots come in contact with fungal material in the soil or old decaying infected roots. Chinese Evergreen Elms of 6-8 years in the ground are particularly sensitive to this disease. Since these trees are ubiquitous in the desert southwestern landscape plant palette I have learned to look for neighborhoods that have a high number of elm trees that are 8” in diameter or larger. These neighborhoods may be relatively free of the soil-borne fungus.
There is no cure for Texas Root Rot. Avoid contracting this fungus by avoiding the use of fertilizers high in nitrogen, as these may reduce the tree’s microbial disease protection network. Some mitigation measures exist, such as air drying soil, improving percolation, lowering pH by adding sulfur products. As soon as symptoms are observed, contact an arborist to schedule a consultation, as this disease can spread to the surrounding plants and trees. Official diagnosis can only be obtained by lab results, but some areas are particularly prone and arborists will know what they are looking for. Avoid replanting susceptible species in the same location.
ARMILLARIA ROOT ROT
Armillaria mellea
Armillaria root rot, known more often as oak root fungus or shoestring disease, can infect mulberry trees. Most of the rot infection will occur underground and internally, heartwood and roots are where the majority of the damage happens. The foliage will be diminutive, leaves may yellow or brown and drop prematurely. Top branches or limbs will be weak and die progressively down from the canopy. Red or brown mushrooms may appear at the base of the trunk or on surface roots.
SOOTY CANKER
Hendersonula toruloidea
Sooty canker is a common fungal disease that affects many species of plants, including mulberries. The disease is particularly prone during stress (sunburn resulting from over pruning is a big one), or after pruning, as spores enter exposed cambium tissue. The fungus sets in during the winter, but evidence is most apparent during the summer when discolored wet spots appear on the branches. Canker wounds appear on the branches and trunk. Leaves wilt and die back. Bark splits and may easily peel off the tree in paper thin strips, exposing a black powdery layer of spores. The mold will continue to spread, often taking several years to kill the tree.
If caught early it may be treatable. Prune off all infected branches, carefully disinfecting each cut with an alcohol or bleach solution. Paint areas with a fungicide or antibacterial mouthwash. Make sure that watering and fertilizing is consistent, but not overdone and that the tree is not stressed.
POPCORN DISEASE
Ciboria carunculoides,
Popcorn disease is a fungus-caused deformity of mulberry fruits that most commonly occurs in the southern United States, in which the individual carpels of the fruits swell to resemble unpopped kernels of corn and usually results in dry texture and drastically reduced palatability of fruits that manage to remain. Morus alba hybrids are particularly prone to this condition, but Morus rubra may occasionally exhibit infection as well. The disease carries on from one season to the next, so collecting and burning all infected and fallen fruits or sealing in bags and disposing of them in municipal waste collection will largely help control it, but the ripe fruit is still sufficiently attractive to birds, and so it may spread via that means. Even with cultural control measures of manually removing infected fruit, a hose-end spray application of Bordeaux fungicide, or Monterey Disease Control may still be necessary as a second line of defense. Unfortunately, weather and environmental conditions are factors and some years may be worse than others.
OTHERS
Other pathogens and pests that may bother mulberries and their fruits are – Cylinderosporiasis, curly-leaf viruses, thrips, beetles, mulberry barbel, wireworm, spider mites, mealy bugs, and various caterpillars including mulberry moths.