| Hosts |
Botanical |
Symptoms |
Disease |
Notes |
Control |
| Fruit trees, esp. almond, nectarine, peach, and plum |
Prunus species. |
Holes in leaves that look like insect damage. Small tan, dead areas fall out to create holes. |
Shothole fungus |
Not harmful at moderate levels, but may get worse without treatment. |
Dormant spray in late November. |
| Lawns, especially Kentucky bluegrass. |
Poa species. |
Orange-red bumps (pustules) on leaf blades, spreading to coat the entire leaf in mid-winter. |
Rust of lawns. |
Most visible on lawns that have a high percentage of bluegrass, and which were not fed in late fall. |
Nitrate-based fertilizers in November and January will help manage it. |
| Lawns, ground covers. |
NA |
Familiar toadstool shaped mushrooms grow randomly in lawn, or in a line (following a decaying root). |
Mushrooms in lawn |
Grow on organic matter that is decomposing. Harmless decomposers, doing their job recycling wood that was incorporated for the lawn or on decaying dying or dead trees. |
No control. May continue to sprout for years. Probably not toxic, but don't count on it. |
| Maples |
Acer species. |
Death of small, twiggy branches and eventually larger ones, apparently randomly through the tree. |
Anthracnose blight (2) |
Attacks in spring and early summer. |
Prune out affected branches. Copper sprays may help prevent spread. |
| Peaches and nectarines; plums, apples, cherries. |
Prunus and Malus species. |
Contorted, curled, discolored, swollen leaves on peaches and nectarines; leaves curled inward on other trees. |
Leaf curl of fruit trees |
Peach leaf curl is caused by a fungus and only affects peaches and nectarines. Does not affect flowers or fruit. Aphids cause curled leaves on the other trees. |
Dormant spray in early February for peach leaf curl. Treat for aphids as needed on other trees, and control ants. |
| Rose family, apple sub-family; especially apples, pears, quince (fruiting); crabapples, hawthorns, loquats; Photinia, firethorn. |
Malus, Pyrus; Cydonia, Crataegus, Eriobotrya; Photinia, Pyracantha. |
Rapid dieback of flowering shoots and new growth. Leaves look burnt and don't fall off. Spreads rapidly down the plant stem. |
Fireblight |
Narrow temperature range: 55 - 80F, but spreads rapidly when conditions are favorable. Spread chiefly by bees as they visit flowers; may also infect through pruning wounds and new growth. Very virulent bacterial disease; can kill the plant entirely. |
Prune out infected branches well below the dead portion. Copper sprays are used on commercial crops when the plants are blooming, but frequent applications and full coverage are necessary. Avoid pruning Photinia in the spring. |
| Rose family--flowering pears, India hawthorn, Carolina cherry laurel, and more. Several different fungi cause similar symptoms. |
Pyrus kawakami; Rhaphiolepis; Prunus caroliniana. |
Dead spots on leaves. |
Leaf spot |
Don't plant Pyrus kawakami or Prunus caroliniana. Leaf spot on India hawthorn is prevalent on nursery stock, especially from coastal growers, but usually goes away here unless the plants are constantly sheared, sprinkled overhead, or planted in too much shade. |
Prune lightly; thin plants, don't shear them. Rake up fallen leaves. |
| Roses |
Rosa |
Yellow and black spots on leaves, coalescing into entire yellow areas, followed by defoliation. Purplish blotches on stems. Spreads very rapidly from leaf to leaf. |
Downy mildew |
Most damaging on overgrown or dense, leafy roses such as miniatures and climbers, or on plants that haven’t been pruned during the winter. Can entirely defoliate the plant. Disease stops with hot, dry weather. |
Blackspot of roses looks similar.
Here are illustrations of common rose diseases. |
| Roses |
Rosa |
Leaves emerge with yellow mottling or striping. Growth may be stunted. |
Mosaic virus of roses |
Virus has been in the plant since it was propagated, even if the symptoms took years to be visible; wholesale growers try to work with only virus-free propagation stock. |
No control. You will not spread this on pruning shears; it is transmitted in grafting. Damage from herbicides looks similar. |
| Roses; snapdragons; hollyhocks; St. John's Wort, and more. |
Rosa, Antirrhinum, Alcea, Hypericum, etc. |
Red or black bumps (pustules) on the undersides of leaves, with a corresponding yellow spot on top. |
Rust of woody plants and perennials. |
Each rust is host-specific; i.e., it lives only on the kind of plant you find it on, so the rust on your roses won't go on your lawn and vice versa. The spores are heavy, so they spread only by splashing water such as from windy rainstorms or sprinklers. |
Dormant season pruning removes overwintering spores. Raking out leaves at that time is important. Picking off affected leaves helps. Irrigation management is most important: use drip irrigation or soakers, avoid sprinklers. |
| Seedlings, bedding plants. |
NA |
Seedlings collapse and die rapidly; stems are brown and soft. White mold (downy mildew) will grow on dying seedlings. Young transplants die shortly after planting. |
Damping off of seedlings |
Caused by Pythium or Rhizoctonia fungus, among others. Seedlings grown under low light conditions, too close together, or in overly rich soil may die suddenly. |
Move seedling trays outside during the day; spread the pots apart for better air movement. Thin seedlings as soon as they have produced true leaves (the second set of leaves to emerge). Avoid planting heat-loving summer annuals too early. |
| Sycamores/ Plane trees |
Platanus species and hybrids |
Irregular-shaped spots on leaves, coalescing and running down the vein; leaves fall off, sometimes in large numbers. |
Anthracnose blight (1) |
Common in April and May. Tree will drop many leaves, but will outgrow the disease. Resistant hybrids include ‘Bloodgood’ and ‘Columbia’. |
No control necessary. Tree will outgrow it. |
| Sycamores/Plane trees; Roses; Crepe myrtles; Japanese maples; lawns, and many more. |
Platanus, Rosa, Lagerstroemia, Acer, etc. |
White mildew growing on leaves, especially on new growth. Disease continues into summer, as it is tolerant of low humidity. |
Powdery mildew |
'Columbia' is a resistant hybrid Plane tree. Hybrid crepe myrtles and many rose varieties are resistant. |
Spores can be blasted off the leaves with water early in the day. Tree will outgrow it. |
| Tomatoes |
Lycopersicon |
Spots on leaves of young plants, spreading up onto new growth. |
Early blight, bacterial speck |
Common on bedding plants and will persist on young transplants. Stops spreading in hot dry weather. More of a problem in humid climates. Late blight disease is a serious problem in areas with summer rain, but not in the Sacramento Valley. |
Pick off affected leaves. |
| Tomatoes, peppers, eggplants. |
Lycopersicon, Capsicum, and Solanum |
Rotten, discolored flesh on the bottom (the blossom end) of the young developing fruit. |
Blossom-end rot |
Long thought to be caused by a calcium deficiency, but actually just a symptom of fluctuating temperature or irregular watering causing damage to the root system. |
Common on the first fruit that sets due to changes in temperatures and soil moisture in spring. Water evenly and thoroughly. Pick off and discard the damaged fruit. No need for calcium supplements. The next fruit that sets will develop normally. |
