Home & Garden

Tree, plant and bush diseases and how to prevent, detect and control them

An anthracnose lesion is seen on an almond nut.
An anthracnose lesion is seen on an almond nut. Modesto Bee file

Several disease pathogens are carried onto susceptible trees and bushes during warm, wet, windy spring weather. “An ounce of prevention’ now, before the spring rains arrive can help reduce disease problems including camellia blight, anthracnose disease on sycamores, elms and oaks as well as fireblight on members of the pome or apple/ plant family.

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Camellia blight is a common fungal disease here in the Central Valley. The fungal spores can survive for several years on soil or mulch surfaces and can be found on the surface of the potting soil in nursery containers. As temperatures warm in spring, small mushrooms form on the soil surface and spurt fungal spores that are wind-carried onto damp camellia petals. Small brown blotches form on petals; the blotches gradually spread over the entire flower and the flower drops.

Pick up all fallen camellias regularly and remove all blotched flowers as soon as you spot them. During dry summer weather, replace mulches underneath camellia bushes that have had camellia blight. Dispose of the flowers and the old mulch in the green waste bin, not the compost pile.

Anthracnose fungi overwinter on fallen leaves and twigs. In spring, the fungi are spread by splashing rain or irrigation water onto new growth and new leaves; mature leaves are seldom affected. The fungi cause dry-looking spots on the leaves and can cause cankers on bark: Chinese elms can develop really large cankers. Infected leaves turn brown and fall prematurely. The early spring leaf loss is usually followed by another crop of leaves in dryer, hotter weather that is not affected by anthracnose.

Rake up all fallen leaf and twig debris regularly underneath susceptible trees. Hire a certified arborist to prune out infected wood and to create good air circulation. Fungicide root injections for anthracnose are not recommended.

Fireblight bacteria live in cankers or patches of dead wood on bark that was infected the previous season. During moderate to warm spring weather, the bacteria multiply and the cankers produce a watery light-tan ooze that is carried by spring rains, bees and other insects onto open flowers. It might be difficult to see the cankers unless they are large. A fireblight infection will become obvious as growth resumes and the disease turns small twigs and branches black with crooked tips.

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Prune out any infected wood that you see now to slow fireblight’s spread. Fixed copper sprays are most effective when applied when daily high and low temperatures average above 120 degrees, say 55 degrees at night and 75 during the day. Early spraying in colder temperatures will not be effective.

Note: Plant a Row for the Hungry (PAR) is once again hosting the annual collection of backyard citrus for delivery to the local food back to be distributed to people in need. The PAR event will take place at the Garden of the Sun, 1750 N. Winery in Fresno this Saturday from 9:30 to 11. A free class on citrus will also be offered at 9:30 a.m.. Fresno County has a citrus quarantine in effect to prevent the spread of citrus greening disease that is spread by the Asian citrus psyllid. Please make sure to remove all leaves and stems from donated fruit before bringing it into the garden. To avoid tearing citrus skins, use pruning shears to cut stems at their base.

Elinor Teague: etgrow@comcast.net
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