April Gardening Topics

Anthracnose on Modesto Ash

Anthracnose is a fungal disease caused by wet spring weather. The disease infects the new shoots as they emerge in spring. The leaves look scorched, turn brown and drop off. Dry weather may arrest the disease. Prune out infected twigs and branches. Fertilize the tree to stimulate vigorous growth. Fungicidal sprays may give some protection if properly applied but coverage is difficult. Spray information may be found at the UC Pest Note on Anthracnose. See below for Verticillium wilt on ash.

Avocado Trees, Brown Spot

The brown patch that looks like a turtle's back is called Carapace Spot. It is corky and usually cracked into angular divisions. It is caused by rubbing or brushing of tender young fruit on leaves or stems in the wind, but the fruit is usually undamaged under the spot.Just cut out the spot. More pictures of avocado problems can be found at UC Avocado information.

Avocado Trees, Pruning

Most avocado trees need little or no pruning except to manage tree size. Always prune sparingly and don't prune in late summer/early fall. If large branches are removed, it will stimulate growth all over the entire tree. Pruning should mainly be done on young trees. Remove dead or damaged wood at any time. Wait until new growth starts in the spring before removing freeze damage. What looks dead may not be. Avocado trees grow irregularly and can be shaped when young by cutting back the tip of a branch or pinching back the terminal bud of the upright shoots. Repeat this method for the first few years to develop a more compact form.

Citrus Fertilizing

In California, most soils contain adequate nutrients for growth except nitrogen. A one year old tree needs about a tenth of a pound of nitrogen and a 5 year old tree will need one to one-and-a-half pounds for the season. It's best to divide the fertilizing into 3 applications during April, June, and August. Purchase a balanced product that contains zinc. Spread the fertilizer evenly over the entire root area and water in.

Citrus Leaf Drop

Leaf drop from citrus trees is normal. Washington Navel oranges may lose over 3,000 leaves a day during peak leaf drop in the spring. Valencia oranges may lose about 1500 a day. Problems that can cause excessive leaf drop beyond these numbers are lack of water and a heavy infestation of spider mites. The tree's leaves will have brown spots if affected by the mites. You can wash them off with a strong water spray. Bud and small fruit drop is also normal.

Citrus Sooty Leaves

Sooty mold on citrus may be a byproduct of sucking insects such as aphid, mealy bug, soft scale or whitefly. Ants will protect these pests against predators in exchange for the honeydew that the pests produce. The sooty mold grows on the honeydew. Try washing off the sucking insects with a strong water stream. Next step is control of the ants. Ants may be managed by applying a sticky compound around the trunk and trimming limbs touching buildings or other access points. Baits at the base of the tree also help. For more information about specific controls, see the UCCE Pest Note on Sooty Mold.

Codling Moth

Codling moth larvae can cause a great deal of damage to apples, pears, plums and walnuts by penetrating the fruit and boring into the core. On apples, look for brown colored holes filled with frass. There are a number of non-chemical steps to control this pest. For that information, refer to the UCCE Pest Note on Codling Moths.

Modesto Ash Verticillium Wilt

Infected ash trees can wilt on only one side. The leaves turn yellow, then brown, and die upward from the base of the branch. The dead leaves may remain attached. Affected branches oftendie back. Verticillium wilt is one of the most widespread, destructive, soil borne fungal diseases. It attacks through the roots, clogging up the water conducting tissues. The tree usually recovers with good irrigation and fertilization. Resistant species are available.


This is a pest of California Live Oaks. The adult oakworm moth is tan-to-gray colored with a wing span of about an inch. It lays white eggs twice a year that turn reddish or brown before hatching. The first hatch is in November and overwinters on the leaves, growing and eating more as the weather warms. At full size, the larva is about an inch long with a yellowish green body, dark stripes down the side and large brown head. Outbreaks occur every eight to ten years in the Bay Area. In late March or April, look for little green pellets (droppings) falling from oak trees. A second generation of eggs hatches in mid to late summer. Trees may suffer no permanent damage beyond being unsightly. If you cannot tolerate the worms and their mess, further treatment methods are outlined in the UC Pest Note on Oakworm.

Peach Leaf Curl

It is too late for chemical control in April. This coming winter, use a dormant spray in December and again at leaf break in February. This year’s damaged leaves will eventually fall off and should be disposed of in the trash. The new leaves that are produced are generally fine, but the vigor of the tree may suffer. For more information see UC Pest Note on Leaf Curl.

Poison Oak

Poison oak is a California native plant that provides shelter and food for many native birds and other creatures. The down side is that at least 75% of humans develop allergic contactdermatitis to the plant. Removal of unwanted poison oak can be done by allergy-resistant people by pulling and digging or by application of herbicides. Under no circumstances should poison oak be burned. Herbicide application details are found in the UC Pest Note on Poison Oak.

Powdery Mildew

Powdery mildew fungus is a common disease on many plants and produces a white powdery appearance on leaves and sometimes other green parts. It can be found on roses, dahlias, chrysanthemums, peas and squash. Some rose varieties are so susceptible that you would be better off removing the plant. A homemade spray with baking soda may be used for control. To each gallon of water, add 2.5 teaspoons of light horticulture oil (or salad oil) and four teaspoons of baking soda. Use a fine spray on affected plants, but sparingly as some plants may show some sensitivity. More control methods are available in the UC Pest Note on Powdery Mildew.

Syrphid Fly

As an adult, it looks like a fly but has yellow and black stripes like a honeybee. In the larval stage, it looks like a soft, fleshy, green slug-like worm with a white stripe down the back about a half an inch long, happily eating aphids. This insect should be treated as a beneficial in the garden and protected. Photos are available of the Syrphid fly or hover fly.

Transplanting Tomato Seedlings

Try to plant your tomatoes after the soil reaches 65F for healthy growth (and nighttime temperatures over 55°F). Some kitchen thermometers will measure temperatures in this range. Here are two methods of transplanting tomatoes into the ground. The first is to plant deep vertically, right up to upper leaves on the plant. Remove those leaves that would be buried. The second method is to dig a trench, lay the plant on its side, cover up the roots and stem with soil. The leaves will start to turn upward and grow vertically. The stem portion that is underground will develop roots. Either method will provide you with a husky, healthy tomato plant. A number of tomato staking methods are available for reference.