Related to jasmine, lilacs, and Forsythia, olive trees have been cultivated since the Bronze Age, some 6,000 years ago, for oil, fruit, and wood.
Growing olives
Unpruned trees can reach a height of 26-49 feet. The trunk tends to twist and becomes beautifully gnarled as it ages. Olive trees are evergreen, retaining their oblong, silvery leaves year round. Small white flowers occur on the previous year’s growth, which then produce the olive fruit. Some people are allergic to the pollen of the olive tree. Botanically, the fruit of an olive tree is known as a drupe, as are plums, cherries, and almonds. Olive trees (Olea europaea) prefer soil that is less than ideal. Like many herbs, olives thrive in rocky, poor quality soil. They can perform well in clay soil as long as it has good drainage. Soggy soil will kill an olive tree. Olive trees grown in nutrient rich soil are more disease prone and they produce poorer quality oil. Olive trees are very drought tolerant and they love lots of direct sunshine. They also seem to have a preference for coastlines. When selecting a site for olive trees, keep in mind that they may live for centuries. Most olive cultivars are self-sterile, which means they cannot pollinate themselves, so you may need to plant two trees. Olive cultivars can be primarily for table olives, olive oil, or both. The Santa Clara County Master Gardeners website recommends Ascolano, Manzanillo, Mission and Sevillano cultivars for the Bay area. You can contact your local County Extension office to see which cultivars are best for your area. Olive trees can be propagated by cuttings and layers, from suckers, or grown from seed. To ensure that you are planting a specific cultivar, it is a good idea to buy root stock from a reputable nursery. Cuttings and suckers can be started by covering with aged manure and watered regularly. Seeds are more likely to germinate if the oily outer flesh (pericarp) is encouraged to rot slightly by placing it in hot water or in an alkaline solution, but olives grown from seed often do not produce fruit. Once trees are established, fertilizer should be applied annually, just before flowering. Olive tree roots tend to be shallow, so avoid digging nearby. This is also what makes them excellent container plants. Pruning olive trees Olives grow very slowly, but pruning is necessary for good health and fruit production. Since fruit is borne on the previous year’s growth, two-year old wood should be removed, to maintain a manageable size. In many commercial orchards, fruit laden branches are simply cut off the tree before the olives are removed. Pests & diseases of olive trees The olive fruit fly is a common pest that lays its eggs in the fruit. Once the eggs are laid, the fruit becomes unfit for consumption. Dusting with kaolin clay is an effective organic preventive measure. Rabbits can cause considerable damage to young trees by eating the bark. If the bark is removed all the way around the tree, girdling it, the tree will likely die. Verticillium wilt is a serious threat to olive trees in California. Curculio beetles, black scale, some caterpillars, and the Cycloconium oleaginum fungus can also cause problems. Once an olive tree is established, its extensive root system can recover from the complete destruction of the above ground portion of the tree. Harvesting olives Olives are harvested in September through February, depending on the cultivar and the use for the fruit. Green (unripe) olives are picked September to November, blonde olives are picked October to November, and black olives are picked mid-November through early February. Generally, olives are picked by hand to preserve the fruits’ shape and texture. Oil quality from fallen fruit is not as good as handpicked fruit because of bruising. Semi-dwarf varieties may produce 30-40 pounds of fruit, each year, while full sized trees may produce 100 pounds each year. Making olives edible Like acorns, uncured olives are quite bitter. This bitterness is caused by oleuropein and other phenolic compounds. Olives must be cured and fermented before they are eaten. The only exception is the Greek Throubes olive, which is allowed to dry on the tree and can be eaten as is. There are several commercial curing methods:
These slow-growing trees can produce fruit for the next several hundred years or more. Some olive trees are over 2,000 years old and still produce fruit!
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Dormant oils are specifically designed for use on trees during the dormant season. They have a heavier viscosity than other horticultural oils and they stay on the plant longer, as a result. This is great when you are trying to suffocate insect pests, but it can be devastating to foliage if temperatures rise, a condition called phytotoxicity. Summer or horticultural oils are lighter weight and evaporate more quickly, reducing the likelihood of burnt leaves. Effectiveness of dormant oils Dormant oil applications create barriers that block respiration of many, but not all, insects and limit the spread of infectious diseases. Spider mites, San Jose scale, leaf curl, powdery mildew, shot hole, and scab infestations are common reasons for applying dormant oil applications in winter or early spring. Pacific or two-spotted spider mites, peach twig borers, navel orangeworm, and oriental fruit moth are not affected by dormant oils alone. These oils are not recommended for aphid control. Dormant oils can suffocate the eggs of many garden pests and deter females from laying eggs on specific trees. As a side benefit, the application of dormant oils has been shown to delay bud break, protecting tender new growth against potential frost damage. It has also been found to enhance the aroma of ‘Golden Delicious’ apples and increases the diameter of oranges. How to use dormant oils Dormant oil application should be done after pruning and is most effective after a foggy or drizzly day. Pump sprayers can be used to apply dormant oils, but it is important that every surface is sprayed: trunk, stems, twigs, and tops and bottoms of any leaves. If you have several trees, this can be a bit of work. Problems associated with dormant oils One of the biggest problems associated with dormant oil is the risk of hot weather. A single sunny day can transform fresh, young, green leaves into cinders. This is especially true up to 30 days after sulfur or other fungicides have been applied. [I speak from personal experience.] Also, heavy dormant oils can harm beneficial insects right along with the pests. Dormant oils are not recommended for use on walnut trees BE SURE TO FOLLOW PACKAGE DIRECTIONS EXACTLY
No, we are not talking about naive carnival “marks” who are easily separated from their money. In the garden and orchard, suckers (basal shoots) are new plants that emerge, not from a seed, but from meristem tissue in the root system or at the base of a mature plant. This is a form of asexual reproduction, also known as vegetative reproduction. The offspring created through vegetative reproduction are clones of the mother plant, or genet. Suckers can be an excellent way to get new, identical plants, or they can suck the life out of a marginally healthy tree. Let’s take a look at suckers and see how they can be used and/or managed. What causes suckers?
Suckers can emerge when a tree is water stressed or as a natural response to warmer weather and moisture. Over pruning can also stimulate a tree to produce suckers. At the same time, regular pruning can help a tree stay healthy without initiating sucker production. And sometimes, trees just put out suckers and we don’t know why. Spring emergence of suckers In spring, it is not uncommon to see a cluster of new stems emerging from the base of the tree, or several feet away from the trunk. Most tree root systems are approximately three times the size of the tree canopy. Suckers can emerge anywhere along that root system. If you are trying to create an orchard or want to gift a clone of your tree to someone else, you can use these suckers to your advantage. When removing suckers for propagation, be sure to get some of the root tissue along with the sucker. These baby trees will need lots of TLC to get started: rich soil, frequent watering and filtered sun will help the roots start supporting themselves. How to remove suckers Unless you are trying to propagate new trees, all suckers should be completely removed. Suckers pull energy and nutrients from the tree. Removing suckers diverts that energy back into fruit production and the overall health of the mother tree. Do not use herbicides to kill suckers. As long as they are attached to the mother tree, you risk poisoning both. Unlike other pruning jobs, where a clean cut is desirable, sucker removal is best done by ripping the sucker from its attachment. By tearing, rather than cutting, the bud is more likely to be damaged, reducing the chances of it coming back. If you (or your neighbor) have a tree that you want to reproduce and no suckers are available, you can always try grafting a scion. NOTE: Most fruit trees are actually two trees grafted together. Horticulturists take the root stock of a growth hardy variety and then graft it to a variety that produces a desirable fruit or flower. You get the benefits of both. The problem with suckers is that they emerge from the root stock and not the fruit-producing variety. This is true of roses, as well. Unless you know for a fact that your fruit tree is not from grafted stock, it is best to tear off suckers and graft scions instead. Stolons & rhizomes Stolons and rhizomes behave very much like suckers. Stolons are stems that grow on or just below the soil surface, while rhizomes are roots that grow in the same region. In both cases, adventitious roots emerge from nodes to establish new plants. Strawberries, blackberries, raspberries, potatoes and mint propagate using stolons. Do you have room for an almond tree? I planted a bare root almond tree two years ago and it just started to blossom last week. The flowers are so pretty! Almonds are California’s third largest agricultural product and the drought has caused prices to skyrocket. Almonds are an incredibly healthful snack and the trees are lovely additions to a landscape. Almond pollination According to Wikipedia, “The pollination of California's almonds is the largest annual managed pollination event in the world, with close to one million hives (nearly half of all beehives in the USA) being trucked in February to the almond groves.” Imagine that! Unless you get a self-pollinating variety, you will need to plant 2 or 3 trees to get any fruit. Almond's bittersweet history Now, I’m not sure how people started eating almonds because the fruit of wild “bitter” almond trees is poisonous. Bitter almond trees contain a chemical called glycoside amygdalin, which turns into deadly hydrogen cyanide (prussic acid) when the fruit is injured by chewing. Apple, cherry, peach, plum, pear, and apricot seeds, and cassava root (tapioca) also contain cyanide compounds, but it takes an awful lot of any of these to get sick. The trees we buy now are called sweet almonds and they are safe and they taste better! The almond tree Almonds are deciduous, which mean they drop their leaves in winter. They can grow 13-33 feet tall, with a 12” diameter trunk. The canopy is 10-15 feet wide. Dwarf varieties are being developed, but their productivity is still questionable. Almonds do not do well in containers. Unlike avocados, which can take 10 years or more to produce, almond trees bear fruit as early as their third year! To improve root development, remove flowers the first couple of years. Almonds are related to peaches, nectarines, cherries, plums, and apricots, all members of the Prunus genus, which, in turn, is a member of the rose (Rosaceae) family. The nut we are all so familiar with is actually the fruit, or drupe, of the almond tree. Botanically, it is not a nut at all. That’s why they are called stone fruits.
How to grow almonds People have been growing almond trees for 6,000 years, in South Asia and the Middle East, and you can, too. Almonds were introduced to California in the 1840s. Almonds grow very well in Mediterranean climates. Your first decision about growing almonds will be location. Almonds need lots of sunlight and they prefer temperatures between 59 and 86°F. The buds have a chilling requirement of 300 to 600 hours below 45°F. Chilling requirements are accumulated hours of cold temperatures that cause vernalization, or the ability of a plant to bud and flower. They do best in mild, wet winters and hot, dry summers. Almonds do not like soggy, heavy soil. They are a deep rooted tree and should be planted 20-25 feet away from any other tree. Almond trees benefit from the following seasonal care: Winter
Almond pests & diseases If you are going to grow almonds, you will need to know what problems to watch for. This include leaf spot, mites, leaf-footed bugs, voles, crown gall, Eutypa dieback, brown rot, shot hole disease, bacterial canker, navel orangeworms, redhumped caterpillars, rust, and peach leaf curl. The better you understand what to look for, the quicker you can nip the problem in the bud. Birds and squirrels can also be a problem. I protect my almond tree with a tree cage. Rather than planting an ornamental tree, almonds can provide 30-40 years of delicious food for you and your family! Unless you have super human strength and are able to lift a young tree, bare root trees are the way to go. January and February are an excellent time to plant bare root trees, such as avocado, apricot, apple, peaches and nectarines. Rather than living in a pot filled with heavy soil, these saplings are dormant and, well, naked. There are many benefits to planting bare root trees:
To ensure the success of a bare root tree, follow these steps:
Before you know it, your bare root trees will be putting out buds! To give the tree the time it needs to develop a strong root system, it is a good idea to remove flower the first 2-4 years. Avocado trees are fascinating. Unlike most fruiting trees, which can be either self-pollinating or not, avocado trees are both and neither. Confused? Read on! Avocado flowers Avocado trees flower with a behavior called synchronous dichogamy. Each flower is both male and female, but at different times. Also, there are two kinds of flowers: Type “A” and Type “B”. "A" avocados include Haas, Gwen, Lamb Haas, Pinkerton, Reed, GEM and Harvest varieties. Bacon, Ettinger, Fuerte, Sharwil, Sir Prize, Walter Hole, Zutano, Marvel and Nobel are "B" avocados. When an "A" avocado flower first opens in the morning, it is female for a few hours and then it closes. The next day, the same flower reopens in the afternoon, but this time it is male. When a "B" avocado flower opens for the first time, in the afternoon, it is female. Then it reopens the next morning as a male. Since a mature tree produces over one million flowers in a season and the flowers open on different days, there is no need for another tree for pollination to occur. How to grow an avocado tree Many of us have used toothpicks on an avocado pit with dreams of a productive tree. You can make that dream a reality with these tips (and a lot of patience).
Young trees need to be watered two or three times a week. Water heavily, but let the soil dry out between waterings. By the end of the first year, water once a week. A mature tree will use as much as 20 gallons of water a day during the peak of summer.
Avocado pests and diseases Common avocado diseases include avocado root rot, bacterial canker, dothiorella canker, leaf blight, phytophthora root and crown rot, stem blight, sunblotch, and verticillium wilt. Avocado lace bugs, latania scale, mealybugs, mites, nematodes, omnivorous loopers, orange tortrix moths, soft scales, thrips, and whiteflies will all be attracted to your avocado tree. Birds and squirrels will join in the feeding fray, so you may want to build a tree cage around part of your avocado tree. If you have the time and the space, growing an avocado tree in your yard can provide decades of the best guacamole ever! Whenever warm, dry areas get much-needed rain, gardeners must be aware of a disease that starts showing symptoms in winter and spring - citrus blast. Also known as bacterial blast or black pit, citrus blast is a bacterial infection that becomes visible after periods of wind-driven rain.
Symptoms of citrus blast The bacteria, Pseudomonas syringae, enter through thorn punctures, wind damage, and insect feeding sites. This disease is more likely to appear on the south-facing side of your citrus tree. The first symptom of citrus blast is dark lesions on the leaf petiole. The petiole is the little stem that connects a leaf to a twig. Once the bacteria enter through these lesions, it travels down the leaf axil, or stem, and into the rest of the tree. Infected leaves wilt quickly, curl up, and dry on the tree before breaking off. Usually, the petiole is left attached, creating a larger wound for further infection. Diseased areas may also show a reddish-brown scabbing, and entire twigs may die. Citrus blast will also leave black spots on the fruit. New growth is especially vulnerable to citrus blast, so it is a good idea to minimize fall and winter feeding and pruning to reduce winter growth in areas prone to citrus blast. Preventing citrus blast Applying fixed copper or Bordeaux sprays before the first rain can reduce the likelihood of bacterial infection. These treatments are also effective against fireblight, walnut blight, black spot on roses, peacock spot on olives, downy mildews and powdery mildew on grapes, and leaf curl, and shot hole on nectarines and peaches. Bordeaux sprays consist of copper sulfate, lime, and water. You can make your own Bordeaux spray by combining 3-1/3 tablespoons of copper sulfate and ten tablespoons of dry hydrated lime (calcium hydroxide) in one gallon of water. These materials are available at most garden centers. Avoid using slaked lime (calcium oxide), as it can burn your skin and eyes. Diseased twigs should be removed and thrown in the trash. As you prune out diseased areas, sanitize your tools with a household cleaner between each cut to avoid spreading it to healthy plant tissue. To prevent citrus blast, plant citrus trees with some wind protection and remove any dead or diseased twigs as early as possible. If you are planting bare root trees this January, you may need to provide tree supports for the first year or two.
Structural support
Structural support, or anchor staking, prevents the root ball from moving while the new roots are established. Tree supports hold the young tree by tying it to 2-4 posts with straps. Do not use rope, wire, or hose segments, as these put too much pressure on a narrow area, risking bark damage. Straps spread the pressure out over a wider area, keeping the bark healthy and intact. Since your tree will be growing, be sure to keep the strap around the trunk loose. Damage caused by tree supports Tree supports are only needed when a young tree cannot stand on its own or if it is being planted in an area with heavy winds. Also, tree supports should be removed as soon as they are not needed. Too many trees have become structurally unsound or vulnerable to pests or disease because the bark was allowed to grow over the support system. Don’t do this to your tree! You may be surprised to learn that unnecessarily staking trees can actually hurt them in the long run. Plants grow in response to their environment. They lean toward sunlight and brace themselves against breezes, developing strength as they do so. This is called thigmomorphogenesis. Young trees that are prevented from developing this strength are more prone to breakage as they get bigger. If you absolutely must provide tree support, it should be installed when the tree is planted, to avoid disturbing or damaging tender root systems. Tree supports should be placed one foot from the tree, with no branches touching. There is a correct height for tree support ties. Too low and no support is given. Too high and the tree won’t learn how to stabilize itself. To determine the correct height, grasp the trunk of your floppy new tree and gently try to bend it over with the other hand. As you move your hand up the trunk, you will reach a point where the flop ends and the tree bounces back to an upright position. This is the magic spot. Your stakes should only be a few inches taller than this height to avoid damaging new branches as they come in. Strong winds ripped a heavily laden branch from one of my orange trees in January 2016. While the damage was unfortunate (and preventable), the heady aroma was purely delicious! After pruning the damaged limb to help it heal faster, I plucked the fruit and gave it a good wash before bringing it in, hoping it was ripe enough. By the way, citrus trees have wicked thorns! Be sure to use caution when working in or around them. Citrus origins There’s no mistaking the heavy, oily skin of citrus. This skin provides moisture holding protection from its subtropical origins. Hailing from Southeast Asia and Australian, modern citrus fruits evolved from small berries found on pummelo, citron and mandarin orange trees. Crossing these three ancestors in different ways has led to the creation of oranges, lemons, limes, grapefruit, tangelos, kumquats and dozens of other variations. How to grow citrus Citrus trees and shrubs grow easily in warmer regions. They can be put in the ground or grown in containers. They prefer well drained soil and as much sun as you can provide. Since the fruit is very heavy, it is a good idea to protect them from heavy winds. Citrus trees can produce for 50-100 years, so use care when selecting a site. Be sure to feed and water your citrus regularly for maximum production. One-year old trees should be given 1/10 of a pound of nitrogen each year, while mature trees will need approximately 1-1/2 pounds. These amounts should be divided into three separate feedings in April, June, and August. If your trees are stressed by drought, you may want to spread those feedings out, using lighter amounts during the growing season, February through May. Blood meal is an excellent source of nitrogen, without all the fillers. Watering citrus Dumping too much water on your orange tree can leading to splitting. Split citrus are usually not ripe enough to eat but they provide the perfect breeding ground for bacteria, fungi, and other pests. Like mummies, they should be discarded as soon as they are seen. Harvesting citrus
Knowing when to harvest your citrus can be tricky. Lemons and limes have distinct colors when they ripen, but Valencia oranges may still have a greenish tint to the skin when they are ripe. The only reliable way to tell if your fruit is ripe is to taste it. Unlike climacteric fruits, citrus does not continue ripening once they are removed from the tree. The best place to store your citrus is on the tree. If you do pick more fruit than you can use (or a branch breaks, dumping two dozen oranges in your basket), you can store them for 4-6 weeks in the refrigerator. You can also treat yourself with some fresh squeezed orange juice or a lemon drop! Personally, I grated the zest from two oranges over some sliced beef, juiced four oranges, and stirred in some corn starch, soy sauce, ginger and a pinch of Ghost Pepper for a delicious Spicy Orange Beef Stir-fry. Citrus pests Once established, citrus trees are pretty rugged. Here are some common citrus pests:
Citrus production Citrus trees are heavy producers. A mature tree can produce up to 300 oranges a year. Do the math and that comes out to over 130 pounds of oranges! If you find yourself swimming in citrus, here are some fun uses for lemons: • Remove fish smell from hands • Neutralize alkalinity from masonry work or Burning Man gear • Combine with salt to clean copper • Apply to stains on fabric and leave in the sun • Grind up peels in the garbage disposal for a fresh scent • Rub lemon on mold and it disappears! • Make your own invisible ink! Do you have any good ideas for using citrus? Share them here! Mummies in the garden?!!? If you have fruit or nut trees, you may have noticed brown, shriveled-up fruits hanging from branches or splattered onto the ground. Other parts of a plant can also experience mummification, but fruits are the most obvious. These fruits are called mummies, and you do not want them around. Fruit mummies are rotted fruits that have turned dark, wrinkled, and hard. The rotting is due to fungal diseases such as brown rot and anthracnose.
Mummies are what happens when fungal structures replace healthy plant tissues. Fruit mummies are breeding grounds for hundreds of millions of fungal spores that can wreak havoc on your current or next summer’s harvest. Mummies can occur in any fruit-producing tree, shrub, or vine. Reduce the chance of spreading the responsible pathogen by bagging the mummy in plastic before removing it from the tree and throwing it in the trash. While scientists debate the Latin name of this little fungus (depending on which plant it attacks and who you talk to), Eutypa dieback is no joke. Also known as dead arm disease, Cytosporina, and gummosis, you often won’t see symptoms in time to save the tree. Symptoms of Eutypa dieback In apricot trees, the leaves on an infected branch will wither and die but remain attached to the tree (flagging). Oozing cankers occur along lower limbs, and the bark turns darker. Two years after Eutypa dieback infection takes hold, grape vines display leaf cupping and distortion, chlorosis, and stunted new growth. A cross-section of the wood shows V-shaped cankers. Vulnerable plants This insidious microorganism moves toward the trunk, killing the entire tree or vine. Also, the fungus responsible for Eutypa dieback seems to be broadening its dietary preferences to include almond, apple, blueberry, citrus, fig, kiwifruit, nectarine, olive, peach, pear, plum, and walnut, as well as Ceanothus spp., chokeberry, crab apple, oak, oleander, poplar, native California buckeye, big-leaf maple, and willow. Remove infected trees and vines immediately to avoid spreading to healthy plants. Preventing Eutypa dieback Like most fungi, moisture is necessary for their development. While most pruning occurs in winter, plants susceptible to Eutypa dieback are best pruned in summer. All pruning cuts are wounds. While trees and vines can develop a protective callus, these cuts need time to dry and heal. Never apply sealants to these wounds. Sealants hold moisture in, creating the perfect habitat for disease. If it rains 2-6 weeks after pruning, the Eutypa dieback fungus can take hold and kill your tree. Improperly aimed sprinklers can cause similar risks. Eutypa dieback controls
If you discover an infected branch, you may be able to save the plant by removing infected limbs at least 12” below any internal symptoms. Examine the exposed cross-section for signs of infection. Dip your pruning tools in a household cleaner between each cut. Keep cutting down the branch until you reach healthy wood. Unfortunately, this method is only marginally successful. The bare branches of January make this an excellent time for pruning.
Winter pruning helps improve the appearance and health of trees, shrubs, and roses. The only exception is apricot and cherry trees, which are susceptible to Eutypa dieback. Apricot and cherry trees are best pruned in the dry months of summer. Pruning goals Different plants have different pruning needs, but the overall goals are the same: a balanced structure, adequate airflow, and the retention of productive limbs. There are two types of pruning cuts: thinning and heading. Heading cuts control height, while thinning improves air flow and sun exposure. Keep in mind, while pruning, that new growth will head in the direction of the remaining buds. The first goal of pruning is to remove dead, diseased or crossing branches. Dead and diseased limbs can allow pests and disease easy access into healthy tissue. Crossed branches will rub against each other, causing similar problems. You will also want to trim away branches that are angled too closely together and those that hang downward. Proper pruning protects people and property Structural pruning reduces the likelihood of uprooted trees falling on you or your house. Trees with too much weight to one side also risk splitting the trunk and killing the tree. Pruning early in the tree’s life can create a safer, more balanced structure. While the depth and spread of tree roots depends on a number of factors (soil structure, irrigation, variety and age of the tree, and more), pruning can help the root system keep your tree upright. To give you an idea of how much weight we are talking about: an average mature hardwood tree, with a circumference of 100” inches at chest height, weighs nearly 13,000 pounds! Your average commuter car weighs 2,800 pounds - so imagine 4 or 5 cars hitting your roof in a storm to see why good pruning is so important. How to prune larger branches Pruning larger branches (those with a diameter of 2" or more), it is important to use multiple cuts to avoid peeling the bark beyond the final cut and damaging the remaining branch. In drought-prone areas with heavy clay soil, moisture retention is an art that most plants have mastered. This also means fungal diseases can be a real problem. Roses and fruit trees are especially vulnerable to brown spot, rust and fireblight. Pruning for good airflow between twigs and branches can help reduce these diseases. It can also provide sunlight to inner leaves, which translates into more vigorous growth and heavier fruit and flower production. Too much pruning is bad Now, as I’ve said before, too much of a good thing can be a bad thing. Excessive pruning can expose interior branches to sunburn. Also, while pruning some or a little can promote new growth, heavy pruning can cause irreparable harm or death to the plant. Before you start pruning, research the specific variety of plant to learn about its natural growth and shape. For example, some trees produce fruit on last year’s growth, while others produce fruit on new growth. There's no sense in cutting off your nose to spite next summer's harvest! Fruit trees The backyard orchardist will generally want trees that are small enough to make harvesting fruit easier, so you will want to use heading cuts to reduce the height of your trees. Branches that grow vertically tend to be more vegetative, while horizontal branches produce more fruit. Branches growing at 45 to 60-degree angles tend to do both. When you cut off the end of a vertical branch, phytohormones, such as auxins, will cause the remaining buds will send out new growth horizontally. When you tip a horizontal branch, it will send out new fruiting wood. This is also a way to prevent too much fruit developing and risking a broken branch. It is always a good idea to remove suckers and water sprouts. Water sprouts are flimsy twigs that quickly grow vertically, directly from the trunk or older branches. Suckers are similar growths that occur at the base of the trunk or from the root system. These growths drain energy from the plant without providing any benefits. Roses In Mediterranean climates, roses never go completely dormant, but winter is still the best time to prune for better spring and summer blooms. Generally speaking, you will want to remove 1/2 to 2/3 of the existing bush. Remove dead, diseased and crossing branches and then reshape the bush for better airflow. You can learn more about pruning roses at the San Jose Heritage Rose Garden. When pruning, it is best to cut close to the branch collar without cutting into it. You also want to avoid leaving nubs that interfere with a plant’s ability to heal itself. There is generally no need to apply sealants to pruning cuts. Plants have evolved an effective system for that all on their own. Finally, be sure to keep your tools sharp and to clean your cutting tools between cuts. Use a household cleaner, such as Lysol. Otherwise, you may be spreading disease to healthy plant tissue. It can be incredibly rewarding to take before and after photographs of your pruning work. Feel free to share them with us! Fire blight is a bacterial disease that frequently attacks trees in the pome family. Pomes include apples, pears, quince, and crabapple. Fire blight can also strike raspberries and blackberries. The Erwinia amylovora bacterium is the cause of fire blight, but you’ll never see it without a microscope. The most common first sign of infection is the die-off of an entire twig. The dead leaves hold fast to the stem throughout the growing season as the infection spreads.
Fire blight can be fatal to fruit trees and is difficult to manage. Carefully monitoring your trees when they flower can provide early warning. Fire blight enters through the blossoms, carried in by bees and other pollinators from neighboring infected trees. As blossoms become infected, they wilt and turn dark brown. The infection then spreads down the twig. Very often, the tip of the diseased twig will curl into a shepherd’s crook shape. Insects pick up the bacteria from small, insignificant-looking cankers that become active in spring. These cankers are dead tissue from the previous year’s infection. A clear, tan ooze may drip from these cankers. Each droplet can contain millions of bacteria. Prevent fire blight by applying a Bordeaux mixture in the fall and winter. Inspect suspect twigs by scraping off the bark and cambium layer to see if pink or orangish-red streaks are visible. Once identified, the only treatment is the removal of the diseased tissue. The cut should be 8-12” below the infected area. Be sure to sanitize the pruners with a household cleaner after each cut to prevent infecting healthy tissue. Are the bottoms of your oranges staying green? If so, your tree (and citrus growers everywhere) are in big trouble. Huanglongbing (HLB), or citrus greening, is a vascular disease of citrus trees that makes the fruit inedible. The HLB story In 1998, Florida citrus growers saw Asian (Diaphorina citri) and African citrus psyllids (Trioza erytreae), or two-spotted citrus psyllids, for the first time. Insects the size of aphids, these citrus psyllids can carry a bacteria (Liberibacter spp.) fatal to citrus trees. American scientists didn't identify the disease until 2005. [China's first case occurred in 1943.] By 2014, HLB had caused $4.6 billion in damage to Florida's citrus crops. As of 2023, HLB has spread to 33 countries, plus California and Texas. HLB: tree killer HLB can kill a tree within five years of infection. Because this disease threatens the entire citrus industry, trees infected with HLB must be destroyed and removed by professional arborists. [You may be able to get assistance from your local Dept. of Agriculture on this.] To do your bit to save the world's oranges, lemons, limes, and grapefruits, start by learning what HLB looks like. Symptoms of HLB The obvious symptom of huanglongbing is the fruit remains green on the bottom. By this time, the disease may have spread far and wide. Watching for earlier signs of HLB can prevent that spread. The first symptom of huanglongbing is yellowing veins. Neighboring tissues may also turn yellow. After that, leaf mottling, early leaf drop, and twig dieback occur. If you scrape away the soil, you will also see the feeder and lateral roots decomposing. Other signs of HLB include:
HLB may be mistaken for a nutrient imbalance. But nutrient deficiencies create symmetrical symptoms, while HLB symptoms are asymmetrical. Preventing the spread of HLB Scientists are looking at oak leaf sprays, antibiotic and peptide injections, and other treatments, but there isn't a cure yet. So prevention is critical. At the government level, quarantines are in place that prohibit moving citrus fruit trees, leaves, and stems out of affected areas. Contact your county officials to see if you are in a quarantine zone. Looking at the maps below, you can see how a quarantine zone can change in just one year. Since the information to create these maps takes time to assemble, you should assume if you live near a quarantine zone, you should act like you are in it. Managing psyllids is one way to slow the spread of HLB. Psyllids are jumping plant lice. They feed on sap. You can control psyllid populations with sticky sheets and insecticidal soap. Do not use dish soap. Like other psyllids, Asian citrus psyllids produce honeydew. Honeydew attracts ants and provides a growth medium for sooty mold. If you see ant trails around citrus trees, take a closer look. And block ant traffic with sticky barriers. You can also help prevent the spread of this disease with these tips:
While commercial growers use pesticides to control HLB disease vectors, backyard growers are less likely to do so, creating a significant threat to citrus trees everywhere. This threat is not to be taken lightly. If you suspect or see signs of the Asian citrus psyllid or Huanglongbing disease, immediately contact the CALIFORNIA DEPARTMENT OF FOOD AND AGRICULTURE HOTLINE: 1‐800‐491‐1899. UPDATE: 3/5/2016 Bloomberg reports that Florida citrus growers are now using dogs trained to sniff out the disease to help with early detection and to reduce the spread of this disease. UPDATE: 4/1/2018 According to Farm Week Now, half of all Florida citrus growers have failed because of this threat. They predicted that the 2018 Florida citrus crop would be one-fourth of what it was ten years ago. UPDATE: 3/24/2023
According to Progressive Farmer, the annual production of oranges has dropped from 200 million boxes to 20 million boxes due to huanglongbing. All citrus crops are the smallest on record since 1929-1930. A nub, or dog's ear, is the piece of a twig or branch that is left behind after a bad pruning job. Leaving a nub sticking out interferes with a plant's natural ability to heal a wound. It also creates a foundation that can catch leaves, providing the perfect shelter for problem bugs and fungi. The nubs themselves, being too far from the branch collar for proper healing, often take longer to heal or don't heal at all. This provides an easy entrance for fungi and borers. To properly prune a twig or small branch, it is best to cut as close to the branch collar as you can. The branch collar is the ring from which a twig emerges. Do not cut the branch collar. There is no need to paint or treat a properly trimmed branch. Plants already know how to handle that on their own.
So, off with their nubs! |
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