Monday, February 27, 2012

Citrus Gummosis

      Why do citrus trees have, in general, an unhealthy appearance?  
 Some citrus trees look unhealthy because of a common fungal disease called gummosis. Such trees are sparsely foliated with much twig dieback. Trees become infected when fungal spores on the ground splash onto the trunk.  If the trunk remains wet for many hours, whether from rain droplets or irrigation, infection takes place.  The fungus attacks and kills the bark but will not penetrate into the wood.  If these lesions are discovered early, the fungus can be stopped and the tree saved.  But once the infection spreads and kills more than a third of the bark tissue around the trunk, the tree will either die or produce very poorly.
                                             

Citrus trees will produce an amber color gum as a defense against the invasion.  The gum exudes from the point of infection, trying to wall off the fungus.  In a rainy climate, the globes of gum readily dissolve in the rain.  Due to fluctuating temperatures, the fungus may die out on its own.  When this happens, the infected bark will dry up and crack.  New bark will eventually begin to grow around the wound.  There is no sense in treating if the bark appears dried up and cracked; the fungus is gone. 
The best control for this disease is prevention. Nothing can be done about the rain, but if trees are irrigated, the water must not hit the trunk of the tree. Keeping the trunk dry is essential to the health of the tree.  There are fungicides registered to control citrus gummosis (Phytophthora species).  But for a practical control measure for the homeowner, simply cutting out the diseased bark and painting the area with a registered copper fungicide will rectify the problem.  In removing the diseased tissue, only the bark should be removed; there is no need to cut into the wood.  The diseased bark will be near the gumming and will be discolored (brown).   Healthy tissue is light in color. Along with cutting out the discolored bark, it is recommended to cut about an inch into the healthy bark. Furthermore, applying a pruning compound to the diseased area is of no value.

Friday, February 24, 2012

Use Pesticides Wisely


                                                 
 There are many hazards when working or playing in the garden – tumbling rocks, falling limbs, and nasty bug bits.  For all of these problems there are some common actions to take in order to prevent a catastrophe.  This is also true when using pesticides.  Following a few common sense rules will save a lot of grief in the future.   

There are two categories of potential ailments when spraying pesticides: 1) Acute – these occur right away, like nausea, headache, and rashes. 2) Chronic- these will manifest themselves much later, like cancer and neurological disorders.  Pesticides always need to be treated with respect.  Here are some good rules to follow: 
·        Make sure the pest is properly identified and choose an appropriate pesticide that is labeled for that pest on that specific plant.   Consider other control measures first before resorting to pesticides. See my article entitled Integrated Pest Management – A New Approach, under the ‘pest management’ label.
·        Read the entire label. It’s the best source of information about that product. 
·        Time your treatments to catch the pest at its most vulnerable stage. 
·        Spot treat whenever possible, rather than spraying the entire garden. 
·        The label on the pesticide container is a legal document.  Follow all directions exactly. 
·        Don’t smoke, eat or drink when handling pesticides. 
·        Follow label directions for wearing protective gear when mixing and applying pesticides - rubber gloves, safety glasses, respirator, long sleeved shirt, long pants or coveralls and closed shoes. 
·        Mix up the smallest quantity that will do the job and use it up.  Many mixed pesticides quickly loose their potency. 
·        Never use kitchen utensils for mixing pesticides.  Use a dedicated set of spoons, cups, etc. for mixing pesticides, and label them as such. 
·        Always store pesticides in their original containers, in a cool, dark and dry place outside the house and out of the reach of children and pets. A locking cupboard in the garage or storage shed is ideal.
·        Never remove labels or transfer pesticides to other containers. 
·        After applying pesticides, take a shower and put on clean clothes. 
·        Teach children that pesticides are poisons that should not be touched or consumed.

Monday, February 20, 2012

Controlling Pests on Houseplants

                                                  
 Houseplants are susceptible to many unsightly insect and mite pests. Some pests cause extensive damage, while others are merely a nuisance.
Here are some control measures:
·        A healthy plant is much more resistant to insect and mite injuries.  Keep house plants well fertilized and adequately watered. Keeping the soil excessively moist favors the development of root rot along with an increase of nuisance pests like the fungus gnat.  When soils are kept too dry, plants are prone to mite problems.
·        Many infestations are brought home with a newly acquired plant. Carefully inspect all plants that are taken home. 
·        Syringing plants - many household plant pests can be controlled, at least in part, by washing the plant periodically with a vigorous jet of water. This is particularly effective for spider mites and aphids, which are readily dislodged.
·        Vacuum – if you have whitefly problems, the regular use of a small, hand-held vacuum can assist in controlling this pest.  Careful not to vacuum up the plant!
·        Sanitation - Seriously infested plants are often best discarded. They can serve as a source for infesting other plants.
·        Alcohol – use  Q-Tips dipped in alcohol to wipe small infestations from the plant.
·        Pyrethrins, synthetic pyrethrins (known as pyrethroids), insecticidal soaps, horticultural oils, Neem (derived from seed extracts of the neem plant) and Neem oil can all help in controlling most houseplant pests. Some insecticides, especially the oils, can burn some of the more delicate houseplants.  When in doubt, spray one or two leaves and wait 3-4 days before spraying the whole plant. 
·        There are also systemic insecticides which are absorbed into the plant. As the insect or mite feeds on the plant, they will die.  Look for an insecticide with the active ingredient, Imidacloprid.
                                                                        Mealybug on Palm

Safety Issues:                                    
Only use pesticides that are specifically labeled for use on houseplants. Most yard and garden pesticides do not allow this use.  If possible, take the plant outdoors before spraying to minimize pesticide exposure within the home. When using aerosol sprays, do not apply closer than 18 inches to the plant or injury may occur from the spray.


Friday, February 17, 2012

Twig Dieback in Podocarpus Trees


The black twigborer (Xylosandrus compactus) is a beetle that attacks over 200 plant species including orchids, citrus, avocados, mango, coffee, eucalyptus, hibiscus and podocarpus. The females tunnel into woody twigs, leaving pin-sized entry holes. Once inside, they excavate galleries and lay eggs.  It is this excavation that causes the damage to the tree. An infestation by one to three females is sufficient to kill the twig or branch. A severe infestation can kill a plant, including large trees. The damage is not caused by feeding, since the beetle larvae feed on a fungus that is introduced by the female beetle.
 Typical symptoms of black twigborer are wilting and death of leaves and wood beyond the beetle's entry hole. The dried, brown leaves frequently stay attached to the tree.

                                                    Entry hole

Cultural control
The best control is to maintain a vigorously growing tree. This will help the tree to resist beetle infestations and recover quickly from existing ones.  Prune and destroy all beetle-infested plant material.

Monday, February 13, 2012

Why Leaves Turn Yellow


 

When the leaves of a plant begin to turn yellow, determining the cause will take some investigation. There are several possibilities:
·        The first consideration is a lack of nitrogen, especially if a number of plants are affected and there has been no recent application of fertilizer.  Apply a high nitrogen fertilizer, and if after a week or so the plants begin to turn green, the problem is solved.

·        If the plants don’t turn green, the problem could be a disease.  Plants can become infected with a fungus, especially when over watered, causing a root or crown rot.  Inspect the roots and the crown of the trunk.  Scratch into the bark of the trunk at the soil line and also into a piece of root.  If the tissue inside is brown or black, rather than light colored, a root or crown rot is evident.     

·       Another common reason for a general yellowing is a lack of oxygen in the root zone.  This is due to too much water – over irrigation or too much rain.  As long as the soil drains well the problem is minimized.  But in clay soils, water does not drain well, resulting in a waterlogged condition.  Without adequate oxygen in the soil, roots cannot function properly, and the plant turns yellow.  If the condition continues, root rot will develop and the plant will die.  That is why so many planting instructions suggest to plant in a well-drained soil. 

·        If plants are yellow and lack vigor, a soil analysis can identify nutrient deficiencies and/or a pH imbalance.  The pH reveals the acidity or alkalinity of the soil. Most plants have a definite acid/alkaline range in which they will properly grow.

·        Although not common, there is always the possibility of persistent chemicals in the soil.  A soil sterilant or preemergent herbicide may have been applied to the soil.  These compounds can persist for many years.  Preemergent herbicides are those that are sprayed on the bare ground and become incorporated into the top few inches of soil.  At label dosages they affect only the target weeds and last from several months to a year.  But if an overdose is applied, the chemical will be there for many years and adversely affect many plants. 

·        An infestation of microscopic round worms called nematodes (example, root knot nematode) can also cause plants to yellow and be stunted.

Friday, February 10, 2012

What are the large, black bees hovering around my house?


 Although these insects look similar to bumble bees, they are actually Sonoran carpenter bees. The female is black, and rather large, approximately one inch in length. They can sting when angry but are considered shy and rarely bother humans. The male bees are golden brown in color and lack a stinger. They inhabit the Hawaiian Islands, the Marianas, China, Japan, New Guinea and the Philippines.

The females fly around homes seeking out nesting sites:  wooden roof shingles, exposed roof rafters, window sills, wooden fences, and picnic tables. They also  prefer dead softwoods such as redwood and pine, as well as dead parts of trees.

The females will burrow into the wood and create galleries to lay her eggs. Egg laying occurs year-round but may decline during the winter months.  A ball of pollen is placed in the tunnel as food, one egg is laid on the pollen and the chamber is sealed with wood shavings.
Control
The first step in protecting the home is to paint exposed wood.  Painted wood has been reported to be far less susceptible to attack. In addition, entrance holes may be dusted with an approved insecticide.

Monday, February 6, 2012

Plant Families


  I often talk about cucurbits, legumes and crucifers.  These are plant families.  Sometimes rather than mentioning each member of a family, like cucumbers, squash, melons, if something is common to all, I refer to the family, such as cucurbits, or cucurbitaceae.  This commonality happens quite frequently.  If a certain disease attacks cucumbers, then it will often affect the other members of that family, and not members of another family. This also holds true with many cultural characteristics.  Even with pest control, cucurbits as a group are sensitive to sulfur sprays. For further reference, here is a list of some of the more common vegetable crops and the family which they belong to.   

·        Amaryllidaceae – chives, garlic, leeks and onions.
·        Cruciferae – broccoli, brussels sprouts, cabbage, cauliflower, Chinese cabbage, kale, kohlrabi, mustard greens, radish, rutabaga and turnip. 
·        Compositae – artichoke, endive and lettuce. 
·        Cucurbitaceae – cucumber, cantaloupe, honeydew, pumpkin, squash and watermelon. 
·        Gramineae – corn. 
·        Leguminosae – beans and peas.  
·        Lilaceae – asparagus. 
·        Solanaceae – eggplant, peppers, potato and tomato. 

Friday, February 3, 2012

Controlling Scale Insects

 
 Many pests are controlled naturally by other insects, “the good guys”, both predators and parasites.  Consequently, if no control measures are taken, the problem will frequently regulate itself.  Sometimes the good guys will completely eradicate the pest; other times they just keep them in check. 
 
Yet biological control doesn’t always work.  There are a couple of reasons for this.   An application of a broad spectrum insecticide will not only kill the target pest, but the good guys as well. Ants also interfere with biological control by protecting the pest from its enemies.  In addition, windy oceanfront locations and hot greenhouse environments are generally not conducive to biological control activity.

If, for whatever reason, biological control is not working in the garden, a pesticide application may be called for. The first choice to control scale insects would be horticultural oil and/or an insecticidal soap. In general, gardeners need to select insecticides that are least toxic to the beneficial insects.

The best time to spray is right after the scale eggs hatch. At this time the young “crawlers” are most susceptible as they move about looking for a place to feed.