Citrus
Citrus
Q: When do I prune my citrus?
A: In general, homegrown citrus trees do not need formal pruning. If, however, you wish to rejuvenate the tree then light pruning should occur just before a major growth flush. Broken, cracked or diseased branches can be removed anytime. This photo shows the proper pruning cut to make on large citrus tree branches.The following is the complete University of Florida/IFAS publication on pruning citrus: http://edis.ifas.ufl.edu/HS121
Q: Citrus problems such as leaf drop, fruit drop, non-blooming or fruit split. What can be done?
A: I have received dozens of questions regarding citrus tree problems so I decided to answer them all together. Citrus do not like "wet feet," meaning they prefer to be irrigated on a regular basis but do not like to have their roots sitting in water. Citrus trees have a tendency to develop root rots and little can be done to correct this problem once it develops. To assist with keeping oxygen at the roots remove mulch from around the root area and never allow it to touch the trunk of any tree or shrub. Toot rots will cause yellowing leaves, fruit or leaf drop and/or twig dieback. Other diseases can cause yellowing leaves, fruit or leaf drop and/or twig dieback. Other diseases can cause these same symptoms, but irrigating more than twice a week may be too much. Fruit splitting often indicates the fruit received too mulch water too quickly and the rind splits as a result of the sudden uptake. Keep lawn grass as far away from your citrus and any tree as possible. When the tree is young the grass will usurp most of the soil nutrients. It takes a tremendous amount of energy to produce juicy, tasty fruit, therefore removing some fruit from the tree before it matures will allow the tree to produce fewer but better fruit. It is best to do it when the fruit is small, no larger than a grape.
Fertilize citrus every six weeks when the tree is young (under 7 years) with a good quality citrus fertilizer. Avoid using fertilizer tree spikes as this only provides nutrients in the immediate area where it is placed in the ground. If you already have tree spikes, break them up and spread them under the tree canopy. Avoid fertilizing from October through February; otherwise fertilize adult trees often but in small increments. It is not uncommon for citrus to experience and occasional fruit or leaf drop.
Q: At what temperatures do I need to worry about my cold-hardy citrus?
A: A hard freeze is considered 28 degrees for 4 hours or more. To be completely safe, protect young trees (under 5 years) whenever temperatures drop below 32 degrees. Be sure you take extra precaution by covering the area where the rootstock and scion were joined. Water the plant 48 hours prior to the freeze. If you tree is healthy and has been watered and fertilized properly, it should be able to survive here.
Q: I have a caterpillar that is eating my citrus trees. At first I thought it was a bird dropping then I saw several of them. What is it?
A: You have discovered the larvae or caterpillar of the Giant Swallowtail butterfly, which is also called the orange dog caterpillar. This caterpillar often feeds on citrus plants as well as Wild lime and Hop trees but it seldom causes any major damage. I allow them to chew my lime tree leaves because, so far, they have not totally defoliated it. However, I have been fighting with grasshoppers who love to chew on the foliage too and I can tell you I don’t mind crushing them. But since I recognize the swallowtail butterfly larvae is a good pollinator I would have a hard time destroying this caterpillar. In addition, I have planted a cluster of wildflowers and lantana which the adult swallowtail butterflies use as nectar plants to encourage these butterflies to visit my lawn.
Q: What is wrong
with my citrus leaves and new stem growth? 
A: I have received nearly a dozen calls on this same problem and although I have addressed it in this column before, it appears to be worth repeating. First, we don’t recommend you bring citrus problems to the extension office because of the ease in spreading citrus canker. However, all the samples brought into the office were in sealed freezer bags and I could easily diagnose the problem through the bag. The leaf problem is caused by a small leafmining moth, Phyllocnistis citrella Stainton, or the citrus leafminer (CLM). Citrus leafminer (CLM) was found in late May 1993 in several citrus nurseries in south Florida. Since that time, CLM has been found everywhere in Florida where citrus is grown, and has spread to other Gulf Coast areas. Adults of the CLM are minute moths (4 mm wingspread) with white and silvery iridescent scales on the forewings, with several black and tan markings, plus a black spot on each wingtip. Adults generally are so small in fact, that people barely notice them. They are active mostly during the day but have been known to continue their normal activities in the early evening hours. Adults live for only a few days but in Florida generations are produced about every three weeks. They are not easily controlled using chemicals as they burrow between leaf and stem tissue and are therefore protected. Infected leaves and small stems should be pruned, bagged and destroyed to help manage the insect populations. A predatory wasp, encyrtid parasitoid, Ageniaspis citricola, was introduced from Australia to Florida in 1994-95, and seems to have the key element in suppressing this leafminer to an acceptable level.
Q: How do I know if my citrus fruit is ripe?
A: Your question is timely for this time of year. It is difficult to give you specific time to know when your fruit is ripe because that differs per species and even per area. For instance, grapefruit ripens between November and March whereas many oranges ripen between October and January. Citrus fruit will not ripen after it is picked like apples or pears because citrus has no carbohydrate reserve so don’t pick it too early. The best way to know when your citrus is ready to eat is to try one fruit at a time until you can taste that it is mature. When you see the fruit wrinkle that is your indication it has been left too long on the tree. Please check out the University of Florida publication titled: Growing Citrus in the Dooryard at http://edis.ifas.ufl.edu/XC005.It will have specific information regarding caring for citrus in Florida plus you will see a table giving you times to expect your fruit to mature.
Q: I have a citrus tree and the leaves are curling, dropping off, and they look pale. What is wrong with my tree?
A: I am glad you brought a clipping of the tree to
me. After examining it closely, I could see the culprit was a citrus
mite.
The
citrus red mite or purple mite, Panonychus citri (McGregor),
was first recognized as a pest of Florida citrus in 1885. From the
late 1930s to about 1960, it reportedly was one of the most serious
economic pests in Florida citrus. Today, growers find this mite to
be a sporadic pest. Citrus red mite populations are usually greatest
on lemon and grapefruit, followed by orange and then tangerine. Infestations
may develop any time of the year, but generally occur between November
and June. Peak infestations usually occur in May or June following
the major plant growth cycle of new spring flush or when prolonged
dry conditions occur. Some citrus varieties such as lemon, lime and
grapefruit have several minor flushes of new growth throughout the
spring, summer and fall in Florida. This allows spider mites to increase
depending upon favorable weather conditions. Citrus red mite prefers
green developing fruit to the more mature yellow fruit. The influence
of undetermined numbers of citrus red mites and weather can result
in heavy leaf drop, twig die-back and even death of large limbs.
Usually there is no direct effect on fruit quality although fruit
drop due to heavy infestations can occur. Reducing or eliminating
pesticides such as copper, copper plus oil, sulfur and lime sulfur
can prevent citrus red and Texas citrus mites from flaring and becoming
serious pests.
Grapefruit
Q: The peeling of my grapefruit on my citrus tree is brown and it feels like sand paper. They are ripe and mature but what is wrong with them?
A: The disease is probably melanose, which is a common
coastal fungal disease 
that
primarily occurs in grapefruit but can attack any citrus. The first
symptoms on leaves are small, circular, dark depressions with a yellow
margin, similar to canker. Later, the spots become raised and
turn dark brown. The leaves may turn yellow and may drop prematurely,
which can also be a symptom of other disease or insect problems. Raised
spots can are also be found on twigs, which may result in twig die
back. These spots can also occur on the fruit, which is why
your fruit had the sand paper feeling on the rind. The disease
can be severe following rainy periods in the spring, particularly
when such periods follow a freeze that has left an abundance of dead
twigs. This disease is also common on older, neglected trees. Copper
sprays are usually applied 2-3 weeks after petal fall and a second
spray 2-3 weeks later. With a particularly wet spring, a second application
may be needed. Citrus should be sprayed for melanose control in the
spring following a freeze. Be sure to use a fungicide specifically
formulated to be used on citrus. Follow the directions on the fungicide
label; remember "the label is the law". The best melanose
management strategy is to remove small, dead twigs, and avoid overhead
irrigation. If you are concerned about citrus canker you can
call the hotline: 800-904-3781. Please do not bring in
diseased citrus specimens into the county extension offices or local
garden centers.
Q: Why isn’t my ruby red grapefruit blooming? It gets some sun in the afternoon and I have used stake fertilizers each year. I am watering it twice a week just like my lawn grass. It looks healthy, and is growing, but still no fruit.
A: Some grapefruit varieties are notorious for taking 7-12 years before they are mature enough to produce fruit – so be patient. However, you might consider moving it to a site that gets full sun, 6-8 hours is best. Any plant (lawn grass, trees or shrubs) will generally need less water and fertilizer when they are in shaded areas. The University of Florida recommends watering lawn grass in full sun once every 5-7 days in the summer and once every 10-14 days in the winter. You are probably over watering the plants in your landscape and could reduce it. However, you should measure your irrigation systems output. Consider placing empty tuna fish cans around your irrigation zones and run the system for 20 minutes then use a ruler to measure the amount of water in each can. Your goal is to have ¾ - 1 inch of water each time you water for your lawn grass. Adjust your system so it matches the maximum output of 1 inch. Citrus also has a tendency to develop root rots so it is important their roots do not stay wet. Do not put mulch over the root area and keep lawn grass as far away from the roots as possible. Be sure to use citrus fertilizer on your citrus and granular fertilizers are preferred over stakes. The stakes are convenient but they do not reach all the roots. Broadcast the granular fertilizer all over the root area (avoid the trunk of the tree). Be sure to follow the directions on the label and look for slow release fertilizer whenever possible.
Lemon
Q: I have Meyer lemon tree that needs to be moved because it now has a tree has gradually shaded it. As a result, it has gradually leaned, grasping for the maximum sun it can get; it only produces fruit in years of maximum sun and less rain. Question: can this tree be transplanted? If answer is yes, then 1) When?, 2) With what precautions?, 3) How much pruning? 4) What fertilization at time of transplant? Thank you again for your assistance.
A: You have seen the results of a true experiment on this plant's need for full sun. It can be transplanted and as you can see it will produce better if given full sun exposure. The best time to transplant citrus is in the spring. Get as much of the root ball as possible, dig the hole wider than deep and add nothing to the hole. Set the plant in the ground slightly (1/2-1 inch) higher than it grew in the ground. Re-fill the hole around the plant about 1/3 to 1/2 full, then water and gently tamp the soil thoroughly to remove air pockets. Allow the water to settle, fill the hole 2/3 full of soil, re-water and tamp again. Finish filling the hole and pack the soil firmly around the tree. Form a water basin around the tree at least 3-4 inches high and 30 inches in diameter. Do not put mulch over the root ball. Water 3 times a week for 2 weeks, and then taper off gradually to once a week during periods of little or no rainfall. The basin should stay in place until the tree is well established. Avoid pruning the tree prior to transplanting (this would apply to any tree or shrub); you want to encourage the tree to put its energy into growing roots. Pruning citrus should not be necessary except to shape the trees or remove water sprouts or suckers. Do not leave stubs as they may be attacked by rotting organisms which could damage the tree. Fertilization could be done in June and then again in the fall between Oct. and November. The recommended 3 applications per year can be made in January - February, May - June and October - November although timing is not especially critical. Good luck.
Q: I have brown, streaked areas on my lemon. It feels like sand paper. What is it?
A: Your description of the condition points to citrus melanose, 
which often occurs on grapefruit, but any citrus can be susceptible. Only
the rind of the fruit is damaged; the fleshy pulp and juice is perfectly
fine to eat or use in cooking. Humid, wet weather or overhead
irrigation is a contributing factor because the dampness provides
the fungal spores a perfect environment to reproduce and spread. The
tiny spores hide and spend the winter in the dead twigs. Melanose
is usually more severe in older, neglected trees and cold-damaged
trees with large amounts of dead wood and twigs. The best management
strategy is to remove dead branches and twigs whenever you see them. Copper
sprays are usually applied 2-3 weeks after petal fall and a second
spray 2-3 weeks later. Be sure you use a fungicide labeled
for use on citrus and follow the directions on the label. Whenever
possible, avoid overhead irrigation. Remember trees and shrubs
prefer to be irrigated at the root area. Chronic wetting of
the leaves promotes disease. Consider changing your irrigation
heads to provide irrigation at the root area. One other note
on irrigation: most established trees and shrubs do not have
the same irrigation needs as lawn grass and therefore should be placed
on different zones.
Lime
Q: I am afraid my lime tree was damaged after these cold nights. How do I prune it?
A: After a severe freeze that causes damage to major limbs, wait several months to prune. During the spring flush following a freeze, leaves on freeze-damaged limbs may grow but then will wilt soon after. After this wilt occurs on the spring flush, you will have a better idea about which limbs to prune. However, limbs with minor cold damage and split bark can continue to reduce fruit production for months, and even years, after a freeze. Sometimes when a tree is weak, frozen back or broken off, a sucker or shoot will grow from the rootstock. The fruit from this rootstock shoot will be different than on the original tree. The tree may produce two kinds of fruit if a portion of the scion remains. Fruits from rootstocks may be sour orange, rough lemon, trifoliate orange, Carrizo citrange, or Swingle citrumelo or other rootstocks. Cut the sucker off to allow the desired variety to become dominant. If your tree is completely destroyed, it is usually better to plant a new tree of the desired variety than to try to bud the rootstock. If you’re thinking of moving a mature tree to a different location, it is also usually more economical to plant a new tree in the site.
Orange
Q: What is the proper timing, amount and type of fertilization for a mature orange (or perhaps tangelo) tree?
A: span style="FONT-SIZE: 10pt; FONT-FAMILY: Arial; 'Times New Roman'">For mature bearing trees on well-drained soils, three applications of slow release citrus fertilizer per year are sufficient, one application in the fall or winter followed by a second application in the late spring or early summer and a third in late summer. I am conducting a class on growing citrus in Northeast Florida on January 17 at 10am at our new satellite office located at 86026 Pages Dairy Rd in Yulee. The class is free so please call the office at 548-1116 or 879-1019 or e-mail me at a title="mailto:rljordi@ufl.edu" href="mailto:rljordi@ufl.edu">rljordi@ufl.eduspan style="FONT-SIZE: 10pt; FONT-FAMILY: Arial; 'Times New Roman'"> if you would like to attend. Plus, we are giving a class called “Crash Course in Florida Gardening” on Jan 29 & 30. The cost for a complete notebook is $25 and it will contain a section on citrus as well as trees, perennials, annuals, vegetables, lawn grass, etc.
Q: I purchased a Mandarin Orange tree called ‘Robinson’ at a local nursery and they told me I needed to buy another orange tree to help pollinate this one or it would not produce fruit. Is that true and if so what should I use to pollinate it?
A : Many citrus trees are self-pollinators meaning they produce fruit by pollinating the blooms on the same tree. However, your orange tree ‘Robinson” does require other pollinators and you should consider using the ‘ Orlando’ tangelo as a cross pollinator. It is important to use a cross-pollinator that has a blooming period that overlaps your tree, produces a good crop of flowers, and has the same cold-hardiness. ‘Robinson’ is one of the most cold-hardy of the mandarin types but it is susceptible to limb breakage if fruit bearing is too heavy. Harvest occurs between October and December with fruit containing 1-20 seeds per fruit.
Q: I have an orange tree that used to produce sweet fruit. We pruned it back a few years ago after a freeze and now it only produces small sour oranges that are full of seeds. Is there some kind of fertilizer we can apply to the tree to make it produce the sweet oranges again?
A: I get this question often especially during the spring after a cold winter. I am afraid I have some bad news for you; there is no fertilizer you can add to the ground to make the sour oranges sweet. I suspect your original orange died as a result of the freeze and the root stock, which is probably a sour orange, is the only living portion of your citrus tree. Sour orange is a common root stock because it is so cold hardy, but as you noticed the fruit is inedible. Once the scion, the grafted portion, dies the hardy root stock will totally take over the tree. On citrus trees, be sure to protect the area where the scion and the root stock join in order for the upper scion portion to survive freezing temperatures. Even if the top portion freezes, the tree may be able to recover once temperatures become warm again. You have several options: graft another sweet orange back onto the sour orange root stock, dig up the tree and replace it, or leave the tree and enjoy it for its beauty.
Q: I have an orange tree I want to protect from the freeze. I am told I can run water over it and it will protect it from freezing but it seems like a waste of water. What should I do?
A : In order to totally protect the tree by water, you would need to start the water before the freeze and continue to water it after the freeze has passed. Although this procedure is used in citrus groves is it not recommended for the home owner. As you indicated, it is a terrible waste of water and not totally fool proof. In addition, citrus is especially sensitive to root rots which can be caused by excessive water – not a condition you want to encourage by adding too much water. Most of the oranges we grow in this area are grafted onto cold hardy root stock so there is less chance of loosing the tree from freeze damage. The portion of the tree you truly need to protect is the grafting part (where the root stock meets the scion). The scion is the upper portion of the tree which produces the desired fruit. You can place an insulating type fabric over this area during cold freezing temperatures to protect the tender upper part of the tree. Plus, you can place a fabric bed sheet or plastic over the top portion. Be sure it reaches the ground so you can trap the warm air coming off the ground to help keep the tree warm. Remove the sheet or plastic once temperatures increase above 30 degrees or once the sun comes out. Watering your tree properly prior to the freeze is also helpful. Cold frames can be built to cover the whole tree, but that should not be necessary for citrus trees grown here.
Q: Do you know of anyplace where I can get some osage oranges? It is supposedly also referred to as monkey balls. I read online somewhere that they are an excellent deterrent to spiders and ants.
A: You can purchase Osage Orange, 
Maclura
pomifera, at any local garden nursery; if they do not have
it they should be willing to order it for you. I could not
find any educational reference to its ability to deter spiders
or ants. This deciduous North American native tree rapidly
grows 30 to 40 feet tall with a spread of 20 to 40 feet and creates
a dense canopy, making it useful as a windbreak. Young trees can
develop an upright, pyramidal habit. The large, three to six-inch
long by two to three-inch-wide, shiny, dark green leaves turn bright
yellow in fall before dropping, although this color change is not
quite as noticeable on trees grown in the southeastern United States.
The bark is deeply furrowed and has an orange tinge to it, and
the strong, durable wood is bright orange in color. Osage
oranges are considered reclamation plants that have been successfully
grown in urban areas where air pollution, poor drainage, compacted
soil, and/or drought are common.It is reported that the Osage Indians
made their hunting bows from this beautiful and hard wood, and
it is also used to make furniture. From April to June, Osage-Orange
puts out its inconspicuous green flowers but these are followed
by the very conspicuous fruits. The fruits are four to five-inch-diameter,
rough textured, heavy green balls which ripen to yellow-green and
fall in October and November. These fruits are not edible, the
juice acid and milky, but squirrels relish the small seeds buried
inside the pulp. When the fruits drop, they can be very messy and,
for this reason, male, fruitless trees should be selected if you
plant this tree. Osage-Orange is thorny, just like true citrus
trees, and forms thickets if left to grow on its own. However,
there are thornless cultivars available. Osage-Orange should
be grown in full sun on well-drained soil. This tough, native plant
can withstand almost anything once established - heat, cold, wind,
drought, poor soil, ice storms, and even some vandalism. It
appreciates regular watering when young until it is established,
which generally takes about 4 months. The thornless, fruitless
cultivars include ‘Witchita’, ‘White Shield’,
and ‘Park’. Propagation is by seed, cuttings,
and root-cuttings. Young trees are easily transplanted. It has
no pests or diseases of major concern.