Late Winter Citrus Management Considerations

Late Winter Citrus Management Considerations

Both niche market farmers and home gardeners may be uncertain about late winter management of Satsuma trees.  Several questions that have come in to the Extension Office recently include: Should I prune my trees? Why are the leaves yellow? How soon should I fertilize?  The focus of this article is to provide some answers to these common questions.

Should I prune my tree?

Jackson County citrus grove with branches allowed to near ground level. Image Credit Jose Perez, UF / IFAS

This is a complicated question that is best answered with “it depends…”  Pruning is not necessary for citrus, as it is in many temperate fruits, to have excellent production quality and quantity. Citrus trees perform excellently with minimal pruning. The only pruning necessary for most citrus is removing crossing or rubbing branches while shaping young trees, removing dead wood, and pruning out suckers from the root-stock. Homeowners may choose to prune citrus trees to keep them small, but this will reduce potential yield in a commercial setting, since bigger trees produce more fruit.

Often, maturing Satsuma trees produce long vertical branches. It is tempting to prune these off, since they make the tree look unbalanced. To maximize yield, commercial Satsuma growers allow these branches to weep with the heavy load of fruit until they touch the ground. This allows increased surface area for the tree, since the low areas around the trunk are not bare. Additionally, weeds are suppressed since the low branches shade out weed growth. The ground under the trees remains bare, thus allowing heat from the soil to radiate up during cold weather events. The extra branches around the trunk offer added protection to the bud union as well. If smaller trees are desired for ease of harvest, ‘flying dragon’ root-stock offers dwarfing benefits, so that the mature scion cultivar size will only grow to 8-10 feet tall.

Why are the leaves yellow?

Leaf deficiency with heavy fruit load. Image credit Matthew Orwat, UF / IFAS Extension

Heavy fruit loads were produced in many groves throughout Northwest Florida last year. When fruiting is heavy, citrus trees translocate nitrogen and other nutrients from older leaves to newer growth and fruit. Therefore, temporary yellowing may occur and last until trees resume growing in the spring. Remember, never fertilize after early September, since fertilizing this late in the year  can reduce fruit quality and increase potential for cold injury. If a deficiency, as in the photo above persists through spring, consider a soil test, or consult a citrus production publication to determine if additional fertilizer should be added to your fertilizer program.

How soon should you fertilize?

Although most Florida citrus publications recommend fertilizing citrus in February, they don’t take into account the potential for late frost in the Panhandle. Thus it makes more sense to wait until mid-March for the first fertilizer application in this region. Citrus trees don’t require a fertilizer with a high percentage of nitrogen, so it is best for fruit quality if an analysis of around 8-8-8 with micro-nutrients is used. Fertilizer should be applied in the drip-line of the tree, not around the trunk. The drip-line of a mature tree is generally considered to extend one foot from the trunk out to one foot from the edge of the furthest branch tip from the trunk. For fertilizer quantity recommendation see the chart below.

Through awareness of the unique managements techniques inherent to Panhandle citrus production, increased yields, better quality and healthier trees can be achieved.

 

For more information on this topic please use the following link to the UF/IFAS Publication:

Citrus Culture in the Home Landscape

 

Satsuma Protection in Cold Weather Extremes

Citrus tree in Jackson County under the protection of a micro-irrigation system. Image Credit Doug Mayo

Citrus tree in Jackson County under the protection of a micro-irrigation system. Image Credit Doug Mayo

This week, Northwest Florida received some of the coldest weather in recent years, with lows ranging from 14 ºF to 20 ºF two nights in a row. This had the potential to impact local citrus production areas heavily. It is still too early to asses the full extent of the damage that this freeze event had on local citrus production, but preliminary surveys indicate that properly protected trees received minimal damage to major limbs and graft union. However, the old adage “time will tell” applies in this case since the full extent of leaf damage will not be visible until next week. If a citrus tree retains the majority of their leaves, than crop loss for the next year should be minimal. If a tree loses most of its leaves, crop loss for the next year may be expected.

Arrow points to microsprinkler irrigation emitter in action. Image Credit Doug Mayo

Arrow points to microsprinkler irrigation emitter in action. Notice that it is positioned to protect the trunk, graft union and inner structural branches of the tree.  Image Credit Doug Mayo

Microsprinkler-irrigation, the option of choice used by Panhandle Citrus producers for cold protection, has  proven to be effective through several tests in central Florida. This practice can protect entire satsuma trees if the trees are short in stature. Keep in mind that the sprinklers must be running throughout the entire freeze event. They need to be turned on at 36º F and left on until the temperature reaches 42 ºF.  For north Florida citrus producers using microsprinkler irrigation In last week’s freeze event this meant that water was turned on at roughly 2:00pm Monday afternoon and left on until 11:00am Wednesday morning.  If the tree is too large for complete coverage, the emitter should be located on the windy side of the tree, roughly 1-2 feet away from the trunk, to be sure that the water covers the graft union.  Most trees will eventually recover from freezing temperatures if the union is not damaged. Microsprinkler-irrigation, will not protect fruit, therefore, all fruit must be harvested before temperatures reach below 25 ºF

A major factor to consider when planting citrus in the Florida Panhandle includes using only cold-adapted  citrus cultivars. Satsumas, or satsuma mandarins, are the most widely planted cold hardy citrus types in North Florida. Three cultivars that have been planted for many years throughout northwest Florida are Owari, Silverhill and Kimbrough, with Owari being the most popular.  For cold-hardy citrus plantings to be successful, the cultivars must be grafted to a cold tolerant rootstock. Trifoliate-orange (Poncirus trifoliata) has been the rootstock of choice for imparting cold-hardiness, but sour orange (Citrus × aurantium) has been used as well for cold hardiness qualities.

Additional tips for citrus protection during extreme freeze events:
  • Generally, satsuma are cold tolerant down to 15° F, but young trees, or trees yet to achieve dormancy, are usually only tolerant to 26°F. Fruit should not sustain damage from temperatures above 25°F. In fact, temperatures between  25°F and 35°F enhance the sweetness of the fruit.
  • Water is a great asset, because well watered soil retains more heat, and a well watered plant has less chance of drying out during an advective freeze (freeze caused by cold air mass, with wind).
  • Extreme winds sometimes make the effects of freeze events worse if the trees are not well watered. A hydrated tree is a well protected tree. On the whole, still, or windless nights (radiational freezes) make for worse freeze events since cold air will “settle” into low areas.
  • Wrap the trunk with commercial tree wrap or mound soil around the base of the tree up to 2 feet. This will protect the graft of the young tree. Thus, if the branches freeze the graft union will be protected.
  • For established citrus trees, mound soil around the tree in a cone formation. Do not mulch the trees over the winter since heat that radiates up from the soil will be blocked somewhat by mulch.
  • Do not cover trees with plastic tarp, these will not protect the tree and can “cook” the tree once the sun comes out.
  • For additional information check out this publication on micro-sprinkler irrigation.

If you have further questions contact your extension office at the Solutions for your Life website.

 

Cottony Cushion Scale – Sighted this Spring in Northwest Florida

Cottony Cushion Scale – Sighted this Spring in Northwest Florida

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Cottony Cushion Scale (Icerya purchasi) is a serious pest on citrus and has already been observed at multiple sites in the Florida Panhandle.

The Satsuma Tangerine, Citrus unshiu, is currently the major citrus of economic importance for fruit production in North Florida. Now is the time to act to prevent infestations of Cottony Cushion Scale (Icerya purchasi) since the weather is warming and this pest insect has already been observed at multiple sites in the Florida Panhandle.

This scale species often reduces tree vitality by ingesting sap that would otherwise be used by the tree for growth and fruit production. It may also cause premature fruit drop and defoliation. A secondary pest that may occur as result of Cottony Cushion Scale is Sooty Mold. Sooty Mold lives off of the surgery secretions of the scale and can cause citrus leaves to look black and eventually drop.

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Close up view of the Cottony Cushion Scale insect.

The good news is that Cottony Cushion Scale is relatively easy to control when managed in winter or early in the spring growing season.  From October through early May growers should use Horticultural Oil to control scale, particularly horticultural oil containing petroleum products.  These products deprive scale insects of oxygen. This will smother them to death.

Applications should be timed correctly since horticultural oils will burn plants once outdoor temperatures reach 94 °F. A good rule of thumb to minimize leaf damage is to apply horticultural oil on cool and cloudy days. Always consult the label of each individual product before applying and never apply more than the recommended amount. This last statement is especially crucial for horticultural oil applications, since increased rates are highly likely to damage plants.

For more information, please consult this UF / IFAS publication on Cottony Cushion Scale and the Citrus Pest Management Guide for Soft Bodied Insects.

 

 

Protect Young Satsuma Trees when Temperatures drop into the 20’s

Satsuma Cold Protection

Mature, dormant Satsuma trees are cold hardy down to 14° – 18 °F, young trees need protection if temperatures dip into the upper 20s.

satsuma__smaller_by_David_W_Marshall

Photo credit David Marshall

According to the National Weather Service a mild freeze is predicted for Northwest Florida this weekend, specifically Saturday night to Sunday morning.  While mature, dormant Satsuma trees are cold hardy down to 14° – 18 °F, young trees need protection if temperatures dip into the upper 20s.

Here are a few techniques to protect young citrus trees from late-season freezes:

  1. Wrap the trunk with commercial tree wrap or mound soil around the base of the tree up to 2 feet. This will protect the graft of the young tree. Thus, if the branches freeze the graft union will be protected.
  2. Cover the tree with a cloth sheet or blanket. For additional protection, large bulb Christmas lights can be placed around the branches of the tree. This will increase the temperature under the cover by several degrees. Be sure to use outdoor lights and outdoor extension cords to avoid the potential of fire.
  3. Water your Satsuma trees. Well watered trees have increased cold hardiness.
  4. Frames may be installed around young trees to hold the cover. This option keeps the blanket or sheet from weighing down the branches.
  5. For large production areas, micro-irrigation is an option. This practice will protect citrus trees up to 5 feet, but must be running throughout the entire freeze event. For additional information click here.
  6. Always remember to remove cold protection once the temperature rises so that the trees  do not overheat.
  7. Do not cover trees with plastic tarps, these will not protect the tree and can “cook” the tree once the sun comes out.

Please see the following publications by retired UF / IFAS Extension agents Theresa Friday and David Marshall for additional information regarding freeze protection of citrus.

Satsuma: a New (Old) Alternative Crop for North Florida

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A Two Year Old Satsuma Grove Near Marianna, Florida around 1920
State Archives of Florida, Florida Memory, http://floridamemory.com/items/show/156264

 

North Florida, specifically Jackson County, according to citrus industry historians was once known as the ‘Satsuma Capital of the World.” During it’s peak, there were more than 3000 total acres dedicated to Satsuma production in the Florida Panhandle alone.  While satsumas are the most cold tolerant cultivar of citrus, with mature dormant trees surviving temperatures as low at 14 degrees F, three major freezes including a particularly brutal one in 1935 virtually eliminated all citrus in this region of the state and country, and by 1980 there were no commercial Satsuma groves in this area of the state.

That all began to change though in the 1990’s, with new plantings of Satsuma beginning to be established in North Florida and throughout other areas of the gulf south. The key to this seems to have been driven by the advancement in freeze protection through methods like in-tree microsprinklers which can protect trees up to a height of approximately five feet, and varietal improvements, advancements made largely in part through research done at the University of Florida and IFAS. This advancement has led to the possibility and promise of bringing back this crop that once dominated the region so many years ago.

While there are several rootstocks used in growing citrus, trifoliate orange is the most commonly used in this area where maximum cold tolerance is a must. This rootstock grows well in fertile clay to loamy soils and does not develop a deep or wide root system. An added bonus is that it is highly resistant to foot rot, a soil borne fungal disease that can wreak havoc in areas where drainage may be an issue.

The most popular varieties of Satsuma grown in North Florida at this time include:

–       Owari Satsuma: matures October to November. Few, if any, seeds

–       Kimbrough Satsuma: matures October to November, few if any seeds. Produces fruit that is larger than those seen on Owari.

–       ‘Brown Select’ Satsuma: matures October to November (generally two weeks ahead of Owari and Kimbrough)

–       ‘Early St. Ann’ Satsuma: matures late September to October (one of the earliest producing varieties available)

For more information, download the UF/IFAS Fact Sheet on Satsumas.

 

Advancements in cold protection

Advancements in freeze protection through methods like in-tree microsprinklers can protect trees up to a height of approximately five feet.