In recent years, not a summer has gone by in which I did not see citrus rust mite (CRM) damage in a garden. I thought this year would be the first. Unfortunately, recently I saw my first rust mite damage of the year.
Unlike the myriad of pests that have been recently introduced into Florida from abroad, the citrus rust mite (Phyllocoptruta oleivora) has been documented as present in Florida since the late 1800s. Along with its companion, pink citrus rust mite (Aculops pelekassi) It can be a major summer pest for satsuma mandarins grown in the Florida Panhandle gardens.
Citrus Rust Mite (CRM) damage manifests itself on fruit in two ways, “sharkskin” and “bronzing“. Sharkskin is caused when mites have fed on developing fruit, and destroyed the top epidermal layer. As the fruit grows, the epidermal layer breaks and as the fruit heals, the brown “sharkskin” look develops. Bronzing occurs when rust mites feed on fruit that’s nearer to mature size. Since the skin is not fractured by growth, the fruits develop a polished bronze look. In both cases, the interior of the fruit may remain undamaged. However, extreme damage can cases cause fruit drop and reduced fruit size. Regardless of the condition of the interior, damaged fruit is not aesthetically pleasing, but fine for slicing or juicing.
“Sharkskin Damage” to fruit caused by past feeding by the Citrus Rust Mite. Image Credit, Matthew Orwat
If a CRM population is present, they will begin increasing on fresh spring new growth in late April, and usually reach peak levels in June and July. By August the damage has often already been done, but is first noticed due to the increased growth of the fruit. Depending upon weather conditions, CRM can have a resurgence in October and November, just as Satsuma and other citrus is getting ready to be harvested, so careful monitoring is necessary. For more information, check out this publication: Guide to Citrus Rust Mite Identification.
Sun spot resulting from where citrus rust mite avoids feeding on most sun exposed portion of the fruit. Image and Caption courtesy of EDIs publication HS-806
If control of CRM is warranted, there are several miticides available for use, but it is not advisable for home gardeners to use these on their citrus plants since they will also kill beneficial insects. Horticultural oil is an alternative to miticide, which is less damaging to beneficial insects. Several brands of horticultural oil are formulated to smother CRM, but care must be taken to not apply horticultural oil when daytime temperatures will reach 94 degrees Fahrenheit. Application of oils at times when temperatures are at this level or higher will result in leaf and fruit damage.
Although Citrus Rust Mite (CRM) has the potential to be aesthetically unsightly on citrus fruit in the Florida Panhandle, strategies of monitoring and treatment in homeowner citrus production have been successful in mitigating their damage.
We’re lucky to live an environment where many citrus varieties can be grown. However, many problems can occur when growing citrus, but none more frustrating than fruit drop or fruit split.
Most citrus varieties are susceptible to fruit drop. This is a major cause of low yield in the Navel orange industry. Quite a few variables can cause the condition. This can be difficult to pin point, however. Ethylene gas production goes into effect when a citrus tree is injured, which can spark fruit drop. Our culprit this year may be the late summer excessive periods of rain, high temperatures and areas of poorly drained soils. Low potassium is thought to also be factor in fruit drop, so be sure to follow a fertilizer schedule every year. Competition between fruitlets and young leaves for carbohydrates, water, and other metabolites can be the reason for fruit drop early in the season, as well.
Figure 1: Fruit Split in Naval Orange. Credit: Ray Bodrey, UF/IFAS Extension Gulf County
Fruit drop can especially affect mature trees. This could mean up to 25% of fruit loss. Brown rot can accompany this condition, if moisture persists for long periods. Fruit drop is usually associated with the lower, shaded areas of the tree canopy.
Fruit split is more severe in Valencia, Hamlin and Navel oranges. Grapefruit (and other acidic fruits like lemons and limes), Tangerines and Temple fruit are much less susceptible. What is thought to be the primary cause of fruit splitting? High temperatures and heavy rainfall during August can easily give rise to the condition. Excess water taken up by a tree during this time will swell the meat of the fruit causing it to grow quickly. Unfortunately, it is believed that the peel does not grow at the same rate. Damage often occurs as the peel eventually caves under the pressure. Nutritional stresses early in fruit development can also be a factor, as low potassium and copper levels have been correlated. The condition is more likely to emerge when no irrigation practices were in place during dry periods that existed earlier in the year
If fruit split has been a problem this year, ensure a recommended fertilizer program next year. Proper tree siting, nutrition and irrigation scheduling are the best defense against fruit drop and fruit split. Although these measures are not a cure all for the conditions, a healthy citrus tree is less likely to be affected. Contact your local county extension office for more information.
Supporting information for this article is from the UF/IFAS Extension EDIS publication: “Citrus Problems in the Home Landscape” by Mongi Zekri and Robert E. Rouse: http://edis.ifas.ufl.edu/pdffiles/HS/HS14100.pdf & information is also provided by Extension Fruit Crop Specialist, Dr. Pete Andersen with IFAS located at Quincy, North Florida Research and Education Center.
UF/IFAS Extension is an equal opportunity institution.
There are a number of plants that are adapted to the climate in the Florida Panhandle. Some can be grown in your yard to provide fresh, nutritious food for your family. In this episode of Home Grown Food, County Agent Doug Mayo, UF/IFAS Extension in Jackson County, Florida shares the rabbit-eye blueberries and satsuma citrus that he grows on the edge of his yard.
During these unusual times, the Gardening in the Panhandle Team has been working to bring you quality remote content through this online newsletter. In that vein, we have developed some new educational programming for our loyal readers.
We are providing one hour “Gardening in the Panhandle LIVE!” sessions on Zoom. These will occur during lunch hour, from 12:00 to 1:00 CDT. They will also be hosted on the Gardening in the Panhandle Facebook page and recorded if you can’t participate live. So, whether you are at home or work, bring your lunch up to your desk (or smart device) and enjoy Gardening in the Panhandle Live!
Click on the topic below to pre-register and submit your questions one week in advance.
Archived videos with closed captioning are linked to topics about one week after event airs.
‘Early Pride’ Tangerine. Photo courtesy of Danielle Sprague.
Citrus is not only a vital part of our economy in Florida but it’s also a major component in our landscapes. Having grown up in the major grapefruit producing region of Florida, the citrus industry is near to my heart. So for me, it is very exciting to see all of the interest in the citrus industry in North Florida despite the devastation the industry is facing in South Florida. With many folks spending more time outdoors and working in the landscape, I wanted to share some ways homeowners can enjoy citrus in their landscape all while protecting the future of the citrus industry in North Florida!
First thing’s first…identification!
It’s important to be aware of some of the major pests and diseases affecting citrus. Fortunately for us in the Panhandle, many of the major pests and diseases troubling citrus to the south haven’t become quite as widespread in our area, and with your help we can keep it that way! Regularly scouting the citrus in your landscape and detecting any major pests or diseases early will be very important to prevent it from spreading.
The first major disease all Floridians should be aware of is citrus greening. Citrus greening or huanglongbing (HLB) is the major disease affecting the citrus industry worldwide. It is a bacterial disease caused by the bacteria Candidatus Liberibacter. The bacterium is spread from tree to tree by a tiny insect known as the Asian citrus psyllid. Psyllids spread the disease by feeding on infected trees and moving on to non-infected trees. Once the tree is infected, there’s little hope for survival as there is no cure for citrus greening.
Citrus greening can be difficult to diagnose as it can be easily confused with nutrient deficiency. Symptoms of citrus greening include yellowing of the veins and a blotchy mottle pattern. Nutrient deficiencies tend to have a symmetrical pattern on each side of the leaf vein whereas citrus greening is asymmetrical. Overall, a tree infected with citrus greening will appear unhealthy with discolored leaves, a thin canopy, and reduced fruit production.
Citrus Canker presenting on a leaf. Photo courtesy of Danielle Sprague.
Another disease to be on the lookout for is citrus canker. Citrus is also caused by a bacterial pathogen but is spread primarily though wind, rain and human movement. Citrus canker is highly contagious and can spread very rapidly. Transporting infected plant material from an area where canker is present is the primary means of spreading the pathogen.
Purchase from a certified nursery!
One of the absolute most important things you can do if you are planting citrus is to purchase your trees from a certified citrus nursery! A certified nursery has been inspected by the state to confirm that the nursery is producing clean, disease free trees. Citrus trees grown in a certified nursery will have a tag with the name of the nursery, registration number, the tree variety, and rootstock.
When buying a tree from a secondary retailer, you will want to be sure to examine the tree for any signs and symptoms of pests and diseases. A healthy tree will have dark green leaves, a smooth trunk and show no signs of wilt.
Certified nursery label. Photo courtesy of Danielle Sprague.
Other ways to protect citrus:
Learn how to properly care for citrus trees. Proper watering an fertilization will make them less susceptible to pest and disease.
Report any suspected pest and diseases to the Florida Department of Agriculture and Consumer Services (FDACS) Division of Plant Industry by calling 1-888-397-1517
Don’t bring back plants or fruit into Florida! They could introduce new pests and diseases.
Keeping the Panhandle free of citrus greening and citrus canker will play a major role in the success of the citrus industry in North Florida. For assistance with pest and disease identification or for more information, contact your local Extension agent.
One of the things to do while stuck at home due to COVID-19 restrictions, is to look for caterpillars and butterflies in your landscape. I’ve noticed giant swallowtail butterflies (Papilio cresphontes) a little early this year. The giant swallowtail is one of the largest and most beautiful butterflies in our area. Its larval stage is known as the orangedog caterpillar. This unusual name comes from the fact that it feeds on young foliage of citrus trees.
Orangedog caterpillar. Photo credit: Donald Hall, University of Florida
The orangedog caterpillar is mostly brown with some white blotches, resembling bird droppings more than a caterpillar. When disturbed, it may try to scare you off by extruding two orange horns that produce a pungent odor hard to wash off.
I’ve had some minor feeding on citrus trees in my landscape from orangedog caterpillars. But I tolerate them. I’m not growing the citrus to sell. Sure the caterpillars eat a few leaves but my citrus trees have thousands of leaves. New leaves eventually replace the eaten ones. I leave the caterpillars alone. They eat a few leaves, develop into chrysalises and then emerge as beautiful giant swallowtail butterflies. The whole experience is a great life lesson for my two teenagers. And, we get to enjoy beautiful giant swallowtail butterflies flying around in our landscape and still get plenty of fruit from the citrus trees. It is a win, win, win.
In some cases, the caterpillars can cause widespread defoliation of citrus. A few orangedog caterpillars can defoliate small, potted citrus trees. Where you cannot tolerate their feeding habits, remove them from the plant. But consider relocating the caterpillars to another area. In addition to citrus, the orangedog caterpillars will use the herb fennel (Foeniculum vulgare) and rue (Ruta graveolens) as a food source. Some butterfly gardens plant citrus trees to provide food for orangedog caterpillars so that they will have giant swallowtail butterflies. So you could plan ahead and grow some fennel, rue or find a butterfly garden in your area for the purpose of relocating the larvae.
Yellow giant swallowtail butterfly on pink garden phlox flowers. Photo credit: Larry Williams
The adult butterflies feed on nectar from many flowers, including azalea, bougainvillea, Japanese honeysuckle, goldenrod, dame’s rocket, bouncing Bet and swamp milkweed. Some plants in this list might be invasive.
Keep in mind that mature citrus trees can easily withstand the loss of a few leaves. If you find and allow a few orangedog caterpillars to feed on a few leaves of a mature citrus tree in your landscape, you and your neighbors might get to enjoy the spectacular giant swallowtail butterfly.
