Biostimulants: An Innovative Approach to Improve Yield, Fruit Quality and Soil Health in Fruit Trees Particularly Citrus

Biostimulants: An Innovative Approach to Improve Yield, Fruit Quality and Soil Health in Fruit Trees Particularly Citrus

Written by: Muhammad Adnan Shahid and Shahid Iqbal.

UF/IFAS Horticultural Sciences Department, North Florida Research and Education Center, Quincy FL

Biostimulants are a type of substance or microorganism applied to plants to improve their nutrient efficiency and resistance against abiotic stress (salinity, cold, heat, UV, flooding, drought, heavy metal toxicity, nutrient deficiency), diseases, and quality traits. Due to the increase in world population, the growing pressure on crop productivity is a demanding challenge; therefore, it is necessary to reduce the use of agrochemicals with negative impacts on human health and the environment. Thus, new strategies from the bio-based industry must be found and adopted. Citrus is a highly desirable and profitable fruit crop with undesirable characteristics like excessive flowering and physiological fruit disorder that negatively affect the market value.

Biostimulant Types and Practical Application

Many crop growers have expressed an interest in biostimulants in recent years. As these products gain popularity, we have found that there’s still a lot of controversy about their efficacy. Before determining whether Extension endorses them, let’s review the various types and their practical usage.

Several types of biostimulants include humic and fulvic acid, seaweed extracts, protein hydrolysates, chitosan, beneficial bacteria, fungi and microbial inoculants, and other types of amino acids and polyamines. These products are commercially available with different formulations and ingredients and have immense potential in horticultural crop production, especially in citrus.

Plant biostimulants can be applied through foliar application, fertigation, or directly through the soil, enhancing crop growth and quality. Biostimulants could reduce plant environmental threats and minimize the negative consequences of unsystematic chemical application.

Benefits of Using Biostimulants in Citrus Crop Production

Biostimulant products improve plants’ overall health and help maximize fruit production and quality by providing complete nutrition. The benefits of using biostimulants are highlighted below.

  • Improve plant metabolism to induce high-yield and quality.
  • Enhance soil fertility by fostering complementary soil microorganisms.
  • Increase tolerance against abiotic stresses.
  • Facilitate nutrients and their movement inside the plant vessels
  • Boost fruit quality attributes like color, sugar content, etc.
Biostimulant Application
Application of biostimulants and its effect on plant growth and quality traits.

Concluding remarks and recommendations

Biostimulants are in the frontline as a novel strategy to achieve the goal of sustainable citrus crop production, yield, and superior quality. Proper management practices are important for high-yield and quality fruit in citrus production. The use of biostimulant products can provide producers with sustainable production. Before using these products, contact a regional extension specialist or citrus expert for their proper application and trail setup. The Fruit Physiology Lab at North Florida Research and Education Centre (NFREC), Quincy, Florida has started a research project on determining the efficacy and efficiency of different microbial and non-microbial biostimulants in cold hardy citrus production, to improve yield, and fruit quality. For any further information on the use of biostimulants please contact Dr. Muhammad Shahid, Fruit Physiologist/Assistant Professor of Horticulture at mshahid@ufl.edu.

Update on Citrus Greening in North Florida

Update on Citrus Greening in North Florida

The Asian citrus psyllid, Diaphorina citri, spreads the bacterium responsible for citrus greening. Photo by Michael Rogers, UF/IFAS.

Asian citrus psyllid, Diaphorina citri. UF/IFAS/Entomology Photo: Michael Rogers.

In late 2016, as many of us were enjoying the harvests from our backyard citrus, a bacterial plant disease that can affect all citrus, citrus greening, was widespread in central and south Florida but had not made it this far north. That year, the vector, the insect that spreads the disease from tree to tree, had been found in Leon County and a few other surrounding Panhandle counties, but the disease had not. By mid-2017, the disease had been confirmed in Franklin County and we hoped that our cooler temperatures could keep the insect and disease at bay. Well, I regret to inform you that the disease has also now been confirmed in Leon County, growing in a residential yard in Tallahassee. Now that it is confirmed in non-coastal (and cooler) north Florida locations, I thought a review of the signs and symptoms – as well as what to do with your tree if you suspect or confirm greening – would be helpful.

The tricky part about diagnosing citrus greening is that it has symptoms that look very similar to soil nutrient deficiency symptoms, especially when first infected. This is a good time to mention that citrus require certain micro-nutrients for optimal growth and a citrus-specific fertilizer product should be used when applying fertilizer. Both the disease and certain nutrient deficiencies cause yellowing of the leaves. With greening, the yellowing is typically blotchy and/or not in any particular pattern. Nutrient deficiencies typically cause unique patterns of yellowing, such as a V-shape or artistic-like symmetrical patterns on each side of the leaf’s midvein. The soil’s acidity, or pH, can also cause some nutrients to not be taken up by the plant even if they are present. Soil testing, available from your local UF/IFAS Extension office, and scheduled fertilizations with a citrus-specific fertilizer can ensure that nutrients are not to blame for the discoloring of leaves. More advanced stages of the disease cause such symptoms as leaf drop, fruit drop, lop-sided fruit, uneven inner fruit cores, and reduced fruit quality.

Citrus greening symptoms of the fruit. Photo by Brooke Moffis.

Citrus greening symptoms of the fruit. Photo by Brooke Moffis.

A more obvious sign of potential problems for your citrus are the presence of the insect vector, the Asian citrus psyllid. This is a tiny little insect that goes from one leaf to the other sucking up plant saps for food and unknowingly spreading the bacterium responsible for citrus greening. You can monitor for them by looking closely at the new flushes of growth. If the psyllids are present, you will likely notice most their small, peach-colored eggs and/or white, waxy secretions. If found, it doesn’t necessarily mean that your tree has greening, but you will want to minimize the chance that they could carry it to your tree. The psyllids can be treated with pesticides, ranging from the less harsh options (horticulture oils, neem oil, kaolin clay) to the more hardcore stuff (malathion, carbaryl, imidacloprid). Of course, always read the label of any pesticide before use and/or consult a qualified landscape professional for assistance.

Blotchy leaf symptom of citrus greening. Photo by Jamie D. Burrow.

Blotchy leaf symptom of citrus greening. Photo by Jamie D. Burrow.

If you suspect your tree is infected, a diagnostic test can be performed by UF/IFAS plant pathologists at the North Florida Research and Education Center (NFREC) in Quincy to confirm. The test does cost $50, which may seem a little steep, but it’s an expensive lab analysis to run and may be worth piece of mind.

If citrus greening is confirmed in your tree, the right thing to do, unfortunately, is to remove and burn the plant material as there is no known cure. While the Florida Department of Agriculture and Consumer Services (FDACS) doesn’t have any removal requirements for infected dooryard citrus, tree removal is best to prevent additional spread of the disease to other trees, especially those grown by commercial producers in our area. This may seem drastic but eventually the health of the tree and quality of the fruit will decline to a point where you will want to remove it anyway. Don’t forget that movement of any citrus plant outside of the state is prohibited for the very reason of preventing spread of citrus diseases.

You may be asking, “Is it okay to replace it with another citrus tree?” The answer is yes you can, but you do risk re-infection and will want to be monitoring the new planting.

You may also be thinking, “What is going to happen to Florida citrus?” That’s a question that many researchers at UF/IFAS are trying to answer. There is some hope that intense irrigation and nutrient management, as well as specific pruning practices, can help infected trees continue to be profitable for commercial growers. Recently, UF/IFAS researchers were awarded several grants to try and figure a way out of this problem. Some of the lines of research focus on exploring the resistance found in different citrus varieties, including an Australian lime that appears to be greening resistant. This could potentially be used as a future rootstock. Another approach is to try and treat the plants with a particular peptide that would prevent the disease from binding in the insect’s gut. Isn’t that amazing?

Until a fix is found, we should be monitoring for this disease in our area and taking steps to reduce its presence through controlling the psyllids and removing infected trees. If you suspect a tree has greening, please contact your local county Extension office to review the symptoms and discuss your options.

Much more information on citrus greening is available at the following Ask IFAS website: https://edis.ifas.ufl.edu/entity/topic/citrus_greening and from this 2017 article – https://nwdistrict.ifas.ufl.edu/phag/2017/03/03/disease-alert-citrus-greening-and-asian-citrus-psyllids-found-in-the-panhandle/.

Sugar Belle Mandarin: A Great Choice for the Florida Panhandle

Sugar Belle Mandarin: A Great Choice for the Florida Panhandle

image of sugar belle mandarin

Sugar Belle mandarin cultivar. Mix of sweet Clementine and Minneola varieties. UF/IFAS File Photo.

Florida is known for citrus and many homeowners love to grow and enjoy it. However, a devastating disease known as citrus greening or HLB has taken a toll on commercial and residential citrus since it first was discovered in Florida in 2005.

Sugar Belle is a cultivar of mandarin citrus developed by the University of Florida citrus geniuses and is tolerant of citrus greening disease if it is properly planted and cared for. Tolerance of the disease does not mean that it doesn’t get citrus greening, rather it means that this cultivar can get infected but still be healthy and productive. The fruit of infected trees is safe to eat as the bacterium that causes it does no harm to humans.

Our chilly winters can be detrimental to many kinds of citrus, but Sugar Belle can withstand temperatures down to 14°F once the tree is well established. That is good news for us in the panhandle. Even so, it is best to choose a spot in your landscape with a southern exposure, preferably with a wind block from northwest winds. Avoid low areas as cooler air falls into those areas.

Symptoms of citrus greening on leaves show a blotchy mottled pattern. UF/IFAS photo.

Make your purchase from a certified nursery to make sure you are getting the right cultivar and a disease-free tree. Spring and fall are the best seasons of the year to plant citrus. When planting, make sure to make slices in the rootball if it is rootbound or if circling roots are present. The rootball should be slightly above the ground level after planting. All weeds and grass should be removed under the canopy of the tree to as they compete for water and nutrients with your newly planted tree. Never place mulch against the trunk as it can hold moisture there and promote disease. Water often the first year until well-established; after establishment citrus has some drought tolerance and may only need supplemental irrigation in times of heat and drought.

A good quality citrus fertilizer with micronutrients is crucial for a healthy tree with good quality fruit. The first fertilization should be about 3 weeks after planting and then follow the label directions for subsequent fertilizations. Newly planted trees should be fertilized 6 times in the first year and the fertilizer should be evenly broadcast under the tree canopy.

The only pruning in the first 3 years should be the removal of suckers that grow from the base, water shoots that grow quickly and straight up, and dead wood. Be sure to clean your pruning tools before and after each tree to avoid spreading any possible disease. First rinse off any dirt or other organic matter and then use a 3% bleach solution or alcohol for sterilization.

Happy Gardening!

For more information:

UF/IFAS Research on Development of Sugar Belle YouTube

Citrus Culture in the Home Landscape

Citrus Greening

 

Choosing the Right Dooryard Fruit Varieties

Choosing the Right Dooryard Fruit Varieties

We have many choices of fruit that can be grown in the Florida Panhandle. For us hobby or dooryard growers, fruit trees can be an interesting crop to manage and most find it to be a beautiful addition to home landscapes. However, temperature and variety selection are key.

Blueberry Crop at UF/IFAS Plant Science Research & Education Unit. Photo Credit: Tyler Jones, UF/IFAS

Most fruit trees grown in the Panhandle are more temperate varieties, rather than tropical and subtropical fruits. Depending on the variety, winters in northern Florida may be too cold or may be too long for some fruit trees. Cold hardiness is a term used on fruit tree labels and reference guides. This refers to the plant’s ability to survive cooler or even freezing temperatures. In contrast, summer heat can also play a role in survivability. Some varieties are intolerant to excessive heat and humidity. The U.S. Department of Agriculture has developed a Plant Hardiness Zone Map that is helpful in selecting a variety of fruit tree: http://planthardiness.ars.usda.gov/PHZMWeb/. This is a standard by which gardeners and growers can determine which plants will thrive in their location. Northern Gulf County is in Zone 8b (15 to 20 degrees F), while coastal Gulf is in Zone 9a (20 to 25 degrees F).

Chilling requirement is another important topic when deciding on variety. Temperate zone fruit go through a “rest period” during the dormant months. For these fruit trees, a minimum length of time of cooler weather is needed for proper flowering to occur once favorable temperatures arrive. This rest period is essentially a reset. For the Panhandle, temperatures below 45 degrees F are known as chilling temperatures. The number of hours during the fall and winter that reach below this temperature equals the total chilling hours. For the Panhandle, this is rarely fewer than 500 hours. A plant that does not receive ample chilling will most likely be slow in bud and leaf development. Leaf expansion will be in increments throughout the year instead of in one period. On the other hand, colder, longer winters can cause fruit trees to end the rest stage early and begin to bud as soon as warmer temperatures arrive. This circumstance can cause cold injury later, as the Panhandle is historically known for late cold spells.

Citrus is a dooryard fruit, however it’s a subtropical fruit tree and not technically temperate. However, there are some varieties that thrive in the Panhandle. Another key to growing citrus, is to select varieties with different fruit maturity seasons. This way you can enjoy citrus year-round.

Some examples of dooryard fruit trees and varieties that are suitable for northern Florida are:

Apple: ‘TropicSweet’, ‘Anna’, ‘Dorsett Golden’

Blueberry: ‘Rabbiteye’, ‘Climax’, ‘Highbush’

Grapefruit: ‘Marsh’, ‘Ruby Red’

Lemon: ‘Myer’

Nectarine: ‘Suncoast’

Orange/Mandarin: ‘Navel’, ‘Parson Brown’, ‘Valencia’, Satsuma

Peach: ‘Gulfcrest’, ‘Gulfking’, ‘Gulfprince’

Pear: ‘Ayers’, ‘Baldwin’, ‘Kieffer’

Pecan: ‘Elliot’, ‘Stuart’, ‘Moreland’

So, where do I find information on varieties? The UF web publication “Dooryard Fruit Varieties” is a great resource. Also contact your local county extension office for more information.

Information for this article can be found in the UF/IFAS EDIS publication: “Dooryard Fruit Varieties” by J. G. Williamson, J. H. Crane, R. E. Rouse, and M. A. Olmstead: http://edis.ifas.ufl.edu/pdffiles/MG/MG24800.pdf

UF/IFAS Extension is an Equal Opportunity Institution.

Shiranui Mandarin: Ugly Fruit, Great Flavor

Shiranui Mandarin: Ugly Fruit, Great Flavor

Shiranui mandarin

You’ve likely seen them in the grocery stores, and you’ll see them now through April. A large, lumpy (some may say ugly) piece of orange fruit with a bump near the stem. But what exactly is this special looking fruit? It’s a Shiranui mandarin!

The name ‘Shiranui’ is the generic term for this variety of citrus. You may have seen the same variety of mandarin marketed in grocery stores as ‘Sumo Citrus’ which is a trademarked name for the variety. In Japan, they are widely known as ‘Dekopons’. No matter what you call them, they are easily recognized by their distinctive appearance.

The Shiranui mandarin is a hybrid between a Ponkan tangerine and a Kiyomi Tangor (sweet orange x satsuma mandarin). They are easy to peel, sweet, and seedless. Shiranuis are considered to be one of the sweetest and most flavorful varieties of citrus on the market. The fruit are large and have a large protruding bump near the stem that resembles the top knot hairstyle of a Japanese sumo wrestler (hence the trademarked name ‘Sumo Citrus’).

While the majority of Shiranui mandarins on the market are grown in California, the variety can be grown here in Florida and several citrus growers in North Florida and South Georgia have began to experiment with plantings in the region. Homeowners, too, can try their hand at growing the variety as many Florida certified citrus nurseries carry the variety. For more information on different citrus varieties, contact your local UF/IFAS Extension Agent.