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.
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 firstname.lastname@example.org.
The weather is the most important factor determining where certain fruits can be successfully grown. Terms such as chilling requirement and cold hardiness play a major role in both species and variety selection.
Most fruits which grow in the Panhandle are deciduous, meaning that during the winter, they lose their leaves and go through a semi to full dormancy period. This period is a much needed rest and reset for the plant. The cool season actually helps the plant to rebound for another fruiting season and affects how well the plant will yield fruit. This is where the term “chilling hours” comes into play.
Temperatures below 45 degrees Fahrenheit are considered “chilling”. The number of hours below 45 degrees accumulated throughout the winter determines the total amount of chilling hours. Different species of citrus and dooryard fruit, along with different cultivars of these plants differ in the amount of chilling hours need for that all important rest & reset period. Satsuma is a popular fruit trees in our area, as it is by far the most cold hardy citrus. Evidence suggests that the satsuma can survive a temperature as low as 14 degrees Fahrenheit.
Figure 1. Mature satsumas ready for harvest.
Credit. Pete Anderson. UF/IFAS Extension.
What happens if the plant doesn’t receive the needed amount of chilling hours? Plant hormones can be disrupted, and both leafing and blooming could be light and come outside of the normal range of the season. So, where do we stand in the Panhandle for overall chilling hours? Typically, we see approximately 500 hours chilling hours. Therefore, its best to plant citrus and dooryard fruit that have the characteristic of needing 500 or less hours for chilling. Please see this informative document on citrus and dooryard fruit varieties: https://edis.ifas.ufl.edu/publication/MG248
Now, on to the term cold hardiness. By definition, this is the plants ability to withstand cool season temperatures without injury. Most tropical fruits cannot tolerate our Panhandle temperatures. Those of us that cut back banana trees every year know this all too well. To check your plant hardiness zone, please see the USDA Plant Hardiness Zone Map: https://planthardiness.ars.usda.gov/
Before you plant a fruit tree, make sure you understand about its cold hardiness and whether or not it has a chilling requirement. This will both save you money and a headache, in the end. If you’re in doubt about a particular variety, contact your local extension office.
Taste and size of citrus fruits are important attributes that determine profit. Since, consumers prefer firm citrus fruit, packing houses only accept fruits of specific size without softness. Therefore, fruit that grow too large and don’t fill out properly are unmarketable and growers discard all these types of fruits. This condition is called puffiness. As fruit diameter becomes ever larger, fruit pith (the area between flesh and the peel of fruits) becomes thick and causes the fruit to shrink inward and lose its normal spherical shape. So far, this problem has been observed in both backyard and commercial Satsuma groves in North Florida, South Georgia, and Southeast Alabama. Citrus puffiness is a threat for all growers from an economic and overall yield point of view, because puffed fruits are unmarketable resulting reduced profit margins.
A few scientific reports suggest that low fruit loads on citrus trees can cause puffiness, but the actual mechanism of puffiness still need to be explored. Based on observations, the team from our lab (Fruit Physiology lab, NFREC, Quincy) and collaborators lead by Dr. Muhammad Shahid has concluded that there are three possible causes of puffiness in citrus i.e., genetic, environmental, or nutritional. In our next phase of research, we will dig deep into this issue and try to determine what is the actual cause of puffiness. Fruit puffiness is observed more in young (4-6 years) satsuma groves than in mature groves. Puffiness on old trees could be due to fruit setting on late blooms during hot conditions. Overall, fruit puffiness is less of a concern in sweet oranges, limes and lemons as compared to satsumas.
Puffiness study by Fruit Physiology Lab, NFREC, Quincy
In our preliminary study, we divided puffiness into five different grades based on fruit size. Grade one is marketable fruits (firm without puffiness). Fruit diameter and puffiness increase gradually in grades 2, 3, 4, and 5, respectively. We have collected fruits from different groves in north Florida and the common denominator among these fruit was decreased Brix value (a common measure of sweetness) with increased puffiness. Average fruit diameter with maximum puffiness was around 40cm and these puffy fruit weighed around 475g. With increasing puffiness, peel weight was increased while juice contents were reduced – not great!
Most satsuma groves in North Florida have some degree of puffiness. However, amount and grade of puffiness varies by grove. In our observations, citrus groves in South Georgia also have puffy fruit, which clearly indicates that puffiness is not geographically specific and can develop in any citrus growing region. After visiting a number of farms in North Florida, we concluded that puffiness is mostly an issue with the Satsuma cultivar ‘Owari’ regardless of different rootstocks. Having said this, we can’t say with confidence that puffiness couldn’t appear on other varieties of citrus without further study. We are carefully monitoring all our variety evaluation trials at the UF/IFAS North Florida Research and Education Center (NFREC), Quincy, in collaboration with citrus breeding and postharvest experts from Citrus Research and Education Center (CREC) and Indian River Research and Education Center (IRREC). We are working on different aspects of citrus production including nutrition, crop load, and pruning to identify the actual cause of puffiness and how to effectively mitigate it in Satsuma groves in north Florida.
Citrus is one of the most cherished fruit trees in the Panhandle. Citrus owners are well aware that every year the main damage to their trees come from citrus leafminer (CLM). CLM is a small moth and its larvae feeds between the tissue layers of new leaf growth, causing serpentine mines to form under the leaf cuticle (Fig. 1). The feeding damage results in leaf curling and distortion, and severe infestations of CLM on young trees can retard the growth of trees. Another threat concerning CLM in Florida is that the mines provide an open wound for citrus canker to enter, a bacterial disease that has been found recently in the Florida Panhandle, Georgia, and Alabama.
Most commercial growers deal with CLM in young trees by a soil application of systemic insecticide before the flush season, followed by a foliar insecticide when the systemic drench’s toxicity is declining. Homeowners, however, have limited access to these chemistries. Garden systemic insecticides that include imidacloprid (Bayer’s Tree & Shrub Insect Control™, Merit®, etc.) and dinotefuran (Greenlight Tree and Shrub Insect Control™, Safari®, etc.) are among the few options for CLM control. For the best efficacy, those insecticides should be applied two weeks before the start of the flushing season to allow time for the insecticide to move from the roots into the canopy. To avoid leaching of insecticide away from the root zone, soil applications should be made within a 24-hour period without rain. Citrus trees usually have several flushes per year, depending upon cultivar, climate, and crop load. However, in the Florida Panhandle, most citrus cultivars have two major flushes in May and September.
Importantly, systemic insecticides are only efficient against CLM for small immature trees; therefore, the only products labeled for use against CLM on mature trees are foliar sprays. Horticultural oils or insecticides with spinosad (such as Monterey® Garden Insect Spray) are some options available for homeowners. However, achieving leafminer control with foliar applications on mature trees is challenging due to unsynchronized flushing of trees. Foliar applications should be timed with the appearance of the first visible leaf mines. In any case, be sure to READ THE LABEL and follow all the label directions.
Cultural practices, and non-insecticidal methods.
For isolated trees in a backyard, cultural practices and control through mass trapping are usually sufficient to control CLM and insecticide use is not recommended, especially for mature trees. One of the basic cultural practices is to remove any stems that grow below the bud union or from the rootstock, also called ‘suckers’ (Fig. 2). Those rootstock shoots compete with the scion shoots and are great reservoirs for CLM; removing them will help reducing CLM population. On isolated trees, mass trapping using CLM pheromone provide good results (Fig. 3). The mass trapping method is constituted of a delta trap baited with a lure that emits a large quantity of CLM sex pheromone. CLM males are attracted by the odor and are captured in the delta trap’s sticky liner. Those traps are commonly used by growers to monitor CLM populations, but for homeowners they are sufficient to control CLM on a single tree. This trap and a lure method should protect a single tree for approximately 3 months. Finally, the last option is the use of biological control. Several natural enemies are predators or parasitize CLM. In some case, biological control can reduce CLM populations by 90%. Primary predators of CLM include ants, lacewings, and spiders, as well as a parasitic wasp, Ageniaspis citricola that was introduced into Florida and has become established (Fig. 4).
Pecans are a flavorful and nutritious nut and an essential component of a southerner’s diet. The trees also provide nice shade and intense fall color to landscapes throughout the south. However, not all pecan tree varieties are suited for the Florida panhandle. There are a number of things you should consider before planting a pecan tree.
Site Selection – Pecan trees are native to the river valleys of North America. They perform best in deep, fertile, well-drained soils. The key is that the soil is well-drained. Pecan trees will not do well in soils that hold a lot of water and do not drain quickly. Pecan trees also need space to grow. Trees should be planted at least sixty feet apart and at least sixty feet from other large trees and structures. This will allow adequate light for the trees produce a good crop.
Disease Resistance – Pecan scab is the most detrimental pecan disease in the southeast. Trees advertised as scab resistant in the past may have become more susceptible over time. A few varieties that seem to be available at tree farms and have maintained their scab resistance are ‘Caddo’, ‘Elliot’, ‘Lakota’, and ‘Gafford’. Newer varieties that currently have good scab resistance are ‘Avalon’, ‘Huffman’, and ‘Whiddon’. However, these newer varieties may be more difficult to find at nurseries and farm stores.
Pollination – Pecan trees produce both female and male flowers on the same tree. Trees are split into two pollination groups. Type I pollinators produce mature pollen before their female flowers are receptive and Type II trees produce receptive female flowers before their pollen is mature. Timing of flower maturity may change with tree age, but it is a good practice to plant a Type I tree along with a Type II tree to ensure a good crop in each tree. A pollination compatibility chart can be found at UGA Pecan Compatibility Chart.
Planting – Commercially, pecan trees are most commonly planted as bare-root transplants, but container-grown trees can also be used. Bare-root trees are usually cheaper and more readily available. They should be planted while dormant, between December and March and should be planted the day they are delivered. If the root system looks dry, soak the trees in water for a few hours before planting. Container-grown trees can be planted any time of the year, but they have the best chance of survival if planted during dormancy. Trees should be planted at the depth they stood at the nursery or the depth they were planted in a container. Planting holes should be at least 18 inches wide and only native soil should be used to fill in the hole. The main causes of death in young trees are planting too deep and inadequate moisture during the first two years following planting.
Are you a homeowner in Florida? Do you have citrus on your property? Consider helping the University of Florida/IFAS Extension by taking a survey!
This survey is part of a research project carried out by the UF/IFAS to gather information on citrus pests in residential settings in Florida. This survey is designated for Florida residentswho have citrus on their property that are not intended for commercial use. The outcomes of this survey will serve to develop appropriate control methods against critical citrus pests for dooryard citrus. We kindly ask that you complete all questions on this survey which will take approximately 20 minutes.