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Stuart Gauthier, Singh, Raghuwinder, Strahan, Ronald E., Turley, Robert M., Polozola, Michael, Fontenot, Kathryn, Kirk-Ballard, Heather
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Weather dipping into the teens in late February damaged citrus trees across Louisiana earlier this year. The less cold hardy citrus types, including limes and lemons, were especially hard hit. Growers require patience because the true extent of freeze damage to limbs will not be fully apparent until the summer months. Often freeze-damaged limbs may initially sprout in March and April only to wither later in the growing season. Research has shown that early pruning does not promote recovery and delaying action until the summer will benefit the tree and the lessen the grower’s workload. By summertime, dead wood will be easily recognizable, making pruning cuts more efficient. To help promote proper healing, cuts should be made when possible at branch junctions or crotches. Incisions should be made into living wood, leaving a smooth and flush surface.
Fertilizer applications to freeze-damaged trees should be reduced to compensate for the reduced canopy size and foliage density. A tree that has lost half of its canopy should have its fertilizer rate cut in half. A standard rule for fertilizing citrus is to apply about 1 pound or 1 pint of 13-13-13 per year of age of tree up to a 12-pound per tree maximum. This is generally applied starting in late January or early February.
In the case of freeze damage, tree growers may want to split this fertilizer amount into monthly applications that would total the overall recommended amount. Fertilizer should always be applied near the tree’s dripline before a rain or deeply watered in following application. Fertilizer applications should end in June or risk promoting late-season growth more prone to freeze damage. Any nutrient deficiency issues that existed prior to the freeze will be intensified in freeze-damaged trees as new growth will increase the nutrient demand.
As the canopy of the tree opens up due to leaf drop in freeze-damaged trees, weeds will flourish. Weed control efforts will have to be intensified to keep weed pressure down. Generally, mulch is not recommended for weed control in citrus orchards due to the increased potential for root rot development in moist soil. Weeds can be controlled using appropriate herbicide applications or light tillage.
Disease control efforts may also need to be increased. Pressure from pathogens like melanose may become more prevalent in freeze-damaged trees. A couple of fungicide applications with fungicides such as copper coupled with nutritional sprays of foliar fertilizers will help enhance disease management.
Stuart Gauthier
Extension Agent
Citrus growth tends to be in flushes with periods of shoot inactivity between flushes. In Louisiana, there are three flushes of growth a year. The first flush occurs in late February and March. This usually the time of the greatest shoot extension because more buds elongate. The second flush occurs in July and August, and the last takes place in October. During growth flushes, the shoots elongate in between the flushes, the leaves expand to full size and root growth occurs.
It is the second and third flushes that the citrus leaf miner moth is active and laying eggs on the new growth flushes. The moths deposit their eggs on the underside of the foliage. Upon emerging, larvae tunnel into the leaf and create winding tunnels between the upper and lower surfaces as they develop and feed.
At maturity, the larvae move to the edge of the leaf, causing it to curl. This protected area is where the larvae pupate. The larval stage lasts from five to 20 days; pupation lasts six to 22 days.
Adult females emerge in the morning and lay their eggs at night. Total development time takes from 13 to 52 days, depending on weather and temperature. Adults are short lived. But there are multiple generations each year, which can occur every three weeks, depending on the environmental conditions.
Control: Apply Spinosad at the rate of 1 teaspoon per gallon of water on new, expanding growth flushes. Allow a minimum of seven days between last application and harvest. Several formulations available for home gardens (i.e., Spinosad, Success, Conserve, Naturalyte). Follow label recommendations.
The western leaf-footed stink bug is widespread and a pest of many crops including fruits, vegetables, grains, nuts and ornamentals. It is a major pest of citrus, and its feeding on ripening fruit causes premature color break and fruit drop. Adults will fly considerable distances and enter orange trees at bloom time to feed on buds and young shoots. Later, adult bugs will attack the ripening fruit, causing drop.
Leaf-footed bugs transmit yeast, Nematospora coryli, that causes dry rot. Leaf-footed bugs primarily attack satsuma mandarins. Injury usually occurs as the fruit matures in the fall.
The leaf-footed bugs will aggregate in large colonies on individual trees while neighboring trees are completely free of bugs. Leaf-footed bugs are parasitized by a tachinid fly, which lays eggs on adults and nymphs. Immature flies hatch from the eggs and consume the leaf-footed bug internally.
Control measures: Monitor your trees for leaf-footed bugs in late summer and early autumn. If present, apply an application of Vegetable Plus (10% permethrin) at the rate of one-quarter to one-half ounce per gallon of water. Good coverage of fruit is necessary. Do not apply insecticide products to plants in full bloom. Follow label recommendations.
Robert Turley
Extension Agent
We are rapidly approaching bud break in pecan trees with some cultivars already flushing out at the time of writing this article. This is a critical time for pecan production, which signals the beginning of fertility, disease and insect management. What I would like to focus on now is pecan phylloxera because I have had several inquiries on them the past few weeks.
The time to treat it is from budbreak until the new growth has grown to about 1 inch. If you wait until you see galls, it is too late. By that time, it will require something systemic, and a large portion of the damage has already been done. Your goal is to kill the offending insect before it has a chance to establish itself within the plant.
Unless your orchard has a serious infestation, you should not need to treat the whole orchard. You should be able to focus on trees you know had it last year and the borders around them. If you have a high neighboring population, it may be worthwhile to do the perimeter of the orchard. As for what chemicals to use. I prefer the University of Georgia’s recommendations of imidacloprid and chlorpyrifos. I lean toward imidacloprid because it has some systemic activity, but if you have a serious infestation, I would consider an application of both to get it under control. If you need any help determining if this is something you should treat for, please feel free to contact me at the LSU AgCenter, 318-473-6520 or mpolozola@agcenter.lsu.edu.
Michael Polozola, Ph.D.
Horticulture Agent and Pecan Expert
This complex of little beetles covers several families or wood infesters. Infestations are brought on by some sort of stress on the trees and woody plants, like a cold snap after warm weather, drought, flooding or root or weed-eater injury. These little beetles are attracted to the pheromones released by the woody plants. The most common injury is in the tips of branches that have started to bud out and we get a frost or freeze that injures the buds and the terminals of the branches. The beetles attack and bore into these injured branches, causing them to die. Sometimes the injury is to the trunks of trees and the attack point is there and you can find pencil-like stacks of sawdust coming from the entrance holes or the sawdust collected at the base of the trees. In many cases the tree branches can be pruned to remove the injury, but sometimes sprays are required. In cases where the trunk is damaged there is little to do to save the tree. That is because many of these little beetles do not feed on the wood as they bore into the trees but feed on a fungus they brought with them that infects the tree. It’s the fungus that causes the tree’s death along with the stress from the infestation. Where possible homeowners can use a pyrethroid to manage these infestations. They should be used with an oil to get better attachment and penetration into the bark of the tree for control.
Robert Turley
Extension Agent
Water is our most precious natural resource. Americans use an average of 29 gallons of water per day, according to the Environmental Protection Agency, with 30% or 8.5 billion gallons each day used for gardening and lawn care. With two-thirds of the world’s population projected to face water scarcity by 2025, it is time to plan for shortages.
You can make water-wise landscaping decisions and create a functional, easily maintained landscape by following a few guidelines that will help conserve water, money and time.
The EPA recommends these key tips for water-smart landscaping:
Planning before you plant is the first step when making water-wise landscape decisions. Did you know that plants help conserve water and improve water quality by slowing and collecting rain?
Next, select the right plant for the right place based on your regional conditions. Take into account the annual rainfall and average temperatures for your area. To achieve the need for minimum irrigation, choose plants that are adapted to low water environments, such as native plants.
For the most water conservation, limit or eliminate turfgrass in your landscape. This will not only conserve water, but it will also conserve time and money spent on maintaining grass and cut back on watering and mowing tasks — bonus! Keep in mind that some grasses are more drought tolerant than others, such as centipedegrass and zoysia. St. Augustinegrass, bermudagrass and carpetgrass require more water.
Group plants with similar water needs in “hydrozones” that reduce water use according to each zone. Turf and bedding plants will require the most water, whereas well-established shrubs and trees with extensive and deep root systems require less.
Timing matters. Automatic irrigation systems can be a real time saver. It can also help you get a little extra shut eye because the best time to water plants is early in the morning between the times of 2 a.m. and 8 a.m.
Watering during the heat of the day reduces the efficiency because more water is lost to evaporation. Watering in the evening between 6 p.m. to midnight can encourage fungal diseases as plants remain wet for extended periods.
Schedule irrigation according to each hydrozone for particular plant needs and in response to decreased rainfall. In addition to conserving water, adequate irrigation is more effective and efficient, encouraging deeper root growth and creating healthier plants that are more drought tolerant.
Work with irrigation specialists when designing, installing and scheduling irrigation systems. A properly designed irrigation system will conserve water, while an improperly designed and scheduled system will waste water and money.
Use mulch. Mulch covers the soil, conserving water by preventing evaporation and preserving water at the root mass while providing a source of organic matter to landscape beds. Mulch can also help prevent compaction and provide weed control and is also attractive.
Lastly, harvest rainwater. Louisiana has an average annual rainfall of 60 inches. Harvest rain with equipment such as barrels and cisterns to help supplement your irrigation program.
Do your part to help conserve water for future generations by following these water-wise guidelines. Consult LSU AgCenter publication No. 3062, Introduction to Landscape Irrigation in Louisiana, at lsuagcenter.com for more tips.
Heather Kirk-Ballard, Ph.D.
Consumer Horticulture Specialist
Heather Kirk-Ballard, Ph.D.
Consumer Horticulture Specialist
Why not plant something new this summer? We have our warm season stand-bys — tomatoes, peppers, okra, cucumbers, melons, squash and others. Tips for these crops are presented at the end of this article. But I challenge you to try and grow pumpkins in Louisiana. Last summer the LSU AgCenter held a statewide pumpkin growing contest for 4-H youth. Over 800 students received seeds of the Cinderella pumpkin variety. Cinderella isn’t really a pumpkin. Rather, it is a large winter squash. In Louisiana, pumpkins can be hard to grow, but decorative and winter (edible) squash are easier. Winter squash are beautiful and come in a range of shapes, sizes and colors. They are called “winter” even though they are grown in the summer because they have a thick rind that allows them to keep for many months, unlike summer squash, which have a short shelf life. Some of my favorite winter squash varieties include Cinderella, which can range from a light tan to a deep coral color and anywhere from 6 pounds to 40 pounds depending on how you fertilize and how great you are at attracting pollinators. Other fun varieties include Shokichi Shiro, which has a light silver-gray color; Silver Moon, a white squat squash; and Turk’s Turban, a beautiful squash that is orange, green and white. There are too many to name and so many you should try growing. If you are interested, here are a few tips.
Winter squash vine out, so be sure to give them plenty of space. In our recent 2020 LSU AgCenter winter squash trial we spaced plants 3 feet apart down each row. Watch out for cucumber beetles, slugs, snails and worms, the major insects that affect this crop. If you must spray to kill these, please do so at dusk. This is because we need bees and other pollinators to bring pollen back and forth from male to female flowers. Fertilize before you plant with a complete fertilizer, such as 13-13-13, and side-dress weekly with nitrogen as flowers begin to develop. Keep an eye out for downy mildew and powdery mildew, two of the most notorious diseases that attack winter squash. To help prevent disease water at the base of the plant, space plants adequately and use a preventative fungicide. Harvest when the rind of the squash is hard enough that your fingernail won’t poke through it. The stem of the winter squash should also look thick and corky, not fresh and light green. Why not give it a try? Even just saying winter in summer might cool you off a bit!
Enjoy the Garden,
Kathryn “Kiki” Fontenot, Ph.D.
Associate Professor, LSU AgCenter School of Plant, Environmental and Soil Sciences
Summer is the peak growing season for lawns in Louisiana. If you did not fertilize during the spring, you still have time to fertilize and get your yard in good shape prior to fall. Keep up a good fertility program through early to late August. Remember to apply all granular materials on a dry lawn and water very soon after application. Make sure your lawns are getting adequate amounts of moisture during the summer months, but don’t overwater. Water deeply only once or twice per week or as needed, based on the amount of rainfall. The purpose of irrigation is to supplement rainfall. I am not a fan of watering lawns everyday unless we are in severe drought.
Consider aerifying compacted soil. I’ve seen aerification completely change thin lawns caused by compacted soil into thick and healthy turf. Aerifying helps with water percolation and increases the turf’s rooting depth and makes for a more drought-tolerant lawn. Lawn care companies can aerate, or you can rent an aerator from a rental store and do it yourself. If your soil is prone to compaction, consider aerating one to three times this growing season. Aeration may be the game changer that your lawn is missing.
St. Augustinegrass and zoysiagrass both respond well to fertilizer applications. St. Augustinegrass may be fertilized up to three times during the growing season — April, June and mid-August. Fertilize zoysiagrass twice per growing season — in April and again in July.
Bermudagrass is an even bigger fertilizer user and can be fertilized from three to five times during the growing season, especially if you like to mow grass. Carpetgrass and centipedegrass are not big fertilizer users. Usually, two applications (April and July) will take care of centipedegrass, and one application will be sufficient for carpetgrass (April).
Centipedegrass should receive its second and final fertilizer application in July. For centipedegrass, apply only one-half pound of actual nitrogen per 1,000 square feet. For example, apply 3 pounds of 17-0-17 per 1,000 square feet or 5 pounds of 10-0-10 per 1,000 square feet. St. Augustinegrass would need 6 and 10 pounds of the aforementioned fertilizers.
If your lawn is not performing well, there could be a nutrient deficiency in the soil. The only surefire way to know what your soil needs is to collect a soil sample and submit it for testing at the LSU AgCenter Soil Testing and Plant Analysis Lab. In order to simplify the soil sampling and submission process, there are pre-addressed submission boxes with sampling instructions at several garden centers throughout the state and at your local parish extension office. Once submitted, the results will be sent to your home mailbox and/or email, usually in less than two weeks. Your parish LSU AgCenter extension agent can help you interpret the results from the soil sample and tell you exactly what’s needed nutrient-wise to make your lawn beautiful.
You may not know this, but there is a correct mowing height for your lawn. St. Augustinegrass is very finicky when it comes to mowing height. Don’t cut it too short and don’t allow it to get too tall. It likes to be maintained around 3 inches, the tallest mowing height of all the lawns grown in Louisiana. If you cut St. Augustinegrass too short, it becomes stressed and more prone to disease and weed infestations.
Centipedegrass is often maintained too tall. Centipedegrass should be mowed to 1 to 1.5 inches. This helps prevent thatch buildup. Zoysiagrass also likes to be mowed in the 1-to-1.5-inch range. Bermudagrass should be mowed from 1 to 2 inches, shorter mowing heights are better when more frequent mowing is possible. Keep mower blades sharp to ensure a clean cut and good lawn health.
Watch for chinch bugs in St. Augustinegrass and bermudagrass lawns and treat with an LSU AgCenter-recommended insecticide such as bifenthrin (Talstar and many other trade names). Chinch bug problems show up as yellowish-brown to straw-colored areas of the lawn during hot, dry weather. These insects extract plant juices from turfgrass stems and crowns while pumping toxic salivary fluids into the lawn. The fluids disrupt the plant’s vascular system. The damage actually resembles herbicide damage.
Check for chinch bugs in the lawn by saturating suspected areas with a gallon of water mixed with a few squirts of lemon dishwashing soap. This soapy solution irritates chinch bugs and brings them up near the grass surface so you can see them and determine if the bugs are causing the lawn damage. If it’s hot and dry and there are dead spots in your St. Augustinegrass, chinch bugs are the first thing that I would consider.
Additional insect problems that appear during the summer include armyworms and tropical sod webworms. These moth larvae or “worms” can cause severe lawn damage very quickly and will need to be killed with insecticides to prevent further damage. Tropical sod webworms can devastate St. Augustinegrass and carpetgrass lawns. Tropical sod webworms crushed St. Augustinegrass in 2020. Let’s hope that our cold winter reduced moth populations for 2021. Armyworms prefer bermudagrass and can completely defoliate acres of pasture and lawns. Carbaryl, bifenthrin and chlorantraniliprole insecticides are options for tropical sod webworms, armyworms and chinch bugs infesting the lawn.
Be mindful of these pests as you walk through your lawns. Investigate damaged areas and treat accordingly.
In late spring to early summer, Virginia buttonweed starts forming mats that can eventually smother out the lawn. Pull up small populations of Virginia buttonweed or carefully treat with herbicides like metsulfuron (MSM Turf and other trade names) or Celsius. These herbicides work well with repeated applications spaced four to six weeks apart. Metsulfuron and Celsius can be safely applied on St. Augustinegrass, centipedegrass, bermudagrass and zoysiagrass during warm weather. Carpetgrass will be damaged by Celsius herbicide. Bahiagrass will not tolerate metsulfuron or Celsius. When it comes to “managing” buttonweed, it is important to start spraying early in the growing season (April) and spray often. Don’t wait until September to make your first herbicide application.
Common lespedeza is a mat-forming annual legume that emerges in the spring and lingers deep into fall throughout Louisiana. By late summer, the plant matures and becomes woody-like and tough on lawnmower blades. Metsulfuron works well on this weed but early summer applications are more effective.
Torpedograss is a perennial grass that’s mainly a problem in south Louisiana, but I do get calls from north Louisiana as well. There are few lawn problems more devastating than a torpedograss infestation. Torpedograss is extremely tolerant of herbicides and easily outcompetes slow growing grasses like centipedegrass.
The weed often starts from soil brought in during flower bed construction. However, it quickly spreads from the flower bed to the lawn. The ability to suppress torpedograss in lawns depends on the turfgrass species. Selectively removing torpedograss out of lawn grasses and sports fields is rarely completely achievable. Quinclorac (Drive and other trade names) is an herbicide that is somewhat effective in suppressing torpedograss in bermudagrass and zoysia. Unfortunately, you cannot use quinclorac in centipedegrass and St. Augustinegrass.
Sethoxydim (Bonide Grass Beater and other trade names) will temporarily injure torpedograss that is infesting centipedegrass, but it does not provide long-term control. The torpedograss recovers, and the weed re-infests the centipedegrass again. Unfortunately, there are no selective herbicide options for torpedograss that is infesting St. Augustinegrass. Often, complete renovation is necessary when centipedegrass and St. Augustinegrass are severely infested.
If you decide to renovate and install a new lawn, consider sodding the lawn with zoysiagrass (semi-shady or full sun lawns) or bermudagrass (for full sun only). Converting to zoysiagrass or bermudagrass will allow the use of quinclorac, the most effective selective herbicide on torpedograss. Installing zoysia may be the better fit for Louisiana because of its good shade and drought tolerance. Zoysia is not a high maintenance grass when managed properly. Maintain zoysia at 1 to 1.5 inches with a sharp mower blade and fertilize twice per year. There are several sod farmers in Louisiana that grow zoysia, so it is readily available.
Proper lawn maintenance keeps your lawn healthy and reduces the need for the use of pesticides. If it becomes necessary to use a pesticide in the lawn, it is highly important to always read and follow their labels before using. The label will tell you how to use the product safely to achieve satisfactory results. You will find the label attached to the product’s container.
Ron Strahan Ph.D.
Associate Professor, LSU AgCenter
Citrus is the most popular fruit tree grown commercially and in home backyards in Louisiana. Satsumas dominated citrus production with 63% of total citrus acreage. In 2018, 183,408 bushels of satsumas were produced in the state with a total gross farm value of $6.2 million, according to the 2018 Louisiana Summary Agriculture and Natural Resources.
During the last decade, satsuma production has drastically reduced by 54,526 bushels, which is attributed to diseases and natural disasters. After Hurricane Katrina in 2005, Louisiana lost the majority of its citrus industry, and the total acreage was greatly reduced. In 2008 and 2010, citrus greening and sweet orange scab were confirmed in the state for the first time, respectively (Hummel and Ferrin, 2010; Singh and Ferrin, 2011). In June of 2013, citrus canker (Figure 1) was re-confirmed in the state for a second time in Orleans Parish (Singh, 2013). The disease was first reported in Louisiana in 1914 (Loucks, 1934) and was considered eradicated in 1940 (Dopson, 1964). Since 2013, citrus canker has been rapidly spreading to all commercial and backyard citrus production areas in the state. Currently, citrus canker is reported in 10 Louisiana parishes, including Plaquemines, where the majority of the commercial citrus is grown (Louisiana Department of Agriculture and Forestry Cooperative Agriculture Pest Survey Report 2019).
All citrus varieties are susceptible to citrus canker; however, some varieties are less susceptible than others. Copper-based fungicides may suppress the disease but not control it. No bactericides have been labeled to use on citrus to manage citrus canker in Louisiana. Without effective management options, citrus canker has the potential to adversely affect the survival of Louisiana’s valuable citrus industry. Therefore, it is critical to develop alternate methods to mitigate the spread of citrus canker in the state. One of the alternate methods is to discover satsuma cultivars that are highly tolerant and can withstand high disease pressure in our canker-conducive environment.
The results from an annual citrus cooperative agricultural pest survey (CAPS) conducted by the LSU AgCenter and the Louisiana Department of Agriculture and Forestry from 2014-2016, revealed that satsumas are highly tolerant to citrus canker with only 2.5% disease incidence. In some situations, the satsuma samples were collected from trees planted in the same backyard with heavily infested grapefruit, Meyer lemon, navel orange and other citrus varieties. The CAPS lacked data on types of satsuma cultivars that were sampled. The cultivar susceptibility data plays a critical role when promoting different types of satsumas to commercial and backyard growers in canker-infested areas. The objective of this study was to screen susceptibility of satsuma cultivars against citrus canker under natural disease inoculum conditions.
Five cultivars of satsuma, including Brown’s Select, Louisiana Early, Miho, Owari and St. Ann were screened along with three citrus varieties with known varying degrees of susceptibility to citrus canker disease ranging from a highly susceptible (HS) Ruby Red grapefruit, a moderately susceptible (MS) Hamlin sweet orange and a least susceptible (LS) sweet kumquat. Trees grown in 3-gallon pots and to 18 months of age were placed under diseased mature grapefruit trees at a public garden in New Orleans and a commercial citrus orchard in Paulina. The study was conducted during 2018 and 2019 growing periods at both experimental sites.
The disease onset among the five satsumas varied at both New Orleans and Paulina sites during 2018 and 2019, but Brown’s Select, Miho and Owari satsumas had consistently delayed onset of citrus canker with only 20% of incidence within weeks two and three after experimental tree were placed (Figure 2). Miho had an additional delayed disease onset that extended into week four with only 20% disease incidence in 2019 in Paulina. Similarly, Owari developed canker lesions during week five at the New Orleans site with 20% disease incidence. Louisiana Early and St. Ann satsumas were highly inconsistent in getting infected with citrus canker. The highly susceptible ruby red grapefruit and moderately susceptible Hamlin sweet orange had a large number of trees getting infected early during the screening periods (Figure 2).
| 2018 | 2019 | ||||
|---|---|---|---|---|---|
| New Orleans | Paulina | New Orleans | Paulina | ||
| Ruby Red grapefruit (HS) | 1.36 | 4.14 | 9.2 | 6.11 | |
| Hamlin sweet orange (MS) | 1.44 | 2.88 | 6.64 | 11.64 | |
| Brown’s Select | 0.48 AB | 1.17 C | 1.20 A | 3.41 AB | |
| LA Early | - | 1.40 C | 3.93 B | 2.52 AB | |
| Miho | 0.21 A | 0.90 B | 3.07 AB | 1.69 A | |
| Owari | 1.10 BC | 0.49 A | 4.92 B | 4.07 B | |
| St. Ann | 1.75 D | 0.43 A | 5.34 B | 2.02 A | |
| Sweet kumquat (LS) | 0.0 | 0.0 | 0.0 | 0.0 | |
In the New Orleans public garden (grapefruits trees planted in a courtyard surrounded by a brick wall), the satsuma cultivars Miho and Brown’s Select showed the lowest average number of lesions in both years (Table 1) and a delayed disease onset compared with the other satsuma cultivars (Figure 3). Miho, for instance, never developed citrus canker symptoms after the three week-period in which the experimental trees were placed. In Paulina, in an opened orchard, Miho and St. Ann had the lowest average number of lesions per leaf in the two years of evaluation (Table 1), and Miho exhibited delayed onset of disease (Figure 3). The cultivars Brown’s Select and Miho in New Orleans had the smallest number of 3.07 and 0.21 lesions per leaf, respectively. In Paulina the satsuma cultivars with the lowest number of lesions per leaf were observed on St. Ann (0.49 lesions per leaf) and Miho (1.69 lesions per leaf) (Table 1).
The disease pressure on mature grapefruit trees at New Orleans and Paulina was 100% during both years, and the weather conditions were conducive for canker at both sites. Despite the high disease pressure and weather conditions, satsumas Brown’s select, Miho and Owari performed the best and had less disease with delayed onset of symptoms.
The size of canker lesions is also an important predictive parameter on canker impact and spread. Lesions on leaves and twigs are probably the most epidemiologically significant inoculum for secondary infections, as canker lesions remain active for many months, and the bacteria produced on lesions are dispersed by water splashes resulting in infection and further production of more canker lesions. In this study difference in canker lesion size among the five satsuma cultivars was observed in New Orleans but not in Paulina (Figure 4).
In Louisiana, environmental conditions are optimal for citrus canker development, and a lack of effective chemicals to manage the disease pose a continuous challenge for citrus growers. The popularity of growing satsumas in Louisiana orchards and backyard gardens may help reduce the disease spread and development. This study provides field-based scientific evidence that Brown’s Select, Miho and Owari consistently had less disease severity with delayed incidence and, therefore, categorized as less susceptible to citrus canker compared to Louisiana Early, St. Ann, Hamlin sweet orange and ruby red grapefruit. Additionally, the smaller lesion size on both Brown’s Select and Miho may result in lesser canker inoculum production for secondary infections. Louisiana growers must incorporate these satsumas in their future plantings as an alternate citrus canker management strategy.
Furthermore, in addition to the satsuma cultivar susceptibility data, this study provides the field-based data on sweet kumquat resistance to citrus canker. This information can be readily incorporated into citrus hybrids by conventional breeding.
In conclusion, this study provides valuable and reliable field-based scientific information on satsuma susceptibility to citrus canker in Louisiana, which can help the growers select less susceptible cultivar to mitigate this high-impact disease.
The project was funded by USDA AMS Specialty Crop Block Grant Program No. AMI7O100XXXXGO24. The authors would like to acknowledge Robert “Butch” Millet and Rene Millet of Paulina, Louisiana, for letting us use their citrus orchard for conducting this study. We would like to extend our sincere thanks to Amy Graham of Longue Vue Gardens for providing us with a second site for comparing our work.
Dopson, R. N. 1964. The eradication of citrus canker. Pl. Dis. Rept. 48: 30-31.
Hummel, N. A. and Ferrin, D. M. 2010. Asian citrus psyllid (Hemiptera: Psyllidae) and citrus greening disease in Louisiana. Southwestern Entomol. 35 (3): 467-469.
Loucks, K. W. 1934. Citrus canker and its eradication from Florida. (Unpublished manuscript, Library) Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Gainesville, FL. 111 pp.
Louisiana Summary Agriculture and Natural Resources. 2018. Online Publication. https://www.lsuagcenter.com/profiles/aiverson/arti...
Louisiana Department of Agriculture and Forestry Cooperative Agriculture Pest Survey Report. 2019. Online Publication. http://www.ldaf.state.la.us/wp-content/uploads/201...
Singh, R., and Ferrin, D. 2011. Sweet orange scab and citrus scab disease identification card. Louisiana State University Agricultural Center Publication 3215.
Singh, R. 2013. Citrus canker. Louisiana State University Agricultural Center Publication 3269.
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