A Look Back at Citrus Variety Development and Disease Management
Citrus varieties have changed through the years with intricate and thoughtful cultivation. Prior to the Great Freeze, Dr. H.J. Webber and Mr. Walter T. Swingle of the United States Department of Agriculture founded the Subtropical Laboratory at Eustis, Florida in 1892. There they implemented frost resistant hybrid varieties research until 1893. Their findings were mostly lost and the laboratory closed after the Great Freeze. However, their research resumed in 1896-97 and pioneered in the breeding of citrus cultivars.[emember_protected custom_msg=”Click here and register now to read the rest of the article!”]
Many of the citrus varieties today are from cooperative efforts between growers and scientists at the University of Florida’s Institute of Food and Agricultural Sciences (UF/IFAS) extension offices. Their scientific goal is to develop fruit that is resistant to fungi, diseases, and pestilence. Today, citrus is not grown from seedlings but the grafting and budding of rootstock, which had its beginnings in Florida at D.D. Dummitt’s grove on Merritt Island back in the 1830s. The sour orange and rough lemon stock would be the two most popular stocks from 1953-74. The 2012 top rootstocks, accounting for 78 percent of all nursery productions, are the Swingle, Kuharske, Sour Orange, Carrizo, and X-639.
The bulk of citrus production locations are found on the North and Central Ridge, Southwest, and Indian River. The current most popular commercial citrus varieties from the Bureau of Citrus Budwood Registration annual report of 2012, which account for 90 percent of varieties in nursery propagations are the following:
Hamlin (1), Valencia (2), Midsweet (3), Navel (5)
Orri (8), Tango (9)
Ray Ruby (4), Ruby Red (6), Flame (7)
|Acid citrus fruit:
Meyer Le (10)
The development of new varieties was largely instigated to combat invasive and exotic threats that have attacked the citrus industry through the years. Botany research in the late 17th through the mid 19th centuries played a significant role in the advancement of citrus cultivation and technology. By 1880, plant-based diseases were being classified and the first “spray-gun” for combating bacterial plant diseases was used in France. The Florida State Horticultural Society was founded in 1888; in 1889, the Florida Agricultural Experiment Station at the University of Florida was established. Biological control was revolutionized when Albert Koebele with the U.S. Department of Agriculture released the Vedalia, ladybird beetle, in California, to attack the cotton cushion scale. The insect was phenomenally eradicated and biological control became a forefront in agricultural pest and disease control. This ignited the work at an experiment station with Dr. P.H. Rolfs and Dr. H.G. Hubbard from the U.S. Bureau of Entomology, whom both studied scale insects in local crops. Analysts H.J. Webber and W.T. Swingle at the Subtropical Laboratory in Eustis were the first to study and describe citrus diseases such as blight, foot rot, die back, melanose, psorosis, and scab. Their findings progressed the treatments and methods of pest and disease control. Many local nurserymen and growers were willing to work with scientists and volunteered their groves as field laboratories. The founding of the Florida State Citrus Experiment Station in Lake Alfred, in 1917, was indicative of the economical boon of commercial citrus and efforts for advancement in treatment for pests and diseases, amongst other research pursuits.
Treatment today consists of integrated pest management (IPM), the principle that takes into account effectiveness, cost, convenience, and risk to human health and the environment. Nurserymen and growers perform scouting (walking/riding through the groves), to discover the presence of pests, diseases, or infections. After a visual presence is confirmed, the growers can determine the best form of treatment. Cultural practices include growing resistant varieties from disease free rootstock, weed and vegetation control between rows, pruning and topping, and tree removal in extreme cases. Biological knowledge and biological control requires a vast knowledge of the threat, and resulting course of action will depend on the infestation or infection of the citrus.
Chemical control is the last measure taken in managing infestations and infections through spray methods. The invasive Mediterranean fly aggressively infested groves in 1925. The infestation was a severe and dangerous enough threat to warrant Federal agencies and the citrus industry to appropriate $10 million for the scientific advancements in spray and cleanup to obliterate the pest. There were smaller recurrences in 1956 and 1962 that were readily managed because of this prior research. Diseases such as citrus blight and citrus tristeza both inhibit nutrients moving up from roots to the tree canopy. Spray programs help replace lost nutrients to these trees and treat invasive or exotic threats.
The different types of citrus sprays include foliar insecticides, fungicides, herbicides, and nutrients, as well as soil-applied insecticides, nematicides, and fungicides. The chemicals are distributed either by handguns or pumps in nurseries, and tractor- or truck-pulled ground sprays such as sprays, misters, and fog machines; aerial sprays are administered via fixed wing aircraft or helicopter. Each applies treatments uniquely and as needed for specific pests, diseases, or deficiencies.
The exotic threat Huanglongbing (HLB, a.k.a., citrus greening) is treated by the Enhanced Foliar Nutrient Program (EFNP) and scout-and-eradicate program. HLB’s presence wasn’t known until 2005, seven years after its manifestation, which is caused by the vector, the Asian citrus psyllid. Insecticide is used to control the psyllid while the EFNP is used on HLB-symptomatic trees. Growers remarked a marginal improvement in yields from infected trees after EFNP treatment. Coordinated grove sprays are another effective effort by growers to prevent re-infestation of groves.
Low-volume applications, using bigger particles than foggers, and potentially less chemical per acreage, are newly emerging technologies and are proven equally effective as conventional sprays. Once sprayed, its broad coverage increases canopy penetration through its slow downward settling with less drift than other methods. There is ongoing research into the effectiveness of alternating rows sprayed versus each row for optimal rates. UF/IFAS Citrus Research Education Center and FAWN are developing an Internet tool that optimizes timing of sprays based on current weather conditions.
The devastation of 9/11 changed the practices of how Florida patrolled its now considered vulnerable ports and coastal borders. Florida is called a “sentinel” early warning state because of its geographical location, diverse agricultural industries, numerous ethnic groups, and climate. In many ways, Florida could be the first place that invasive or exotic threats are introduced accidentally or intentionally. Hence, border security is run by federal, state, and local organizations with vital regulations to protect consumers and Florida’s vast agricultural industry from invasive or exotic threats.
story by J.P. SMITH