What is conservation tillage?
Conservation tillage refers to soil cultivation with direct drilling (no tillage) and minimum tillage. Conservation tillage is often used in conjunction with cover crops to allow surface incorporation of crop residues. Conservation tillage maintains a minimum of 30% of the soil surface covered by residue after drilling. Oppositely, conventional systems of tillage leave less than 30% of crop residues, and often none, on the soil surface after crop establishment. Conservation tillage conserves soil moisture, reduces run-off, increases the surface soil organic matter, reduces soil erosion and water contamination. Conservation tillage has been promoted in the US because it provides substantial environmental benefits, including reduction of soil erosion. This has become more important with climate change that is exacerbating the problem of soil erosion with erratic rainfall events and greater frequency of storms.
What are the effects of conservation tillage on beneficial insects?
Conservation tillage along with cover crops helps promote year-round natural enemy populations by providing alternate prey, reproductive sites, and protection from adverse conditions. Conservation tillage increases grass weeds and retains organic matter, leading to an increase of detritus feeding species upon which beneficial predators depend.
Conservation tillage can also reduce the environmental impact of insecticides by modifying the soil structure and affecting the degradation of insecticides in the soil. The fate of insecticide following application depend of many factors including insecticide’s active ingredient and adjuvants, environmental conditions, and soil properties. Insecticides may cause severe or chronic effects on beneficial organisms before they are degraded into harmless compounds.
A recent study conducted in peanuts at the North Florida Research and Education Center in Quincy demonstrated that predators of soil pests were protected by conservation tillage. The experiment consisted in a peanut field planted after a cover crop of oats. The field was divided into areas with conservation or conventional tillage. The peanut field was then treated with different types of insecticides. Soil pests found in the peanut field included mole crickets, click beetles, and peanut burrowing bugs, whereas soil pest predators included earwigs and ground beetles. Both soil pests and predators increased significantly under conservation tillage (Fig. 1). However, the application of insecticides on conventional tillage, such as imidacloprid, decreased significantly the number of soil pests as well as the number of predators.
Fig. 1: Increased of natural enemies in peanut soil, under conservation tillage vs conventional tillage.
Interestingly, under conservation tillage the number of soil pests also decreased following insecticide application, but the predator populations remained at the same level as in the untreated area. The conclusion of this study was that conservation tillage increased significantly the number of soil pest predators and potentially protected them against the non-target effect of insecticides. Therefore, conservation of natural enemy population can be added to the numerous advantages of conservation tillage in peanuts.
For more information on this topic, use the following publication link:
Fig. 1: Digitonthophagus gazelle collected in Marianna, FL. Credit: Xavier Martini, UF/IFAS
Authors: Derrick Conover, and Xavier Martini, UF/IFAS North Florida Research and Education Center
Throughout the world, dung beetles are important beneficial insects to cattle pasture ecosystems, as they support the processing and removal of livestock waste. With approximately 1.7 million beef cows and calves, and 115,000 dairy cows that contribute $848 million in combined revenue every year in beef and milk sales, the cattle industry is an important aspect of the Florida economy. Dung beetles are an important component of the cattle industry in the Southeastern United States, where beef and dairy production is typically pasture-based. There are approximately 11 million acres of grasslands in Florida alone. Florida has a highly diverse population of dung beetles and many exotic species have entered the state after being released throughout the Southeast United States in the 1970s in order to increase cattle dung degradation.
Although, the removal of dung deposits is the most recognized benefit of dung beetles, there are multitudes of other benefits cattle producers get from these small decomposers: nitrification prevention in water bodies, reducing greenhouse gas emission from pastures, and potential pestiferous fly reduction. Blood feeding flies such as the Horn Fly (Haematobia irritans) reproduce in fresh cow dung, and as adults, can stress and render cows anemic in high numbers. When dung beetles consume and bury dung, they remove the resources horn flies need to reproduce.
Figure 2: Euoniticellus intermedius adults collected in Marianna, FL. Credit: Xavier Martini, UF/IFAS
Researchers at the University of Florida recently evaluated dung beetle communities in North Florida, and how they respond to different habitat types. Pastures were dominated by the introduced species Digitonthophagus gazella (Fig. 1 top) in late summer, and Euoniticellus intermedius (Fig. 2 above) became the dominant species in the fall. Among the native species present in these pastures, the most common species was the large and colorful Phaeneus vindex (Fig. 3 below).
Figure 3: Phaeneus vindex adults collected in Marianna, FL. Credit: Xavier Martini, UF/IFAS
In forest and open field, researchers observed a different story. They did not collect any of the introduced species that had been captured in pastures. Instead, they collected low numbers of 17 different native species of dung beetles, that appeared to be active throughout the season, peaking in early to mid-summer (Fig. 4 below). This lack of exotics may be indicative that exotic and introduced dung beetles are unable to survive without the consistent presence of livestock, and are unable to expand to natural areas. Forest habitat hosted a higher amount of diversity, but a lower total population of collected beetles. The forest was dominated by Ateuchus leucontei, and Ateuchus histeroides, while the open field was dominated by Onthophagus oklahomensis, though this species was collected in both areas. Phaeneus vindex, the large colorful beetles, that were also collected in pastures, showed a significant preference for the open field. The dispersion and distribution of the different species appeared to be influenced by habitat design.This study demonstrated that dung beetles are quite sensitive to habitat changes and eco-design. Different habitats can either encourage or exclude different species, based on the ecological profile of the property.
Figure 4. Dung beetles population distribution in forest and open field in Quincy, FL.
Many livestock producers have asked about increasing the dung beetle population on their farms, but this study, along with past research, shows that there are already large populations of beetles that are well established, where livestock have been continuously raised. Therefore, land management practices are encouraged to increase beetle diversity. Conservation of unexploited open field and woodland adjacent to pastures should help in increasing local dung beetle population within the pasture. Relying only on exotic dung beetles may turn out to be problematic, as they can be more susceptible to North American pathogens, and are unfit to sustain populations off wildlife only, if the livestock are removed from a property for an extended period. In addition, different species of dung beetles display different behaviors of processing dung (tunneling, rolling, and dwelling); therefore, keeping a high diversity population of dung beetles could help in processing dung more efficiently. Having more diverse habitats mixed with their pastures should encourage greater diversity of dung beetle species, which in turn can lead to more effective dung removal and fly control.
Xavier Martini, Pete Andersen, UF/IFAS North Florida Research and Education Center
In May 2017, Asian citrus psyllids (Diaphorina citri) were found in the experimental citrus grove at the Suwannee Valley Extension Center in Live Oak. The trees were quickly treated with an insecticide containing the active ingredient, cyantraniliprole. This treatment was highly justified as the Asian citrus psyllid is the vector of Candidatus liberibacter asiaticus, the presumed causal agent of citrus greening. Citrus greening has devastated the citrus industry in south and central Florida, and this was the first time that Asian citrus psyllid were found in Suwannee County. Considering that citrus groves of satsuma have been planted in close proximity to this psyllid population, it was important and justified to apply insecticide.
Fig. 1: Citrus Russ mite damage (credit photo: Betsy Martin)
Then the story got even more interesting. A few days following the insecticide treatment of the citrus grove, rust mites started to build up very fast on the trees. The fruits exhibited the typical bronzing damage due to rust mites observed on mature trees (Fig. 1). Rust mites are microscopic elongated mites about 0.15 mm in length (Fig. 2). Severe damage (over 60% of the fruit surface) from rust mites could lead to fruit drop and size reduction; however, the damage is often only cosmetic. Therefore, most of the time rust mite control is typically only required if the fruits are designated for the fresh market
Fig. 2: Citrus Russ mites (Credit photo: Michael Roger)
An outbreak of mites often occurs on citrus after the application of pyrethroid insecticides. Citrus rust mites, as well as other mites found on citrus (such as spider mites), are usually well controlled by a complex of natural enemies, including predatory mites. However, these predatory mites are usually quite sensitive to insecticides, so the elimination of these predators allows for the drastic increase of the pest mite population. This is the likely explanation of what we observed in these particular groves.
Outbreaks of mites following insecticide treatments have been documented as early as 1956, following the broad adoption of insecticide use in modern agriculture. It was observed that spraying fruit trees or row crops such as cotton with organophosphate or pyrethroid insecticides was followed by an outbreak of secondary pests such as spider mites. In fact, spider mites were not considered a serious pest until the “green revolution” with the widespread use of insecticides causing the drastic reduction of their natural enemies. This phenomenon, called “secondary pest resurgence” is well known in many crops. For instance in peanut crops, resurgence of the two-spotted spider mite (Fig. 3) is induced by the application of foliar insecticides and fungicides to control primary pests. Excessive spraying of citrus could lead to the resurgence of other pests that are usually well controlled by natural enemies, including citrus whiteflies, mealybug, or scale insects.
This short story is a reminder that spraying an insecticide may not be a harmless action, as it usually kills more than just the target species. It is, therefore, very important to follow label recommendations, and to apply insecticides only when the economic threshold, indicated by the number of pests, is reached. Economic threshold values for citrus pests are available in the publications listed below. To accurately monitor these values, it is also advisable to scout your citrus grove for insect pests twice per week.
To minimize risk of secondary pest resurgence, use of biorational insecticides, that are less detrimental to natural enemies, are recommended. To re-balance the natural enemy’s population, predatory mites can be purchased from biocontrol companies, and can be released on the crops a few days after the insecticidal spray.
Fig. 3: Two-spotted spider mites (credit photo: Lyle Buss)
For more information on citrus rust mites and other mites in citrus, please see the following UF/IFAS Publications
Fig. 1 Asian citrus psyllid nymphs. Photo by Lyle Buss UF/IFAS Department of Entomology and Nematology
The Asian citrus psyllid (Fig 1), the carrier of the causative agent of citrus greening or Huanglongbing (HLB), is certainly the most devastating pest in citrus worldwide. Since it was first spotted in Florida in 1998, the Asian citrus psyllid has spread across the state, and starting in 2005, the first cases of HLB were detected in Florida. Since then, HLB and the Asian citrus psyllid quickly became established throughout the state in all citrus production areas. The disease has a disastrous impact on citrus production by decreasing yields, lowering fruit quality, and killing trees a few years after pathogen infection.
Fig. 2. Population of Asian citrus psyllid during spring 2017 in Franklin County. (A) Number of nymphs per flush of new leaves, (B) number of adult psyllids found on citrus trees after 8 min of observation.
Until recently, the Asian citrus psyllid was only found occasionally in the Florida panhandle. This summer, however, Asian citrus psyllids were found in four panhandle counties – Gulf, Bay, Franklin, and Suwannee Counties. So far in the panhandle, Asian citrus psyllid have only been found in backyard gardens, but the population along the coast has been high enough to warrant a responsive action (Fig. 2).
Fig. 3 The wasp Tamarexia radiata is a parasitoid of the Asian citrus psyllid. Photo by Lyle Buss
In partnership with local growers and Dr. Kerr from the Florida Department of Agriculture and Consumer Service (FDACS), a biological agent was released in Franklin and Suwannee Counties to fight the recent infestation of the Asian citrus psyllid. This tiny wasp called Tamarixia radiata (Fig. 3) only attacks the Asian citrus psyllid, and will find its host by following attractive odors emitted by the citrus plant and by chemical cues emitted directly by psyllid nymphs. The female wasp will lay eggs on the ventral (under) side of 3rd to 5th instar psyllid nymphs. The parasitoid larvae then grow and develop by sucking the hemolymph (fluid equivalent to blood in most invertebrates), from their host, and eventually emerge as an adult through a small hole on the thorax of the dead psyllid (Fig 4). In addition, the female wasps also feed directly on psyllid nymphs; therefore this wasp controls psyllids by both parasitism and predation.
Fig. 4: Asian citrus nymphs with a hole on their thorax where a wasp emerged. Photo by Dr. Michael Roger UF/IFAS Citrus Research and Education
Interestingly, the FDACS has developed a biological control program to release the wasp across Florida, and homeowners interested can contact FDACS to request free delivery of the wasp. This could be particularly useful in cases where Asian citrus psyllid infestations occur and insecticide spray is not possible or not desired. It is important that the parasitic wasp is released outside of any insecticidal spray to minimize mortality, and in the presence of psyllid nymphs as this is the only stage attacked by the wasp.
Another important aspect to consider is the presence of ants. Ants feed on honeydew secreted by psyllid nymphs and will protect them from predator and parasitoids. Presence of ants can decrease efficiency of Tamarixia radiata biocontrol by 85%! Therefore, to obtain optimal control of Asian citrus psyllid by the wasp it is recommended to keep ants under control. This can be accomplished, for example, by smearing a 2-cm wide barrier of sticky Tangelfoot or other non-insecticidal barrier at the base of the trunk to exclude ants from the citrus tree.
The parasitic wasp, Tamarixia radiate, is an important tool to control the Asian citrus psyllid. It is important to keep in mind, however, that while this biological control can lower the numbers of Asian citrus psyllid, it cannot completely eradicate this pest. Even though this biological control will not eradicate psyllids, it can lower the risk of having psyllids invading citrus groves in the panhandle. Management recommendations for citrus growers in the panhandle include routine and thorough scouting for psyllids by examining the trees, especially newly flushed leaves, and using yellow sticky traps in their groves.
Further information on this topic can be found at the following sites:
FDACS – Asian Citrus Psyllid Biological Control
FDACS – Tamarixia Release Application
UF/IFAS Featured Creatures – Asian citrus psyllid
UF/IFAS Featured Creatures – Asian citrus psyllid parasitoid –Tamarixia radiata
F. Iriarte, X. Martini, M. Paret, UF/IFAS North Florida Research and Education Center (NFREC) Quincy, and E. Lovestrand, UF/IFAS Franklin Co. Extension
Huanglongbing (HLB), also known as Yellow Shoot or Citrus Greening is a devastating disease of citrus worldwide. The disease is caused by a bacteria named Candidatus Liberibacter asiaticus. This bacterium is transmitted by the Asian citrus psyllid (ACP), which was discovered for first time in the US in Palm Beach County in June 1998. The first cases of HLB were discovered in south Miami-Dade County-FL in August 2005. Since then, the disease and its vector have affected most of Florida’s citrus-producing areas leading to a dramatic decline in Florida’s citrus industry. The Florida Panhandle is one of the last regions in Florida where HLB and ACP had not established; however, the very first HLB case in North Florida was discovered December 6, 2016 in Carrabelle, Florida. Even though psyllids were not found in Carrabelle, some were captured in Bay and Gadsden counties in 2016, therefore it is likely that other citrus trees in the area may be also infected.
Figure 1. Leaves of a HLB infected Citrus tree. Note the asymmetrical chlorosis on the leaves across the midvein.
Affected leaves develop a pattern of yellow and green areas giving a “blotchy mottled” appearance. The patterns are asymmetrical on the two halves of the leaf and will be visible on both sides of the leaf (Figure 1). Leaves can become thicker, with veins enlarged and corky in appearance (Figure 2A) and zinc-like deficiency symptoms may develop (Figure 2B). Zinc deficiency typically appears on new foliage throughout the tree, in contrast to early HLB symptoms, which are restricted to a single or a few shoots. On severely infected trees, leaf drop, twig dieback and extensive fruit drop occurs (Figure 3A). Fruit may be small, poorly colored, lopsided and may taste medicinal or sour (Figure 3B and 3C).
Figure 2 Citrus tree showing (A) vein corking symptom, (B) “zinc-pattern-deficiency” interveinal chlorosis symptoms (picture by time Gotwald).
Fig. 3. (A) 2 to 3 year old sweet orange tree in south Florida with HLB-induced fruit drop, dieback, and defoliation leading to thin canopy (picture by Mike Irey). (B) Lopsided citrus fruit (C) Asymmetrical “lopsided” sweet orange fruit (picture by Tim Gotwald).
The psyllid vector feeds on a wide variety of host plants including the common Orange Jasmine. The bacteria that causes greening can also be transmitted by grafting, and by dodder (parasitic plant), but not seed. The pathogen does not spread by casual contamination of personnel and tools or by wind and rain. It severely affects most sweet oranges, mandarins, and mandarin hybrids, as well as some citrus relatives.
The Asian citrus psyllid is a small insect about 1/8 inches long at the adult stage, with black coloration at the end of the wing. Adults jump when approached and sit in a vertical position with abdomen up in the air. Nymphs have a flat yellow body and produce distinctive white honeydew. They also distort the young leaves when they feed on them. Nymphs and adults are found on the new emerging leaves; therefore, regular inspection of these new leaves is a good way to assess the presence of psyllids.
Fig. 4 (A) Asian citrus psyllid adult. (B) Asian citrus psyllid nymphs; note the white honeydew and the leaf distortion.
University of Florida Citrus Research and Education Center faculty recommend scouting for the disease and for the Asian citrus psyllid for early detection. Other management actions include removal of HLB trees plus applying herbicides to the stump; propagation of clean nursery stock; psyllid control with insecticide applications; removal of potential inoculum sources, and removal of alternate hosts such as orange jasmine and box orange from around a commercial citrus grove.
The entire state of Florida is under quarantine with specific regulations and inspection procedures regarding the propagation, shipping, and transport of citrus trees and fruit. FDACS DPI officials stated that while there are currently no regulations for moving dooryard citrus within Florida (except in citrus black spot quarantine areas), having your homegrown citrus inspected by an FDACS DPI inspector before moving it within Florida is strongly recommended.
Considering the situation in North Florida, where citrus greening is not well established, UF scientists recommend removal of any infected tree to avoid further spread of the disease to nearby healthy plants. Citrus growers in the area should be familiar with the symptoms of Huanglongbing and be able to recognize the Asian citrus psyllid. Growers should monitor their plants routinely, as early detection will slow down further spread of the disease with removal of infected trees and control of the insect vector.
For more information, watch the following video or use the links to the following websites: