- Author: Jeanette Warnert
Newly appointed UC Cooperative Extension agricultural engineering advisor Alireza Pourreza has been awarded the 2016 Giuseppe Pellizzi Prize by the Club of Bologna, an honor presented every other year to the best doctoral dissertations focused on agricultural machinery and mechanization. The Club of Bologna is a world taskforce on strategies for the development of agricultural mechanization.
Pourreza, who earned his Ph.D. at the University of Florida in 2014, worked on early detection of Huanglongbing disease of citrus. Huanglongbing, an incurable disease that is spread by Asian citrus psyllid, has seriously impacted citrus production in Florida. The disease has been found in commercial and residential sites in all counties with commercial citrus.
Early detection allows growers to remove infected trees before the disease can spread to healthy trees. Currently HLB infection is confirmed when leaves with yellowing and blotches are submitted for PCR testing, which is expensive and time consuming. However, the yellowing can be also symptomatic of other conditions, such as nutrient deficiency.
“We discovered we could see the symptoms of Huanglongbing using a camera, a set of cross-polarizers and narrow band lighting before it is visible to the human eye,” Pourreza said.
He said the yellow blotches on HLB-infected leaves are caused by starch accumulation.
“If we could detect abnormal levels of starch in the leaf, we could tell it is affected with HLB,” Pourreza said. “Starch showed the ability to rotate the polarization plain of light. We used this optical characteristic to develop the sensing methodology.”
Pourreza said the team has patented the technique and is working on developing a commercial product. He is seeking funding to continue the research in California, where, to date, HLB has only been detected in isolated Los Angeles neighborhoods. Asian citrus psyllid is found in important California commercial citrus production regions from the Mexican border to as far north as Placer County.
Pourreza is based at the UC Kearney Agricultural Research and Extension Center in Parlier.
- Author: Ben Faber
Entomology Specialist and Lindcove Research and Education Center Director keeps her Asian Citrus Psyllid website for homeowners up-to-date at: http://ucanr.edu/sites/ACP/Homeowner_Options/Homeowner_Resources/
Check it out.
Photo: ACP Adult and Nymphs with wax tubules
- Author: Ben Faber
The International Citrus Conference was just held and about 1,500 people came from all over the world to share their experiences and research in citrus. It included marketers, growers, government officials and researchers who all had citrus as their interest. It was remarkable the volume of information, everything from world production figures and marketing, new varieties, breeding technology, plant diseases and pests, water management and of course HLB and ACP, probably the two most fearsome world-wide problems.
On the whole it was most hopeful to realize how much has been accomplished in the last several years to deal with the threat of HLB. The biology of ACP is better understood in different situations, the disease progression in different citrus species is being recognized as being more or less aggressive, and how to manage the insect and disease are better understood. Unfortunately, new threats (however none as mush as HLB) are being identified, such as citrus longhorn beetle. Oh, my.
Read the Abstracts at:
- Author: Ben Faber
There are numerous species of ants present in citrus orchards, however, the most common are the Argentine ant (southern and coastal California), the native gray ant (San Joaquin Valley) and the southern fire ant (statewide). The red imported fire ant has been found in Southern California, but is not yet established in citrus orchards. It is important to identify the primary ant species in the orchard, because management tactics depend on which ant species is present.
The Argentine ant, is a small, uniformly deep brown ant. Worker ants travel in characteristic trails on trees, the ground, or irrigation lines and build their nests underground. Ant populations peak in mid-summer through early fall.
The southern fire ant is light reddish brown with a black abdomen. These ants build nests of loose mounds or craters near bases of trees, do not aggregate in colonies as large as those of the Argentine ant, and will sting and bite.
Native gray ants are gray and considerably larger than the other two species. They nest in topsoil or under rocks and debris and move in irregular patterns. In contrast to Argentine and fire ants, the native gray ant is solitary and its importance in disrupting biological control is often underestimated.
Red imported fire ant is new to California and can make large, dome-shaped mounds. They feed on almost any plant or animal material.
Damage
Most ant species feed on honeydew excreted by various soft scales, mealybugs, cottony cushion scales, whiteflies, psyllids, and aphids. As part of this relationship, they protect these pest insects from their natural enemies, thus interrupting biological control. They also protect some non honeydew-producing pests, such as California red scales.
Argentine and native gray ants are the most common ant species that aggressively protect pest insects. In addition, Argentine ants and fire ants can plug up irrigation sprinklers. Fire ants directly damage citrus by chewing twigs and tender bark of newly planted trees; they also sting people working in the orchard and may cause allergic reactions.
No effective natural enemies of ants are known.
Cultural Control
Skirt prune trees, i.e., remove branches within 12 to 30 inches of the ground, and apply sticky material to the trunk to prevent access to the trees by ants. Use polybutenes, as oil-based materials may cause phytotoxicity and should not be used.
The application of sticky polybutene materials directly to the trunk of citrus trees can cause bark cracking, especially if multiple applications are applied to the same area of the trunk, the area is exposed to sunlight (topworked trees), or both. The sticky material can be applied on top of a tree wrap or a base layer of latex paint. Young trees, which have a very thin cambium layer, are most susceptible to damage.
Sticky material should last from 1 to 4 months and will also prevent the access by Fuller rose beetles. If the sticky material contains tribasic copper sulfate, it will also control brown garden snails. The persistence of sticky material can be increased by applying it higher above the ground to reduce dust and dirt contamination and to decrease irrigation wash-off.
Baits
Argentine ant adults are liquid-feeding only and have physical digestive "blocks" in the mouth and gut to prevent them from swallowing and digesting solid food particles. They may bring back solid food to the colony to feed the brood (but solid-food digestion not been confirmed in Argentine ant brood), or harvest the bodily fluids inside of insect prey/moisture in food items. Dry insects or food items are of little use to them, even though they may pick these things up. Feeding studies have shown ants feed several times faster on liquids than gels and gels than solids. This faster feeding resulted in much higher toxicity with liquid. Gel was intermediate, and solids provided the lowest control.
Put out bait in the shade to increase feeding and overall kill. You do not need to obscure it. The soil temperature and moisture are going to be more moderate in the shade, particularly under the canopy. This is the environment the ants will prefer to feed in. There will be less evaporative loss in the shade, as well. Sometimes when the toxins become too concentrated they are less attractive to the ants. The other issue is that many toxins (like borax products) may photodegrade at a faster rate in direct sunlight.
- Author: Ben Faber
Get ready for more rotting avocado fruit if you have leaf blight showing up in your tree canopy. The fungal spores (one of the Botryosphaerias we once lumped as Dothiorella) that create the infection spread in an irregular pattern over the leaf and down the stem (then called “stem blight”). This is often confused with salt or tip burn. The two conditions are caused by the same problem, water and or salt stress. However, in the case of leaf blight, this is a pathogen that can pass to neighboring fruit and begin the process of rot. This starts happening when the fruit starts ripening and softening, so it's often not seen in the orchard, but the packhouse or in the market.
Control is basically gaining control over the soil moisture and salinity in the root zone and when the leaf blight starts showing up in the canopy, cutting as much out back to green tissue as is economically possible.
Leaf blights from this group of fungi have also been reported as infecting other fruits, such as citrus, apple, peach and grape among others. The solution is the same - water right and cut the stuff out when and if it shows up.
Photos:
Body rots
Rot spreading to flesh
Leaf Blight